Chapter 5 The Working Cell · 2018. 8. 29. · 5.5 Water balance between cells and their...
Transcript of Chapter 5 The Working Cell · 2018. 8. 29. · 5.5 Water balance between cells and their...
© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
Chapter 5 The Working Cell
Introduction
Some organisms use energy-converting reactions to
produce light in a process called bioluminescence.
– Many marine invertebrates and fishes use
bioluminescence to hide themselves from predators.
– Scientists estimate that 90% of deep-sea marine life
produces bioluminescence.
The light is produced from chemical reactions that
convert chemical energy into visible light.
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Figure 5.0_1
Chapter 5: Big Ideas
Membrane Structure
and Function
Energy and the Cell
How Enzymes Function
Cellular respiration
Figure 5.0_2
Introduction
Bioluminescence is an example of the multitude of
energy conversions that a cell can perform.
Many of a cell’s reactions
– take place in organelles and
– use enzymes embedded in the membranes of these
organelles.
This chapter addresses how working cells use
membranes, energy, and enzymes.
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MEMBRANE STRUCTURE
AND FUNCTION
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5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Membranes are composed of
– a bilayer of phospholipids with
– embedded and attached proteins,
– in a structure biologists call a fluid mosaic.
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5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Many phospholipids are made from unsaturated
fatty acids that have kinks in their tails.
These kinks prevent phospholipids from packing
tightly together, keeping them in liquid form.
In animal cell membranes, cholesterol helps
– stabilize membranes at warmer temperatures and
– keep the membrane fluid at lower temperatures.
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Figure 5.1
Fibers of
extracellular
matrix (ECM)
Enzymatic
activity
Phospholipid
Cholesterol
CYTOPLASM
CYTOPLASM
Cell-cell
recognition
Glycoprotein
Intercellular
junctions
Microfilaments
of cytoskeleton
ATPTransport
Signal
transduction
Receptor
Signaling
molecule
Attachment to the cytoskeleton
and extracellular matrix (ECM)
5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Membrane proteins perform many functions.
1. Some proteins help maintain cell shape and coordinate
changes inside and outside the cell through their
attachment to the cytoskeleton and extracellular matrix.
2. Some proteins function as receptors for chemical
messengers from other cells.
3. Some membrane proteins function as enzymes.
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5.1 Membranes are fluid mosaics of lipids and proteins with many functions
4. Some membrane glycoproteins are involved in cell-cell
recognition.
5. Membrane proteins may participate in the intercellular
junctions that attach adjacent cells to each other.
6. Membranes may exhibit selective permeability,
allowing some substances to cross more easily than
others.
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Animation: Signal Transduction PathwaysRight click on animation / Click play
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Animation: Overview of Cell SignalingRight click on animation / Click play
5.2 EVOLUTION CONNECTION: Membranes form spontaneously, a critical step in the origin of life
Phospholipids, the key ingredient of biological
membranes, spontaneously self-assemble into
simple membranes.
The formation of membrane-enclosed collections of
molecules was a critical step in the evolution of the
first cells.
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Figure 5.2
Water-filledbubble made ofphospholipids
Figure 5.2Q
Water
Water
5.3 Passive transport is diffusion across a membrane with no energy investment
Diffusion is the tendency of particles to spread out
evenly in an available space.
– Particles move from an area of more concentrated
particles to an area where they are less concentrated.
– This means that particles diffuse down their
concentration gradient.
– Eventually, the particles reach equilibrium where the
concentration of particles is the same throughout.
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5.3 Passive transport is diffusion across a membrane with no energy investment
Diffusion across a cell membrane does not require energy, so it is called passive transport.
The concentration gradient itself represents potential energy for diffusion.
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Animation: DiffusionRight click on animation / Click play
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Animation: Membrane SelectivityRight click on animation / Click play
Figure 5.3A
Molecules of dye Membrane
Pores
Net diffusion Net diffusion Equilibrium
Figure 5.3B
Net diffusion Net diffusion
Net diffusion Net diffusion
Equilibrium
Equilibrium
5.4 Osmosis is the diffusion of water across a membrane
One of the most important substances that crosses
membranes is water.
The diffusion of water across a selectively
permeable membrane is called osmosis.
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Animation: OsmosisRight click on animation / Click play
5.4 Osmosis is the diffusion of water across a membrane
If a membrane permeable to water but not a solute
separates two solutions with different
concentrations of solute,
– water will cross the membrane,
– moving down its own concentration gradient,
– until the solute concentration on both sides is equal.
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Figure 5.4
Osmosis
Solute molecule
with cluster of
water molecules
Water
molecule
Selectively
permeable
membrane
Solute
molecule
H2O
Lower
concentration
of solute
Higher
concentration
of solute
Equal
concentrations
of solute
5.5 Water balance between cells and their surroundings is crucial to organisms
Tonicity is a term that describes the ability of a
solution to cause a cell to gain or lose water.
Tonicity mostly depends on the concentration of a
solute on both sides of the membrane.
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5.5 Water balance between cells and their surroundings is crucial to organisms
How will animal cells be affected when placed into solutions of various tonicities? When an animal cell is placed into
– an isotonic solution, the concentration of solute is the same on both sides of a membrane, and the cell volume will not change,
– a hypotonic solution, the solute concentration is lower outside the cell, water molecules move into the cell, and the cell will expand and may burst, or
– a hypertonic solution, the solute concentration is higher outside the cell, water molecules move out of the cell, and the cell will shrink.
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5.5 Water balance between cells and their surroundings is crucial to organisms
For an animal cell to survive in a hypotonic or
hypertonic environment, it must engage in
osmoregulation, the control of water balance.
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5.5 Water balance between cells and their surroundings is crucial to organisms
The cell walls of plant cells, prokaryotes, and fungi
make water balance issues somewhat different.
– The cell wall of a plant cell exerts pressure that
prevents the cell from taking in too much water and
bursting when placed in a hypotonic environment.
– But in a hypertonic environment, plant and animal cells
both shrivel.
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Video: ChlamydomonasUse window controls to play
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Video: PlasmolysisUse window controls to play
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Video: Paramecium VacuoleUse window controls to play
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Video: Turgid ElodeaUse window controls to play
Figure 5.5
Animal
cell
Plant
cell
Turgid
(normal)
Flaccid Shriveled
(plasmolyzed)
Plasma
membrane
Lysed Normal Shriveled
Hypotonic solution Isotonic solution Hypertonic solution
H2O H2O H2O H2O
H2O H2O H2O
5.6 Transport proteins can facilitate diffusion across membranes
Hydrophobic substances easily diffuse across a
cell membrane.
However, polar or charged substances do not
easily cross cell membranes and, instead, move
across membranes with the help of specific
transport proteins in a process called facilitated
diffusion, which
– does not require energy and
– relies on the concentration gradient.
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5.6 Transport proteins can facilitate diffusion across membranes
Some proteins function by becoming a hydrophilic
tunnel for passage of ions or other molecules.
Other proteins bind their passenger, change
shape, and release their passenger on the other
side.
In both of these situations, the protein is specific
for the substrate, which can be sugars, amino
acids, ions, and even water.
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5.6 Transport proteins can facilitate diffusion across membranes
Because water is polar, its diffusion through a
membrane’s hydrophobic interior is relatively slow.
The very rapid diffusion of water into and out of
certain cells is made possible by a protein channel
called an aquaporin.
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Figure 5.6
Solute
molecule
Transport
protein
5.7 SCIENTIFIC DISCOVERY: Research on another membrane protein led to the discovery of aquaporins
Dr. Peter Agre received the 2003 Nobel Prize in
chemistry for his discovery of aquaporins.
His research on the Rh protein used in blood
typing led to this discovery.
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Figure 5.7
5.8 Cells expend energy in the active transport of a solute
In active transport, a cell
– must expend energy to
– move a solute against its concentration gradient.
The following figures show the four main stages of
active transport.
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Animation: Active TransportRight click on animation / Click play
Figure 5.8_s1
Transportprotein
Solute
Solute binding1
Figure 5.8_s2
Transportprotein
Solute ADPATP P
Solute binding Phosphateattaching
21
Figure 5.8_s3
Transportprotein
Solute ADPATP P
PProteinchanges shape.
Solute binding Phosphateattaching
Transport21 3
Figure 5.8_s4
Transportprotein
Solute ADPATP P
P PProteinchanges shape.
Phosphatedetaches.
Solute binding Phosphateattaching
Transport Proteinreversion
4321
5.9 Exocytosis and endocytosis transport large molecules across membranes
A cell uses two mechanisms to move large
molecules across membranes.
– Exocytosis is used to export bulky molecules, such as
proteins or polysaccharides.
– Endocytosis is used to import substances useful to the
livelihood of the cell.
In both cases, material to be transported is
packaged within a vesicle that fuses with the
membrane.
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5.9 Exocytosis and endocytosis transport large molecules across membranes
There are three kinds of endocytosis.
1. Phagocytosis is the engulfment of a particle by wrapping
cell membrane around it, forming a vacuole.
2. Pinocytosis is the same thing except that fluids are taken
into small vesicles.
3. Receptor-mediated endocytosis uses receptors in a
receptor-coated pit to interact with a specific protein,
initiating the formation of a vesicle.
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Animation: Exocytosis and Endocytosis IntroductionRight click on animation / Click play
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Animation: Exocytosis Right click on animation / Click play
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Animation: PinocytosisRight click on animation / Click play
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Animation: PhagocytosisRight click on animation / Click play
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Animation: Receptor-Mediated EndocytosisRight click on animation / Click play
Figure 5.9Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
EXTRACELLULARFLUID
CYTOPLASM
Pseudopodium
“Food” orother particle
Foodvacuole
Foodbeingingested
Plasma membrane
Plasma membrane
Vesicle
Receptor
Specificmolecule
Coatedpit
Coatedvesicle
Coat protein
Coatedpit
Material boundto receptor proteins
Figure 5.9_1
Phagocytosis
EXTRACELLULARFLUID
CYTOPLASM
Pseudopodium
“Food” orother particle
Foodvacuole
Foodbeingingested
Figure 5.9_2
Pinocytosis
Plasma membrane
Plasma membrane
Vesicle
Figure 5.9_3
Receptor-mediated endocytosis Plasma membrane
Receptor
Specificmolecule
Coatedpit
Coatedvesicle
Coat protein
Coatedpit
Material boundto receptor proteins
Figure 5.9_4
Foodbeingingested
Figure 5.9_5
Plasma membrane
Figure 5.9_6
Plasma membrane
Coatedpit
Material boundto receptor proteins
ENERGY AND THE CELL
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5.10 Cells transform energy as they perform work
Cells are small units, a chemical factory, housing
thousands of chemical reactions.
Cells use these chemical reactions for
– cell maintenance,
– manufacture of cellular parts, and
– cell replication.
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5.10 Cells transform energy as they perform work
Energy is the capacity to cause change or to
perform work.
There are two kinds of energy.
1. Kinetic energy is the energy of motion.
2. Potential energy is energy that matter possesses as a
result of its location or structure.
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Figure 5.10
Fuel Energy conversion Waste products
Gasoline
Oxygen
Oxygen
Glucose
Heatenergy
Combustion
Kinetic energyof movement
Energy conversion in a car
Energy conversion in a cell
Energy for cellular work
Cellular respiration
ATP ATP
Heatenergy
Carbon dioxide
Carbon dioxide
Water
Water
Figure 5.10_1
Fuel Energy conversion Waste products
Gasoline
Oxygen
Heatenergy
Combustion
Kinetic energyof movement
Energy conversion in a car
Carbon dioxide
Water
Figure 5.10_2
Oxygen
Glucose
Energy conversion in a cell
Energy for cellular work
Cellular respiration
ATP ATP
Heatenergy
Carbon dioxide
Water
Fuel Energy conversion Waste products
5.10 Cells transform energy as they perform work
Heat, or thermal energy, is a type of kinetic energy
associated with the random movement of atoms or
molecules.
Light is also a type of kinetic energy, and can be
harnessed to power photosynthesis.
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5.10 Cells transform energy as they perform work
Chemical energy is the potential energy available
for release in a chemical reaction. It is the most
important type of energy for living organisms to
power the work of the cell.
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Animation: Energy ConceptsRight click on animation / Click play
5.10 Cells transform energy as they perform work
Thermodynamics is the study of energy
transformations that occur in a collection of matter.
Scientists use the word
– system for the matter under study and
– surroundings for the rest of the universe.
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5.10 Cells transform energy as they perform work
Two laws govern energy transformations in
organisms. According to the
– first law of thermodynamics, energy in the universe is
constant, and
– second law of thermodynamics, energy conversions
increase the disorder of the universe.
Entropy is the measure of disorder, or
randomness.
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5.10 Cells transform energy as they perform work
Cells use oxygen in reactions that release energy
from fuel molecules.
In cellular respiration, the chemical energy stored
in organic molecules is converted to a form that the
cell can use to perform work.
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5.11 Chemical reactions either release or store energy
Chemical reactions either
– release energy (exergonic reactions) or
– require an input of energy and store energy
(endergonic reactions).
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5.11 Chemical reactions either release or store energy
Exergonic reactions release energy.
– These reactions release the energy in covalent bonds of
the reactants.
– Burning wood releases the energy in glucose as heat
and light.
– Cellular respiration
– involves many steps,
– releases energy slowly, and
– uses some of the released energy to produce ATP.
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Figure 5.11A
Reactants
EnergyProducts
Amount of
energy
released
Po
ten
tia
l e
nerg
y o
f m
ole
cu
les
5.11 Chemical reactions either release or store energy
An endergonic reaction
– requires an input of energy and
– yields products rich in potential energy.
Endergonic reactions
– begin with reactant molecules that contain relatively
little potential energy but
– end with products that contain more chemical energy.
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Figure 5.11B
Reactants
Energy
Products
Amount of
energy
required
Po
ten
tia
l e
ne
rgy o
f m
ole
cu
les
5.11 Chemical reactions either release or store energy
Photosynthesis is a type of endergonic process.
– Energy-poor reactants, carbon dioxide, and water are
used.
– Energy is absorbed from sunlight.
– Energy-rich sugar molecules are produced.
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5.11 Chemical reactions either release or store energy
A living organism carries out thousands of
endergonic and exergonic chemical reactions.
The total of an organism’s chemical reactions is
called metabolism.
A metabolic pathway is a series of chemical
reactions that either
– builds a complex molecule or
– breaks down a complex molecule into simpler
compounds.
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5.11 Chemical reactions either release or store energy
Energy coupling uses the
– energy released from exergonic reactions to drive
– essential endergonic reactions,
– usually using the energy stored in ATP molecules.
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ATP, adenosine triphosphate, powers nearly all
forms of cellular work.
ATP consists of
– the nitrogenous base adenine,
– the five-carbon sugar ribose, and
– three phosphate groups.
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
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5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
Hydrolysis of ATP releases energy by transferring
its third phosphate from ATP to some other
molecule in a process called phosphorylation.
Most cellular work depends on ATP energizing
molecules by phosphorylating them.
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Figure 5.12A_s1
AdenineP P P
Phosphategroup
ATP: Adenosine Triphosphate
Ribose
Figure 5.12A_s2
ADP: Adenosine Diphosphate
P P P Energy
H2OHydrolysis
Ribose
AdenineP P P
Phosphategroup
ATP: Adenosine Triphosphate
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
There are three main types of cellular work:
1. chemical,
2. mechanical, and
3. transport.
ATP drives all three of these types of work.
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Figure 5.12B
ATP ATP ATP
ADP ADP ADPP P P
P
P
P
PP
P
Chemical work Mechanical work Transport work
Reactants
Motorprotein
Solute
Membrane protein
Product
Molecule formed Protein filament moved Solute transported
5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
ATP is a renewable source of energy for the cell.
In the ATP cycle, energy released in an exergonic
reaction, such as the breakdown of glucose,is used
in an endergonic reaction to generate ATP.
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Figure 5.12C
Energy fromexergonicreactions
Energy forendergonicreactions
ATP
ADP P
HOW ENZYMES FUNCTION
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5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Although biological molecules possess much
potential energy, it is not released spontaneously.
– An energy barrier must be overcome before a chemical
reaction can begin.
– This energy is called the activation energy (EA).
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5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
We can think of EA
– as the amount of energy needed for a reactant molecule
to move “uphill” to a higher energy but an unstable state
– so that the “downhill” part of the reaction can begin.
One way to speed up a reaction is to add heat,
– which agitates atoms so that bonds break more easily
and reactions can proceed but
– could kill a cell.
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Figure 5.13A
Activation
energy barrier
Reactant
Products
Without enzyme With enzyme
Reactant
Products
Enzyme
Activation
energy
barrier
reduced by
enzyme
En
erg
y
En
erg
y
Figure 5.13A_1
Activation
energy barrier
Reactant
Products
Without enzyme
En
erg
y
Figure 5.13A_2
Activation
energy
barrier
reduced by
enzyme
Reactant
Products
With enzyme
En
erg
y
Enzyme
Figure 5.13Q
Reactants
Products
En
erg
y
Progress of the reaction
a
b
c
5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Enzymes
– function as biological catalysts by lowering the EA
needed for a reaction to begin,
– increase the rate of a reaction without being consumed
by the reaction, and
– are usually proteins, although some RNA molecules can
function as enzymes.
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Animation: How Enzymes WorkRight click on animation / Click play
5.14 A specific enzyme catalyzes each cellular reaction
An enzyme
– is very selective in the reaction it catalyzes and
– has a shape that determines the enzyme’s specificity.
The specific reactant that an enzyme acts on is
called the enzyme’s substrate.
A substrate fits into a region of the enzyme called
the active site.
Enzymes are specific because their active site fits
only specific substrate molecules.
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5.14 A specific enzyme catalyzes each cellular reaction
The following figure illustrates the catalytic cycle of
an enzyme.
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Figure 5.14_s1
1
Enzyme
(sucrase)
Active site
Enzyme available
with empty active
site
Figure 5.14_s2
2
1
Enzyme
(sucrase)
Active site
Enzyme available
with empty active
site
Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Figure 5.14_s3
3
2
1
Enzyme
(sucrase)
Active site
Enzyme available
with empty active
site
Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Substrate is
converted to
products
H2O
Figure 5.14_s4
4
3
2
1
Products are
released
Fructose
Glucose
Enzyme
(sucrase)
Active site
Enzyme available
with empty active
site
Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Substrate is
converted to
products
H2O
5.14 A specific enzyme catalyzes each cellular reaction
For every enzyme, there are optimal conditions
under which it is most effective.
Temperature affects molecular motion.
– An enzyme’s optimal temperature produces the highest
rate of contact between the reactants and the enzyme’s
active site.
– Most human enzymes work best at 35–40ºC.
The optimal pH for most enzymes is near
neutrality.
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5.14 A specific enzyme catalyzes each cellular reaction
Many enzymes require nonprotein helpers called
cofactors, which
– bind to the active site and
– function in catalysis.
Some cofactors are inorganic, such as zinc, iron, or
copper.
If a cofactor is an organic molecule, such as most
vitamins, it is called a coenzyme.
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5.15 Enzyme inhibitors can regulate enzyme activity in a cell
A chemical that interferes with an enzyme’s activity
is called an inhibitor.
Competitive inhibitors
– block substrates from entering the active site and
– reduce an enzyme’s productivity.
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5.15 Enzyme inhibitors can regulate enzyme activity in a cell
Noncompetitive inhibitors
– bind to the enzyme somewhere other than the active
site,
– change the shape of the active site, and
– prevent the substrate from binding.
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Figure 5.15A
Substrate
Enzyme
Allosteric site
Active site
Normal binding of substrate
Competitive
inhibitorNoncompetitive
inhibitor
Enzyme inhibition
5.15 Enzyme inhibitors can regulate enzyme activity in a cell
Enzyme inhibitors are important in regulating cell
metabolism.
In some reactions, the product may act as an
inhibitor of one of the enzymes in the pathway that
produced it. This is called feedback inhibition.
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Figure 5.15B
Feedback inhibition
Starting
molecule
Product
Enzyme 1 Enzyme 2 Enzyme 3
Reaction 1 Reaction 2 Reaction 3A B C D
5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors
Many beneficial drugs act as enzyme inhibitors, including
– Ibuprofen, inhibiting the production of prostaglandins,
– some blood pressure medicines,
– some antidepressants,
– many antibiotics, and
– protease inhibitors used to fight HIV.
Enzyme inhibitors have also been developed as pesticides and deadly poisons for chemical warfare.
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Figure 5.16
1. Describe the fluid mosaic structure of cell membranes.
2. Describe the diverse functions of membrane proteins.
3. Relate the structure of phospholipid molecules to the structure and properties of cell membranes.
4. Define diffusion and describe the process of passive transport.
You should now be able to
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5. Explain how osmosis can be defined as the
diffusion of water across a membrane.
6. Distinguish between hypertonic, hypotonic, and
isotonic solutions.
7. Explain how transport proteins facilitate diffusion.
8. Distinguish between exocytosis, endocytosis,
phagocytosis, pinocytosis, and receptor-mediated
endocytosis.
You should now be able to
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9. Define and compare kinetic energy, potential
energy, chemical energy, and heat.
10. Define the two laws of thermodynamics and
explain how they relate to biological systems.
11. Define and compare endergonic and exergonic
reactions.
12. Explain how cells use cellular respiration and
energy coupling to survive.
You should now be able to
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You should now be able to
13. Explain how ATP functions as an energy shuttle.
14. Explain how enzymes speed up chemical
reactions.
15. Explain how competitive and noncompetitive
inhibitors alter an enzyme’s activity.
16. Explain how certain drugs, pesticides, and
poisons can affect enzymes.
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Figure 5.UN01
Lower solute concentration
Lower free water
concentration
Lower solute
concentration
HIgher free water
concentration
HIgher solute
concentration
HIgher solute concentration
Solute
WaterATP
Facilitated
diffusion
Passive transport
(requires no energy)Active transport
(requires energy)
Diffusion Osmosis
Figure 5.UN02
ATP cycle ATP
ADP P
Energy from
exergonic
reactions
Energy for
endergonic
reactions
Figure 5.UN03
Molecules cross
cell membranes
passive
transport
polar molecules
and ions
diffusion
moving
down
moving
againstrequires
by by
may be
uses
uses
of of
ATP
(a)
(b)
(c)
(d)
(e)
Figure 5.UN04
a.
b.
c.
d.
e.
f.
Table 5.UN05
Figure 5.UN06
pH
Ra
te o
f re
ac
tio
n
109876543210