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

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

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

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

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

CYTOPLASM

Glycolysis

Electron Transfer

Phosphorylation

Krebs CYCLE ATP

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+

ATP 2 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

A simple sugar

(C6H12O6)

Atoms held together by covalent bonds

In-text figure Page 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

GLUCOSE

glucose

GYCOLYSIS

pyruvate

to second stage of aerobic respiration or to a different energy-releasing pathway

Fig. 8-4a, p.126

Glycolysis

ATP

ATP

2 ATP invested

ENERGY-REQUIRING STEPS OF GLYCOLYSIS

glucose

ADP

ADP

P

P

P

P

glucose–6–phosphate

fructose–6–phosphate

fructose–1,6–bisphosphate DHAP

Fig. 8-4b, p.127

Glycolysis

ATP ADP

ENERGY-RELEASING STEPS OF GLYCOLYSIS

NAD+

P

PGAL

1,3–bisphosphoglycerate

substrate-level phsphorylation

Pi

1,3–bisphosphoglycerate

ATP

NADH NADH

P

PGAL NAD+

Pi

P P P P

3–phosphoglycerate 3–phosphoglycerate

P P

2 ATP invested

ADP

Fig. 8-4c, p.127

Glycolysis

2 ATP produced

ATP ADP

P

substrate-level phsphorylation

2–phosphoglycerate

ATP

P

pyruvate pyruvate

ADP

P P

2–phosphoglycerate

H2O H2O

PEP PEP

Fig. 8-4d, p.127

Glycolysis

2 ATP invested

Energy-Requiring Steps of Glycolysis

glucose

PGAL PGAL

P P

ADP

P

ATP

glucose-6-phosphate

P fructose-6-phosphate

ATP

fructose1,6-bisphosphate

P P

ADP

Figure 8-4(2)

Page 127

ADP ATP

pyruvate

ADP ATP

pyruvate

H2

O P

PEP

H2

O P

PEP

P

2-phosphoglycerate

P

2-phosphoglycerate

ADP ATP

P 3-phosphoglycerate

ADP ATP

P 3-phosphoglycerate

NAD+ NADH Pi

1,3-bisphosphoglycerate P P

NAD+ NADH Pi

1,3-bisphosphoglycerate P P

PGAL P

PGAL 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

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

Fig. 8-5a, p.128

mitochondrion

mitochondrion

inner mitochondrial

membrane

outer mitochondrial

membrane

inner compartment

outer compartment

Fig. 8-6a, p.128

Second Stage Reactions

Two pyruvates cross the inner mitochondrial membrane.

outer mitochondrial compartment

NADH

NADH

FADH2

ATP

2

6

2

2

Krebs Cycle

6 CO2

inner mitochondrial compartment

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

pyruvate

NAD+

NADH

coenzyme A (CoA)

O O carbon dioxide

CoA acetyl-CoA

Acetyl-CoA Formation

acetyl-CoA

(CO2)

pyruvate

coenzyme A NAD+

NADH

CoA

Krebs Cycle CoA

NADH

FADH2

NADH

NADH

ATP ADP + phosphate group

NAD+

NAD+

NAD+ FAD

oxaloacetate citrate

Fig. 8-7a, p.129

Preparatory Reactions

glucose

GLYCOLYSIS

pyruvate

KREBS CYCLE

ELECTRON TRANSFER PHOSPHORYLATION

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

NAD+

NADH

=CoA acetyl-CoA

oxaloacetate citrate

CoA

H2

O

malate isocitrate

H2

O H2

O

FAD

FADH2 fumarate

succinate

ADP + phosphate

group ATP

succinyl-CoA

O O

CoA NAD+

NADH

O O NAD+

NADH

a-ketoglutarate

Figure 8-6 Page 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

Glycolysis 2 NADH Preparatory reactions 2 NADH Krebs cycle 2 FADH2 + 6 NADH

Total 2 FADH2 + 10 NADH

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

glucose

GLYCOLYSIS

pyruvate

KREBS CYCLE

ELECTRON TRANSFER PHOSPHORYLATION

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–

KREBS CYCLE

electron transfer

phosphorylation

2 PGAL

2 pyruvate

2 NADH

2 CO2

ATP

ATP

2 FADH2

H+

2 NADH

6 NADH

2 FADH2

2 acetyl-CoA

ATP 2 Krebs Cycle

4 CO2 ATP

ATP

ATP

36

ADP + Pi

H+

H+

H+

H+

H+

H+ H+

H+

Fig. 8-9, p.131

Phosphorylation

NADH

OUTER COMPARTMENT

INNER COMPARTMENT

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

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

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+

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

Do not use oxygen

Produce less ATP than aerobic pathways

Two types

◦ Fermentation pathways

◦ Anaerobic electron transport

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+

C6H12O6

ATP

ATP NADH

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 H2O

2 CO2

Fig. 8-10d, p.132

Alcoholic Fermentatio

n

C6H12O6

ATP

ATP

NADH

2 lactate

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

lactate fermentation

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

FOOD

complex carbohydrates

simple sugars

pyruvate

acetyl-CoA

glycogen fats proteins

amino acids

carbon backbones

fatty acids

glycerol

NH3

PGAL

glucose-6-phosphate

GLYCOLYSIS

KREBS CYCLE

urea

FOOD

fats glycogen complex

carbohydrates proteins

simple sugars (e.g., glucose)

amino acids

glucose-6-phosphate

carbon backbones

NH3

urea

ATP

(2 ATP net)

PGAL

glycolysis ATP 2

glycerol fatty acids

NADH pyruvate

acetyl-CoA

NADH CO2

Krebs Cycle

NADH, FADH2

CO2

ATP

ATP

ATP

many ATP

water H+

e– + oxygen

e–

4

ATP 2

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

p.136b

Processes Are Linked