Post on 01-Jul-2018
© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
Chapter 3 The Molecules of Cells
Adapted and delivered by Sharaf Al-Tardeh (Ph.D.) Al-Tardeh S. 1
Introduction
Most of the world’s population cannot digest
milk-based foods.
– These people are lactose intolerant, because
they lack the enzyme lactase.
– This illustrates the importance of biological
molecules, such as lactase, in the daily
functions of living organisms.
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Al-Tardeh S. 2
3.1 Life’s molecular diversity is based on the
properties of carbon
Diverse molecules found in cells are
composed of carbon bonded to
– other carbons and
– atoms of other elements.
Carbon-based molecules are called organic
compounds.
Therefore, carbon is considered as a chief
elements in organic compounds.
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By sharing electrons, carbon can
– bond to 4 other atoms and
– branch in up to 4 directions.
For example: Methane (CH4) is one of the
simplest organic compounds.
– Four covalent bonds link four hydrogen
atoms to the carbon atom.
– Each of the four lines in the formula for
methane represents a pair of shared
electrons. © 2012 Pearson Education, Inc.
Al-Tardeh S. 5
Structural formula
Ball-and-stick model
Space-filling model
The four single bonds of carbon point to the corners of a tetrahedron.
Al-Tardeh S. 6
Methane and other compounds
composed of only carbon and
hydrogen are called hydrocarbons.
A carbon skeleton is a chain of carbon
atoms that can be
– branched or
– unbranched.
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Carbon Skeletons can vary in several ways
1. Length: Carbon skeletons vary in length.
Ethane Propane
Al-Tardeh S. 8
Butane Isobutane
2. Branching:
Skeletons may be unbranched or branched.
ISOMERS: are Molecules with the same
formula but with a different arrangement of
their atoms
Al-Tardeh S. 9
3.2 A few chemical groups are key to the
functioning of biological molecules
An organic compound has unique properties that
depend upon the:
1. size and shape of the molecule
2. groups of atoms (functional groups) attached
to it.
A functional group affects a biological molecule’s
function in a characteristic way.
Compounds containing functional groups are
hydrophilic (water-loving).
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The functional groups are:
1. hydroxyl group: consists of a hydrogen bonded
to an oxygen.
2. carbonyl group: a carbon linked by a double
bond to an oxygen atom.
3. carboxyl group: consists of a carbon double-
bonded to both an oxygen and a hydroxyl group
4. amino group: composed of a nitrogen bonded to
two hydrogen atoms and the carbon skeleton.
5. phosphate group: consists of a phosphorus
atom bonded to four oxygen atoms. Al-Tardeh S.
13
– Male and female sex hormones differ only in
functional groups.
– The differences cause varied molecular
actions.
– The result is distinguishable features of
males and females.
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An example of similar compounds that differ only
in functional groups is sex hormones.
Figure 3.2
Testosterone Estradiol
Al-Tardeh S. 17
Results in the different actions of these molecules,
which help produce the contrasting features of males
and females in lions and other vertebrates
3.3 Cells make a huge number of large molecules
from a limited set of small molecules
There are four classes of molecules
(macromolecules) important to
organisms:
1. carbohydrates
2. proteins
3. Lipids
4. nucleic acids.
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They are very large molecules.
– They are often called macromolecules
because of their large size.
– They are also called polymers because
they are made from identical building
blocks strung together.
– The building blocks of polymers are
called monomers.
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Monomers are linked together to form
polymers through dehydration reactions =
remove water.
Polymers are broken apart by hydrolysis,
the addition of water.
All biological reactions of this sort are
mediated by enzymes, which speed up
chemical reactions in cells.
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A cell makes a large number of
polymers from a small group of
monomers.
For examples:
– proteins are made from only 20
different amino acids
– DNA is built from just four kinds of
nucleotides.
The monomers used to make polymers
are universal.
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Short polymer Unlinked
monomer
Al-Tardeh S. 22
Figure 3.3 Dehydration reaction building a
polymer chain (step 1)
Figure 3.3A_s2
Short polymer Unlinked
monomer
Dehydration reaction
forms a new bond
Longer polymer
Al-Tardeh S. 23
3.4 Monosaccharides are the simplest
carbohydrates
Carbohydrates range from small sugar molecules
(monomers) to large polysaccharides.
Sugar monomers are monosaccharides, such as
those found in honey,
1. glucose
2. fructose.
Monosaccharides can be hooked together to form
– more complex sugars
– polysaccharides.
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The carbon skeletons of monosaccharides vary
in length.
– Glucose and fructose are six carbons long.
– Others have three to seven carbon atoms.
Monosaccharides are
1. the main fuels for cellular work
2. used as raw materials to manufacture other
organic molecules.
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Many monosaccharides form rings.
The ring diagram may be
– abbreviated by not showing the carbon
atoms at the corners of the ring and
– drawn with different thicknesses for the
bonds, to indicate that the ring is a relatively
flat structure with attached atoms extending
above and below it.
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Figure 3.4C
Structural
formula Abbreviated
structure
Simplified
structure
6
5
4
3 2
1
Al-Tardeh S. 31
3.5 Two monosaccharides are linked to form a
disaccharide
Two monosaccharides (monomers) can bond to
form a disaccharide in a dehydration reaction.
The disaccharide sucrose is formed by
combining:
1. a glucose monomer
2. a fructose monomer.
The disaccharide maltose is formed from two
glucose monomers. Al-Tardeh S. 32
3.6 CONNECTION: What is high-fructose corn syrup,
and is it to blame for obesity?
Sodas or fruit drinks probably contain high-fructose
corn syrup (HFCS).
Fructose is sweeter than glucose.
To make HFCS, glucose atoms are rearranged to
make the glucose isomer, fructose.
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High-fructose corn syrup (HFCS) is
1. used to sweeten many beverages
2. may be associated with weight gain.
Good health is promoted by
– a diverse diet of proteins, fats, vitamins, minerals, and complex carbohydrates and
– exercise.
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Al-Tardeh S. 37
Figure 3.6 High-fructose corn syrup (HFCS), a main
ingredient of soft drinks and processed foods
3.7 Polysaccharides are long chains of sugar units
Polysaccharides are
– macromolecules
– polymers composed of thousands of
monosaccharides.
Polysaccharides may function as
1. storage molecules
2. structural compounds.
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Starch is
– a polysaccharide
– composed of glucose monomers
– used by plants for energy storage.
Glycogen is
– a polysaccharide
– composed of glucose monomers
– used by animals for energy storage
– Stored in the liver and muscles of the body
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Cellulose
– is a polymer of glucose
– forms plant cell walls.
Chitin is
– a polysaccharide
– used by insects and crustaceans to
build an exoskeleton.
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Starch granules in potato tuber cells
Glycogen granules in muscle tissue Glycogen
Glucose monomer
Starch
Cellulose
Hydrogen bonds
Cellulose molecules
Cellulose microfibrils in a plant cell wall
Al-Tardeh S. 41
Figure 3.7_3
Cellulose
Hydrogen bonds
Cellulose molecules
Cellulose microfibrils in a plant cell wall
Al-Tardeh S. 44
Polysaccharides are usually hydrophilic
(water-loving).
i.e., Bath towels are:
– often made of cotton, which is mostly
cellulose
– water absorbent.
Al-Tardeh S. 45
3.8 Fats are lipids that are mostly energy-storage
molecules
Lipids:
– are water insoluble (hydrophobic, or water-
fearing) compounds
– are important in long-term energy storage
– contain twice as much energy as a
polysaccharide
– consist mainly of carbon and hydrogen atoms
linked by nonpolar covalent bonds.
Al-Tardeh S. 47
Lipids differ from carbohydrates, proteins,
and nucleic acids in that they are:
1. not huge molecules.
2. not built from monomers.
Lipids vary a great deal in
1. structure
2. function.
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We will consider three types of lipids:
1. fats
2. phospholipids
3. steroids.
A fat is a large lipid made from two kinds of
smaller molecules:
1. glycerol
2. fatty acids.
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A fatty acid can link to glycerol by a
dehydration reaction.
A fat contains one glycerol linked to three
fatty acids.
Fats are often called triglycerides because
of their structure.
Al-Tardeh S. 51
Fatty acid
Glycerol
Al-Tardeh S. 52
Figure 3.8B A dehydration
reaction linking a fatty acid
molecule to a glycerol
molecule
Some fatty acids contain one or more double
bonds, forming unsaturated fatty acids that:
– have one fewer hydrogen atom on each carbon
of the double bond
– cause kinks or bends in the carbon chain
– prevent them from packing together tightly and
solidifying at room temperature.
Fats with the maximum number of hydrogens are
called saturated fatty acids.
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For examples:
Unsaturated fats include corn and olive oils.
Most animal fats are saturated fats.
Hydrogenated vegetable oils are unsaturated
fats that have been converted to saturated fats by
adding hydrogen.
This hydrogenation creates trans fats associated
with health risks (trans is unhealthy).
Al-Tardeh S. 55
Cis - Trans Fatty acids
Living Organisms Produce “cis” acids which cause the
molecules to take on a bent shape.
Hydrogenation causes a random mix of both “cis” and
“trans”. Trans fatty acids are straight rather than bent.
They are also associated with “Bad Cholesterol”
Al-Tardeh S. 56
3.9 Phospholipids and steroids are important
lipids with a variety of functions
Phospholipids are:
1. the major component of all cells
2. Phospholipids are structurally similar
to fats:
Fats contain three fatty acids attached to
glycerol.
Phospholipids contain two fatty acids
attached to glycerol.
Al-Tardeh S. 57
Hydrophobic tail
Hydrophilic head
Phosphate group
Glycerol
Al-Tardeh S. 58
Figure 3.9A Chemical structure
of a phospholipid molecule
Phospholipids cluster into a bilayer of phospholipids.
The hydrophilic heads are in contact with:
the water of the environment
the internal part of the cell.
The hydrophobic tails band in the center of the bilayer.
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Water
Hydrophobic tails
Water
Hydrophilic heads
Symbol for phospholipid
Phosphate group
Glycerol
Al-Tardeh S. 60
Figure 3.9A-B Detail of a
phospholipid membrane
Steroids: are lipids in which the carbon skeleton
contains four fused rings.
Cholesterol is a:
– common component in animal cell
membranes
– starting material for making steroids,
including sex hormones.
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Steroids are important lipids with a variety of
functions
3.10 CONNECTION: Anabolic steroids pose health
risks
Anabolic steroids:
– are synthetic variants of testosterone
– can cause a buildup of muscle and bone
mass
– are often prescribed to treat general anemia
and some diseases that destroy body muscle.
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Anabolic steroids are abused by some athletes with serious consequences, including:
1. violent mood swings
2. depression
3. liver damage
4. cancer
5. high cholesterol
6. high blood pressure.
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3.10 CONNECTION: Anabolic steroids pose health
risks
3.11 Proteins are made from amino acids linked
by peptide bonds
Proteins are:
– involved in nearly every dynamic function
in your body
– very diverse, with tens of thousands of
different proteins, each with a specific
structure and function, in the human body.
Proteins are composed of differing
arrangements of a common set of just 20
amino acid monomers. Al-Tardeh S. 70
Amino acids (structure) have:
1. an amino group
2. a carboxyl group (which makes it an acid).
3. Also bonded to the central carbon by
a hydrogen atom
a chemical group symbolized by R: which
determines the specific properties of each
of the 20 amino acids used to make
proteins.
Al-Tardeh S. 71
• Amino acids are classified as either
– hydrophobic
or
– hydrophilic.
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Amino acid monomers are linked together
– in a dehydration reaction
– joining carboxyl group of one amino acid to
the amino group of the next amino acid,
creating a peptide bond.
Additional amino acids can be added by the
same process to create a chain of amino acids
called a polypeptide.
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Carboxyl group
Amino group
Amino acid Amino acid Dipeptide
Peptide bond
Dehydration reaction
Al-Tardeh S. 78
3.12 A protein’s specific shape determines its
function
Probably the most important role for proteins is
as enzymes, that
– serve as metabolic catalysts
– regulate the chemical reactions within cells.
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Other proteins are also important.
– Structural proteins provide associations between body parts.
– Contractile proteins are found within muscle.
– Defensive proteins include antibodies of the immune system.
– Signal proteins are best exemplified by hormones and other chemical messengers.
– Receptor proteins transmit signals into cells.
– Transport proteins carry oxygen.
– Storage proteins serve as a source of amino acids for developing embryos.
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Protein denaturation
If a protein’s shape is altered, it can no longer
function.
In the process of denaturation, a polypeptide
chain
– unravels
– loses its shape,
– loses its function.
Proteins can be denatured by changes in salt
concentration, pH, or by high heat.
Al-Tardeh S. 83
3.13 A protein’s shape depends on four levels of
structure
A protein can have four levels of structure:
– primary structure
– secondary structure
– tertiary structure
– quaternary structure
Al-Tardeh S. 84
Primary structure
The primary structure of a protein is its unique
amino acid sequence.
– The correct amino acid sequence is determined
by the cell’s genetic information.
– The slightest change in this sequence may affect
the protein’s ability to function.
© 2012 Pearson Education, Inc.
The amino acid sequence of
hemoglobin. glu at #6 represents
normal hemoglobin, when valine
is at position #6 this represents
sickle cell.
Al-Tardeh S. 85
Secondary structure
Protein secondary structure results from coiling or
folding of the polypeptide.
– Coiling results in a helical structure called an
alpha helix.
– A certain kind of folding leads to a structure
called a pleated sheet, which dominates some
fibrous proteins such as those used in spider
webs.
– Coiling and folding are maintained by regularly
spaced hydrogen bonds between hydrogen
atoms and oxygen atoms along the backbone of
the polypeptide chain. Al-Tardeh S. 87
Figure 3.13B
Secondary structure
Amino acid Amino
acid
Hydrogen
bond
Alpha helix
Beta pleated
sheet
Al-Tardeh S. 88
Tertiary structure
The overall three-dimensional shape of a
polypeptide is called its tertiary structure.
– Tertiary structure generally results from
interactions between the R groups of the
various amino acids.
– Disulfide bridges may further strengthen the
protein’s shape.
Al-Tardeh S. 91
Quaternary structure
Two or more polypeptide chains (subunits)
associate providing quaternary structure.
– i.e., Collagen
– Collagen’s triple helix gives great strength to
connective tissue, bone, tendons, and
ligaments.
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3.14 DNA and RNA are the two types of nucleic
acids
The amino acid sequence of a polypeptide is
programmed by a discrete unit of inheritance
known as a gene.
Genes consist of DNA(deoxyribonucleic acid), a
type of nucleic acid.
DNA is inherited from an organism’s parents.
DNA provides directions for its own replication.
DNA programs a cell’s activities by directing the
synthesis of proteins.
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DNA does not build proteins directly.
DNA works through an intermediary,
ribonucleic acid (RNA).
– DNA is transcribed into RNA.
– RNA is translated into proteins.
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Figure 3.14_s3
Gene
DNA
Transcription
RNA
Protein Translation
Amino acid
Nucleic acids
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3.15 Nucleic acids are polymers of nucleotides
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides.
Nucleotides have three parts:
1. a five-carbon sugar called ribose in RNA and deoxyribose in DNA.
2. a phosphate group.
3. a nitrogenous base.
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DNA nitrogenous bases are
– adenine (A).
– thymine (T).
– cytosine (C).
– guanine (G).
RNA
– also has A, C, and G.
– but instead of T, it has uracil (U).
Al-Tardeh S. 103
A nucleic acid polymer: a polynucleotide,
forms:
– from the nucleotide monomers
– when the phosphate of one nucleotide
bonds to the sugar of the next nucleotide by
dehydration reactions
– by producing a repeating sugar-phosphate
backbone with protruding nitrogenous bases.
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DNA double helix
Two polynucleotide strands wrap around each
other to form a DNA double helix.
– The two strands are associated because
particular bases always hydrogen bond to one
another.
– A pairs with T, and C pairs with G, producing
base pairs.
RNA is usually a single polynucleotide strand.
Al-Tardeh S. 106