Chapter 7: Respiration

Respiration: The release of stored energy (sugar). Usually involves oxygen (the reason we breath is to release energy from our food).

Aerobic vs Anaerobic: Aerobic means in the presence of oxygen.

Mitochondrion

Inner Space

Inner Membrane Outer Membrane

Outer Space/

Intermem

brane Space

First Stage: Glycolysis

BASICS:

Glycolysis doesn’t require oxygen (anaerobic)!

Glycolysis doesn’t occur in the mitochondria, so it can happen in prokaryotes (lacking organelles). Glycolysis occurs in the cytoplasm.

Glycolysis begins with glucose and ends with two pyruvate molecules, yielding minimal energy gain.

First Stage: Glycolysis

1. Two ATP are invested to rearrange glucose.

2. When glucose is split into two 3-carbon compounds, energy is released.

3. Released energy is stored in 4 ATP (through substrate-level phosphorylation, or direct transfer of phosphate group).

4. NAD+ picks up e- and H+ to become NADH

Fig. 8.4b, p. 135

ATP

ATP

glucose

glucose-6-phosphate

fructose-6-phosphate

fructose-1,6-bisphosphate

2 ATP invested

ENERGY-REQUIRING STEPS OF GLYCOLYSIS

ADP

ADP

P

P

P

(see next slide)

Fig. 8.4c, p. 135

ATP

PGAL PGAL

ATP

NADH NADH

ATP ATP

2 ATP invested

ENERGY-RELEASING STEPS OF GLYCOLYSIS

2 ATP invested

NAD+

Pi

NAD+

Pi

3-phosphoglycerate 3-phosphoglycerate

2-phosphoglycerate 2-phosphoglycerate

PEP PEP

ADP ADP

1,3-bisphosphoglycerate 1,3-bisphosphoglycerateP P P P

P P

P P

P P

pyruvate pyruvate

to second set of reactions

substrate-level phosphorylation

substrate-level phosphorylation

H2O H2O

Second Step: Krebs Cycle

1. Two pyruvate molecules enter the mitochondrion (enter into the inner compartment of mito).

2. Coenzyme-A strips a carbon, yielding CO2.

3. Acetyl-CoA enters Krebs Cycle/Citric Acid Cycle, yielding more CO2.

4. Final yield: ATP, NADH, FADH2.

Fig. 8.5b, p. 136

Krebs Cycle

NADH

NADH

NADH

ATP ATP

ATP

ATP

ADP + Pi

INNER COMPARTMENT

OUTER COMPARTMENT

acetyl-CoA

free oxygen

6 Following its gradients, H+ flows back into inner compartment, through ATP synthases. The flow drives ATP formation.

1 Pyruvate from cytoplasm inters inner mitochondrial compartment.

3 NADH and FADH2 give up electrons and H+ to membrane-bound electron transport systems.

2 Krebs cycle and preparatory steps: NAD+ and FADH2

accept electrons and hydrogen stripped from the pyruvate. ATP forms. Carbon dioxide forms.

5 Oxygen accepts electrons, joins with H+ to form water.

4 As electrons move through the transport system, H+ is pumped to outer compartment.

Fig. 8.6, p. 137

oxaloacetate

malate

citrate

isocitrate

-ketogluterate

fumarate

succinate

CoA

succinyl–CoA

ATP

NADH

NADH

NADH

NADH

FADH2

NAD+

NAD+

FAD NAD+ CoA

CoA

H2O

H2O

H2O

ADP + phosphate group (from GTP)

KREBS CYCLE

PREPARATORY STEPS

pyruvate

NAD+

CoAAcetyl–CoA

coenzyme A (CoA)

(CO2)

Step 3: Electron Transfer Phosphorylation

1. NADH and FADH2 transfer e- and H+ to inner membrane of mitochondria, buiding up concentration of protons in intermembrane space.

2. When protons flow through ATP synthases, up to 34 ATP are produced.

3. Oxygen will accept extra hydrogens, resulting in water.

Electron Transport Chain

ATP Synthase

Fig. 8.5b, p. 136

Krebs Cycle

NADH

NADH

NADH

ATP ATP

ATP

ATP

ADP + Pi

INNER COMPARTMENT

OUTER COMPARTMENT

acetyl-CoA

free oxygen

6 Following its gradients, H+ flows back into inner compartment, through ATP synthases. The flow drives ATP formation.

1 Pyruvate from cytoplasm inters inner mitochondrial compartment.

3 NADH and FADH2 give up electrons and H+ to membrane-bound electron transport systems.

2 Krebs cycle and preparatory steps: NAD+ and FADH2

accept electrons and hydrogen stripped from the pyruvate. ATP forms. Carbon dioxide forms.

5 Oxygen accepts electrons, joins with H+ to form water.

4 As electrons move through the transport system, H+ is pumped to outer compartment.

Possible Pathways

Glucose

Glycolysis

(if oxygen)

Aerobic Respiration (in mitochondria)

(no oxygen for yeast, bacteria)

Alcoholic Fermentation

(no oxygen, for muscle)

Lactate Fermentation

Alcoholic Fermentation (anaerobic)

If no oxygen is available, only glycolysis can occur.

In this case, pyruvate doesn’t enter the mitochondrion but rather is modified in the cytoplasm.

The result is ethanol and carbon dioxide.

Very little energy release as compared to aerobic respiration, so not an option for large, active animals.

Lactic Acid Fermentation (anaerobic)If no oxygen is available, only glycolysis can occur.

In this case, pyruvate doesn’t enter the mitochondrion but rather is modified in the cytoplasm.

The result is lactate.

Very little energy release as compared to aerobic respiration, so only used for short bursts of energy.