Chp 3 Composition of Cells

3 Composition of cells

Figure 3.1 Footprints at a crime scene. No blood was visible to the naked eye but murder had occurred. The luminescence you see here is due to the reaction of minute traces of haemoglobin, a protein in blood, with a chemical called BLUESTAR ® FORENSIC. The chemical was sprayed because detectives suspected this was the scene of the crime. BLUESTAR ® FORENSIC is a recently developed

product and gives a better result than those obtained with Luminol, a chemical that has starred in many television shows about forensic investigations. In this chapter, we explore the major compounds of cells and the functions of those compounds, including their links with the biochemical reactions of photosynthesis and cellular respiration.

KEY KNOWLEDGEThis chapter is designed to enable students to:

• develop a knowledge and understanding of the composition of cells

• understand the relationship between the nature of various substances found in cells and the functions they perform in those cells

• understand the general role that enzymes play in cellular biochemical processes

• understand the inputs and outputs of the significant stages in the biochemical processes of photosynthesis and cellular respiration

• analyse and evaluate unfamiliar problem situations related to cells.

52 NATURE OF BIOLOGY BOOK 1

Symbol Element

C Carbon

H Hydrogen

N Nitrogen

O Oxygen

P Phosphorus

S Sulfur

Figure 3.2 The luminescence

indicates that an ‘invisible’ compound

has reacted with BLUESTAR ®

FORENSIC that was sprayed in this

area. Further testing proved the

compound was haemoglobin.

Cells reveal clues to a crimeDate: 5 May 2000. Place: Palo Alto, California, USA. A woman’s body lies at

the foot of the stairs leading from the kitchen to the basement of her home. Her

grief-stricken husband tells police that he arrived home to find his dead wife in

the basement near the foot of the stairs. The only blood visible is on the basement

floor, around the woman’s head. Upstairs, the kitchen is spotlessly clean. Appar-

ently, a tragic accident has caused the fatal head injuries to Kristine Fitzhugh,

wife of Kenneth Fitzhugh.

A post-mortem examination shows that the injuries Kristine suffered are not

those that would result from falling downstairs. Five days later, police return to

the Fitzhugh house. In the dark, they spray a chemical solution around the kitchen.

They take photographs which show glowing patches of bluish-green luminescence

on areas of the kitchen wallpaper, on a chair and a cabinet and on the floor leading

from the kitchen to the top of the basement stairs. The solution they sprayed is

known as Luminol (BLUESTAR® FORENSIC is a new product).

Luminol is a chemical that produces a short-lived bluish glow when it reacts

with the oxygen-carrying protein (haemoglobin) found in red blood cells.

Luminol can detect minute traces of blood, fresh or old, even at a dilution of one

part per million. Because of this extreme sensitivity, Luminol can reveal blood

traces even in a crime scene that has been wiped clean of any visible traces of

blood.

Luminol can also react with substances other than blood, for example, bleach.

Consequently, further tests are carried out in the Fitzhugh home which show

the substance in question is indeed blood. Samples taken from clothing in the

laundry basket and from between the kitchen floorboards are identified as blood,

and then more specifically as Kristine’s blood.

Kenneth Fitzhugh is charged with his wife’s murder. The prosecution asserts

that, during an argument in the kitchen, Kenneth Fitzhugh beat his wife,

inflicting fatal head injuries. He moved her body to the foot of the basement

stairs, arranging it to appear as if she had died as a result of a fall. He then

cleaned the blood from the kitchen and left the house. Kenneth Fitzhugh was

found guilty of his wife’s murder, due in part to his wife’s red blood cells and the

haemoglobin they contained.

In this chapter, we investigate the major groups of compounds that make up

cells and explore how some of these compounds are associated with processes

such as photosynthesis and cellular respiration.

Materials to build and fuel cellsWe have already mentioned some of the kinds of materials found in living cells

in chapter 2. The main groups of compounds found in cells are carbohydrates,

proteins, lipids and nucleic acids. These carbon-based compounds are called

organic compounds and all contain the elements carbon, hydrogen and oxygen.

Some also contain the elements nitrogen, phosphorus and sulfur. These elements

comprise the main elements in the human body. In addition to these compounds

we will also consider water, minerals and vitamins.

Water — essential for lifeWater is the most abundant compound in our bodies. About 50 per cent of an

average adult female is water. Males have less fat than females and have an

average water content of 60 per cent. Newborn babies are about 75 per cent

water.

COMPOSITION OF CELLS 53

Figure 3.3 The average distribution

of water for an average adult female in

three body regions

Intracellular water

(in cytosol)

60%Water

in plasma8%

Interstitial water(in tissue, the fluid

that surrounds cells)32%

Table 3.1 Typical water content

of some organisms

The average adult human body contains about 40 to 42 litres of water dis-

tributed across three interconnected compartments. The distribution of water in

these broad locations of the body, for an adult female, is shown in figure 3.3. As

indicated in table 3.1, a high water content is typical of living organisms.

OrganismAverage percentage

water by mass

human

adult male

adult female

newborn baby

60

50

75

bacterium 80

jellyfish 95

rat 67

mushroom 88

typical green plant 75

The water content in plants also varies. The raw

vegetables shown in figure 3.4 vary between 82 per cent

and 96 per cent water.

Metabolism goes well in waterMetabolism includes all the chemical reactions that occur

in an organism. It involves catabolism, the breakdown

of compounds to release energy and other compounds or

atoms, as well as anabolism, the synthesis of new com-

pounds from simpler ones. These reactions occur most

readily in solution. Water is the predominant solvent in

the body and, as many organic compounds dissolve in

water, metabolism occurs in a watery solution. Water

facilitates metabolism.

Water molecules stick togetherEach water molecule consists of a combination of a single oxygen atom with two

hydrogen atoms (see figure 3.5a). Each hydrogen atom is linked to the oxygen

atom by a strong covalent bond. Although a water molecule overall has a neutral

charge, the oxygen at the end of a covalent bond is slightly negative and the

Figure 3.4 Water content of the

raw vegetables shown here ranges

between 82 and 96 per cent. The value

will change for some on cooking.


Cl–

Cl–

Na+

Na+

Cl–

Cl–

Cl–

Cl–

Cl–

Cl–

Cl–

Cl–

Cl–

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

+ +–

+ +–

+ +–

+

+

–

+ +–

+ +–

+ +–

++–

++–

++–

++–

++–

++

–

++

–

+

+–

+

+–

+

+–

Cl–+

+–

+

+–

+

+–

++–

+

+–

++

–Cl–+

+–

+

+– +

+–

++

–++–

++–

+

+ –+

+

–

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+

+–

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+

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+

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+

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–

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–

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–

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+ –

+

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+

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+

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+

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+

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+

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+

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+

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+

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+

+

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+

+

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+

+

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+

+

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+

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+

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+

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+

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+

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hydrogen atoms are slightly positive areas. Individual molecules of water are

highly attracted to each other such that the negative oxygen of one molecule of

water is attracted to the positive hydrogen of another water molecule. In fact,

the oxygen of a water molecule attracts one hydrogen in each of two other water

molecules. Water molecules are said to be highly cohesive. They stick together,

held by so-called hydrogen bonds, which are weaker than covalent bonds (see

figure 3.5).

Water is a

versatile solventWater is the predominant solvent in

living organisms. Its versatility as a

solvent is due to the cohesive nature

of the molecule that we examined

in the previous section. Substances

that dissolve readily in water are

called hydrophilic or polar. Sub-

stances that tend to be insoluble in

water are called hydrophobic or

non-polar. How would you classify

fats?

How do substances dissolve in

water? A substance such as sodium

chloride (salt, NaCl) dissociates

into its parts — positively charged

sodium ions and negatively charged

chloride ions — when it comes

into contact with water molecules.

This occurs because the positive

sodium ions are attracted by the

negative oxygen and the negative

chloride ions are attracted by the

positive hydrogen of water. These

attractions are sufficient to break

the bonds between sodium and

chloride. A ring of water mol-

ecules surrounds each sodium and

chloride atom and they remain in

solution (see figure 3.6).

Table 3.2 Water content in tissues

Tissue Percentage

blood (red cell) 60

blood (plasma) 92

muscle 75

cartilage 70

Figure 3.5 Each water molecule

is made of a single oxygen atom

combined with two hydrogen atoms.

(a) The hydrogen atoms are joined

to the oxygen with covalent bonds.

(b) Water molecules are attracted to

each other and hydrogen bonds form

between them. Hydrogen bonds are

shown as broken lines in the diagram.

Figure 3.6 A grain of salt contains many sodium chloride

molecules. When salt is placed in water, salt molecules dissociate

because of the attraction of sodium and chloride to different parts

of the water molecules. A ring of water molecules surrounds each

sodium and chloride atom and they remain in solution.

= oxygen

= hydrogen

(a) (b)


Other chemicals

70% 18% 4% 3% 2% 2% 1.1% 0.25%

Pro

tein

s

Inorg

anic

ions

and s

mall m

ole

cule

s

Phosp

holipid

s

Oth

er

lipid

s

Poly

sacchari

des

RN

A

DN

A

Wate

r

70%Water

30%Other chemicals

Figure 3.7 The graphs show the percentage of total cell weight of major chemicals in a

typical human cell.

Carbohydrates, proteins, lipids and nucleic acids are organic compounds.

Metabolism refers to all the chemical reactions that occur in a living

organism.

Water is the predominant solvent in living organisms.

Water molecules are highly cohesive because of the attraction between

hydrogen and oxygen atoms.

Substances vary in their ability to dissolve in water.

•

•

•

•

•

KEY IDEAS

QUICK-CHECK

1 Name the three elements found in all organic compounds.

2 What is the difference between:

a catabolism and anabolism?

b hydrophilic and hydrophobic substances?

3 Which is the stronger: a covalent bond or a hydrogen bond?

Water is the major component of cellsWater is by far the main component of living human cells. Although the per-

centage of water in different cells may vary (see table 3.2, page 54), 70 per

cent is a reasonable average for us to consider. In such a human cell, the

percentage of major chemicals are as outlined in figure 3.7.


Organic compoundsOrganic molecules are often large molecules made of smaller sub-units that are

bonded together in various ways. Compounds formed in this way are called

polymers. The sub-units are called monomers. We can classify molecules on the

basis of the kind of sub-unit they contain. Some examples are shown in figure 3.8.

The kinds of organic molecules we will consider are carbohydrates, proteins,

lipids, and nucleic acids. We will examine the basic unit of structure of each,

how the basic units combine to form the complex molecules, where each kind

of molecule is found in a cell and the function of the molecules. We will also

examine minerals and vitamins and their importance in cells.

Carbohydrates — energy-richThe basic unit of carbohydrates is a sugar molecule also called a monosaccharide.

The most common monosaccharide is glucose and units of glucose combine in

different ways to form different kinds of polysaccharides. Carbohydrates con-

taining one or two sugar units are sometimes called simple; those containing

many sugar units are called complex carbohydrates or polysaccharides. Starch,

cellulose and glycogen are all polysaccharides composed entirely of glucose mol-

ecules and yet their properties are very different. The difference in property relates

to the way in which the glucose molecules are linked together (see table 3.3).

Type Example Function Structure

monosaccharides glucose energy source in plant

and animal cell

disaccharides sucrose form of carbohydrate

for transport in plants

polysaccharides starch

glycogen

cellulose

form of energy storage

in plants

form of energy storage

in animals

structural carbohydrate

in plant cell walls

Figure 3.8 The four main groups of

organic molecules in cells. Note the

monomers that make up the polymers

of each group.

Table 3.3 Basic structure and

function of various groups of

carbohydrates

building blocks of the cell larger units of the cell

Sugars

MONOMERS:

Polysaccharides

POLYMERS:

Fatty acids Fats, lipids, membranes

Amino acids Proteins

Nucleotides Nucleic acids


Starch

Glycogen

CellulosemoleculesCellulosemolecules

Microfibril

Primary cell wall

Secondary cell wall

Liver

Chloroplast

Carbohydrates are important in plants as structural material. The firm

outer covering of insects and spiders is also a polysaccharide — chitin.

Cellulose is the most abundant organic compound on Earth. Carbohydrates

are also stored and used as a source of energy for plant and animal cells (see

figure 3.9).

Cells require energy all the time. Energy is used for movement, for making

new material for growth and repair, for maintaining internal conditions within

a narrow range and for detecting and responding to environmental changes.

When glucose is broken down in cells to smaller products during cellular res-

piration, the chemical energy present in the glucose is released. A portion of

this energy is harvested and captured in ATP molecules (discussed further on

pages 69–70).

Proteins

Proteins are large molecules built of sub-units called amino acids (figure 3.10a).

Note that all amino acids and hence proteins contain nitrogen as well as carbon,

hydrogen and oxygen. Some proteins also contain sulfur.

There are 20 naturally occurring amino acids (refer to appendix B) and each

amino acid has one part of its molecule different from other amino acids (figure

3.10a and b). Two amino acids join together when a peptide bond forms between

them (figure 3.10c). When a number of amino acids join in this way, a poly-

peptide is formed (figure 3.10d). Each type of protein has its own particular

sequence of amino acids. Polypeptide chains become folded in different ways

depending on their function.

Figure 3.9 Carbohydrates are made of sugar units. Note the

structure, location and function of each of the carbohydrates. What are

the similarities and differences between each of the polysaccharides?


Short chains of carbohydrate molecules attach to protein

Phospholipids form bilayer of plasma membrane

Glycerol (b) (a)

Fatty acid

Triglyceride

Cell membrane Cytoplasm

Fat storage

Adipose cell

Nucleus Protein

Proteins may be structural, for example in cell membranes (see figure 3.11)

or the protein filaments within a cell (refer to figure 2.24, page 41). The hae-

moglobin of red blood cells is protein. The enzymes that take part in all the

metabolic processes of every living cell are also proteins. Some hormones are

proteins.

Figure 3.10 Proteins are large

molecules made from amino acid

sub-units.

Figure 3.11 (a) Fats are important

energy stores, particularly in adipose cells.

(b) Phospholipids are an important component of

cell membranes. Note the carbohydrate molecule

attached to the protein in the cell membrane.

(b) Pool of amino acids

(d) Polypeptide chain of amino acids

Peptide bond(c) Dipeptides

(a) Generalised structure of an amino acidR = variable group

H3N+

C C

R

H

O

O


ODD FACT

Animals would have to carry twice as much

carbohydrate, compared with a weight of fat, to have the same

energy store.

LipidsLipid is the general term for fats, oils and waxes. They have little affinity for water. Fats and waxes are generally solid at room temperature and oils are liquid. A fat molecule is made of two kinds of molecules, fatty acids and glycerol. Triglycerides (figure 3.11a, page 58) are a common form of fats. These fats have a single glycerol molecule to which three fatty acid molecules are attached. The fatty acid molecules may be the same or different and lack affinity for water. Hence, fats also have little or no attraction for water and are insoluble in it. Fats and other compounds insoluble in water are called hydrophobic. Phospholipids, another kind of fat, have two fatty acids attached to a glycerol. They also have a phosphate group attached to the glycerol and other small groups attached to the phosphate to make different kinds of phospholipids. Phospho-lipids are a major component of cell membranes (see figure 3.11b). On a weight basis, fat stores twice as much energy as the same weight of polysaccharide so fats are important energy stores in cells, particularly animal

cells because animals carry their energy store around with them. Plants are able

to rely more heavily on polysaccharide energy storage.

Nucleic acidsThere are two kinds of nucleic acid. One is deoxyribonucleic acid (DNA) that

is located in chromosomes in the nucleus of eukaryotic cells. It is the genetic

material that contains hereditary information and is transmitted from generation

to generation. The second kind is ribonucleic acid (RNA) that is formed against

DNA which acts as the template.

Deoxyribonucleic acidThe genetic material deoxyribonucleic acid (DNA) is a polymer of nucleotides.

Each nucleotide unit has a sugar (deoxyribose) part, a phosphate part and an

N-containing base. The sugar and phosphate parts are the same in each nucleo-

tide. There are four different kinds of nucleotides because four different kinds

of N-containing bases are involved. The four different N-containing bases are

adenine, thymine, cytosine and guanine and the four different nucleotides are

denoted by the letters A, T, C and G because of the kind of base each contains

(figure 3.12).

P

S T

A

T

S

P

S

P

S G

P

S

P

C

(a) (b) (c)

Nucleotide

Nucleotidesjoin toform chain

P

P

P

P

A

G

C

P

T

P

P

P

A T

G

C

5'

3'

3'5'

Complementarypairing ofnucleotide basesof two chains to form a DNA doublehelix (DNA molecule)

Figure 3.12 Deoxyribonucleic acid

is made from nucleotide sub-units.

Each DNA molecule is made of two

complementary chains of nucleotides.


DNA double helix

Each DNA moleculecombines with protein to form a chromosome.

Chromosome700 nm

2 nm

3.4 nm

0.34 nm

Chromosomesin cell nucleus Each

chromosomecontains one DNA molecule.

(a) (b) (c)

Examine figure 3.12 (page 59). The nucleotide sub-units (a) are assembled

together to form a chain (b) in which the sugar of one nucleotide is bonded with

the phosphate of the next nucleotide in the chain. Each DNA molecule contains

two chains (c) that bond with each other because the bases in one chain pair with

the bases in another. The base pairs between the two strands, namely A with T,

and C with G, are said to be complementary base pairs.

Now examine figure 3.13. The two chains form a double-helical molecule of

DNA (a) that combines with certain proteins to form a chromosome (b). These

chromosomes reside in the nucleus of a cell (c) and the DNA they contain carries

genetic instructions that control all functions of the cell.

Figure 3.14 The four

nucleotide sub-units, uracil,

adenine, guanine and cytosine,

from which the three RNAs

are constructed.

QUICK-CHECK

4 Two proteins in a cell each contain the same number of amino acids and

yet have quite different functions. Explain.

5 Consider the carbohydrates glucose, starch, cellulose and glycogen.

In what ways are these compounds similar and in what ways are they

different?

6 Explain how the hydrophobic and hydrophilic parts of phospholipid

molecules influence the way they orientate in cell membranes.

7 In addition to C, H and O, which element is found in all proteins?

The major compounds that make up living cells are different kinds of

carbohydrates, lipids, proteins and nucleic acids.

Each major compound has a specific role. Some exist only in either plant

or animal cells; others play an important role in both.

•

•

KEY IDEAS

Figure 3.13 In eukaryotic cells,

each DNA molecule combines with

proteins to form a chromosome.

Ribonucleic acidRibonucleic acid (RNA) is also a polymer of nucleotides. It differs from DNA

in that it is an unpaired chain of nucleotide bases and exists in three different

forms. RNA is constructed from four different bases, three of which — adenine,

guanine and cytosine — are identical to those in DNA. The fourth nucleotide is

uracil that is capable of pairing with A (figure 3.14). The three different forms of RNA are:

messenger RNA (mRNA), formed against DNA as a template. mRNA carries the genetic message to the ribosomes where the message is translated into a particular protein.ribosomal RNA (rRNA) which, together with particular proteins, makes the ribosomes found in cytosoltransfer RNA (tRNA), molecules that carry amino acids to ribosomes where

they are used to construct proteins.

The strand of nucleotides in each of the RNAs is folded in a different way.

•

•

•

A

U

S

P

S

P

S G

P

S

P

C


MineralsMinerals are inorganic ions required by both animal and plant cells. In humans,

minerals make up about six per cent of the body (see table 3.4). Some, for

example calcium and phosphorus, are present in relatively large amounts. Others,

for example cobalt and molybdenum, are present only in trace amounts.

Mineral Percentage Mineral Percentage

calcium 2.0 copper 0.000 15

potassium 1.0 iodine 0.000 04

phosphorus 1.0 manganese 0.000 03

sulfur 0.25 cobalt trace

sodium 0.15 molybdenum trace

chloride 0.15 fluoride trace

magnesium 0.05 selenium trace

iron 0.005 chromium trace

zinc 0.002

Minerals play a role in metabolic processes of cells and are incorporated into

many structures produced by cells. For example, animal body structures such as

bone and teeth have significant mineral content in the form of calcium. The cell

walls of plants contain minerals such as silicon and boron and rely on calcium

for their middle lamella. Minerals also contribute to cell manufacture of many

hormones, enzymes and vitamins.

Plants and animals cannot manufacture minerals. Animals must obtain their

minerals from their diet; plants generally obtain theirs from the soil. Table 3.5

shows a sample of minerals important for plants and animals.

Mineral nutrient

FUNCTIONS

Animals Plants

Calcium Bones and teeth, transmission of

nerve impulses, enzyme reactions

Middle lamella of cell

walls, enzyme reactions

Potassium Osmotic balance of cells,

transmission of nerve impulses

Establishing cell turgor,

co-factor for many

enzyme reactions

Sodium Osmotic balance of cells,

transmission of nerve impulses

Substitutes for potassium

in some functions

Phosphorus Metabolism of fat, protein and

carbohydrate, cellular respiration

Cellular respiration

Iron Cytochromes — needed by all

cells for respiration

Cytochromes — involved

in photosynthesis,

nitrogen fixation and

cellular respiration

ODD FACT

Some metals, for example mercury,

cadmium and lead, are extremely toxic to cells even in

very small doses. Lead was once a common ingredient of paint. It is now banned from general

use in paints because of deaths associated with its ingestion.

Table 3.4 Percentages of minerals

in the body mass of humans

Table 3.5 A sample of minerals

important for animal and plant

processes


Although some minerals are required in relatively small amounts, they are still

vital for normal healthy functioning of cells. For example, copper is an essential

mineral for cellular respiration. A deficiency of copper supply to cells results in a

significant deficiency of production of energy-rich ATP. Some babies are unable

to supply sufficient copper to their cells and this has a fatal effect. Read about

Professor Julian Mercer and his work on copper deficiency in babies.

BIOLOGIST AT WORK

Professor Julian Mercer — Molecular geneticist

Professor Julian Mercer is a Research Scientist and

Director of the Centre for Cellular and Molecular

Biology, School of Biological and Chemical Sciences,

Deakin University in Melbourne. Julian writes:

From my school days I was always interested in chem-

istry. After school I completed a BSc majoring in

biology and chemistry at the Australian National Uni-

versity. After completing my honours year in organic

chemistry, I decided that the biological sciences were

more interesting to me than pure chemistry, and the

developing field of molecular biology was particularly

exciting. At the time, the mechanisms of protein syn-

thesis on the ribosome were still being worked out, and

I undertook a PhD to work in this area in the Biochem-

istry department at the University of Adelaide. My PhD

involved a lot of organic synthesis; I was making the

end of transfer RNA to see if it would work in peptide

bond formation.

After completing a PhD, a young scientist needs

to find a laboratory to continue postdoctoral research

training. I chose to return to the Australian National

University because I had an offer of a Fellowship to

work on mRNA isolation, which moved me closer to

molecular biology than chemistry.

After three years in Canberra, I moved to the Lab-

oratory of Molecular Biology in Cambridge, UK, for

another two years postdoctoral work. What an exciting

place to work in! The Laboratory of Molecular Biology

was, and still is, an amazing place. At the time I was

there, five Nobel Prize winners were working in the

same building. These included Francis Crick who, with

James Watson, successfully worked out the structure

of DNA. It was truly awe-inspiring to meet and talk

with these famous scientists — people who had laid

the foundations of molecular biology. One of the won-

derful aspects of science is the opportunity to meet and

work with extraordinary people from all cultures, and

also to live and work in other countries. You realise that

science is an international culture, one that overcomes

many of the cultural barriers that may arise in other

aspects of life.

I completed my conversion into a molecular geneticist

when I joined Professor David Danks in the Genetics

Research Unit (which later became the Murdoch Insti-

tute) at the Children’s Hospital in Melbourne. The field

was just entering the era of cloning disease genes and

I undertook projects aimed at cloning the gene affected

in PKU and the gene affected in the X-linked copper

disorder, Menkes disease. I did not know then, but my

investigation of Menkes disease would occupy me for

more than twenty years.

Figure 3.15 Professor Julian Mercer in his laboratory

It is not widely known that copper is an essential

element, and an adequate supply of this metal is vital

for normal development. Copper forms part of many

important enzymes. Perhaps the most important is

cytochrome c oxidase which is involved in aerobic

respiration in mitochondria. Babies with Menkes

disease cannot supply enough copper to cytochrome

c oxidase and this impairs their ability to form ATP. The

deficient ATP production has a catastrophic effect on


brain development (the brain is a big user of ATP) and

boys with Menkes disease usually die within 3 years.

Fortunately the disease is rare.

Menkes disease is an X-linked condition found in

about 1/100 000 boys born; very few girls are known to

have had the condition. Affected children have a range

of other abnormalities that can be related to copper

deficiency:

reduced hair pigmentation because tyrosinase, which

is part of the pathway that makes the dark pigment

melanin, needs copper

Figure 3.16 Copper deficiency in sheep causes ‘steely wool’, as

in this sample. The white banding in the black wool of this sheep

is due to the lack of copper that results in reduced tyrosinase and

hence reduced pigment.

•

weak artery walls leading to aneurisms and weak

bones, because copper is needed for an enzyme that

helps in connective tissue formation

unusual hair, which tends to be a bit like steel wool in

texture and is an important diagnostic feature.

Interestingly, Professor Danks discovered that Menkes

disease was caused by copper deficiency because he was

aware of Australian research that showed copper defi-

ciency in sheep causes ‘steely wool’ (see figure 3.16),

very like the unusual hair in boys with Menkes disease.

We worked for many years to try to find the gene

affected in this disease, but had success only when a rare

female was diagnosed with Menkes disease. Her condi-

tion arose as a result of a genetic accident at a very early

stage of her development. A portion of one chromosome

broke away and became inserted into the Menkes gene,

disrupting the normal function of that gene. If we could

find the location at which the piece had been inserted

— that is, the breakpoint in the X-chromosome — we

could locate the position of the Menkes gene. After much

work we were successful. The rare female was a chance

event that we were able to use to our advantage.

Chance events over the years have provided scientists

with opportunities for insights about situations that have

long puzzled them. The isolation of the Menkes gene

was an international race between four laboratories.

Eventually three succeeded and the three papers were

published together, so each laboratory received credit

for their discovery. The fourth laboratory isolated the

wrong gene.

•

•

VitaminsVitamins are a group of organic compounds that occur in minute quantities in

food. Although the requirement for vitamins may vary from animal to animal,

they are unable to make them and hence require vitamins in their diets. Although

it was known for centuries that certain diseases could be ‘cured’ by the addition

of a range of fresh foods to the diet, vitamins were not discovered and extracted

from food until early in the twentieth century.

When vitamins were first discovered, their chemical structures were unknown.

This resulted in the use of a series of letters — A, B, and so on — to designate

different vitamins. Now, the chemical structures are known and vitamins tend to

be called by their chemical names.

Vitamins can be divided on the basis of their chemical nature into two groups:

fat-soluble and water-soluble vitamins. Refer to table 3.6 (page 64) for more

information about vitamins.

Vitamins are essential for many of the chemical reactions that occur in cells.

The water-soluble vitamins, except for vitamin C, are components of co-enzymes.

Co-enzymes are small molecules necessary for the normal functioning of many

of the enzyme-controlled reactions within cells. The function of fat-soluble

enzymes is not as well understood as that of water-soluble ones but it is known

that they have an important role in blood coagulation, bone structure and vision

(see the information on ‘Enzyme function and specificity’ on page 65).

ODD FACT

The name of thewater-soluble vitamin folic

acid is derived from folium, Latin for ‘leaf’, and is found in green

plants, fresh fruit, yeast and liver. The active co-enzyme form of folic acid is tetrahydrofolate.


Vitamin Source Required for Recommended daily intake

Fat-soluble vitamins

A retinol

fish-liver oils, butter and margarine, green and yellow vegetables, carrots, yellow-fleshed fruits, tomatoes, egg yolk, liver and kidneys, whole milk

epithelial tissues — skin, linings of nose, mouth, digestive and urinary tracts; vision in dim light — forms visual purple in retina of eye

infants and children 250–750 µg; adults 750 µg; lactating women 1200 µg

D calciferol

liver, eggs, and can be made by the body

stimulates absorption of calcium and phosphorus in bone and teeth formation

5–10 µg; children and pregnant women have greatest need because of bone growth

E tocopherols

wheatgerm, butter and margarine, bread, green leafy vegetables, whole-grain products

prevents damage to cell membranes; protects fats and vitamin A from destruction by oxidation

10–15 mg

K phytomenadione

green vegetables, tomatoes, cabbage, cauliflower, potatoes, cereal, eggs

formation of prothrombin, essential for blood clotting

children 15–100 mg; adults 70–100 mg

Water-soluble vitamins

B1 thiamine

seafood, meat, whole-grain products the release of chemical energy from carbohydrate

children 0.5–1.2 mg; women 0.6–0.8 mg; men 0.8–1.1 mg

B2 riboflavin

meat, eggs, green vegetables, mushrooms, whole-grain products, pasta

protein metabolism; helps maintain healthy skin and eyes; growth of new body tissue

children 0.5–1.2 mg; women 0.8–1.0 mg;men 1.0–1.4 mg

B3 niacin

leafy vegetables, whole-grain products, peanut butter, potatoes, tuna, eggs

enzyme systems that convert carbohydrates, proteins and fats into energy; aids synthesis of hormones

children 9–20 mg; women 10–13 mg; men 14–18 mg

B6 pyridoxine

yeast, wheat germ, cereals, liver, meat, soya beans, peanuts, egg yolk

many enzyme reactions and for development of red blood cells

adolescents 1–2.2 mg; adults 1–1.5 mg; lactating women 1.6–2.2 mg

B12 cyanocobalamin

liver, meat, eggs, oysters, sardines development of red and white blood cells; also involved in metabolism

adults 2 µg; pregnant and lactating women 3–3.5 µg

folate liver, kidneys, yeast, mushrooms, leafy green vegetables

reduction of neural tube defects; development of red blood cells and metabolism of protein; linked with vitamin B12

adults 200 µg; pregnant women 400 µg; lactating women 300 µg

biotin liver, meat, fish, yeast, egg yolk, milk, smaller amounts in grains and vegetables

metabolism of fat and protein; growth and function of nerve cells

children 65–200 µg; adults 100–200 µg

pantothenic acid liver, meat, fish, egg yolk, yeast, cereals, peanuts and vegetables; also found in ‘royal jelly’ (fed to the queen bee) but this is most expensive and not in any way a source superior to others

metabolism of carbohydrate, fat and protein

estimated 5–10 mg

C ascorbic acid

citrus and other fruits, tomatoes, leafy vegetables, potatoes, rosehips

connective tissues, bones, teeth; promotes wound healing and absorption of iron

children 30–50 mg; adults 30 mg; pregnant and lactating women 60 mg

Note: In an attempt to set a standard for an adequate diet for groups of the population, health authorities introduced a scheme of recom-

mended dietary intakes (RDI). These recommendations are often quoted now in labelling of nutrients on foods, but it is important to realise

that an RDI does not necessarily equal the requirement of a particular individual.

Variation exists in the amount of nutrients required by different individuals. Variation is due to a number of factors including genetic

factors, body size, activity level and state of health. An RDI value should satisfy the requirements of 95 per cent of the population but some

people require less than the RDI and others require more. A person with a varied and well-balanced diet will receive adequate amounts of

vitamins and minerals.

Table 3.6 Vitamins — their source and functions


8 Name, and give the function of, two minerals that the body requires in

relatively large amounts and two that it requires in trace amounts.

9 a Name four foods that are a source of fat-soluble vitamins.

b Name four foods that are rich in water-soluble vitamins.

10 What feature of enzymes controls which substrate they act on?

QUICK-CHECK

The body requires a number of minerals, some in relatively large amounts,

others in trace amounts.

Minerals play a role in metabolic processes of cells and are incorporated

into many structures produced by cells.

Copper is an essential mineral for cellular respiration.

Vitamins are a group of organic compounds and are essential for many of

the chemical reactions that occur in cells.

Vitamins can be divided on the basis of their chemical nature into two

groups: fat-soluble and water-soluble vitamins.

Each enzyme acts on only one kind of substrate.

•

•

•

•

•

•

KEY IDEAS

ENZYME FUNCTION AND SPECIFICITY

Enzymes are protein molecules that increase the rate

of the reactions that occur in living organisms. Without

enzymes, metabolism would be so slow at body temper-

ature and pH that insufficient energy would be available

to maintain life. Many enzymes are intracellular; they

are used within cells that produce them. Others (for

example, the digestive enzymes) are extracellular. They

are secreted by cells and act outside those cells.

The compound being acted on by an enzyme is called

a substrate. The compounds obtained as a result of the

enzyme action are called the products. Enzymes are

highly specific in their action; each enzyme acts on only

one kind of substrate. This is because the shape of one

enzyme matches that of one substrate at a particular

region known as the active site of the enzyme, as shown

in figure 3.17.

An enzyme is named for the substrate it associates

with. The enzyme maltase acts on the disaccharide

maltose. Lipase acts on lipid, and amylase on amylose.

Note the -ase endings in the name of most enzymes. The

few exceptions include trypsin and pepsin.

Although enzymes participate in reactions, they are

not used up in the reactions and are available for reuse.

The rate of an enzyme reaction is influenced by pH,

temperature, enzyme concentration and substrate con-

centration. Why do you think the activity of an enzyme

is destroyed at high temperatures?

Many enzymes require the presence of other factors

before they act. If the factor is an organic molecule

(for example a vitamin), it is called a coenzyme. Some

poisons, for example cyanide and arsenic, block the

active sites of enzymes and hence interfere with cell

metabolism.

Figure 3.17 Representation showing that each enzyme reacts

with only one kind of substrate. This is because the active site of

an enzyme matches the shape of a particular substrate and the

two are able to come closer together. This matching of shapes is

often called the ‘lock and key’ theory of enzyme action.

Active

site

Enzyme Possible substrates Only one substrate

fits the active site

Enzyme Substrate Enzyme–substrate

complex

Enzyme Products


Autotrophs are also called

producers and heterotrophs are

called consumers.

Figure 3.18 The inputs and outputs

of the process of photosynthesis

Producers at work: photosynthesisHow do carbohydrates originate? Using the energy of sunlight, plants, algae

and some protists (such as phytoplankton) can make organic molecules, such as

sugars, by photosynthesis. Organisms with this ability are termed autotrophic.

Other organisms, such as animals and fungi, that depend, directly or indirectly,

on the organic compounds produced by producers are called heterotrophic.

Photosynthesis is the process in which light energy is transformed into

chemical energy stored in sugars. In a typical producer, such as a terrestrial

flowering plant, the complex series of reactions in photosynthesis can be sum-

marised as follows:

In fact, the complete balanced equation for photosynthesis is

6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O light

This is often simplified to:

6CO2 + 6H2O C6H12O6 + 6O2

light

showing net consumption of water only.

The general word equation for photosynthesis is the summary for a chain of

biochemical reactions, as we will see later. One way of summarising the inputs

and outputs of photosynthesis is shown in figure 3.18.

In fact, the details of the chemical reactions that make up photosynthesis are

more complex than the equation shown here. You will be introduced to more

information about the chemistry of photosynthesis as you progress through your

biology studies. For now, we will explore where photosynthesis occurs and how

different wavelengths of light can influence the process.

Light

+

Carbon dioxide

+

Water

Glucose

+

Oxygen

INPUTS OUTPUTS

carbon dioxide + water glucose + oxygen

chlorophyll

carbon dioxide + water glucose + oxygen

chlorophyll

ELight


Porp

hyri

n r

ing

CH3 in chlorophyll

in chlorophyll

a

CHO b

C N

CH3

CH3

CH3

CH3

CH3

C

C

C

C

C

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

H

CH

CH H

O C O

CH2

CH2

C

CC

H

H

H3C

C

C

HC

C

C

C CH3

CH2CH3

N C

CH

N C

Mg

C N

HC

C

CC

C

C

C

C

CH H

CH2

C O

C O

OCH3

H3

Chloroplasts: where the action is!The cytoplasm of cells in the leaf tissue where photosynthesis occurs contains

specialised organelles, known as chloroplasts. Each chloroplast has an outer

membrane and folded inner membranes joined to form stacks of flattened discs,

know as grana (singular = granum) (see figures 2.20 (page 37) and 3.19).

The enzymes needed for the reactions in photosynthesis are located inside the

chloroplasts, with some located in the grana membranes and some in solution in

the stroma.

Light-trapping pigmentsRadiant energy from the sun includes a range of wavelengths:

visible light, in the range from about 0.4 to 0.7 µm

infra-red (IR), with wavelengths greater than 0.7 µm

ultraviolet light (UV), with wavelengths shorter than 0.4 µm.

Various pigments can trap light energy. The major light-trapping pigments

are green chlorophylls (see figure 3.20) located on the grana membranes. Other

kinds of light-trapping pigments, known as accessory pigments, are also found

in the chloroplasts of various organisms (see table 3.7).

Table 3.7 Occurrence of various light-trapping pigments in plants and algae

Pigment Organisms where found

chlorophyll a all plants and all algae

chlorophyll b all plants and green algae

chlorophyll c brown algae and phytoplankton

chlorophyll d red algae

carotenoids all plants and green algae

phycobilins red algae

Carotenoids are red, orange and yellow pigments that are normally masked by

the green chlorophylls. In temperate climates in early autumn, deciduous trees

begin to withdraw the chlorophyll from their leaves, exposing the carotenoids and

other pigments that are normally hidden (see figure 3.21). Phycobilins are blue-

green (phycocyanin) and red (phycoerythrin) water-soluble pigments.

•

•

•Figure 3.20 Molecular structure of

chlorophyll a

(a) Air spaces

(b) Stroma Granum

Chloroplasts in cell

Stoma (pore) Lower epidermis

Upper epidermis

Figure 3.19 (a) Features of a leaf

(b) Internal structure of chloroplast showing

many layers of membranes, the grana, and

stroma, the fluid part

Figure 3.21 Deciduous leaves in

early autumn


The various pigments trap light energy of different wavelengths (see figure

3.22). Consequently, the presence of accessory pigments extends the range of

light wavelengths that can be absorbed by a plant and converted to chemical

energy. Light energy absorbed by accessory pigments must be transferred to

chlorophyll a before it can be converted into chemical energy. If the accessory

pigments were removed from a plant cell, what would you predict would happen

to the rate of photosynthesis?

Photosynthesis is most efficient in light of red and blue wavelengths. These

wavelengths do not penetrate very far below the surface of water. In deeper

waters most of the light wavelengths available are blue-green, which accessory

pigments can absorb. The phycobilins, in particular, contribute to photosynthesis

in deeper waters and these are found in seaweeds (see figure 3.23). Seaweeds

that have colour when brought to the surface of the water often look black when

looked at in water. Can you determine why this is so? Think about absorption and

reflection of different wavelengths of light.

Figure 3.22 Absorption of light

of various wavelengths for different

plant pigments. Which pigment

absorbs yellow light best? What

wavelengths of light (colours) are

best absorbed by chlorophylls?

Figure 3.23 Different algae: (a) green seaweed, Caulerpa remotifolia, found at depths of up to 10 metres (b) brown seaweed,

Macrocyctis pyrifera, also found at depths of up to 10 metres (c) red seaweed, Callophyllis lambertii, found at depths of up to 35 metres

ODD FACT

Trees that lose their leaves during one short

period of the year are said to be deciduous. In contrast, Australian native trees drop

leaves in small numbers over the entire year. Because these trees do not become leafless, they are

termed evergreens.

80

60

40

20

0.4 0.5 0.6 0.7

Wavelength ( m)

Rela

tive a

bsorp

tion (

%)

Chlorophyll a

Chlorophyll b

Carotenoids

Phycoerythrin Phycocyanin

Violet Blue Green RedViolet Blue Green Yellow Red

Gamma rays X-rays Ultraviolet Microwaves Radio waves

Visible light in

electromagnetic spectrum

Infra-red

(a) (b) (c)


Accessing energy: cellular respirationAll living organisms require energy to maintain life. The energy required to

maintain cellular functions is in the form of adenosine triphosphate (ATP) (see

figure 3.24). Where does this ATP come from? As we saw on pages 29 and 32,

ATP is formed when energy is released during cellular respiration of glucose,

a carbohydrate.

Figure 3.24 Energy is necessary for life. ATP, a high-energy compound, is a major source of

energy for many functions in the human body, some of which are outlined here.

The transfer of chemical energy from glucose to ATP occurs through a coupling

of chemical reactions (see figure 3.25).

The process of energy transfer from glucose to ATP is not 100 per cent

efficient. Some of the chemical energy is converted to and ‘lost’ as heat energy.

In general, the energy transfers in cellular respiration are 40 per cent efficient

— about 40 per cent of the chemical energy present in glucose is transferred

Muscle

contraction

Nervous

tissue

Digestive

system

Excretory

system

New tissue and

structure production

Manufacturing

chemicals

heart

muscle

skeletal

muscle

muscle

in gut migration of

vesiclesconduction

of impulses

transmitter

substances

blood

proteins

secretion

of enzymes

active

secretion of

ions

active

reabsorption

of water

active

transport across

membranes

nails

hair

blood

skin

antibodies

enzymes

hormones

diaphragm

peristalsis

wound tissue

ATP

Figure 3.25 Energy released

from reactions involving glucose is

transferred to the energy-requiring

process of ATP production. Is the

process 100% efficient?

(Pi � inorganic phosphate;

ADP � adenosine diphosphate)

OutIn

Breakdown

products

CO2, H2O

ATP

ADP + Pi

High

energy level

Low

energy levelHeat energy

E

Chemical

Glucose


Like all living tissue, fruit and vegetables carry out

cellular respiration and produce some heat energy. The

higher the rate of respiration, the more heat energy is

produced and the greater the chance that deterioration

of the plant material will occur. The rate of respiration

varies in different produce (see table 3.8).

Respiration rates depend on the storage tempera-

ture and the stage of ripeness of the plant material. For

example, broccoli at 20°C respires nearly 15 times faster

than broccoli at 0°C. Produce that is highly perishable

generally has a high respiration rate and a high rate of

heat evolution. Unless this heat is removed, the tem-

perature of the produce increases resulting in an even

higher rate of respiration, greater release of heat energy

and more rapid deterioration.

Several techniques are used to slow respiration rate

and prevent deterioration:

cooling of fruit and vegetables after harvesting and

transport to markets in refrigerated trucks

keeping the produce in a confined space in an atmos-

phere with reduced oxygen and increased carbon

dioxide. The reduced oxygen results in a slower

rate of aerobic respiration and lower heat produc-

tion. However, the level of gases must be carefully

controlled because too little oxygen can cause anaer-

obic respiration or fermentation which can also ruin

produce.

•

•

coating the surface of produce, such as apples and

bananas, with wax. This coating lengthens shelf life

by slowing the intake of oxygen and the escape of

carbon dioxide.

Table 3.8 Examples of approximate

respiration rates (watts/tonne)

Fruit or vegetable

Respiration rate

storage at 0°C

broccoli 212

lettuce 72

celery 61

peaches 23

cabbage 15

plums 6

storage at 2°C

asparagus 155

storage at 14°C

bananas

(ripening)

111

bananas

(green)

40

•

CELLULAR RESPIRATION IN FRUIT AND VEGETABLES

Figure 3.26 The living

cells in fruit and vegetables

respire.

to ATP and the remaining 60 per cent appears as heat energy. So, living cells

produce heat. The box below describes how heat production from respiring fruit

and vegetables contributes to their deterioration.

Cells cannot use heat energy to drive energy-requiring activities, such as

muscle contraction or transport against a concentration gradient. However, in

mammals and birds, the heat energy released from cellular respiration is trapped

by insulating layers of fat, fur or feathers and is the internal source of the heat

needed to maintain their core body temperatures within narrow ranges.

When cellular respiration involves the use of oxygen, the term aerobic

respiration or aerobic cellular respiration is used and the overall equation is:

Aerobic respiration of glucose generally yields 36 molecules of ATP per molecule

of glucose.

In some tissues, respiration occurs without the involvement of oxygen and is

referred to as anaerobic respiration. Anaerobic respiration is far less efficient

than aerobic respiration in converting the energy in glucose into energy in ATP

yielding just 2 ATP molecules per molecule of glucose. The end products of

anaerobic respiration in human muscle are lactic acid and carbon dioxide.

E

C6H

12O

6 + 6O

2

glucose carbon dioxide wateroxygen

ADP + Piin the form

of ATP

6CO2 + 6H

2O

ODD FACT

The end productsof anaerobic respiration in

yeast are the alcohol ethanol and carbon dioxide.

ODD FACT

Built-in electric blanket! Brown

fat tissue is found in young mammals and in adult mammals of species that hibernate. Brown

fat is metabolised and the energy released appears as heat energy, not as chemical energy

in the form of ATP.


Levels of biological organisationIn chapter 2 (pages 42–46), we introduced you to the various levels of organ-

isation of cells. Figure 3.27 shows how the molecules and compounds we have

discussed in this chapter fit in the organisation of cells and of the living world.

The progression of complexity from subatomic to atomic extends into molecules

and compounds, then to cells that become functional entities, capable of sus-

taining life and being the basic building block of all living organisms.

11 What is the difference between an autotroph and a heterotroph?12 Where in a cell is light energy transformed to chemical energy?13 Name the inputs and outputs in photosynthesis.14 Where in a cell does aerobic respiration occur?15 Name the inputs and outputs of (a) aerobic respiration; (b) anaerobic

respiration.

QUICK-CHECK

Photosynthesis is the process of converting light energy to chemical energy stored in sugars. Organisms that can make organic molecules by photosynthesis are called autotrophs and include all plants, algae and some bacteria.Adenosine triphosphate (ATP) is formed when energy is released during cellular respiration of glucose, a carbohydrate.

•

•

•

KEY IDEAS

ECOSYSTEM

Dynamic systemof organismsinteracting witheach other andtheir environment

MOLECULES

Two or more atoms bonded together

ORGANELLES

and CYTOPLASM

Components from which cells are constructed

CELL

The smallest unit that is itself alive

MULTICELLULAR

ORGANISM

Individual composedof many specialised cells

POPULATION

Group of organismsof the same species in the same area

COMMUNITY

Populations oforganisms livingtogether in the same habitat

BIOSPHERE

Entire surface of the earth and its organisms

Ability toperform simplebiologicalfunctions

Capacity toperform complexbiologicalfunctions

Higher biologicalproperties e.g. sight, emotion,intelligence

Social order;evolution

Species interaction(predation,parasitism,mutualism, etc.)

LIFE

Unique phenomena that emerge as complexity increases

SUBATOMIC PARTICLES

Protons, neutrons,and electrons

ATOMS

Smallest unit of a substance that retains the properties of that substance

Figure 3.27 Levels of

biological organisation. As each

level increases, structural

complexity increases and unique

phenomena may emerge.

BIOCHALLENGE


1 2

3

4

Many compounds contain the element carbon, symbol C. For

example, the formula for the mineral calcite is CaCO3.

Explain whether you would classify calcite as an organic

compound.

Mammalian tissue cells live in a moist environment of tissue

fluid. This fluid contains many different materials in solution.

Would you expect these materials to be monomers or

polymers?

The temperature at which an enzyme is most efficient is the

temperature at which the rate of a reaction involving the enzyme

is at its highest point. It is reasonable to assume that this

temperature is close to the body temperature of an organism.

Scientists investigated the rates of reaction of three enzymes

over a range of temperatures. The enzymes were taken from the

following warm-body organisms:

• Arctic gull, body temperature 34°C

• human, body temperature 37°C

• western pewee bird, body temperature 44.8°C.

The results for two of the enzymes investigated are given in the

following graph.

a From which organism is enzyme B likely to have come?

b If the results from the third enzyme were plotted, where would

you expect them to be in relation to the two results already on

the graph?

Examine the illustrations above. Which of the structures is:

a an amino acid?

b a lipid polymer?

c a carbohydrate monomer?

d an amino acid polymer?

e a nucleic acid polymer?

f a carbohydrate polymer?

A B C D

E F G H

Temperature °C

Enzyme A Enzyme B

17 21 25 29 33 37 41 45 49

Rate of

enzyme

reaction


CHAPTER REVIEW

accessory pigments

active site

adenine

aerobic cellular

respiration

aerobic respiration

amino acids

anabolism

anaerobic respiration

autotrophic

bonds

carbohydrates

catabolism

cellular respiration

cellulose

chemical energy

chitin

chlorophylls

chloroplasts

coenzyme

cohesive

complex carbohydrates

covalent bond

cytosine

deoxyribonucleic acid

(DNA)

enzymes

fatty acids

glucose

glycerol

glycogen

grana

guanine

heterotrophic

hydrogen bonds

hydrophilic

hydrophobic

light energy

lipids

metabolism

minerals

monomers

monosaccharide

non-polar

nucleic acids

organic compounds

phospholipids

photosynthesis

polar

polymers

polysaccharides

proteins

ribonucleic acid

(RNA)

starch

stroma

substrate

thymine

triglycerides

vitamins

Key words

Questions

1 Making connections between concepts ³�Prepare a concept map, using key

words and phrases from the list above. You may use any additional concepts

that you wish.

2 Understanding scientific terminology ³ Many vitamins are called

coenzymes. What is the function of such vitamins?

3 Applying understanding to new contexts ³ When phospholipids

are added to water, they aggregate

(come together) as shown in figure

3.28. Explain why the molecules

come together in this way.

4 Interpreting and communicating ideas ³ Discuss the validity of each

of the following statements.

a The source of oxygen used in

aerobic respiration is the same for

plants and animals.

b All nucleic acids are identical.

c All enzymes act in the same way

because they are all made of

proteins.

CROSSWORD

Figure 3.28


5 Making connections between concepts ³ The diagram in figure 3.29 is

sometimes called the ‘biology energy wheel’. Process A is photosynthesis.

a Name process B.

b Name the input element X.

c Name the output product at Y.

d In what form must energy be before it can be used for metabolic processes

in a cell?

6 Analysing information and making connections ³ All living cells in

humans are close to a blood supply that delivers oxygen that is then avail-

able for aerobic cellular respiration. Skeletal muscle is also capable of

carrying out anaerobic respiration and does so at certain times.

a What is the advantage of skeletal muscle being able to carry out anaerobic

respiration as well as aerobic respiration?

b Describe the conditions that individuals might be under when their

skeletal muscles engage in anaerobic respiration.

7 Application of concepts ³ Fruit and vegetables are sometimes transported

over very long distances between grower and consumer. For many products,

refrigerated transport is essential. Why is such transport needed to ensure

that the produce is in good order on its arrival at markets?

8 Analysing and evaluating information ³ Suggest explanations for the

following observations.

a It is cheaper to keep a large pot plant alive than a small dog.

b A greengrocer found that his refrigerator costs were greater when he

stored broccoli in his cold room than when he stored the same amount of

cabbages.

9 Analysing and evaluating information ³ Discuss the validity of each of

the following statements.

a A tissue contains groups of cells where each group has quite a different

function.

b Delivery mechanisms are important if a group of small cells is to operate

more effectively than one large cell.

c The surface-area-to-volume ratio of a cell influences the rate at which

substances can enter or exit the cell.

10 Using the web ³ Go to www.jaconline.com.au/natureofbiology/natbiol1-3e

and click on the ‘Photosynthesis’ weblink for this chapter. Select ‘Center

for Study of Early Events in Photosynthesis’ from the given list. Read ‘The

Power of Green’ and examine the drawing on the page.

a The drawing on the page implies some similarity between photosynthesis

in a plant and the water wheel of a mill. Explain what similarity you think

the artist was indicating in the drawing.

b Select ‘Educational Resources’ from the index bar. Then select ‘What

is photosynthesis?’ Select ‘Introduction to Photosynthesis and its

Applications’ and read the section headed ‘Basics’.

i Why do we see most leaves as the colour green?

ii Suggest why wavelengths of light below 330 nm are likely to damage

cells.

Eradiant

E

X

Process B

Process A

Energy formetabolicprocesses

carbon dioxide + waterY

Figure 3.29

http://www.jaconline.com.au/natureofbiology/natbiol1-3e

Chp 3 Composition of Cells

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