Cellular RespirationChapter 7

• An overview of cellular respiration

Figure 6.8

High-energy electrons carried by NADH

GLYCOLYSIS

Glucose Pyruvicacid

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

MitochondrionCytoplasmic

fluid

• Details of glycolysis in the cytoplasm

Figure 6.9B

Steps – A fuelmolecule is energized,using ATP.

1 3

1

GlucosePREPARATORY

PHASE(energy investment)Step

2

3

4

Glucose-6-phosphate

Fructose-6-phosphate

Glyceraldehyde-3-phosphate (G3P)

Step A six-carbonintermediate splits into two three-carbon intermediates.

4

Step A redoxreaction generatesNADH.

55 ENERGY PAYOFF

PHASE1,3-Diphosphoglyceric acid(2 molecules)

6

Steps – ATPand pyruvic acidare produced.

6 9 3-Phosphoglyceric acid(2 molecules)7

2-Phosphoglyceric acid(2 molecules)8

2-Phosphoglyceric acid(2 molecules)

9

(2 moleculesper glucose molecule)

Pyruvic acid

Fructose-1,6-diphosphate

What happens if oxygen is not present?

• Fermentation– Occurs in the cytosol– Generate NAD+ for recycling to glycolysis– No ATP production– Lactic acid and alcoholic fermentation

Lactic acid fermentation and alcoholic fermentation

Efficiency of glycolysis and fermentation

• In the matrix of the mitochondria, each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle

When Oxygen is present : Pyruvic acid is chemically groomedfor the Krebs cycle which takes place in the mitochondria

Figure 6.10

Pyruvicacid

CO2

Acetyl CoA(acetyl coenzyme A)

• The Krebs cycle, in the matrix of the mitochondria, is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group

When Oxygen is present: The Krebs cycle completes the oxidation of organic fuel,

generating many NADH and FADH2 molecules

Figure 6.11A

Acetyl CoA

KREBSCYCLE

2CO2

Figure 6.11B

Oxaloaceticacid

Step Acetyl CoA stokesthe furnace

1

2 carbons enter cycle

Citric acid

Steps and NADH, ATP, and CO2 are generatedduring redox reactions.

2 3

CO2 leaves cycle

Alpha-ketoglutaric acid

CO2 leaves cycle

Succinicacid

KREBSCYCLE

Steps and Redox reactions generate FADH2

and NADH.

4 5

Malicacid

1

2

3

4

5

• The electrons from NADH and FADH2 travel down the electron transport chain to oxygen

• Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes

• In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

Chemiosmosis powers most ATP production in the inner membrane

• Chemiosmosis in the mitochondrion inner membrane

Figure 6.12

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex

Electroncarrier

Electronflow

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Connection: Certain poisons interrupt critical events in cellular respiration

Figure 6.13

Rotenone Cyanide,carbon monoxide

Oligomycin

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

• For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules

Review: Each molecule of glucose yields many molecules of ATP

KREBSCYCLE

Electron shuttleacrossmembranes

Cytoplasmic fluid

GLYCOLYSIS

Glucose2

Pyruvicacid

2AcetylCoA

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

Mitochondrion

by substrate-levelphosphorylation

used for shuttling electronsfrom NADH made in glycolysis

by substrate-levelphosphorylation

by chemiosmoticphosphorylation

Maximum per glucose:Figure 6.14

• Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP – But a cell must have a way of replenishing

NAD+

Fermentation is an anaerobic alternative to aerobic respiration