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2010 Pearson Education, Inc.


Lectures by Chris C. Romero, updated by Edward J. Zalisko

PowerPoint

Lectures forCampbell Essential Biology, Fourth EditionEric Simon, Jane Reece, and Jean Dickey

Campbell Essential Biology with Physiology, Third EditionEric Simon, Jane Reece, and Jean Dickey

Chapter 50

The Working Cell
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Biology and Society:Natural Nanotechnology

Cells control their chemical environment using Energy Enzymes

The plasma membrane

Cell-based nanotechnology may be used to powermicroscopic robots.



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Figure 5.00


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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.


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Climbing the stepsconverts kineticenergy of musclemovement topotential energy.

On the platform,the diver has morepotential energy.

Diving convertspotential energyto kinetic energy.

In the water, thediver has lesspotential energy.

Figure 5.1


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Machines and organisms can transform kineticenergy to potential energy and vice versa.

In all such energy transformations, total energy isconserved.

Energy cannot be created or destroyed.

This is the principle ofconservation of energy.



Entropy

Every energy conversion releases some randomizedenergy in the form of heat.

Heat is a

Type of kinetic energy

Product of all energy conversions



Scientists use the term entropy as a measure ofdisorder, or randomness.

All energy conversions increase the entropy of theuniverse.



Chemical Energy

Molecules store varying amounts of potential energyin the arrangement of their atoms.

Organic compounds are relatively rich in suchchemical energy.



Living cells and automobile engines use the samebasic process to make chemical energy do work.



Fuel rich inchemicalenergy

Energy conversionWaste productspoor in chemicalenergy

Gasoline

Oxygen

Carbon dioxide

Water

Energy conversion in a car

Energy for cellular work

Energy conversion in a cell

Heatenergy

Heatenergy

Carbon dioxide

Water

Food

Oxygen

Combustion

Cellularrespiration

Kinetic energyof movement

ATP

Figure 5.2



Cellular respiration is the energy-releasing chemicalbreakdown 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.



Food Calories

A calorieis the amount of energy that raises thetemperature of one gram of water by 1 degree

Celsius. Food Calories are kilocalories, equal to 1,000

calories.


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(a) Food Calories (kilocalories) invarious foods

(b) Food Calories (kilocalories) weburn in various activities

CheeseburgerSpaghetti with sauce (1 cup)

Pizza with pepperoni (1 slice)

Peanuts (1 ounce)

Apple

Bean burrito

Fried chicken (drumstick)

Garden salad (2 cups)

Popcorn (plain, 1 cup)

Broccoli (1 cup)

Baked potato (plain, withskin)

FoodCalories

Food

295

241

220

193

181

166

81

56

189

31

25

Activity Food Calories consumed perhour by a 150-pound person*

979

510

490

408

204

73

61

245

28

Running (7min/mi)

Sitting (writing)

Driving a car

Playing the piano

Dancing (slow)

Walking (3 mph)

Bicycling (10 mph)

Swimming (2 mph)

Dancing (fast)

*Not including energy necessary for basic functions, such

as breathing and heartbeat

Figure 5.3


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2010 Pearson Education, Inc.(a) Food Calories (kilocalories) in various foods

Cheeseburge

rSpaghetti with sauce (1 cup)

Pizza with pepperoni (1 slice)

Peanuts (1 ounce)

Apple

Beanburrito

Fried chicken (drumstick)

Garden salad (2 cups)

Popcorn (plain, 1cup)Broccoli (1 cup)

Baked potato (plain, withskin)

FoodCalories

Food

295

241

220

193

181

166

81

56

189

31

25

Figure 5.3a


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2010 Pearson Education, Inc.(b) Food Calories (kilocalories) we burn in various activities

Activity

Food Calories consumed perhour by a 150-poundperson*

979

510490

408

204

73

61

245

28

Running (7min/mi)

Sitting(writing)

Driving a car

Playing thepiano

Dancing(slow)

Walking (3mph)

Bicycling (10mph)Swimming (2 mph)

Dancing (fast)

*Not including energy necessary for basic functions,such as breathing and heartbeat

Figure 5.3b


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The energy of calories in food is burned off by manyactivities.


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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


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Triphosphate Diphosphate

Adenosine Adenosine

Energy

ATP ADP

P P P P P P

Phosphate(transferred to

another molecule)

Figure 5.4


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Phosphate Transfer

ATP energizes other molecules by transferringphosphate groups.

This energy helps cells perform

Mechanical work

Transport work

Chemical work


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ATP

ATP

ATP

ADP

ADP

ADP

P

P

P

ADP P

P P

P

PX X Y

Y

(a) Motor protein performing mechanical work

(b) Transport protein performing transport work

(c) Chemical reactants performing chemical work

Solute

Solutetransported

Protein moved

Product madeReactants

Transportprotein

Motorprotein

Figure 5.5


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ATP ADP PADP P

(a) Motor protein performing mechanical workProtein moved

Motorprotein

Figure 5.5a


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ATP ADP P

P P

(b) Transport protein performing transport work

Solute

Solutetransported

Transportprotein

Figure 5.5b


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ATP ADP P

P

PX X Y

Y

(c) Chemical reactants performing chemical work

Product madeReactants

Figure 5.5c

Th ATP C l


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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 10million ATP molecules per second.


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Cellular respiration:chemical energy

harvested from

fuel molecules

Energy for

cellular work

ATP

ADPP

Figure 5.6

ENZYMES


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ENZYMES

Metabolism is the total of all chemical reactions inan organism.

Most metabolic reactions require the assistance ofenzymes, proteins that speed up chemicalreactions.

A ti ti E


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Activation Energy

Activation energy

Activates the reactants

Triggers a chemical reaction

Enzymes lower the activation energy for chemicalreactions.


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(a) Without enzyme (b) With enzyme

Reactant Reactant

Products Products

Activationenergy barrier Activation

energy barrierreduced byenzyme

Enzyme

Energylevel

Energyle

vel

Figure 5.7

Activation


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2010 Pearson Education, Inc.(a) Without enzyme

Reactant

Products

Activationenergy barrier

Energylevel

Figure 5.7a


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2010 Pearson Education, Inc.(b) With enzyme

Reactant

Products

Activationenergy barrierreduced byenzyme

Enzyme

Energy

leve

l

Figure 5.7b

The Process of Science:


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The Process of Science:Can Enzymes Be Engineered?

Observation: Genetic sequences suggest thatmany of our genes were formed through a type ofmolecular evolution.

Question: Can laboratory methods form newenzymes through artificial selection?

Hypothesis: An artificial process could modify thegene that codes for lactase into a new gene with anew function.



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Experiment: Many copies of the lactase gene wererandomly mutated and tested for new activities.

Results: Directed evolution produced a newenzyme with a novel function.



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Gene for lactase

Mutated genes(mutations shown in orange)

Mutated genes screenedby testing new enzymes

Gene duplicated andmutated at random

Genes coding for enzymesthat show new activity

Genes coding for enzymesthat do notshow new activity

Genes duplicated andmutated at random

Mutated genesscreened

by testing newenzymes

After seven rounds, somegenes code for enzymes that canefficiently perform new activity.

Ribbon model showing the polypeptidechains of the enzyme lactase

Figure 5.8

Gene for lactase


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Gene for lactase

Mutated genes(mutations shown in orange)

Mutated genes screenedby testing new enzymes

Gene duplicated andmutated at random

Genes coding for enzymesthat show new activity

Genes coding for enzymesthat do notshow new activity

Genes duplicated and

mutated at random

Mutated genesscreened

by testing new enzymes

After seven rounds, somegenes code for enzymes that can

efficiently perform new activity. Figure 5.8a


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2010 Pearson Education, Inc. Figure 5.8b

Ribbon model showing the polypeptidechains of the enzyme lactase

Induced Fit


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Induced Fit

Every enzyme is very selective, catalyzing a specificreaction.


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Each enzyme recognizes a substrate, a specificreactant molecule.

The active site fits to the substrate, and the enzymechanges shape slightly.

This interaction is called induced fit.


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Enzymes can function over and over again, a keycharacteristic of enzymes.


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2010 Pearson Education, Inc. Figure 5.9-1

Active site

Enzyme(sucrase)

Sucrase can accept amolecule of its substrate.


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Active site

Enzyme(sucrase)


Substrate (sucrose)

Substrate bindsto the enzyme.

Figure 5.9-2


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Active site

Enzyme(sucrase)


Substrate (sucrose)


The enzymecatalyzes thechemical reaction.

H2O

Figure 5.9-3


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Active site

Enzyme(sucrase)


Substrate (sucrose)


The enzymecatalyzes thechemical reaction.

H2O

Fructose

Glucose

The productsare released.

Figure 5.9-4

Enzyme Inhibitors


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Enzyme Inhibitors

Enzyme inhibitors can prevent metabolicreactions by binding to the active site.

(a) Enzyme and substrate Substrate


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(a) Enzyme and substratebinding normally

(b) Enzyme inhibition bya substrate imposter

(c) Enzyme inhibition bya molecule that causesthe active site to changeshape

Substrate

Substrate

Active site

Active site

Active site

Inhibitor

Inhibitor

Enzyme

Enzyme

Enzym

e Figure 5.10


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(a) Enzyme and substrate binding normally

Substrate

Enzyme

Activesite

Figure 5.10a


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2010 Pearson Education, Inc. Figure 5.10b

(b) Enzyme inhibition by a substrate imposter

Substrate

Active site

Inhibitor

Enzyme


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(c) Enzyme inhibition by a molecule thatcauses the active site to change shape

Substrate

Active site

Inhibitor

Enzyme

Figure 5.10c


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Other enzyme inhibitors

Bind at a remote site

Change the enzymes shape

Prevent the enzyme from binding to its substrate


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Some products of a reaction may inhibit the enzymerequired for its production.

This is called feedback regulation.

It prevents the cell from wasting resources.

Many antibiotics work by inhibiting enzymes ofdisease-causing bacteria.

MEMBRANE FUNCTION


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MEMBRANE FUNCTION

Working cells must control the flow of materials toand from the environment.

Membrane proteins perform many functions.

Transport proteins

Are located in membranes

Regulate the passage of materials into and out of thecell


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Cellsignaling

Attachment tothe cytoskeleton

and extracellularmatrix

Enzymatic activity

Cytoskeleton

Cytoplasm

Cytoplasm

Transport

Fibers of

extracellularmatrix

Intercellularjoining

Cell-cellrecognition

Figure 5.11

Passive Transport: Diffusion across Membranes


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Passive Transport: Diffusion across Membranes

Molecules contain heat energy that causes them tovibrate and wander randomly.

Diffusion is the tendency for molecules of anysubstance to spread out into the available space.


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Passive transport is the diffusion of a substanceacross a membrane without the input of energy.

Diffusion is an example of passive transport.

Substances diffuse down their concentrationgradient, a region in which the substancesdensity changes.

Molecules of dye Membrane


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(a) Passive transport of one type of molecule

(b) Passive transport of two types of molecules

Net diffusion Net diffusion Equilibrium



Figure 5.12


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Molecules of dye Membrane

(a) Passive transport of one type of molecule


Figure 5.12a


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(b) Passive transport of two types of molecules

Netdiffusion

Netdiffusion

Equilibrium

Netdiffusion Netdiffusion Equilibrium

Figure 5.12b


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Some substances do not cross membranesspontaneously.

These substances can be transported via facilitateddiffusion.

Specific transport proteins act as selective corridors.

No energy input is needed.

Osmosis and Water Balance


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The diffusion of water across a selectivelypermeable membrane is osmosis.


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Hypotonic solution Hypertonic

solution

Sugarmolecule

Selectively

permeablemembrane

Osmosis

Figure 5.13-1


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Hypotonic solution Hypertonic

solution

Sugarmolecule

Selectively

permeablemembrane

Osmosis

Isotonic solutions

Osmosis

Figure 5.13-2


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A hypertonic solution has a higher concentration ofsolute.

A hypotonic solution has a lower concentration ofsolute.

An isotonic solution has an equal concentration ofsolute.

Water Balance in Animal Cells


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Osmoregulation is the control of water balancewithin a cell or organism.

Most animal cells require an isotonic environment.

Water Balance in Plant Cells


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Plant have rigid cell walls.

Plant cells require a hypotonic environment, which

keeps these walled cells turgid.

Animal cell


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Plant cell

Normal

Flaccid (wilts)

Lysing

Turgid

Shriveled

Shriveled

Plasmamembrane

H2OH2O H2O H2O

H2OH2OH2O H2O

(a) Isotonic

solution

(b) Hypotonic

solution

(c) Hypertonic

solution Figure 5.14

Animal cell


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Plant cell

Normal

Flaccid (wilts)

H2OH2O

H2O H2O

(a) Isotonic

solution Figure 5.14a


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Lysing

Turgid

H2O

H2O

(b) Hypotonicsolution

Figure 5.14b


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Shriveled

Shriveled

Plasmamembrane

H2O

H2O

(c) Hypertonicsolution

Figure 5.14c


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As a plant cell loses water,

It shrivels.

Its plasma membrane may pull away from the cell wallin the process ofplasmolysis, which usually killsthe cell.


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2010 Pearson Education, Inc. Figure 5.15

Active Transport: The Pumping of MoleculesA M b


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Across Membranes

Active transport requires energy to move

molecules across a membrane.



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Lower solute concentration

Higher soluteconcentration

ATP

Solute

Figure 5.16-1


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ATP

Solute

Figure 5.16-2

Exocytosis and Endocytosis: Traffic of LargeM l l


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Molecules

Exocytosis is the secretion of large molecules

within vesicles.



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Outside of cell

Cytoplasm

Plasmamembrane

Figure 5.17


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Endocytosis takes material into a cell withinvesicles that bud inward from the plasma

membrane.


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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 invery specific molecules

The Role of Membranes in Cell Signaling


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The plasma membrane helps convey signalsbetween

Cells Cells and their environment


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Receptors on a cell surface trigger signaltransduction pathways that

Relay the signal Convert it to chemical forms that can function within

the cell


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Outside ofcell

Cytoplasm

Reception Transduction

ResponseReceptorprotein

Epinephrine(adrenaline)from adrenalglands

Plasma membrane

Proteins of signal transduction pathway

Hydrolysisof glycogenreleasesglucose forenergy

Figure 5.19


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Outside of cell Cytoplasm

ReceptionTransduction Response

Receptor

protein

Epinephrine(adrenaline)from adrenalglands

Plasma membrane

Proteins of signal transductionpathway

Hydrolysisof glycogenreleasesglucose forenergy

Figure 5.19a

Evolution Connection:The Origin of Membranes


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The Origin of Membranes

Phospholipids

Are key ingredients of membranes

Were probably among the first organic compoundsthat formed before life emerged

Self-assemble into simple membranes



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Energy for cellular work

Adenosine

Adenosinediphosphate

Energy fromorganic fuel

Phosphate

ATPcycle

ATP ADP

P P P P P PAdenosine

Adenosine

triphosphate

Figure 5.UN01


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Reactant Reactant

ProductsProducts

Enzyme added

Activ

ationener g

y

Figure 5.UN02


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Passive Transport

(requires no energy)

Active Transport

(requires energy)

Diffusion Facilitated diffusion Osmosis

Higher solute concentration


Higher water concentration(lower solute concentration)

Lower water concentration(higher soluteconcentration)

Solute


Lower soluteconcentration

ATP

Solute

Solute

Water

Solute

MEMBRANE TRANSPORT

Figure 5.UN03


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Exocytosis Endocytosis

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