Chapter 6

The Tour of the Cell

The Fundamental Units of Life

• All living things composed of cells

• Cell structure correlated to cell function

• All cells descend from existing cells

Microscopy

• Light microscope = visible light passes through specimen magnified by lenses

– Up to 1000X

Electron microscope to view organelles

pollen

H1N1 virus

• Electron microscopes (EMs)

• Scanning EM (SEM) focus beam of electrons onto surface 3-D image

• Transmission EM (TEM)

• focus beam of electrons through specimen

• internal structures

Cell Fractionation

centrifuge

separates cell components

Homogenization

Homogenate

Differential centrifugation

Tissuecells

TECHNIQUE

Supernatant poured into next tube

TECHNIQUE (cont.)

Homogenate

Pellet

Supernatant

1000 g 10 min

20,000g 20 min

80,000g 60 min

150,000g 3 hr

Nuclei, debris mitochondria membranes ribosomes

• Prokaryotic cells= Archaea and Bacteria• No nucleus, no membrane-bounded organelles

• DNA in nucleoid region

0.5 µm

Eukaryotic cells = Plants, Animals, Fungi, Protista

•DNA in nucleus•Organelles

•Membrane bounded•Cytoplasm = fluid-like interior+ organellesCytosol = fluid

• The plasma membrane = selective barrier allows passage of oxygen, nutrients, waste etc

• Composed of phospholipid bilayer

Features of cells

• Surface to Volume ratio high

• Small cells have greater surface area relative to volume

• Larger organisms do not have larger cells than smaller organisms

Human Rat

The Eukaryotic Cell

• Plant and animal cells have most of the same organelles

1. The Nucleus

Nuclear envelope– double membrane; each a lipid bilayer

– Pores regulate entry and exit of molecules from nucleus

• Chromatin = DNA + proteins

• Chromosomes = strands of chromatin

• Nucleolus

– within nucleus

– rRNA synthesis

2. Ribosomes: Protein Factories

• Composed of rRNA and protein

• Protein synthesis in two locations:

– cytosol (free ribosomes)

– ER or the nuclear envelope (bound ribosomes)

3. The Endomembrane System

• Components– Nuclear envelope

– Endoplasmic reticulum (ER)

– Golgi apparatus

– Lysosomes

– Vacuoles

– *Plasma membrane

The Endoplasmic Reticulum

• >half of total membrane

• continuous with the nuclear envelope

– Smooth ER lacks ribosomes

1. Synthesizes lipids

• Rough ER (RER)

– Ribosomes assemble proteins thread through ER lumen

transport vesicles

– Membrane factory

The Golgi Apparatus

• flattened membranous sacs called cisternae

• cis and trans face

trans face(“shipping” side of Golgi apparatus)

• Functions of the Golgi apparatus:

– Modifies proteins from ER

– Manufactures polysaccharides

– Packages into transport vesicles

Smooth ER

Nucleus

Rough ER

Plasma membrane

cis Golgi

trans Golgi

Lysosomes

• membranous sac of enzymes that digest macromolecules

• recycle cell components (autophagy)

Lysosome

• phagocytosis A cell engulfs another cell to form a food vacuole

• A lysosome fuses with food vacuole and digests molecules

– Central vacuoles

• found in many plant cells

• hold organic compounds and water

4. Mitochondria

• cellular respiration generates ATP (energy)

• contain mtDNA

• all eukaryotic cells have mt

– Some have 1, some 1000sOuter membrane

Cristae

Mitochondria

• outer membrane and inner membrane fold into cristae– large surface area for enzymes that synthesize ATP

5. Chloroplasts (plastid)• found in plants and algae

• sites of photosynthesis

– green pigment chlorophyll, enzymes, other molecules

6. Peroxisomes

• metabolic compartments bounded by a single membrane

• detoxify

catalase

2 H2O2 2H2O + O2

(toxic)

7. Cytoskeleton

• Network of protein fibers organize structures and activities in cell

• Anchors organelles

• Maintains cell shape

Components of the Cytoskeleton

• types of fibers :

– Microtubules

• thickest

– Microfilaments

• actin filaments

• thinnest

8. Centrosomes and Centrioles

• Centrosome

– “microtubule-organizing center”

Centrosome

Microtubule

Centrioles0.25 µm

Longitudinal section of one centriole

Cross sectionof the other centriole

– centrioles

• animal cells

• centrosome has pair

centrosome

9. Cilia and Flagella

• Locomotor appendages of some cells

• Movement pattern controlled by microtubules

10. Extracellular materials

• Cells secrete materials external to plasma membrane

A. Cell Walls of PlantsAlso, prokaryotes, fungi, some protists

• protects, maintains shape, prevents excessive uptake of water

• cellulose fibers

• Plasmodesmata -channels between adjacent plant cells for water, nutrients…..

B. Extracellular Matrix (ECM) of Animal Cells

• No cell walls

• Functions :Support, Adhesion, Movement, Regulation

Integrins “glue cytoskeleton to ECM

Chapter 7

Membrane Structure and Function

Overview: Life at the Edge

• The plasma membrane exhibits selective permeability

– some substances to cross more easily than others

Cellular membranes are fluid mosaics of lipids and proteins

• Phospholipids

• - most abundant lipids in the plasma membrane

• - amphipathic = contain hydrophobic and hydrophilic regions

• fluid mosaic model = membrane is fluid structure with a “mosaic” of proteins embedded

Hydrophilichead

WATER

Hydrophobictail

WATER

Membrane Models: Scientific Inquiry

Note hydrophilic heads and hydrophobic tails in bilayer

Phospholipid

bilayer

Hydrophobic regionsof protein

Hydrophilicregions of protein

The Fluidity of Membranes

Phospholipids in membrane move within bilayer, rarely flip flop

• Lipids, proteins, may move laterally

(a) Movement of phospholipids

Lateral movement

( 107 times per second)

Flip-flop

( once per month)

• Membrane fluidity affected by:

– Type of phospholipid/hydrocarbon saturation

– Cholesterol

– Temperature

• Temperature and membrane fluidity

• cool = fluid gel

– Tightly packed hydrocarbons

• warm (37oC) fluid

Cholesterol

• Stabilizes membrane fluidity with changing temperature

Cholesterol

(c) Cholesterol within the animal cell membrane

Membrane Proteins and Their Functions

• mosaic of proteins embedded in lipid bilayer

• Proteins determine most of membrane’s functions

Membrane Proteins

1. Peripheral proteins

– bound to surface of membrane

2. Integral proteins

– penetrate hydrophobic core

– Transmembrane proteins

• span membrane

• Channel proteins have a hydrophilic channel

Fibers ofextracellularmatrix (ECM)

Glyco-protein

Microfilamentsof cytoskeleton

Cholesterol

Peripheralproteins

Integralprotein

CYTOPLASMIC SIDEOF MEMBRANE

GlycolipidEXTRACELLULARSIDE OFMEMBRANE

Carbohydrate

N-terminus

C-terminus

Helix

CYTOPLASMICSIDE

EXTRACELLULARSIDE

– Transport

– Enzymatic activity

– Signal transduction

– Cell-cell recognition

– Intercellular joining

– Attachment to the cytoskeleton and extracellular matrix (ECM)

Six major functions of membrane proteins:

Cell-Cell Recognition: Carbohydrates

• Cells recognize each other by binding to surface molecules on membrane

Permeability of Lipid Bilayer

• Hydrophobic molecules dissolve in bilayer and pass through membrane rapidly

– O2, CO2, Hydrocarbons

• Hydrophilic (polar) molecules do not cross easily

– Sugar, water, ions

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Transport Proteins

Integral membrane proteins (transmembrane) Specific for substance moved

1. channel proteins = hydrophilic channel

Ex. aquaporins channel for water Ex. ion channels

2. carrier proteins, bind to molecules and change shape to shuttle across membrane

Ex. glucose transporter

Passive transport = no energy used

1. Diffusion = molecules spread out evenly into available space

• molecules move randomly

• Molecules diffuse down their concentration gradient from high to lower concentration until equilibrium

Molecules of dye

WATER

Net diffusion Net diffusion

(a) Diffusion of one solute

Equilibrium

• 2. Osmosis is diffusion of water across a selectively permeable membrane

• Water diffuses across a membrane from region of higher water (lower solute) concentration to the region of lower water (higher solute) concentration until equilbrium

Lower

concentrationof sugar)

H2O

Higher

Concentrationof sugar

Selectivelypermeable

membrane

Same concentration

of sugar

Osmosis

Water Balance of Cells Without Walls

• Tonicity =ability of solution to cause cell to gain or lose water

• Isotonic solution: Solute concentration same as that the cell; no net water movement across membrane

• Hypertonic solution: Solute concentration greater than inside cell; cell loses water

• Hypotonic solution: Solute concentration is less than inside cell; cell gains water

Hypotonic solution

(a) Animal

cell

H2O

Lysed

H2O H2O

Normal

Isotonic solution

H2O

Shriveled

Hypertonic solution

Solution type? Isotonic, hypotonic, hypertonic?

• Osmoregulation, control of water balance, is necessary adaptation for life in different environments

Filling vacuole50 µm

(a) A contractile vacuole fills with fluid that enters froma system of canals radiating throughout the cytoplasm.

Contracting vacuole

(b) When full, the vacuole and canals contract, expelling

fluid from the cell.

Water Balance of Cells with Walls (ex. plants)

• Hypotonic solution cell swells turgid(firm)

• Isotonic no net movement of water into cell flaccid (limp)

• Hypertonic cells lose water; membrane pulls away from the wall plasmolysis (lethal)

Hypotonic solution

(b) Plant

cell

H2O

Turgid (normal)

H2O H2O

Isotonic solution

Flaccid

H2O

Plasmolyzed

Hypertonic solution

3. Facilitated Diffusion: Passive Transport Aided by Proteins

• Channel proteins

• Carrier proteins

EXTRACELLULARFLUID

Channel protein

(a) A channel protein

SoluteCYTOPLASM

SoluteCarrier protein

(b) A carrier protein

Active transport

• Energy (ATP) required to move solutes againsttheir gradients

• Membrane proteins!

1. Pumps Ex. sodium-potassium pump

EXTRACELLULAR

FLUID [Na+] high

[K+] low

Na+

Na+

Na+[Na+] low

[K+] high CYTOPLASM

Cytoplasmic Na+ binds to

the sodium-potassium pump.1

Na+ high outside cellK+ low

Na+ low inside cellK+ high

According to diffusion?

• 1. Cytoplasmic Na+ binds to pump protein

Na+ binding stimulatesphosphorylation by ATP.

Na+

Na+

Na+

ATP P

ADP

2

2. ADP is phosphorylated to ATP

Phosphorylation causesthe protein to change its

shape. Na+ is expelled tothe outside.

Na+

P

Na+

Na+

3 Phosphorylation causesthe protein to change its

shape. Na+ is expelled tothe outside.

Na+

P

Na+

Na+

3

3. Na+ out of cell

K+ binds on theextracellular side andtriggers release of thephosphate group.

PP

4

4. K+ binds to pump and P released from ATP (energy used)

Loss of the phosphaterestores the protein’s original

shape.

5 + 6 K+ inside cell Pump animation

6. K+ released

Passive transport

Diffusion Facilitated diffusion

Active transport

ATP

Ion Pumps And Membrane Potential

• Membrane potential = voltage difference across membrane

• Due to differences in distribution of + and - ions

• Inside of cell more electronegative than out

• Electrochemical gradient drives diffusion of ions across membrane:

– chemical = concentration gradient

– electrical = membrane potential and ion’s movement

3. Bulk transport

• Exocytosis

– To secrete products from cell

– Vesicles fuse with membrane

2. Endocytosis

cell takes in macromolecules by forming vesicles from membrane

a. Phagocytosis – for large

particle

Vesicle fuses with lysosome

to digest particle

b. Pinocytosis – for fluids/small molecules

PINOCYTOSIS

Plasmamembrane

Vesicle

0.5 µm

Pinocytosis vesicles

forming (arrows) in

a cell lining a small

blood vessel (TEM)

Chapter 8

An Introduction to Metabolism

METABOLISM

• All of an organism’s chemical reactions• Thousands of reactions in a cell

• Example: digest starch use sugar for energy and to build new molecules

•

Metabolic Pathways

• Begin with starting molecule chemical reactions product(s)

• Each step catalyzed by specific enzyme

Enzyme 1 Enzyme 2 Enzyme 3

DCBAReaction 1 Reaction 3Reaction 2

Startingmolecule

Product

• Catabolic pathways -

– break down complex molecules into simpler compounds

– releases energy for cells to use

• Ex. Glucose metabolism produces ATP

• Anabolic pathways - use energy to build complex molecules from simpler ones

• Ex. Protein synthesis from amino acids

Energy

• Energy

– capacity of a system to do work– can be converted from one form to another

• Kinetic energy = energy of motion A moving object can do work on anything it hits

Potential energy = energy stored within system (ex. water behind a dam). Chemical energy = PE available for release in chemical reaction

Ex. Glucose has high CE

The Laws of Energy Transformation

• Thermodynamics – study of energy transformation

• In open system (organisms), energy and matter can be transferred between system and surroundings

First Law of Thermodynamics

• The energy of the universe is constant: • Energy can be transferred and transformed, but it

cannot be created or destroyed.

• Total energy is conserved

• This is the principle of conservation of energy

Second Law of Thermodynamics

• Every energy transfer or transformation increases entropy (disorder) of the universe

• Living systems are open systems and increase entropy in the environment

• During energy transfer some energy is unusable, often released as heat

(a) First law of thermodynamics (b) Second law of thermodynamics

Chemicalenergy

Heat CO2

H2O

+

First Law: chemical E in

food converted to kinetic E

Second Law: disorder is entered into

environment as heat, CO2

• Spontaneous processes occur without energy input;

– ex. explosion, rusting of a car

– releases energy, usually heat

Glycerol and potassium permanganate

Iron and oxygen into iron oxide

Biological Order and Disorder

• Cells create ordered structures from less ordered materials

Example: proteins built from amino acids

• Organisms replace ordered forms of matter and energy with less ordered forms

Example: catabolism breaks down molecules, releases heat

• Energy flows into an ecosystem in the form of light and exits in the form of heat

Free-energy and metabolism

• Free energy (G) = amount of energy available to do work under conditions of a biochemical reaction

Δ G = change in free energy, unstable systems tend to change to stable equilibrium

• Spontaneous reaction = gives up free energy• Negative Δ G

• Moves towards stability, equilibrium• System at equilibrium does no work (low Δ G)

•

• -Δ G = exergonic reaction

– releases energy

– spontaneous

– “downhill”

Exergonic reaction

• Cellular respiration (1 mole glucose = 180g)

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

ΔG = -686kcal/mol available for work

Starch has high free energy

• positive Δ G = endergonic rxn

– Absorbs free energy from surroundings

– Nonspontaneous

• Endergonic example:

• Photosynthesis

6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2

686kcal/mol

Equilibrium and Metabolism

• Reactions in closed system eventually reach equilibrium and then do no work

(a) An isolated hydroelectric system

∆G < 0 ∆G = 0

Equilibrium and Metabolism

• Cells are open systems

– constant flow of materials

– not in equilibrium

(b) An open hydroelectric system

∆G < 0

Equilibrium and Metabolism

• catabolic pathway releases free energy in series of reactions

(c) A multistep open hydroelectric system

∆G < 0

∆G < 0

∆G < 0

ATP powers cellular work

• Coupling = Use exergonic reactions to drive endergonic rxns (overall exergonic)

• Chemical potential energy stored in ATP drives cell activities

– Build proteins, active transport, muscle contraction………..

ATP

• ATP =adenosine triphosphate

Energy released when terminal phosphate bond broken by hydrolysis

Energy

Adenosine triphosphate (ATP)

P P

P P P

P ++

H2O

i

ATP --- ADP + PΔ G = -7.3kcal/mol

phosphorylation

• Transfer P from ATP to another molecule to phosphorylate it

• The phosphorylated molecule is less stable

Phosphorylation opens an aquaporin(spinach)

http://www.sciencedaily.com/releases/2005/12/051222085140.htm

Regeneration of ATP

• Add phosphate group to ADP

• Ex. muscle cell 10 million ATP per second

ADP + P ATPΔ G = 7.3kcal/mol

Energy to regenerate ATP from? (catabolism)

P iADP +

Energy fromcatabolism (exergonic,energy-releasingprocesses)

Energy for cellularwork (endergonic,energy-consumingprocesses)

ATP + H2O

Enzymes speed up metabolic reactions by lowering energy barriers

• catalyst =chemical agent that speeds up a reaction

– Unchanged by reaction

• enzyme = catalytic protein (organic)

• Ex. Hydrolysis of sucrose by sucrase

Activation Energy Barrier

• chemical reaction = bonds broken/formed

• free energy of activation = activation energy (EA) = energy to start chemical reaction

• EA contorts molecule makes bonds unstable

How Enzymes Lower the EA

• 37oC reactants do not reach EA

• Enzymes do not affect ∆G • Enzymes speed rxn rate by lowering EA

• Transition state– Reactants most unstable– EA has been reached

Progress of the reaction

Products

Reactants

∆G < O

Transition state

EA

DC

BA

D

D

C

C

B

B

A

A

Substrate Specificity of enzymes

• Substrate = reactant

• Enzyme-substrate complex

• Product(s)

Sucrose Glucose

Sucrase E-S complex Fructose

Water Sucrase

• Active site region on enzyme where substrate binds

• Induced fit - enzyme shape changes to fit to substrateSubstrate

Active site

Enzyme Enzyme-substratecomplex

(b)(a)

Progress of the reaction

Products

Reactants

∆G is unaffectedby enzyme

Course ofreactionwithoutenzyme

EA

without

enzyme EA withenzymeis lower

Course ofreactionwith enzyme

Catalysis in Active Site

• 1000 – 1,000,000 rxns/sec

• Can catalyze forward or reverse rxn

• Active site can lower an EA barrier by– Orient substrates

– Contort substrate bonds

– Provide microenvironment

– Covalently bond to substrate

Local Conditions

• activity affected by

– temperature , pH (each has optimal)

– chemicals

Cofactors

• Nonprotein

• Assist enzyme

• inorganic cofactor

Metal ion (trace elements)

• Coenzyme = organic cofactor

Vitamins

Enzyme Inhibitors

• Competitive inhibitors – bind to active site of enzyme– compete with substrate at active site

• Noncompetitive inhibitors – bind to another part of enzyme– change shape of active site– May not be reversible

• toxins, poisons, pesticides, and antibiotics

• Substrate and enzyme activity – competitive and non-competitive

(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition

Noncompetitive inhibitor

Active site

Competitive inhibitor

Substrate

Enzyme

Regulation of enzyme activity helps control metabolism

• metabolic pathways are tightly regulated

Allosteric Regulation

• Regulatory molecule binds to enzyme but not at the active site!

• Normal regulation of enzyme activity

• Activator

– Stabilizes shape of active site

– Ex. ADP speeds enzymes of catabolism

• Inhibitor

– Stabilizes inactive form of enzyme

Allosteric inhibition flash

Allosteric activation

(a) Allosteric activators and inhibitors

InhibitorNon-functionalactivesite

Stabilized inactiveform

Inactive form

Oscillation

Activator

Active form Stabilized active form

Regulatorysite (oneof four)

Allosteric enzymewith four subunits

Active site(one of four)

This enzyme has subunits

The activator has stabilized the active enzyme form

The inhibitor has stabilized the inactive form

• Cooperativity =type of allosteric regulation that boosts enzyme activity

• substrate binds to one active site stabilizes favorable shape changes at other subunits

Substrate

Feedback Inhibition

• end product of metabolic pathway turns off pathway

• prevents cell from wasting chemical resources by synthesizing more product than is needed

Intermediate C

Feedbackinhibition

Isoleucineused up bycell

Enzyme 1(threoninedeaminase)

End product

(isoleucine)

Enzyme 5

Intermediate D

Intermediate B

Intermediate A

Enzyme 4

Enzyme 2

Enzyme 3

Initial substrate(threonine)

Threoninein active site

Active siteavailable

Active site ofenzyme 1 nolonger bindsthreonine;pathway isswitched off.

Isoleucinebinds toallostericsite

Chapter 9

Cellular Respiration: Harvesting Chemical Energy

Life Is Work

• Living cells require energy from outside sources

• Plants E from ?

• Animals E from ? And ?

Build a chemical cycling system activity Ch 8 Overview

Lightenergy

ECOSYSTEM

Photosynthesisin chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules

+ O2

ATP powers most cellular work

Heatenergy

ATP

Energy flows into ecosystem as sunlight

Energy leaves as heat

ATP powers work

• Photosynthesis

– Organelle = chloroplasts

– Generates O2 and organic molecules

• Cellular respiration

– Organelle = mitochondria

– Uses organic molecules to generate ATP

Catabolic Pathways

• Organic molecules have potential (chemical) energy

• Exergonic rxns break down organic molecules energy (and heat)

Cellular Respiration

• Aerobic respiration – Uses O2

– ATP produced

Fuel = organic molecules (carbohydrates, fats, proteins)

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP+ heat)

• Anaerobic respiration – Uses organic molecules

– Does not use O2

– ATP produced

– Glycolysis and fermentation

Cellular respiration 1. Glycolysis (“split sugar”)Occurs in the cytoplasm

Anaerobic

Glucose + 2NAD+ + 2ATP 2 pyruvate+ 2NADH + 4ATP

• Net gain of 2ATP per glucose molecule

• 1 glucose 2 ATP and 2 pyruvate

• Glucose oxidized to pyruvate

• NAD+ reduced to NADH

• No O2 required, no CO2 produced

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Glycolysis Glucose + 2NAD + 2ATP 2 pyruvate+ 2NADH + 4ATP

CYTOSOL

Glycolysis

• Energy investment phase uses 2 ATP

• Energy payoff phase

– 4 ATP

– 2NAD+ reduced to 2NADH

– 1 glucose split to 2 pyruvate

Cellular Respiration: Bioflix animationActivity: Glycolysis

Animation BIO231

Energy investment phase

Glucose

2 ADP + 2 P 2 ATP used

formed4 ATP

Energy payoff phase

4 ADP + 4 P

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2OGlucoseNet

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2. Citric acid cycle (Krebs) (mitochondrial matrix)

2Pyruvate + NAD+ + FADH 2ATP + NADH +

FADH2 + CO2 + H2O

– 2 ATP per 1 glucose

– CO2 generated

– NADH and FADH2 (electron donors)

Mitochondrion

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Substrate-levelphosphorylation

ATP

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Citric Acid CYCLE: PYRUVATE 2ATP + NADH and FADH2

MITCHONDRION

Before citric acid cycle

• Formation of acetyl CoA from 2 pyruvate

• Acetyl CoA links glycolysis to cycle

BIO 231 TCA cycle animation: Acetyl CoA formation

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

8 enzymatic steps

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

Summary of citric acid cycle

• Per molecule glucose (2 pyruvate)

– NADH and FADH2 (electron donors)

– 2 ATP (1 per turn) per glucose

• CO 2 produced (2 per turn)

• Occurs in mitochondrial matrix

• Does not directly require O2, but electron transport chain requires oxygen.

• So, cycle is aerobic.

Krebs Animation BIO 231

Text Activity: The Citric Acid Cycle

• 3. oxidative phosphorylation mitochondria cristae

– NADH and FADH2 donate electrons to electron transport chain is series of steps

– Oxygen , H+

– ~34 ATP per glucose

Mitochondrion

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Substrate-levelphosphorylation

ATP

Electrons carriedvia NADH and

FADH2

Oxidativephosphorylation

ATP

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

Oxidative phosphorylation: NADH, FADH2, O2 34 ATP

Electron Transport Chain = linked steps in oxidative phosphorylation

• BIO 231 Electron transport animation

Note:NADH and FADH2 transfer electronsOxygen requiredH+ gradientATP synthesized

Stepwise Energy Harvest via Electron Transport Chain

• Controlled rxns

(a) Uncontrolled reaction

H2 + 1/2

O2

Explosiverelease ofheat and

lightenergy

(b) Cellular respiration

Controlledrelease ofenergy forsynthesis

ofATP

2 H+ + 2 e–

2 H 1/2

O2(from food via NADH)

1/2

O2

NADH

NAD+2FADH2

2 FADMultiproteincomplexesFAD

Fe•S

FMN

Fe•S

Q

Fe•S

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

50

40

30

20

10 2

(from NADHor FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

Electron Transport:Fall in free energy during each step to control release of fuel energy

Chemiosmosis couples energy of electron transport to ATP synthesis

• Wiley animation: chemiosmosis

• Note:

– proteins of electron transport/cytochromes

– NADH, FADH2

– Oxygen

– H+ ions pumped out/H+ gradient

– ATP

H+ gradient, a proton motive force• Electron transport chain e- used to pump H+

across mt membrane

• H+ gradient drives ATP production

Virtual Cell: Electron Transport Chain animation

• ATP synthase

– Many polypeptides and subunits

– H+ ion enters for one turn

– ADP + P ATP

INTERMEMBRANE SPACE

Rotor

H+

Stator

Internalrod

Catalyticknob

ADP+

P ATPi

MITOCHONDRIAL MATRIX

Protein complexof electroncarriers

H+

H+H+

Cyt c

QV

FADH2 FAD

NAD+NADH

(carrying electronsfrom food)

Electron transport chain

2 H+ + 1/2O2 H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

21

An Accounting of ATP Production by Cellular Respiration

• Most energy:

glucose NADH electron transport chain proton-motive force ATP

= ~38 ATP total

Maximum per glucose: About36 or 38 ATP

+2 ATP +2ATP + about 32 or 34 ATP

Oxidativephosphorylation:electron transport

andchemiosmosis

Citricacidcycle

2Acetyl

CoA

Glycolysis

Glucose2

Pyruvate

2 NADH 2 NADH 6 NADH 2 FADH2

2 FADH2

2 NADHCYTOSOL Electron shuttlesspan membrane

or

MITOCHONDRION

Glycolysis Citric Acid Cycle Ox. Phos.Cytosol mt mt

Anaerobic respiration (no O2)

Prokaryotes

Eukaryotes

Generate ATP without O2

1. Glycolysis

2. Fermentation

Anaerobic respiration (cytoplasm)

Fermentation

No electron transport chain

NAD+ reused in glycolysis (way to keep generating ATP without O2)

Alcohol fermentation

• Pyruvate + NADH ethanol + NAD+ + CO2

• Bacteria

• Yeast

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH2 NAD+

+ 2 H+CO2

2 Acetaldehyde2 Ethanol

(a) Alcohol fermentation

2

Lactic acid fermentation

Pyruvate + NADH lactate + NAD+

• Bacteria, fungi in cheese making

• Human muscle cells use lactic acid fermentation to generate Pyruvate + NADH lactate + NAD+

• ATP when O2 is low.

Glucose

2 ADP + 2 P i 2 ATP

Glycolysis

2 NAD+ 2 NADH

+ 2 H+

2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fermentation (no O2) vs. Aerobic Respiration

• Both use glycolysis to oxidize glucose (and other organic fuels ) to pyruvate

• ATP

– Cellular respiration 38 ATP per glucose

– Fermentation 2 ATP per glucose

• Obligate anaerobes – fermentation – cannot survive in the presence of O2

– Ex. clostridium botulinum

• Facultative anaerobes – Yeast and many bacteria – can survive using either fermentation or cellular

respiration (pyruvate can be used either way)– Ex. E. coli, Streptococcus

Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:Fermentation

O2 present:

Aerobic cellular

respiration

MITOCHONDRIONAcetyl CoAEthanol

orlactate

Citricacidcycle

Facultative anaerobe

The Evolutionary Significance of Glycolysis

• Glycolysis occurs in nearly all organisms

• Glycolysis probably evolved in ancient prokaryotes before O2 on planet

Glycolysis and the citric acid cycle connect to other metabolic pathways

The Versatility of Catabolism

• Glycolysis and fuel

– Carbohydrates – many accepted

– Proteins amino acids; glycolysis or the citric acid cycle

– Fats glycerol glycolysis

– Fatty acids acetyl CoA

– An oxidized gram of fat produces >2X ATP as oxidized gram of carbohydrate