_05_Lecture_Presentation_PC.ppt

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PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh Edition

Reece, Taylor, Simon, and Dickey

Chapter 5

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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

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Figure 5.0_1

Chapter 5: Big Ideas

Membrane Structure and Function

Energy and the Cell

How Enzymes Function

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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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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

 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

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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 ATP Transport Signal transduction Receptor Signaling molecule

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5.1 Membranes are fluid mosaics of lipids and

 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.

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5.1 Membranes are fluid mosaics of lipids and

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 Pathways

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Animation: Overview of Cell Signaling

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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

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Figure 5.2

Water-filled

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Figure 5.2Q

Water

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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

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Animation: Diffusion

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Animation: Membrane Selectivity

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Figure 5.3A

Molecules of dye Membrane

Pores

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Figure 5.3B

Net diffusion Net diffusion

Equilibrium

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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: Osmosis

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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

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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

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5.5 Water balance between cells and their

 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

 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.

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Video: Plasmolysis

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Video: Paramecium Vacuole

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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

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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

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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

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Figure 5.6

Solute molecule

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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

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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

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Animation: Active Transport

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Figure 5.8_s1

Transport protein

Solute Solute binding

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Figure 5.8_s2

Transport protein

Solute ATP _ADP

P

Solute binding Phosphate attaching

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Figure 5.8_s3

P Protein P

changes shape. Solute binding Phosphate

attaching Transport

2

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Figure 5.8_s4

P Protein P P

changes shape. Phosphatedetaches. Solute binding Phosphate

attaching Transport Proteinreversion

4 3

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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

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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 Introduction

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Animation: Exocytosis

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Animation: Pinocytosis

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Animation: Phagocytosis

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Animation: Receptor-Mediated Endocytosis

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Figure 5.9 _Phagocytosis

Pinocytosis

Receptor-mediated endocytosis EXTRACELLULAR

FLUID _Pseudopodium CYTOPLASM

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Figure 5.9_1

Phagocytosis

EXTRACELLULAR

FLUID CYTOPLASM

Pseudopodium

“Food” or other particle

Food vacuole

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Figure 5.9_2

Pinocytosis

Plasma membrane Plasma

membrane

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Figure 5.9_3

Receptor-mediated endocytosis Plasma membrane

Receptor Specific molecule Coated pit Coated vesicle Coat protein Coated pit Material bound

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Figure 5.9_4

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Figure 5.9_5

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Figure 5.9_6

Plasma membrane

Coated pit

Material bound

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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.

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Figure 5.10

Fuel Energy conversion Waste products

Gasoline Oxygen Oxygen Glucose     Heat energy Combustion Kinetic energy of movement

Energy conversion in a car

Energy conversion in a cell Energy for cellular work

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Figure 5.10_1

Fuel Energy conversion Waste products

Gasoline

Oxygen

 

Heat energy

Combustion Kinetic energy of movement

Energy conversion in a car

Carbon dioxide

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Figure 5.10_2

Oxygen Glucose

 

Energy conversion in a cell Energy for cellular work

Cellular respiration

ATP ATP Heat

energy

Carbon dioxide

Water

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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

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 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 Concepts

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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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 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

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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

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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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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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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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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

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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.

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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

Adenine P P P

Phosphate group

ATP: Adenosine Triphosphate

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Figure 5.12A_s2

ADP: Adenosine Diphosphate

P P P Energy

H₂O Hydrolysis

Ribose

Adenine P P P

Phosphate group

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5.12 ATP drives cellular work by coupling

 There are three main types of cellular work:

1. chemical,

2. mechanical, and

3. transport.

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Figure 5.12B

ATP ATP ATP

ADP P ADP P ADP P

P P P P P P Chemical work Mechanical work Transport work

Reactants Motor protein Solute Membrane protein Product

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5.12 ATP drives cellular work by coupling

 ATP is a renewable source of energy for the cell.

 _{In the ATP cycle, energy released in an exergonic}

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Figure 5.12C

Energy from exergonic reactions

Energy for endergonic reactions ATP

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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 (E_A).

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5.13 Enzymes speed up the cell’s chemical

reactions by lowering energy barriers

 We can think of E_A

– 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

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Figure 5.13A

Activation energy barrier

Reactant

Products

Without enzyme With enzyme

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Figure 5.13A_1

Activation

energy barrier

Reactant

Products

Without enzyme

E

n

er

g

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Figure 5.13Q

Reactants

Products

E

n

er

g

y

Progress of the reaction a

b

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5.13 Enzymes speed up the cell’s chemical

reactions by lowering energy barriers

 Enzymes

– function as biological catalysts by lowering the E_A 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 Work

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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

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Figure 5.14_s1

1

Enzyme (sucrase) Active site

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Figure 5.14_s2 2 1 Enzyme (sucrase) Active site Enzyme available with empty active site

Substrate (sucrose)

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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

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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

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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

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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

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Figure 5.15A

Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitive

inhibitor Noncompetitiveinhibitor

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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

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Figure 5.15B

Feedback inhibition

Starting molecule

Product

Enzyme 1 Enzyme 2 _{Enzyme 3}

Reaction 1 Reaction 2 Reaction 3

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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

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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.

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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.

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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

Water ATP

Facilitated diffusion

Passive transport

(requires no energy) (requires energy)Active transport

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Figure 5.UN02

ATP cycle ATP

ADP _P

Energy from exergonic reactions

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Figure 5.UN04

a.

b.

c.

d.

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