Chapter9cellrespirationppt2blank

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 9

Cellular Respiration: Harvesting Chemical Energy

• Overview: Life Is Work

• Living cells

– Require transfusions of energy from outside sources to perform their many tasks

• The giant panda

– Obtains energy for its cells by eating plants

Figure 9.1

• Energy

– Flows into an ecosystem as sunlight and leaves as heat Light energy

ECOSYSTEM

CO2 + H2O

Photosynthesisin chloroplasts

Cellular respiration

in mitochondria

Organicmolecules+ O2

powers most cellular work

HeatenergyFigure 9.2

• Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

• These fuels can consists of high energy molecules such as ____________ and ________

• These molecules are rich in Carbon and Hydrogen. The actual energy is found in the bonds of the molecule. Hydrogen atoms provide an excellent source of energy by means of their _________.

Catabolic Pathways and Production of ATP• The breakdown of organic molecules is exergonic

• All exergonic reactions release ________.

• All endergonic reactions require _________.

• Free energy can be defined as the energy available for a system to perform work when temperature and pressure are constant throughout the system. This environment is present within certain cellular components of the body.

• The quantitative value of free energy (G) in exergonic reactions is always negative because there is a net release of free energy. (-G) In endergonic reactions, since energy is required the free energy would be ______, due to a net gain in free energy.

• The ________ the decrease in free energy, the greater amount of work the reaction can perform.

• Cellular respiration

– Is the most prevalent and efficient catabolic pathway

– Consumes oxygen and organic molecules such as glucose

– Yields ATP

ATP is the energy currency of the cell.

• To keep working

– Cells must regenerate _______

Redox Reactions: Oxidation and Reduction

• Catabolic pathways yield energy

– Due to the transfer of electrons

The Principle of Redox

• Redox reactions

– Transfer electrons from one reactant to another by oxidation and reduction

• In oxidation

– A substance loses electrons, or is oxidized

• In reduction

– A substance gains electrons, or is reduced

– The reducing agent is the substance that __________ electrons.

– The oxidizing agent is the substance that ________ the electrons.

• Examples of redox reactions

Na + Cl Na+ + Cl–

becomes oxidized(loses electron)

becomes reduced(gains electron)

• Some redox reactions

– Do not completely exchange electrons

– Change the degree of electron sharing in covalent bonds

– The greater the atoms electronegativity, the stronger its pull on electrons.

– _______ has the greatest electronegativity among all the elements.

C O O O O OC

Methane(reducingagent)

Oxygen(oxidizingagent)

Carbon dioxide Water

+ 2O2CO

2+ Energy + 2 H2O

becomes oxidized

becomes reduced

Reactants Products

Figure 9.3

Oxidation of Organic Fuel Molecules During Cellular Respiration• During cellular respiration

– Glucose is oxidized and oxygen is reduced

– The transfer of electrons are in the form of ________ atoms.

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

becomes oxidized

becomes reduced

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain

– Oxidizes glucose in a series of steps

• Electrons from organic compounds

– Are usually first transferred to NAD+, a coenzyme

OO O–

HO OHH

HHO OH

Nicotinamide(oxidized form)

NH2+ 2[H](from food)

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+

2 e– + H+

Nicotinamide(reduced form)

Figure 9.4

• NADH, the reduced form of NAD+

– Passes the electrons to the electron transport chain

• If electron transfer is not stepwise

– A large release of energy occurs

– As in the reaction of hydrogen and oxygen to form water

(a) Uncontrolled reaction

Explosiverelease of

heat and lightenergy

Figure 9.5 A

H2 + 1/2 O2

• The electron transport chain

– Passes electrons in a series of steps instead of in one explosive reaction

– Uses the energy from the electron transfer to form ATP

2 H 1/2 O2

(from food via NADH)

2 H+ + 2 e–

2 e–

1/2 O2

Controlled release of energy for synthesis of

ATP ATP

Electron transport chain

(b) Cellular respiration

Figure 9.5 B

The Stages of Cellular Respiration: A Preview

• Respiration is a cumulative function of three metabolic stages

– Glycolysis

– The citric acid cycle

– Oxidative phosphorylation

• Anaerobic: Without Oxygen

• Aerobic: With Oxygen

• Glycolysis

– Breaks down glucose into two molecules of pyruvate

• The citric acid cycle

– Completes the breakdown of glucose

– It does this when oxygen is not available

• Oxidative Phosphorylation

– Is driven by the electron transport chain (ETC).

– Generates ATP by transferring an inorganic phosphate to ADP.

– Generates ATP by means of a hydrogen ion gradient.

• An overview of cellular respiration

Figure 9.6

Electronscarried

via NADH

GlycolsisGlucos

ePyruvate

Substrate-levelphosphorylation

Electrons carried via NADH and

Citric acid cycle

Oxidativephosphorylation:

electron transport and

chemiosmosis

ATPATP

Substrate-levelphosphorylation

Oxidativephosphorylation

MitochondrionCytosol

• Both glycolysis and the citric acid cycle

– Can generate ATP by _________ level phosphorylation. An inorganic phosphate is added to a substrate. The reaction is enzymatically catalyzed to produce ATP and a product.

Figure 9.7

Enzyme Enzyme

Product

SubstrateP

• Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate

• Glycolysis

– Means “splitting of sugar”

– Breaks down glucose into pyruvate

– Occurs in the cytoplasm of the cell

• Glycolysis consists of two major phases

– Energy investment phase

– Energy payoff phase

Glycolysis Citricacidcycle

ATP ATP ATP

formed

Glucose

2 ATP + 2 P

4 ADP + 4 P

2 NAD+ + 4 e- + 4 H +

2 NADH + 2 H+

2 Pyruvate + 2 H2O

Energy investment phase

Energy payoff phase

Glucose 2 Pyruvate + 2 H2O

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H +

2 NADH

+ 2 H+

Figure 9.8

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

CH2OHH H

OHHO OH

CH2O P

P O CH2O CH2 O P

HOH HO

OP CH2

C OCH2OH

HCCHOHCH2

ADPHexokinase

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Phosphoglucoisomerase

Phosphofructokinase

Fructose-1, 6-bisphosphate

Aldolase

Isomerase

Glycolysis

CH2OHOxidative

phosphorylation

Citricacidcycle

Figure 9.9 A

2 NAD+

NADH2+ 2 H+

Triose phosphatedehydrogenase

2 O–

1, 3-Bisphosphoglycerate2 ADP

Phosphoglycerokinase

CH2 O P

3-Phosphoglycerate

Phosphoglyceromutase

2-Phosphoglycerate

2 O–

Enolase

CH2Phosphoenolpyruvate

2 ATPPyruvate kinase

Pyruvate

Figure 9.8 B

• Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules

• The citric acid cycle

– Takes place in the ________ of the mitochondrion

• Before the citric acid cycle can begin

– Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis

CYTOSOL MITOCHONDRION

NADH + H+NAD+

CO2 Coenzyme APyruvate

Acetyle CoA

Transport protein

Figure 9.10

• An overview of the citric acid cycle

3 NAD+

3 NADH

+ 3 H+

ADP + P i

Citricacidcycle

CoA Acetyle CoA

NADH+ 3 H+

Pyruvate(from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Citricacidcycle

Figure 9.11

• A closer look at the citric acid cycle

Figure 9.12

Acetyl CoA

Oxaloacetate

CitrateMalate

Fumarate

SuccinateSuccinyl

-Ketoglutarate

Isocitrate

Citricacidcycle

CoA SH

GTP GDP

CoA SH

+ H+ H2O

O C COO–

COO–

HO C COO–

COO–

HC COO–

HO CHCOO–

COO–

Glycolysis Oxidativephosphorylation

Citricacidcycle

Figure 9.12

• Concept 9.4: During oxidative phosphorylation, ____________ couples electron transport to ATP synthesis

• NADH and FADH2

– Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

The Pathway of Electron Transport

• In the electron transport chain

– Electrons from NADH and FADH2 lose energy in several steps

• At the end of the chain

– Electrons are passed to oxygen, forming water

– Oxygen has the greatest affinity

– for electrons (electronegative)

FMNFe•S Fe•S

Fe•S

Cyt c1Cyt c

Cyt aCyt a3

2 H + + 12

Multiproteincomplexes

Figure 9.13

Chemiosmosis: The Energy-Coupling Mechanism

• ATP synthase

– Is the enzyme that actually makes ATPINTERMEMBRANE SPACE

A rotor within the membrane spins clockwise whenH+ flows past it down the H+

gradient.

A stator anchoredin the membraneholds the knobstationary.

A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.

Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. MITOCHONDRIAL MATRIXFigure 9.14

• At certain steps along the electron transport chain (ETC)

– Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space.

– These Hydrogen ions are from the electron carriers _______ and ________ after they become _______.

• The resulting H+ gradient

– Stores energy

– Drives chemiosmosis in ATP synthase

– Is referred to as a ________-motive force

• Chemiosmosis

– Is an energy-coupling mechanism that uses ________ in the form of a H+ gradient across a membrane to drive cellular work

• Chemiosmosis and the electron transport chain

Oxidativephosphorylation.electron transportand chemiosmosis

Glycolysis

ATP ATP ATP

InnerMitochondrialmembrane

ATPP i

Protein complexof electron carners

(Carrying electronsfrom, food)

FAD+ 2 H+ + 1/2 O2

Electron transport chainElectron transport and pumping of protons (H+),

which create an H+ gradient across the membrane

ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane

ATPsynthase

Oxidative phosphorylation

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Figure 9.15

An Accounting of ATP Production by Cellular Respiration• During respiration, most energy flows in this

sequence

– Glucose to NADH to electron transport chain to proton-motive force to ATP

• There are three main processes in this metabolic enterprise

Electron shuttlesspan membrane

CYTOSOL 2 NADH

2 FADH2

2 NADH 6 NADH 2 FADH22 NADH

Glycolysis

Glucose2

Pyruvate

2AcetylCoA

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

MITOCHONDRION

by substrate-levelphosphorylation

by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol

Maximum per glucose:About

36 or 38 ATP

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

Figure 9.16

• About 40% of the energy in a glucose molecule

– Is transferred to ATP during cellular respiration, making approximately 38 ATP

• Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen

– Relies on oxygen to produce ATP

• In the absence of oxygen

– Cells can still produce ATP through fermentation

• Glycolysis

– Can produce ATP with or without oxygen, in aerobic or anaerobic conditions

– Couples with fermentation to produce ATP

Types of Fermentation

• Fermentation consists of

– Glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis

• In alcohol fermentation

– Pyruvate is converted to ethanol in two steps, one of which releases CO2

• During lactic acid fermentation

– Pyruvate is reduced directly to NADH to form lactate as a waste product

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH

2 Pyruvate

2 Acetaldehyde 2 Ethanol

(a) Alcohol fermentation

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH

2 Lactate

(b) Lactic acid fermentation

CH3OC O

Figure 9.17

Fermentation and Cellular Respiration Compared

• Both fermentation and cellular respiration

– Use glycolysis to oxidize glucose and other organic fuels to pyruvate

• Fermentation and cellular respiration

– Differ in their final electron acceptor

– Produces more ATP

• Pyruvate is a key juncture in catabolismGlucose

CYTOSOL

PyruvateNo O2 presentFermentation

O2 present Cellular respiration

Ethanolor

lactate

Acetyl CoAMITOCHONDRION

Citricacidcycle

Figure 9.18

The Evolutionary Significance of Glycolysis

• Glycolysis

– Occurs in nearly all organisms

– Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

• Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

The Versatility of Catabolism

• Catabolic pathways

– Funnel electrons from many kinds of organic molecules into cellular respiration

• The catabolism of various molecules from food

Amino acids

Sugars Glycerol Fattyacids

GlycolysisGlucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

Citricacidcycle

FatsProteins Carbohydrates

Figure 9.19

Biosynthesis (Anabolic Pathways)

• The body

– Uses small molecules to build other substances

• These small molecules

– May come directly from food or through glycolysis or the citric acid cycle

Regulation of Cellular Respiration via Feedback Mechanisms• Cellular respiration

– Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle

• The control of cellular respirationGlucose

Glycolysis

Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphateInhibits Inhibits

Pyruvate

ATPAcetyl CoA

Citricacidcycle

Citrate

Stimulates

+– –

Figure 9.20

Chapter9cellrespirationppt2blank

citric acid

electron transport

nad

electron transport

gradient

cellular respiration

level phosphorylation

oxidizing

Technology