Figure 5.1

Fibers ofextracellularmatrix (ECM)

Enzymatic activity

Phospholipid

Cholesterol

CYTOPLASM

CYTOPLASM

Cell-cellrecognition

Glycoprotein

Intercellularjunctions

Microfilamentsof cytoskeleton

ATPTransport

Signaltransduction

Receptor

Signalingmolecule

Attachment to the cytoskeletonand extracellular matrix (ECM)

Passive transport

Passive transport = diffusion across cell membrane

– No energy required!!

Moves with concentration gradient

Examples:

– Urea, CO2, O2, Water, small hydrophobic

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Animation: Membrane Selectivity

Animation: Diffusion

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

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Osmosis

Solute moleculewith cluster ofwater molecules

Watermolecule

Selectivelypermeablemembrane

Solutemolecule

H2O

Lowerconcentration

of solute

Higherconcentration

of solute

Equalconcentrations

of soluteOsmosis = diffusion of water across a membrane

Figure 5.5

Animalcell

Plantcell

Turgid(normal)

Flaccid Shriveled(plasmolyzed)

Plasmamembrane

Lysed Normal Shriveled

Hypotonic solution Isotonic solution Hypertonic solution

H2O H2O H2O H2O

H2O H2O H2O

Osmoregulation = Water Balance

Osmoreguatation = all organisms must regulate internal water concentrations to remove excess water or prevent water loss

– Remove excess water:

– Contractile vacuoles - protists

– Freshwater organisms – kidneys, gills

– Prevent water loss:

– Guard cells in plants

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Video: Paramecium Vacuole

Video: Chlamydomonas

Video: Turgid Elodea

Video: Plasmolysis

Facilitated Diffusion = Passive diffusion of solute using a transport protein

Solutemolecule

Transportprotein

Only moves solutes with concentration gradient!Examples: ion channels, aquaporin

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

Active Transport

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.

Examples: Na-K-ATP Pump, H+ Pump, Na-Glucose Cotransporter

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Animation: Active Transport

Figure 5.8_s4

Transportprotein

Solute ADPATP P P PProtein

changes shape.Phosphatedetaches.

Solute binding Phosphateattaching

Transport Proteinreversion

4321

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: Phagocytosis

Animation: Exocytosis

Animation: Receptor-Mediated Endocytosis

Animation: Pinocytosis

Animation: Exocytosis and Endocytosis Introduction

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

ENERGY AND THE CELL

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5.10 Cells transform energy as they perform work

Energy = capacity to cause change or to perform work.

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.

Heat = thermal energy

Chemical energy = potential energy available in bonds within molecules and released in a chemical reaction.

– Most relevant energy to living organisms

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Animation: Energy Concepts

Figure 5.10

Fuel Energy conversion Waste products

Gasoline

Oxygen

Oxygen

Glucose

Heatenergy

CombustionKinetic 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

Thermodynamics = study of energy transformations

First law of thermodynamics = energy in the universe is constant

– Biological organisms cannot produce energy - only convert forms of energy

Second law of thermodynamics = energy conversions increase the disorder (entropy) of the universe.

– No energy transformations are 100 % efficient

– Usuable energy lost as heat

– Energy transformations are one-way street

– Biological organisms require constant supply of energy to maintain order!!

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Metabolism = total of an organism’s chemical reactions

Chemical reactions are either

– Exergonic reactions release energy.

– These reactions release the energy in covalent bonds of the reactants.

– Cellular respiration

An endergonic reaction

– requires an input of energy; products contain more chemical/potential energy

– Photosynthesis

Energy coupling = energy released from exergonic reactions drive endergonic reactions!!

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Figure 5.11A

Reactants

EnergyProducts

Amount ofenergy

released

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Figure 5.11B

Reactants

Energy

Products

Amount ofenergy

required

Po

ten

tial

en

erg

y o

f m

ole

cule

s

Cells need energy to perform work!!

There are three main types of cellular work:

1. chemical

2. mechanical

3. transport

ATP drives all three of these types of work.

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ATP = Adenosine triphosphate

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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

ATP drives cellular work

Hydrolysis of ATP releases energy by transferring phosphate from ATP to some other molecule

– phosphorylation.

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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

How Does Cell Regenerate ATP?

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Energy fromexergonicreactions

Energy forendergonicreactions

ATP

ADP P

ATP = renewable source of energy for the cell.

ATP cycle = energy released in an exergonic reaction is used in an endergonic reaction to generate ATP.

HOW ENZYMES FUNCTION

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Enzymes = Organic catalysts

Increase RATE of chemical reaction by decreasing activation energy (EA).

– EA = energy barrier must be overcome before any chemical reaction can begin.

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Activationenergy barrier

Reactant

Products

Without enzyme With enzyme

Reactant

Products

Enzyme

Activationenergy barrierreduced byenzyme

En

erg

y

En

erg

y

Animation: How Enzymes Work

Reactants

Products

En

erg

y

Progress of the reaction

a

b

c

Enzymes Only Increase RATE of reaction, NOT the energyLevel of reactants or products!!!

A specific enzyme catalyzes each cellular reaction

An enzyme

– Is specific in substrate(s) it binds

– And reaction it catalyzes

Substrate = reactant

A substrate binds at enzyme active site.

Enzymes are specific because their active site fits only specific substrate molecules

– Active site is result of 3D folding of protein

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4

3

2

1

Products arereleased

Fructose

Glucose

Enzyme(sucrase)

Active site

Enzyme availablewith empty activesite

Substrate(sucrose)

Substrate bindsto enzyme withinduced fit

Substrate isconverted toproducts

H2O

Catalytic cycle of an enzyme

Factors that Effect Enzyme-Catalyzed Reactions

For every enzyme, there are optimal conditions under which it is most effective.

– Temperature

– pH

– Substrate Concentration

– Enzyme Concentration

– Cofactors/coenzymes

– Inhibitors

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Factors that Affect Enzyme-Catalyzed Reactions

Many enzymes require nonprotein helpers called cofactors, which

– bind to the active site and function in catalysis.

– Inorganic molecules

Coenzymes

– Organic

molecule

that acts as

cofactor

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Enzyme Concentration

Substrate Concentration

Temperature - affects molecular motion

pH

Enzyme inhibitors can regulate enzyme activity Inhibitor = chemical that interferes with an enzyme’s activity.

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Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitiveinhibitor

Noncompetitiveinhibitor

Enzyme inhibition

Competitive inhibitors

– block substrates from entering the active site and

– reduce an enzyme’s productivity.

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.

Feedback inhibition

Startingmolecule

Product

Enzyme 1 Enzyme 2 Enzyme 3

Reaction 1 Reaction 2 Reaction 3A B C D

Enzyme inhibitors are important in regulating cell metabolism.

– Feedback inhibition = product of metabolic pathway acts as an inhibitor of one of the enzymes in the pathway

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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Table 5.UN05

Figure 5.UN06

pH

Rat

e o

f re

acti

on

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