1. Describe the steps of the scientific method.hhh.gavilan.edu/jcrocker/documents/Ch01-4_000.pdf ·...

1. Describe the steps of the scientific method.2. Define the terms hypothesis, theory, and law.3. What are the common characteristics of all living things?4. Describe the levels of organization of life beginning with the smallest living unit and

progressing up in complexity to ecosystems.5. Compare and contrast DNA and RNA.6. Describe the 3 types of molecular bonds. Which is strongest and which is weakest?7. What properties of water make it important for life? Briefly describe each of these

properties.8. What properties of Carbon make it important for life? How do those properties

make life possible?9. How are biological molecules formed? How are they broken down?10. What are carbohydrates and what functions do they perform?11. What are proteins and what functions do they perform?12. What are lipids and what functions do they perform?13. What are nucleic acids and what functions do they perform?14. What is a plasma membrane? What is it composed of? What functions does it

serve?15. Define diffusion and osmosis.16. Describe the processes of passive transport across a plasma membrane.17. Describe the processes of active transport across a plasma membrane.18. Compare and contrast prokaryotic and eukaryotic cells.19. Describe the form and function of the organelles common to most eukaryotic cells.20. Describe the endosymbiont hypothesis of organelle formation and provide an

example.

Scientific Principles

Biology is a scientific discipline

All scientific inquiry is based on a small set of assumptions or principles• Natural causality – events have natural causes• Uniformity in space and time• Similar perception – observations of other

humans are reliable

The Scientific Method

Scientific inquiry is a rigorous method for making observations

The Scientific Method for inquiry follows stepwise…

The Scientific Method

Scientific experimentation tests the assertion that a single variable causes a particular observation

The experiment must rule out the influence of other possible variables on the recorded observations

Controls are incorporated into experiments

Controls keep untested variables constant

Scientific method is illustrated by Francesco Redi’s experiment

Limitations of the Scientific Method

Can never be sure all untested variables are controlled

Conclusions based on the experimental data must remain tentative

Results of experimentation must be communicated thoroughly and accurately to other scientists for repetition

Repetition by other scientists adds verification that findings can be used as the basis for further studies

Scientific Theory

A scientific theory is a general explanation for important natural phenomena• It is extensively and reproducibly tested• It is more like a principle or natural law

(e.g. atomic, gravitational, and cell theories)• If compelling evidence arises, a theory may

be modified

Biosphere

Ecosystem• All organisms• All abiotic factors

Community

Population

Organism• organ systems• organs• tissues• cells• molecules

ECOSYSTEM LEVEL Eucalyptus forest

COMMUNITY LEVEL All organisms in eucalyptus forest

POPULATION LEVEL Group of flying foxes

ORGANISM LEVEL Flying fox

ORGAN SYSTEM LEVEL Nervous system

ORGAN LEVEL Brain

Brain Spinal cord

Nerve

TISSUE LEVEL Nervous

tissue

CELLULAR LEVEL Nerve cell

MOLECULAR LEVEL Molecule of DNA Figure 1.1

Fig. 1-8

1.3 What Is Life?

Characteristics of living things• Living things are organized and complex. • Living things grow and reproduce. • Living things respond to stimuli. • Living things acquire and use material and

energy. • Living things use DNA to store information.

Each level of organization builds on the one below it

At each level, new properties emerge

ATOMS AND MOLECULES

Biological function starts at the chemical level

2.1 What Are Atoms?

Elements:

substances that cannot be broken down by ordinary chemical means (ex/ carbon)

all atoms belong to one of 96 types of naturally occurring elements

life requires about 25 of these elements

2.1 What Are Atoms?

Atoms:

basic structural unit of matter

consist of charged particles

protons (+)

neutrons (0)

electrons (-)

smallest particle of an element

each element has a unique number of protons (atomic number)

Atoms are electrically neutral because they have and equal number of positive protons and negative electrons

Helium atom

2

2

2

Protons

Neutrons

Electrons

Nucleus

HYDROGEN (H)Atomic number = 1

CARBON (C)Atomic number = 6

NITROGEN (N)Atomic number = 7

OXYGEN (O)Atomic number = 8

Electron

Outermost electron shell (can hold 8 electrons)

First electron shell (can hold 2 electrons)

Electrons are arranged in shells

Electrons orbit around atomic nuclei at specific distances called electron shells

the outermost shell determines the chemical properties of an atom

Energy Capture and Release

Life depends on electrons capturing and releasing energy• Electron shells correspond to energy levels• Energy exciting an atom causes an electron

jump from a lower- to higher-energy shell• Later, the electron falls back into its original

shell, releasing the energy

2.2 How Do Atoms Form Molecules?

Molecules: two or more atoms of one or more elements held together by interactions among their outermost electron shells• Atoms interact with one another according to

two basic principles:• An inert atom will not react with other atoms

when its outermost electron shell is completely full or empty.

• A reactive atom will react with other atoms when its outermost electron shell is only partially full.

Atoms Interact

Reactive atoms gain stability by electron interactions (chemical reactions)• Electrons can be lost to empty the outermost

shell• Electrons can be gained to fill the outermost

shell• Electrons can be shared with another atom

where both atoms have full outermost shells• When atoms combine to fill their outer shells

they gain stability

Formed by passing an electron from one atom to another

One partner becomes positive, the other negative, and they attract one another.• Na+ + Cl– becomes NaCl (sodium chloride)

Positively or negatively charged atoms are called ions.• + cation• - anion

Ionic Bonds

Covalent Bonds

Atoms with partially full outer electron shells can share electrons

Two electrons (one from each atom) are shared in a single covalent bond

Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond) and H2 O

Covalent bonds are much stronger than ionic bonds but vary in their stability

Covalent Bonds

Covalent bonds produce either nonpolar or polar molecules.

Nonpolar molecule: atoms in a molecule equally share electrons that spend equal time around each atom, producing a nonpolar covalent bond

Polar Covalent Bonds

Atoms within a molecule may have different nuclear charges

Those atoms with greater positive nuclear charge pull more strongly on electrons in a covalent bond

A molecule with polar bonds may be polar overall

H2 O is a polar molecule • The (slightly) positively charged pole is

around each hydrogen• The (slightly) negatively charged pole is

around the oxygen

Hydrogen Bonds

Polar molecules like water have partially charged atoms at their ends

Hydrogen bonds form when partial opposite charges in different molecules attract each other

The partially positive hydrogens of one water molecule are attracted to the partially negative oxygen on another

Hydrogen bonds are rather weak but can collectively be quite strong

Hydrogen bonds

Fig. 2-7

hydrogen bonds

O (–)

H (+)

H (+)

O (–)

H (+)

H (+)

Why Is Water So Important To Life?

Water interacts with many other molecules.• Oxygen released by plants during

photosynthesis comes from water.• Water is used by animals to digest food. • Water is produced in chemical reactions that

produce proteins, fats, and sugars.

Many molecules dissolve easily in water.• Water is an excellent solvent, capable of

dissolving a wide range of substances because of its positive and negative poles.

• example NaCl dropped into H2 O• The positive end of H2 O is attracted to Cl–. • The negative end of H2 O is attracted to Na+. • These attractions tend to pull apart the

components of the original salt.


Water-insoluble molecules are hydrophobic• Water molecules repel and drive together

uncharged and nonpolar molecules like fats and oils

• The “clumping” of nonpolar molecules is called hydrophobic interaction


Hydrogen bonding between water molecules causes them to stick together.• Cohesion: water molecules stick together

• Water molecules can form a chain in delivering moisture to the top of a tree

• Cohesion of water molecules along a surface produces surface tension

Water molecules stick to polar or charged surfaces in the property called adhesion• Adhesion helps water climb up the thin tubes

of plants to the leaves (capillary effect)



Water can form ions.• Water dissociates to become H+ and OH–.• The relative abundance of ions determine pH

hydrogen ion (H+)

hydroxide ion (OH–)

water(H2 O)

+(+)(–)

O

HH

O

H

H

The relative concentrations of H+ and OH-

ions determine pH.• Acid solutions have more H+ (protons). • Alkaline solutions have more OH– (hydroxyl

ions).• A base is a substance that combines with H+,

reducing their numbers.• pH measures the relative amount of H+ and

OH– in a solution.

Acid, Basic, and Neutral Solutions


The degree of acidity of a solution is measured using the pH scale• pHs 0-6 are acidic (H+ > OH-)• pH 7 is neutral (H+ = OH-)• pH 8-14 is basic (OH- > H+)


A buffer is a compound that accepts or releases H+ in response to pH change

The bicarbonate buffer found in our bloodstream prevents pH change

Water stabilizes temperature• Temperature reflects the speed of molecular

motion• It requires 1 calorie of energy to raise the

temperature of 1g of water 1oC (specific heat), so it heats up very slowly

• Because it heats up very slowly water moderates the effect of temperature change

• Very low or very high temperatures may damage enzymes or slow down or halt important chemical reactions


Water Stabilizes Temperature

Water requires a lot of energy to turn from liquid into a gas (heat of vaporization)• Evaporating water uses up heat from its

surroundings, cooling the nearby environment (ex/ sweating)

Water requires a lot of energy to be withdrawn in order to freeze (heat of fusion)• Therefore the nearby environment will be

warmer than it otherwise would be

Water Forms an Unusual Solid: Ice

Most substances become more dense when they solidify from a liquid

Water molecules spread slightly during crystallization (freezing)

Because of this ice is less dense than liquid water

Water Forms an Unusual Solid: Ice

Because of its lower density ice floats in liquid water

Ponds and lakes freeze from the top down

Lower water is protected by the surface layer of ice.

• Large bodies of water rarely freeze completely• Life can survive in cold water underneath ice.• Spring thaw pushes nutrient-rich bottom water

to surface

Like no other common substance on earth, water naturally exists in all three physical states: solid, liquid, and gas


Organic refers to molecules containing a carbon skeleton

Inorganic refers to carbon dioxide and all molecules without carbon

Organic vs. Inorganic in Chemistry

2.4 Why Is Carbon So Important To Life?

Carbon can combine with other atoms in many ways to form a huge number of different molecules.

Carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms (4 covalent bonds).

Carbon atoms are versatile and can form single, double, or triple bonds and rings.

Structural formula

Ball-and-stick model

Space-filling model

Methane

The 4 single bonds of carbon point to the corners of a tetrahedron.

Arrangement of atoms determines molecular shape.

Shape determines function of molecules

Why Is Carbon So Important To Life?

The great variety of substances found in nature is constructed from a limited pool of atoms.

Organic molecules have a carbon skeleton and some hydrogen atoms.

Much of the diversity of organic molecules is due to the presence of functional groups.

Why Is Carbon So Important To Life?

Functional groups in organic molecules confer chemical reactivity and other characteristics• groups of atoms that participate in chemical

reactions• determine the chemical properties of

molecules• Examples: acidity, solubility

Functional (R) Groups

What affects solubility in water?

Molecules with +/- charge are usually hydrophilic or “water-loving”

Molecules with no charge and non-polar are usually hydrophobic and not soluble in water

2.5 How Are Biological Molecules Joined Together Or Broken Apart?

Biomolecules are polymers (chains) of subunits called monomers

A huge number of different polymers can be made from a small number of monomers

Biomolecules Are Joined Through Dehydration and Broken by Hydrolysis

Organic Molecule Synthesis

Monomers are joined together through dehydration synthesis

An H and an OH are removed, resulting in the loss of a water molecule (H2 O)


Polymers are broken apart through hydrolysis (“water cutting”)

Water is broken into H and OH and used to break the bond between monomers


All biological molecules fall into one of four broad categories:• Carbohydrates• Lipids• Proteins• Nucleic Acids

2.6 What Are Carbohydrates?

Composition:

C, H, and O in the ratio of 1:2:1

Types by size:

• Simple or single sugars are monosaccharides

• Two linked monosaccharides are disaccharides

• Long chains of monosaccharides are polysaccharides

Monosaccharides

Basic monosaccharide structure

• Backbone of 3-7 carbon atoms• Many –OH and –H functional groups• Usually found in a ring form in cells

Simple sugars provide important energy sources for organisms.

Most small carbohydrates are water- soluble due to the polar OH functional groups

Disaccharides

Disaccharides are two-part sugars• Sucrose (table sugar) = glucose + fructose• Lactose (milk sugar) = glucose + galactose• Maltose (malt sugar)= glucose + glucose

glucose fructose sucrose

dehydration synthesis

OHO

HOCH2

OH

HO

CH2 OH

H H

OH

H OH

H

H

O HO

OCH2 OH

H H

OH

H OH

H

H

H

H

HOCH2 OHH

HOCH2 H

H

H

HOCH2 OH

O

OH

O

OHH

OH

+

Polysaccharides

Monosaccharides are linked together to form chains (polysaccharides)

Polysaccharides are used for energy storage and structural components

Polysaccharides

Storage polysaccharides• Starch (polymer of glucose)

• Formed in roots and seeds as a form of glucose storage

• Glycogen (polymer of glucose)• Found in liver and muscles

Polysaccharides

Structural polysaccharides• Cellulose (polymer of glucose)• Found in the cell walls of plants

• Indigestible for most animals due to orientation of bonds between glucoses

• Chitin (polymer of modified glucose units)• Found in the outer coverings of insects,

crabs, and spiders• Found in the cell walls of many fungi

2.7 What Are Lipids?

Molecular characteristics of lipids• Lipids are molecules with long regions

composed almost entirely of carbon and hydrogen.

• The nonpolar regions of carbon and hydrogen bonds make lipids hydrophobic and insoluble in water.

What Are Lipids?

Lipids are diverse in structure and serve in a variety of functions• Energy storage• Waterproofing• Membranes in cells• Hormones

Lipid classification• Group 1: Oils, fats, and waxes• Group 2: Phospholipids• Group 3: Steroids

What Are Lipids?

Group 1: Oils, fats, and waxes• Formed by dehydration synthesis

• 3 fatty acids + glycerol triglyceride• Contain only carbon, hydrogen, and oxygen• Contain one or more fatty acid subunits in long

chains of C and H with a carboxyl group (–COOH)

• Ring structure is rare

Lipids

Group 1: Oils, fats, and waxes (continued)• Fats and oils form by dehydration synthesis

from three fatty acid subunits and one molecule of glycerol.

Fig. 2-16

glycerol fatty acids

CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O

CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O

CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CHO

C OHHH

C OHH

C OHHH

CH2CH

CH2

CH2

etc.

+

Lipids

triglyceride 3 water molecules

OHH

OHH

OHH

+

+

CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O

CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2

CH2

CH2 etc.O

CH2C CH2 CH2 CH2 CH2 CH2 CH2 CHO

CHH

CH

C

O

O

OHH

CH2CH

CH2

CH2

etc.

+

Group 1: Oils, fats, and waxes (continued)• Fats and oils formed by dehydration synthesis

are called triglycerides.• Triglycerides are used for long-term energy

storage in both plants and animals.

Fig. 2-16

Lipids

Group 1: Oils, fats, and waxes (continued)• Characteristics of fats

• Solidity is due to the prevalence of single or double carbon bonds

• Fats are solid at room temperature.• Fats have all carbons joined by single

covalent bonds.• The remaining bond positions on the

carbons are occupied by hydrogen atoms.

Lipids

Beef fat (saturated)(a)

Group 1: Oils, fats, and waxes (continued)• Fatty acids of fats are said to be saturated and

are straight molecules that can be stacked.

Fig. 2-18a

Lipids

Group 1: Oils, fats, and waxes (continued)• Characteristics of oils

• Oils are liquid at room temperature.• Some of the carbons in fatty acids have

double covalent bonds.• There are fewer attached hydrogen atoms,

and the fatty acid is said to be unsaturated.

Lipids

Peanut oil (unsaturated)(b)

Group 1: Oils, fats, and waxes (continued)• Unsaturated fatty acids have bends and kinks

in fatty acid chains and can’t be efficiently stacked.

Fig. 2-18b

Lipids

Group 1: Oils, fats, and waxes (continued)• Characteristics of waxes

• Waxes are solid at room temperature.• Waxes are highly saturated.• Waxes are not a food source.• Waxes are composed of long hydrocarbon

chains and are strongly hydrophobic

Lipids

Group 1: Oils, fats, and waxes (continued)• Waxes form waterproof coatings

• Leaves and stems of plants• Fur in mammals• Insect exoskeletons

• Used to build honeycomb structures

Lipids

Group 2: Phospholipids• Phospholipids: form dual layered plasma

membranes around all cells• Construction

• like oils except one fatty acid is replaced by a phosphate group attached to glycerol.

• 2 fatty acids + glycerol + a short polar functional group

• water-soluble heads and water-insoluble tails.

Lipids

polar head glycerol

(hydrophilic) (hydrophobic)

fatty acid tails

CH3 O–

OO

CH3

CH CH2CH2

CH2CH2

CH2CH2

CH2CH3

H3 C N+- CH2 - CH2-O-P-O-CH2 O

HC-O-C-CH2-CH2- CH2 -CH2- CH2 - CH2-CH2 -CH

H2 C-O-C-CH2-CH2 - CH2 -CH2 - CH2 - CH2-CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH3

-

Group 2: Phospholipids (continued)• The phosphate end of the molecule is water

soluble; the fatty acid end of the molecule is water insoluble.

Fig. 2-19

Lipids

Group 3: Steroids• Steroids contain four fused carbon rings.• Various functional groups protrude from the

basic steroid “skeleton”.• Examples of steroids

• Cholesterol• Found in membranes of animal cells

• Male and female sex hormones

Lipids

2.8 What Are Proteins?

Functions of proteins• Proteins act as enzymes to catalyze (speed)

many biochemical reactions.• They provide structure (ex/ elastin)• They can act as energy stores.• They are involved in carrying oxygen around

the body (hemoglobin).• They are involved in muscle movement.

Proteins are formed from chains of amino acids.

All amino acids have the same basic structure:• A central carbon• An attached amino group• An attached carboxyl group• An attached variable group (R group)

• Some are hydrophobic• Some are hydrophilicamino

group

hydrogen

variable group

carboxylic acid group

Amino acid monomers join to form chains by dehydration synthesis.• Proteins are formed by dehydration reactions

between individual amino acids.• The –NH2 group of one amino acid is joined to

the –COOH group of another, with the release of H2 O and the formation of a new peptide (two or more amino acids).

• The resultant covalent bond is a peptide bond

Long chains of amino acids are known as polypeptides or just proteins

The sequence of amino acids in a protein dictates its three dimensional structure

This structure gives proteins their functions.• Long chains of amino acids fold into three-

dimensional shapes in cells, which allows the protein to perform its specific functions.

• When a protein is denatured, its shape has been disrupted and it may not be able to perform its function.

Four Levels of Structure

Proteins exhibit up to four levels of structure• Primary structure is the sequence of amino

acids linked together in a protein• Secondary structures are helices and

pleated sheets• Tertiary structure refers to complex foldings

of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds

• Quaternary structure is found where multiple protein chains are linked together

Three Dimensional Structures

The type, position, and number of amino acids determine the structure and function of a protein• Precise positioning of amino acid R groups

leads to bonds that determine secondary and tertiary structure

• Disruption of these bonds leads to denatured proteins and loss of function

Nucleic Acids

Nucleotides are the monomers of nucleic acid chains

All nucleotides are made of three parts• Phosphate group • Five-carbon sugar• Nitrogen-containing base

Molecules of Heredity

Two types of polymers of nucleic acids• DNA (deoxyribonucleic acid) found in

chromosomes • Carries genetic information needed for

protein construction• RNA (ribonucleic acid)

• Copies of DNA used directly in protein construction


Two types of nucleotides• Ribonucleotides (A, G, C, and U) found in

RNA• Deoxyribonucleotides (A, G, C, and T) found

in DNA


Each DNA molecule consists of two chains of nucleotides that form a double helix

Other Nucleotides

Nucleotides act as intracellular messengers

Nucleotides act as energy carriers• Adenosine triphosphate (ATP) carries

energy stored in bonds between phosphate groups

Nucleotides as enzyme assistants

3.1 What Does The Plasma Membrane Do?

The cell plasma membrane separates the cell contents from the external environment.

The membrane acts as a gatekeeper, regulating the passage of molecules into and out of the cell.

Plasma Membrane

Functions of the plasma membrane• Isolates the cell’s contents from

environment• Regulates exchange of essential

substances• Communicates with other cells • Creates attachments within and between

other cells• Regulates biochemical reactions

Structure Of The Plasma Membrane

Fig. 3-2head

(hydrophilic)

tails (hydrophobic)

H2 C OOC CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

CH

CH2 CH2 CH2 CH2 CH2 CH2 CH2 CHHC O C

OH3 C N CH2 CH2 O P O CH2

CH3

CH3+

–

O

O

Phospholipids are the basis of membrane structure• Polar, hydrophilic head• Two non-polar, hydrophobic tails

The Phospholipid Bilayer

Hydrophobic and hydrophilic interactions drive phospholipids into bilayers• Double row of phospholipids• Polar heads face outward and inward• Non-polar tails mingle within the membrane• Cholesterol in animal membranes keeps

them flexible

The Phospholipid Bilayer

Individual phospholipid molecules are not bonded to one another

Some of the phospholipids have unsaturated fatty acids, whose double bonds introduce “kinks” into their “tails”

The above features make the membrane fluid

Plasma Membrane as Gatekeeper

The phospholipid bilayer blocks the passage of most molecules.

The embedded proteins selectively transport, respond to, and recognize molecules.

There are three types of membrane proteins— transport proteins, receptor proteins, and recognition proteins.

Membrane Proteins Form a Mosaic

Proteins are embedded in the phospholipid bilayer

• Some proteins can float and drift• Other proteins are anchored by protein

filaments in the cytoplasm• Many proteins have attached

carbohydrates (glycoproteins)

Movement of Molecules in Fluids

Definitions relevant to substance movement• A fluid is a substance that can move or

change shape in response to external forces• A solute is a substance that can be

dissolved (dispersed as ions or molecules) in a solvent

• A solvent is a fluid capable of dissolving a solute


Definitions relevant to substance movement (continued)• The concentration of molecules is the

number of them in a given volume unit• A gradient is a physical difference in

temperature, pressure, charge, or concentration in two adjacent regions


Why molecules move from one place to another• Substances move in response to a

concentration gradient• Molecules move from high to low concentration (diffusion) until dynamic equilibrium is reached


The greater the concentration gradient, the faster the rate of diffusion

Diffusion cannot move molecules rapidly over long distances

3.6 How Do Diffusion And Osmosis Affect Transport Across The Plasma Membrane?

Concentration gradients of ions and molecules exist across the plasma membranes of all cells

There are two types of movement across the plasma membrane • Passive transport• Energy-requiring transport

Movement Across Membranes

Passive transport• Substances move down their concentration

gradients across a membrane• No energy is expended• Membrane proteins and phospholipids may

limit which molecules can cross, but not the direction of movement

Movement Across Membranes

Energy-requiring transport• Substances are driven against their

concentration gradients• Energy is expended

Passive Transport

Plasma membranes are selectively permeable• Different molecules move across at different

locations and rates• A concentration gradient drives all three

types of passive transport: simple diffusion, facilitated diffusion, and osmosis

Passive Transport

Simple diffusion• Lipid soluble molecules (e.g. vitamins A and E,

gases) and very small molecules diffuse directly across the phospsholipid bilayer

Passive Transport

Facilitated diffusion• Water soluble molecules like ions, amino acids, and

sugars diffuse with the aid of channel and carrier transport proteins

Passive Transport

Osmosis – the special case of water diffusion• Water diffuses from high concentration (high

purity) to low concentration (low purity) across a membrane

• Dissolved substances reduce the concentration of free water molecules (and hence the purity of water) in a solution

• The flow of water across a membrane depends on the concentration of water in the internal or external solutions

Passive Transport

Comparison terms for solutions on either side of a membrane• Isotonic solutions have equal concentrations

of water and equal concentrations of dissolved substances• No net water movement occurs across the

membrane

Passive Transport

• A hypertonic solution is one with lower water concentration or higher dissolved particle concentration• Water moves across a membrane towards

the hypertonic solution

• A hypotonic solution is one with higher water concentration or lower dissolved particle concentration• Water moves across a membrane away

from the hypotonic solution

3.7 How Do Molecules Move Against A Concentration Gradient?

Energy-requiring transport processes• During active transport, the cell uses energy to

move substances against a concentration gradient.

• Membrane proteins regulate active transport.

Active Transport

Active-transport membrane proteins move molecules across using ATP• Proteins span the entire membrane• Often have a molecule binding site and an

ATP binding site• Often referred to as pumps

Endocytosis

Cells import large particles or substances via endocytosis

Plasma membrane pinches off to form a vesicle in endocytosis• Types of endocytosis

• Pinocytosis • Receptor-mediated endocytosis• Phagocytosis

Endocytosis

Types of endocytosis • Pinocytosis (“cell drinking”) brings in droplet of

extracellular fluid

Endocytosis

Types of endocytosis • Receptor-mediated endocytosis moves specific

molecules into the cell

Endocytosis

Types of endocytosis • Phagocytosis (“cell eating”) moves large particles or

whole organisms into the cell

Exocytosis

Exocytosis• Vesicles join the membrane, dumping out contents in

exocytosis

What Is the Cell Theory?

Tenets of Modern Cell Theory• Every living organism is made of one or more

cells• The smallest organisms are made of single

cells while multicellular organisms are made of many cells

• All cells arise from pre-existing cells

4.1 What Features Are Shared By All Cells?

Cells are the smallest unit of life.

Cells are enclosed by a plasma membrane.

Cells use DNA as a hereditary blueprint.

Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region.

Cells obtain energy and nutrients from their environment.

4.1 What Features Are Shared By All Cells?

Cell function limits cell size.• Most cells are small, ranging from 1 to 100

micrometers in diameter• Cells need to exchange nutrients and wastes

with the environment• No part of the cell can be far away from the

external environment

Cell Function Limits Cell Size

• Diffusion of molecules across cell membranes limits the diameter of cells.

• As cells get bigger, their nutrient and waste elimination needs grow faster than the membrane area to accommodate them.

Fig. 4-1

frog embryo

most eukaryotic cells

mitochondrion

most bacteria

virus

proteinsdiameter of DNA double helix

chicken egg

atoms1 micrometer (m) = 1/1,000,000 m1 nanometer (nm) = 1/1,000,000,000 m

1 centimeter (cm) = 1/100 m1 millimeter (mm) = 1/1,000 m

Units of measurement:1 meter (m) = 39.37 inches

adult human

tallest treesDiameter

visi

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with

una

ided

hum

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ye

visi

ble

with

lig

ht m

icro

scop

e

visi

ble

with

con

vent

iona

lel

ectr

on m

icro

scop

e

visi

ble

with

spec

ial e

lect

ron

mic

rosc

opes

100 m

10 m

1 m

10 cm

1 cm

1 mm

100 m

10 m

1 m

100 nm

10 nm

1 nm

0.1 nm

Relative sizes

All Cells Share Common Features

A plasma membrane encloses all cells and regulates material flow

Cytoplasm is the fluid interior where a cell’s metabolic reactions occur• Contains organelles• Fluid portion (cytosol) contains water, salts,

and organic molecules


All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint

All cells use RNA (ribonucleic acid) to copy DNA to make proteins


All cells obtain energy and nutrients from the environment

All cells use common building blocks to build the molecules of life

Some Cell Types Have Cell Walls

Stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists are cell walls

• Cells walls support and protect fragile cells and are usually porous

• Cell walls are composed of polysaccharides like cellulose or chitin

4.2 How Do Prokaryotic And Eukaryotic Cells Differ?

There are two kinds of cells.• Prokaryotic cells

• Are found only in two groups of single- celled organisms—the bacteria and archaea

• Eukaryotic cells• Are structurally more complex cells• Possess a membrane-enclosed nucleus• Probably arose from prokaryotic cells

Prokaryotic Cells

No nuclear membrane or membrane- bound organelles present

Some have internal membranes used to capture light

Cytoplasm contains ribosomes used for protein synthesis

Cytoplasm may contain food granules

Prokaryotic Cells

Much smaller than eukaryotic cells (< 5 µm long)

Have a simple internal structure

Surrounded by a stiff cell wall, which provides shape and protection

Can take the shape of rods, spheres, or helices

Prokaryotic Cells

Some propelled by flagella

Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces

Pili and fimbriae are protein projections in some bacteria that further enhance adhesion

There Are Two Basic Cell Types

Eukaryotic• True nucleus• Includes Protist, Fungi, Plant, and

Animal cells

4.3 What Are The Main Features Of Eukaryotic Cells?

Eukaryotic cells are > 10 µm long

The cytoskeleton provides shape and organization

A variety of membrane-enclosed organelles perform specific functions

Major Features

Nucleus: contains DNA

Mitochondria: produce energy

Endoplasmic reticulum: synthesizes membrane components and lipids

Golgi apparatus: molecule sorting center

Lysosomes: digest cellular membranes or defective organelles

Microtubules: make up the cytoskeleton

4.4 What Role Does The Nucleus Play?

The nucleus is the largest organelle in the cell.• It is bounded by a nuclear envelope.• It contains granular-looking chromatin.• It contains the nucleolus.

The Nucleus

The nuclear envelope separates chromosomes from cytoplasm• Envelope is a double membrane with

nuclear pores for transport• Some smaller materials can move through

the pores, while others, such as DNA, are excluded.

• Outer membrane is studded with ribosomes

The Nucleus

The nucleus

nucleus

nuclearpores

(b) Yeast cell

nuclearenvelope

nuclearpores

nucleolus

chromatin

(a) Structure of the nucleus

Fig. 4-5

The Nucleus

The nucleus contains DNA in various configurations• Compacted chromosomes (during cell

division)• Diffuse chromatin (as DNA directs reactions

through an RNA intermediate by coding for proteins)

The Nucleus

Darker area within the nucleus called the nucleolus• Functions as the site of ribosome synthesis• Ribosomes synthesize proteins• Ribosomes are composed of RNA and

proteins

4.5 What Roles Do Membranes Play In Eukaryotic Cells?

The plasma membrane isolates the cell, and alternately, helps it interact with its environment.• The phospholipid bilayer contains globular

proteins that regulate the transport of molecules into and out of the cell.

• Plant, fungi, and some protist cells also have a cell wall outside the plasma membrane, which acts as a protective coating.

System of Membranes

Vesicles are membranous sacs that transport substances among the separate regions of the membrane system

System of Membranes

The endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell• There are two forms of ER:

• Rough endoplasmic reticulum: is studded with ribosomes

• Smooth endoplasmic reticulum: has no ribosomes

System of Membranes

Smooth ER has no ribosomes• Contains enzymes that detoxify drugs (in liver

cells) • Synthesizes phospholipids and cholesterol.• Together with rough ER are the sites of new

membrane synthesis for the cell.

System of Membranes

Rough ER is studded with ribosomes on outside• Produces proteins and phospholipids destined

for other membranes or for secretion (export)• Together with rough ER are the sites of new

membrane synthesis for the cell.

System of Membranes

The Golgi Apparatus is a set of stacked flattened sacs • Receive proteins from ER (via transport

vesicles) and sorts them by destination• Modify some molecules (e.g. proteins to

glycoproteins)• Package material into vesicles for transport

System of Membranes

Three fates of substances made in the membrane system:

1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane

2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell

3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes

Vacuoles

Fluid-filled sacs with a single membrane

Functions of vacuoles• Contractile vacuoles in freshwater

organisms used to collect and pump water out

• Many plant cells have a large central vacuole.

Mitochondria Extract Food Energy

Function as the “powerhouses of the cell”• Mitochondria extract energy from food

molecules• Extracted energy is stored in high-energy

bonds of ATP• Energy extraction process involves anaerobic

and aerobic reactions

Major Features

Animal and plant cells differ with regards to cell walls, chloroplasts, plastids, central vacuoles, and centrioles

Chloroplasts

Chloroplasts are specialized organelles to convert solar energy into sugars

The thylakoid membranes in chloroplasts contain chlorophyll and other pigments that capture sunlight and make sugar, CO2 , and water (photosynthesis)

Plants Use Plastids for Storage

Plastids found only in plants and photosynthetic protists

Surrounded by a double membrane

Functions

• Storage for photosynthetic products like starch

• Storage of pigment molecules giving color to ripe fruit

Cytoskeleton

The cytoskeleton provides shape, support, and movement.• All organelles in the cell do not float about the

cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.

Cilia and Flagella

Functions• Cilia or flagella may be used to move cell

about• Cilia may be used to create currents of moving

fluid in their environment

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