CELLULAR RESPIRATIONChapter 8

How Cells Release Stored Energy

More than 100 mitochondrial disorders are known

Friedreich’s ataxia, caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems

Animal, plants, fungus, and most protists depend on structurally sound mitochondria

Defective mitochondria can result in life threatening disorders

Impacts, Issues: When Mitochondria Spin Their Wheels

p.123

When Mitochondria Spin Their Wheels

Descendents of African honeybees that were imported to Brazil in the 1950s

More aggressive, wider-ranging than other honeybees

Africanized bee’s muscle cells have large mitochondria

“Killer” Bees

Photosynthesizers get energy from the sun Animals get energy second- or third-hand

from plants or other organisms Regardless, the energy is converted to the

chemical bond energy of ATP

ATP Is Universal Energy Source

Anaerobic pathways

Evolved first Don’t require oxygen Start with glycolysis

in cytoplasm Completed in

cytoplasm

Aerobic pathways

Evolved later Require oxygen Start with

glycolysis in cytoplasm

Completed in mitochondria

Main Types of Energy-Releasing Pathways

start (glycolysis) in cytoplasm

completed in mitochondrion

start (glycolysis) in cytoplasm

completed in cytoplasm

Aerobic Respiration

Anaerobic Energy-Releasing Pathways

Fig. 8-2, p.124

Main Types of Energy-Releasing Pathways

C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon

water dioxide

Summary Equation for Aerobic Respiration

Overview of Aerobic Respiration

CYTOPLASM

Glycolysis

Electron Transfer

Phosphorylation

Krebs CYCL

EATP

ATP

2 CO2

4 CO2

2

32

water

2 NADH

8 NADH

2 FADH2

2 NADH 2 pyruvate

e- + H+

e- + oxygen

(2 ATP net)

glucose

Typical Energy Yield: 36 ATP

e-

e- + H+

e- + H+

ATP

H+

e- + H+

ATP2 4

Fig. 8-3, p. 135

NAD+ and FAD accept electrons and hydrogen

Become NADH and FADH2

Deliver electrons and hydrogen to the electron transfer chain

The Role of Coenzymes

A simple sugar(C6H12O6)

Atoms held together by covalent bonds

Glucose

In-text figurePage 126

Energy-requiring steps◦ ATP energy activates glucose and its six-

carbon derivatives Energy-releasing steps

◦ The products of the first part are split into three-carbon pyruvate molecules

◦ ATP and NADH form

Glycolysis Occurs in Two Stages

GLUCOSE

glucoseGYCOLYSIS

pyruvate

to second stage of aerobicrespiration or to a differentenergy-releasing pathway

Fig. 8-4a, p.126

Glycolysis

ATP

ATP

2 ATP invested

ENERGY-REQUIRING STEPSOF GLYCOLYSISglucose

ADP

ADPP

P

P

P

glucose–6–phosphate

fructose–6–phosphate

fructose–1,6–bisphosphate DHAP

Fig. 8-4b, p.127

Glycolysis

ATPADP

ENERGY-RELEASING STEPSOF GLYCOLYSIS

NAD+

PPGAL

1,3–bisphosphoglyceratesubstrate-levelphsphorylation

Pi

1,3–bisphosphoglycerate

ATP

NADHNADH

PPGAL

NAD+

Pi

P PP P

3–phosphoglycerate 3–phosphoglycerateP P

2 ATP invested

ADP

Fig. 8-4c, p.127

Glycolysis

2 ATP producedATPADP

P

substrate-levelphsphorylation

2–phosphoglycerate

ATP

P

pyruvate pyruvate

ADP

P P

2–phosphoglycerateH2O H2O

PEP PEP

Fig. 8-4d, p.127

Glycolysis

Energy-Requiring Steps 2 ATP invested

Energy-Requiring Steps of Glycolysis

glucose

PGAL PGALPP

ADPP

ATP

glucose-6-phosphate

Pfructose-6-phosphate

ATP

fructose1,6-bisphosphate

P PADP

Figure 8-4(2)

Page 127

Energy-Releasing Steps

ADPATP

pyruvate

ADPATP

pyruvate

H2OP

PEP

H2OP

PEP

P2-phosphoglycerate

P2-phosphoglycerate

ADPATP

P3-phosphoglycerate

ADPATP

P3-phosphoglycerate

NAD+NADHPi

1,3-bisphosphoglycerateP P

NAD+

NADHPi

1,3-bisphosphoglycerateP P

PGAL

PPGAL

P

Figure 8-4 Page 127

Energy requiring steps: 2 ATP invested

Energy releasing steps:2 NADH formed 4 ATP formed

Net yield is 2 ATP and 2 NADH

Glycolysis: Net Energy Yield

Preparatory reactions◦ Pyruvate is oxidized into two-carbon acetyl units

and carbon dioxide◦ NAD+ is reduced

Krebs cycle◦ The acetyl units are oxidized to carbon dioxide◦ NAD+ and FAD are reduced

Second Stage Reactions

Fig. 8-5a, p.128

mitochondrion

mitochondrion

Second Stage Reactions

innermitochondrial

membrane

outermitochondrial

membrane

innercompartment

outercompartment

Fig. 8-6a, p.128

Second Stage Reactions

Two pyruvates cross the innermitochondrial membrane.

outer mitochondrialcompartment

NADH

NADH

FADH2

ATP

2

6

2

2

KrebsCycle

6 CO2

inner mitochondrialcompartment

Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions.

The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO

Fig. 8-6b, p.128

Preparatory Reactions

pyruvate

NAD+

NADH

coenzyme A (CoA)

O Ocarbon dioxide

CoAacetyl-CoA

Acetyl-CoAFormation

acetyl-CoA

(CO2)

pyruvatecoenzyme A NAD+

NADHCoA

Krebs Cycle CoA

NADH

FADH2

NADH

NADH

ATP ADP + phosphategroup

NAD+

NAD+

NAD+

FAD

oxaloacetate citrate

Fig. 8-7a, p.129

Preparatory Reactions

glucose

GLYCOLYSIS

pyruvate

KREBSCYCLE

ELECTRON TRANSFERPHOSPHORYLATION

Fig. 8-7b, p.129

Preparatory Reactions

Overall Reactants

Acetyl-CoA 3 NAD+

FAD ADP and Pi

Overall Products

Coenzyme A 2 CO2 3 NADH FADH2 ATP

The Krebs Cycle

Krebs Cycle

NAD+

NADH

=CoAacetyl-CoA

oxaloacetate citrate

CoA

H2O

malate isocitrate

H2OH2O

FAD

FADH2

fumarate

succinate

ADP + phosphate

groupATP

succinyl-CoA

O OCoANAD+

NADH

O ONAD+

NADH

a-ketoglutarate

Figure 8-6Page 129

All of the carbon molecules in pyruvate end up in carbon dioxide

Coenzymes are reduced (they pick up electrons and hydrogen)

One molecule of ATP forms Four-carbon oxaloacetate regenerates

Results of the Second Stage

Glycolysis 2 NADH Preparatory

reactions 2 NADH Krebs cycle 2 FADH2 + 6 NADH

Total 2 FADH2 + 10 NADH

Coenzyme Reductions during First Two Stages

Occurs in the mitochondria Coenzymes deliver electrons to electron

transfer chains Electron transfer sets up H+ ion gradients Flow of H+ down gradients powers ATP

formation

Electron Transfer Phosphorylation

glucose

GLYCOLYSIS

pyruvate

KREBSCYCLE

ELECTRON TRANSFERPHOSPHORYLATION

Fig. 8-8a, p.130

Phosphorylation

Fig. 8-8b, p.130

OUTER COMPARTMENT

INNER COMPARTMENT

Electron Transfer Chain ATP Synthase

ATP

H+

H+H+ H+

H+

H+H+ H+

H+H+

H+

H+H+

H+

H+

H+

H+

H+H+

H+

H+

H+

H+

H+

NADH + H+NAD+ + 2H+ FAD + 2H+FADH2 2H+ + 1/2 02 H2O ADP + Pi

e-e- e-

Phosphorylation

glucose

glycolysis

e–

KREBSCYCLE

electrontransfer

phosphorylation

2 PGAL

2 pyruvate2 NADH

2 CO2

ATP

ATP

2 FADH2

H+

2 NADH

6 NADH

2 FADH2

2 acetyl-CoA

ATP2 KrebsCycle

4 CO2

ATPATP

ATP

36

ADP + Pi

H+

H+

H+

H+

H+

H+H+

H+

Fig. 8-9, p.131

Phosphorylation

Creating an H+ Gradient

NADH

OUTER COMPARTMENT

INNER COMPARTMENT

Making ATP: Chemiosmotic Model

ATP

ADP+Pi

INNER COMPARTMENT

Electron transport phosphorylation requires the presence of oxygen

Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

Importance of Oxygen

Glycolysis◦ 2 ATP formed by substrate-level

phosphorylation Krebs cycle and preparatory reactions

◦ 2 ATP formed by substrate-level phosphorylation

Electron transport phosphorylation◦ 32 ATP formed

Summary of Energy Harvest(per molecule of glucose)

NADH formed in cytoplasm cannot enter mitochondrion

It delivers electrons to mitochondrial membrane

Membrane proteins shuttle electrons to NAD+ or FAD inside mitochondrion

Electrons given to FAD yield less ATP than those given to NAD+

Energy Harvest Varies

686 kcal of energy are released 7.5 kcal are conserved in each ATP When 36 ATP form, 270 kcal (36 X 7.5) are

captured in ATP Efficiency is 270 / 686 X 100 = 39 percent Most energy is lost as heat

Efficiency of Aerobic Respiration

Do not use oxygen Produce less ATP than aerobic pathways Two types

◦ Fermentation pathways◦ Anaerobic electron transport

Anaerobic Pathways

Begin with glycolysis Do not break glucose down completely to

carbon dioxide and water Yield only the 2 ATP from glycolysis Steps that follow glycolysis serve only to

regenerate NAD+

Fermentation Pathways

C6H12O6ATP

ATPNADH

2 acetaldehyde

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

ethanol formation

2 ATP net

2 ethanol

2 H2O2 CO2

Fig. 8-10d, p.132

Alcoholic Fermentati

on

C6H12O6

ATP

ATPNADH

2 lactate

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

lactate fermentatio

n

2 ATP net

Fig. 8-11, p.133

Lactate Fermentation

Fig. 8-12, p.133

Lactate Fermentation

Carried out by certain bacteria Electron transfer chain is in bacterial

plasma membrane Final electron acceptor is compound from

environment (such as nitrate), not oxygen ATP yield is low

Anaerobic Electron Transport

FOOD

complex carbohydrates

simple sugars

pyruvate

acetyl-CoA

glycogenfats proteins

amino acids

carbon backbones

fatty acidsglycerol

NH3

PGAL

glucose-6-phosphateGLYCOLYSIS

KREBS CYCLE

urea

FOOD

fats glycogencomplex

carbohydrates proteins

simple sugars(e.g., glucose) amino acids

glucose-6-phosphate

carbon backbone

s

NH3

urea

ATP

(2 ATP net)

PGALglycolysisATP2

glycerolfatty acids

NADH pyruvate

acetyl-CoA

NADH CO2

KrebsCycle

NADH,FADH2

CO2

ATP

ATPATP

many ATPwaterH+

e– + oxygen

e–

4

ATP2

Fig. 8-13b, p.135

electron transfer phosphorylation

Alternative Energy Sources

When life originated, atmosphere had little oxygen

Earliest organisms used anaerobic pathways

Later, noncyclic pathway of photosynthesis increased atmospheric oxygen

Cells arose that used oxygen as final acceptor in electron transport

Evolution of Metabolic Pathways

p.136b

Processes Are Linked