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Chapter 5
The Working Cell
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
0
Biology and Society:
Natural Nanotechnology
• Cells control their chemical environment using
– Energy
– Enzymes
– The plasma membrane
• Cell-based nanotechnology may be used to power microscopic
robots.
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Figure 5.00
SOME BASIC ENERGY CONCEPTS
• Energy makes the world go around.
• But what is energy?
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Conservation of Energy
• Energy is defined as the capacity to perform work.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy.
Animation: Energy Concepts
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On the platform,
the diver has more
potential energy.
Climbing the steps
converts kinetic
energy of muscle
movement to
potential energy.
Diving converts
potential energy
to kinetic energy.
In the water, the
diver has less
potential energy.
Figure 5.1
• Machines and organisms can transform kinetic energy to potential
energy and vice versa.
• In all such energy transformations, total energy is conserved.
– Energy cannot be created or destroyed.
– This is the principle of conservation of energy.
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Entropy
• Every energy conversion releases some randomized energy in the
form of heat.
• Heat is a
– Type of kinetic energy
– Product of all energy conversions
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• Scientists use the term entropy as a measure of disorder, or
randomness.
• All energy conversions increase the entropy of the universe.
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Chemical Energy
• Molecules store varying amounts of potential energy in the
arrangement of their atoms.
• Organic compounds are relatively rich in such chemical energy.
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• Living cells and automobile engines use the same basic process to
make chemical energy do work.
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Fuel rich in
chemical
energy
Energy conversion
Waste products
poor in chemical
energy
Heat
energy
Gasoline
+
Combustion
Kinetic energy
of movement
Oxygen
Carbon dioxide
+
Water
Energy conversion in a car
Heat
energy
Cellular
respiration
Food
+
Oxygen
ATP
Energy for cellular work
Carbon dioxide
+
Water
Energy conversion in a cell
Figure 5.2
• Cellular respiration is the energy-releasing chemical breakdown
of fuel molecules that provides energy for cells to do work.
• Humans convert about 40% of the energy in food to useful work,
such as the contraction of muscles.
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Food Calories
• A calorie is the amount of energy that raises the temperature of
one gram of water by 1 degree Celsius.
• Food Calories are kilocalories, equal to 1,000 calories.
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Food
Food Calories
Cheeseburger
295
Spaghetti with sauce (1 cup)
241
Baked potato (plain, with skin)
220
Activity
Food Calories consumed per
hour by a 150-pound person*
Running (7min/mi)
979
Dancing (fast)
510
Bicycling (10 mph)
490
Fried chicken (drumstick)
193
Swimming (2 mph)
Bean burrito
189
Walking (3 mph)
Pizza with pepperoni (1 slice)
181
Dancing (slow)
Peanuts (1 ounce)
166
Playing the piano
73
Driving a car
61
Apple
Garden salad (2 cups)
81
56
Popcorn (plain, 1 cup)
31
Broccoli (1 cup)
25
(a) Food Calories (kilocalories) in
various foods
Sitting (writing)
408
245
204
28
*Not including energy necessary for basic functions, such
as breathing and heartbeat
(b) Food Calories (kilocalories) we
burn in various activities
Figure 5.3
Food
Food Calories
Cheeseburger
295
Spaghetti with sauce (1 cup)
241
Baked potato (plain, with skin)
220
Fried chicken (drumstick)
193
Bean burrito
189
Pizza with pepperoni (1 slice)
181
Peanuts (1 ounce)
166
Apple
Garden salad (2 cups)
81
56
Popcorn (plain, 1 cup)
31
Broccoli (1 cup)
25
(a) Food Calories (kilocalories) in various foods
Figure 5.3a
Activity
Food Calories consumed per
hour by a 150-pound person*
Running (7min/mi)
979
Dancing (fast)
510
Bicycling (10 mph)
490
Swimming (2 mph)
408
Walking (3 mph)
245
Dancing (slow)
204
Playing the piano
73
Driving a car
61
Sitting (writing)
28
*Not including energy necessary for basic functions,
such as breathing and heartbeat
(b) Food Calories (kilocalories) we burn in various activities
Figure 5.3b
• The energy of calories in food is burned off by many activities.
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ATP AND CELLULAR WORK
• Chemical energy is
– Released by the breakdown of organic molecules during cellular
respiration
– Used to generate molecules of ATP
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• ATP
– Acts like an energy shuttle
– Stores energy obtained from food
– Releases it later as needed
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The Structure of ATP
• ATP (adenosine triphosphate)
– Consists of adenosine plus a tail of three phosphate groups
– Is broken down to ADP and a phosphate group, releasing energy
Blast Animation: Structure of ATP
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Energy
Triphosphate
Adenosine
P
ATP
P
P
Diphosphate
Adenosine
ADP
P
P
P
Phosphate
(transferred to
another molecule)
Figure 5.4
Phosphate Transfer
• ATP energizes other molecules by transferring phosphate groups.
• This energy helps cells perform
– Mechanical work
– Transport work
– Chemical work
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Motor
protein
ATP
ADP
P
ADP
P
ADP
P
ADP
P
Protein moved
(a) Motor protein performing mechanical work
Transport Solute
protein
P
P
ATP
Solute transported
(b) Transport protein performing transport work
P
ATP
X
P
X
Y
Y
Reactants
Product made
(c) Chemical reactants performing chemical work
Figure 5.5
Motor
protein
ATP
ADP
P
ADP
P
Protein moved
(a) Motor protein performing mechanical work
Figure 5.5a
Transport Solute
protein
P
P
ATP
ADP
P
Solute transported
(b) Transport protein performing transport work
Figure 5.5b
P
ATP
X
P
X
Y
ADP
P
Y
Reactants
Product made
(c) Chemical reactants performing chemical work
Figure 5.5c
The ATP Cycle
• Cellular work spends ATP.
• ATP is recycled from ADP and a phosphate group through
cellular respiration.
• A working muscle cell spends and recycles about 10 million ATP
molecules per second.
Blast Animation: ATP/ADP Cycle
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ATP
Cellular respiration:
chemical energy
harvested from
fuel molecules
Energy for
cellular work
ADP
P
Figure 5.6
ENZYMES
• Metabolism is the total of all chemical reactions in an organism.
• Most metabolic reactions require the assistance of enzymes,
proteins that speed up chemical reactions.
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Activation Energy
• Activation energy
– Activates the reactants
– Triggers a chemical reaction
• Enzymes lower the activation energy for chemical reactions.
Blast Animation: How Enzymes Work: Activation Energy
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Activation
energy barrier
Reactant
Energy level
Energy level
Enzyme
Reactant
Products
(a) Without enzyme
Activation
energy barrier
reduced by
enzyme
Products
(b) With enzyme
Figure 5.7
Activation
energy barrier
Energy level
Reactant
Products
(a) Without enzyme
Figure 5.7a
Enzyme
Activation
energy barrier
reduced by
enzyme
Energy level
Reactant
Products
(b) With enzyme
Figure 5.7b
The Process of Science:
Can Enzymes Be Engineered?
• Observation: Genetic sequences suggest that many of our genes
were formed through a type of molecular evolution.
• Question: Can laboratory methods form new enzymes through
artificial selection?
• Hypothesis: An artificial process could modify the gene that
codes for lactase into a new gene with a new function.
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• Experiment: Many copies of the lactase gene were randomly
mutated and tested for new activities.
• Results: Directed evolution produced a new enzyme with a novel
function.
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Gene for lactase
Gene duplicated and
mutated at random
Mutated genes
(mutations shown in orange)
Mutated genes screened
by testing new enzymes
Genes coding for enzymes
that show new activity
Genes duplicated and
mutated at random
Genes coding for enzymes
that do not show new activity
Ribbon model showing the polypeptide
chains of the enzyme lactase
Mutated genes screened
by testing new enzymes
After seven rounds, some
genes code for enzymes that can
efficiently perform new activity.
Figure 5.8
Gene for lactase
Gene duplicated and
mutated at random
Mutated genes
(mutations shown in orange)
Mutated genes screened
by testing new enzymes
Genes coding for enzymes
that show new activity
Genes coding for enzymes
that do not show new activity
Genes duplicated and
mutated at random
Mutated genes screened
by testing new enzymes
After seven rounds, some
genes code for enzymes that can
efficiently perform new activity.
Figure 5.8a
Ribbon model showing the polypeptide
chains of the enzyme lactase
Figure 5.8b
Induced Fit
• Every enzyme is very selective, catalyzing a specific reaction.
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• Each enzyme recognizes a substrate, a specific reactant
molecule.
– The active site fits to the substrate, and the enzyme changes shape
slightly.
– This interaction is called induced fit.
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• Enzymes can function over and over again, a key characteristic of
enzymes.
Animation: How Enzymes Work
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Active site
Sucrase can accept a
molecule of its substrate.
Enzyme
(sucrase)
Figure 5.9-1
Substrate (sucrose)
Active site
Sucrase can accept a
molecule of its substrate.
Substrate binds
to the enzyme.
Enzyme
(sucrase)
Figure 5.9-2
Substrate (sucrose)
Active site
Sucrase can accept a
molecule of its substrate.
Substrate binds
to the enzyme.
Enzyme
(sucrase)
H2O
The enzyme
catalyzes the
chemical reaction.
Figure 5.9-3
Substrate (sucrose)
Active site
Sucrase can accept a
molecule of its substrate.
Substrate binds
to the enzyme.
Enzyme
(sucrase)
Fructose
H2O
Glucose
The products
are released.
The enzyme
catalyzes the
chemical reaction.
Figure 5.9-4
Enzyme Inhibitors
• Enzyme inhibitors can prevent metabolic reactions by binding to
the active site.
Blast Animation: Enzyme Regulation: Competitive Inhibition
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(a) Enzyme and substrate
binding normally
Substrate
Active site
(b) Enzyme inhibition by
a substrate imposter
Enzyme
Substrate
Inhibitor
Active site
Enzyme
(c) Enzyme inhibition by
a molecule that causes
the active site to change
shape
Active site
Substrate
Inhibitor
Enzyme
Figure 5.10
Substrate
Active site
Enzyme
(a) Enzyme and substrate binding normally
Figure 5.10a
Inhibitor
Substrate
Active site
Enzyme
(b) Enzyme inhibition by a substrate imposter
Figure 5.10b
Substrate
Active site
Inhibitor
Enzyme
(c) Enzyme inhibition by a molecule that
causes the active site to change shape
Figure 5.10c
• Other enzyme inhibitors
– Bind at a remote site
– Change the enzyme’s shape
– Prevent the enzyme from binding to its substrate
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• Some products of a reaction may inhibit the enzyme required for
its production.
– This is called feedback regulation.
– It prevents the cell from wasting resources.
• Many antibiotics work by inhibiting enzymes of disease-causing
bacteria.
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MEMBRANE FUNCTION
• Working cells must control the flow of materials to and from the
environment.
• Membrane proteins perform many functions.
• Transport proteins
– Are located in membranes
– Regulate the passage of materials into and out of the cell
Animation: Membrane Selectivity
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Enzymatic activity
Cytoplasm
Fibers of
extracellular
matrix
Cell signaling
Attachment to
the cytoskeleton
and extracellular
matrix
Cytoplasm
Cytoskeleton
Transport
Intercellular
joining
Cell-cell
recognition
Figure 5.11
Passive Transport: Diffusion across Membranes
• Molecules contain heat energy that causes them to vibrate and
wander randomly.
• Diffusion is the tendency for molecules of any substance to
spread out into the available space.
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• Passive transport is the diffusion of a substance across a
membrane without the input of energy.
• Diffusion is an example of passive transport.
• Substances diffuse down their concentration gradient, a region
in which the substance’s density changes.
Blast Animation: Diffusion
Animation: Diffusion
Blast Animation: Passive Diffusion Across a Membrane
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Molecules of dye
Net diffusion
Membrane
Net diffusion
Equilibrium
(a) Passive transport of one type of molecule
Net diffusion
Net diffusion
Net diffusion
Net diffusion
(b) Passive transport of two types of molecules
Equilibrium
Equilibrium
Figure 5.12
Molecules of dye
Net diffusion
Membrane
Net diffusion
Equilibrium
(a) Passive transport of one type of molecule
Figure 5.12a
Net diffusion
Net diffusion
Net diffusion
Net diffusion
Equilibrium
Equilibrium
(b) Passive transport of two types of molecules
Figure 5.12b
• Some substances do not cross membranes spontaneously.
– These substances can be transported via facilitated diffusion.
– Specific transport proteins act as selective corridors.
– No energy input is needed.
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Osmosis and Water Balance
• The diffusion of water across a selectively permeable membrane
is osmosis.
Animation: Osmosis
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Hypotonic solution
Hypertonic solution
Sugar
molecule
Selectively
permeable
membrane
Osmosis
Figure 5.13-1
Hypotonic solution
Hypertonic solution
Isotonic solutions
Osmosis
Sugar
molecule
Selectively
permeable
membrane
Osmosis
Figure 5.13-2
• A hypertonic solution has a higher concentration of solute.
• A hypotonic solution has a lower concentration of solute.
• An isotonic solution has an equal concentration of solute.
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Water Balance in Animal Cells
• Osmoregulation is the control of water balance within a cell or
organism.
• Most animal cells require an isotonic environment.
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Water Balance in Plant Cells
• Plant have rigid cell walls.
• Plant cells require a hypotonic environment, which keeps these
walled cells turgid.
Video: Plasmolysis
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Animal cell
H2O
H2O
H2O
Normal
Lysing
H 2O
Flaccid (wilts)
(a) Isotonic
solution
Shriveled
Plasma
membrane
Plant cell
H2O
H2O
H2O
Turgid
(b) Hypotonic
solution
H 2O
Shriveled
(c) Hypertonic
solution
Figure 5.14
Animal cell
H2O
H2O
Normal
Plant cell
H 2O
H2O
Flaccid (wilts)
(a) Isotonic
solution
Figure 5.14a
H2O
Lysing
H2O
Turgid
(b) Hypotonic
solution
Figure 5.14b
H 2O
Shriveled
Plasma
membrane
H 2O
Shriveled
(c) Hypertonic
solution
Figure 5.14c
• As a plant cell loses water,
– It shrivels.
– Its plasma membrane may pull away from the cell wall in the process of
plasmolysis, which usually kills the cell.
Video: Turgid Elodea
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Figure 5.15
Active Transport: The Pumping of Molecules
Across Membranes
• Active transport requires energy to move molecules across a
membrane.
Blast Animation: Active Transport: Sodium-Potassium Pump
Animation: Active Transport
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Lower solute concentration
Solute
ATP
Higher solute concentration
Figure 5.16-1
Lower solute concentration
Solute
ATP
Higher solute concentration
Figure 5.16-2
Exocytosis and Endocytosis: Traffic of Large
Molecules
• Exocytosis is the secretion of large molecules within vesicles.
Blast Animation: Endocytosis and Exocytosis
Animation: Exocytosis and Endocytosis Introduction
Animation: Exocytosis
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Outside of cell
Plasma
membrane
Cytoplasm
Figure 5.17
• Endocytosis takes material into a cell within vesicles that bud
inward from the plasma membrane.
Animation: Phagocytosis
Animation: Pinocytosis
Animation: Receptor-Mediated Endocytosis
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Figure 5.18
• There are three types of endocytosis:
– Phagocytosis (“cellular eating”); a cell engulfs a particle and packages it
within a food vacuole
– Pinocytosis (“cellular drinking”); a cell “gulps” droplets of fluid by
forming tiny vesicles
– Receptor-mediated endocytosis; a cell takes in very specific molecules
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The Role of Membranes in Cell Signaling
• The plasma membrane helps convey signals between
– Cells
– Cells and their environment
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• Receptors on a cell surface trigger signal transduction pathways
that
– Relay the signal
– Convert it to chemical forms that can function within the cell
Animation: Overview of Cell Signaling
Animation: Signal Transduction Pathways
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Outside of cell
Receptor
protein
Reception
Cytoplasm
Transduction
Proteins of signal transduction pathway
Epinephrine
(adrenaline)
from adrenal
glands
Response
Hydrolysis
of glycogen
releases
glucose for
energy
Plasma membrane
Figure 5.19
Outside of cell
Reception
Receptor
protein
Cytoplasm
Transduction
Proteins of signal transduction
pathway
Epinephrine
(adrenaline)
from adrenal
glands
Response
Hydrolysis
of glycogen
releases
glucose for
energy
Plasma membrane
Figure 5.19a
Evolution Connection:
The Origin of Membranes
• Phospholipids
– Are key ingredients of membranes
– Were probably among the first organic compounds that formed before
life emerged
– Self-assemble into simple membranes
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Figure 5.20
Energy for cellular work
Adenosine
P
P
P
ATP
cycle
Adenosine
P
ATP
ADP
Adenosine
triphosphate
Adenosine
diphosphate
Energy from
organic fuel
P
P
Phosphate
Figure 5.UN01
Activation energy
Enzyme added
Reactant
Reactant
Products
Products
Figure 5.UN02
MEMBRANE TRANSPORT
Passive Transport
(requires no energy)
Active Transport
(requires energy)
Lower solute concentration
Higher solute
concentration
Lower water concentration
(higher solute concentration)
Solute
Water
Solute
Solute
Diffusion
Facilitated diffusion
Osmosis
Higher water concentration
Higher solute concentration
(lower solute concentration)
Solute
ATP
Lower solute
concentration
Figure 5.UN03
Exocytosis
Endocytosis
Figure 5.UN04