Energy Production And Electron Transport

Metabolism and Energy Production Citric Acid Cycle Electron Transport Chain ATP Energy from Glucose Oxidation of Fatty Acids Metabolic Pathways for Amino Acids

1

Citric Acid Cycle A reaction series that • Operates under aerobic conditions only • Oxidizes the 2 carbon atoms of acetyl CoA to CO2 • Provides reduced coenzymes O || CH3–C –CoA

2 CO2 , FADH2, 3 NADH, + ATP

acetyl CoA 2

Steps 1-3 in Citric Acid Cycle COO-

O

+ CH3

C CoA

COO O C

CH2 HO C COO

CH2

CH2

-

COO-

COO

oxaloacetate

+ CoA

acetyl CoA

citrate -

COO CH2 CH2

α-ketoglutarate

NAD+ + CO2

+ NADH

C O COO-

3

Steps 4-5 of citric acid cycle In the next reactions, α-ketoglutarate is oxidized to succinate. COO-

COO

CH2

CH2

CH2

-

+ NAD

C O

+

CH2

+ CO2 + NADH

COO-

COO-

α-ketoglutarate

succinate

4

Steps 6-8 of citric acid cycle More oxidations convert succinate to oxaloacetate. The C=C requires FAD. -

COO CH2

COO+ FAD

CH2

COOsuccinate COOHO C H + NAD+ CH -

COO

malate

CH

+ FADH2

CH

H2O

-

COO fumarate COOC O + NADH CH -

COO oxaloacetate

5

Coenzymes Produced in the Citric Acid Cycle 1.

Acetyl CoA (2C) + oxaloacetate (4C) to citrate (6C)

•

Citrate (6C) to α-ketoglutarate (5C) + CO2

3.

α-ketoglutarate (5C) to succinate (4C) + CO2. GDP picks up Pi.

•

Succinate(4C) to fumarate (C=C) to malate

•

Malate to oxaloacetate. Start again. Total: 2CO2 + 3 NADH + 1 FADH2 + GTP

Coenzymes

1 NADH 1 NADH 1 GTP 1 FADH2

1 NADH 6

Learning Check E1 Complete the following statements: • When 1 acetyl CoA enters the citric acid cycle, the C atoms produce ____CO2. • •

In 1 cycle, a total of ____NADH are produced. In 1 cycle, a total of ____FADH2 are produced.

7

Solution E1 Complete the following statements: • When 1 acetyl CoA enters the citric acid cycle, the C atoms produce 2 CO2. • •

In 1 cycle, a total of 3 NADH are produced. In 1 cycle, a total of 1 FADH2 are produced.

8

Regulation of Citric Acid Cycle • Operates when ATP is needed • High levels of ATP and/or NADH inhibit citrate synthetase (first step in cycle) • High levels of ADP and NAD+ activate isocitrate dehydrogenase • Low levels of ATP or high levels of acetyl CoA speed up the cycle to give energy ATP 9

Electron Transport Chain • A series of electron carriers • Transfers H+ and electrons from coenzymes NADH and FADH2 (citric acid cycle) • Energy released along chain to make ATP NADH + 3 ADP FADH2 + 2 ADP

NAD+ + 3 ATP FAD + 2 ATP 10

Electron Carriers • Found in three protein complexes • Attached to inner membrane of mitochondria • H+ move into intermembrane space to create proton gradient • As H+ return to matrix, ATP synthase uses energy to synthesize ATP • Oxidation phosphorylation ADP + Pi + Energy ATP 11

Enzyme Complexes 1. NADH dehydrogenase Coenzyme A

•

Cytochrome c reductase Cytochrome c

3. Cytochrome c Oxidase 12

Chemiosmotic Model Intermembrane space

H+ H+

H+ H+ H+

H+

Cytc

Q

eNADH + H+

FADH

HO

13

Learning Check E2 Classify each as (1) a product of the citric acid cycle, (2) a product of the electron transport chain A. CO2 B. FADH2 C. NAD+ D. NADH E. ATP 14

Solution E2 Classify each as (1) a product of the citric acid cycle, (2) a product of the electron transport chain A. 1 CO2 B.

1

FADH2

C. D. E.

2 1 2

NAD+ NADH ATP 15

ATP Energy from Glycolysis (Aerobic) • In the electron transport system NADH = 3 ATP FADH2 = 2 ATP • Glycolysis Glucose 2 pyruvate + 2 ATP + 2 NADH NADH in cytoplasm FADH2 mitochondria Glucose

2 pyruvate + 6 ATP 16

ATP Energy from Pyruvate 2 pyruvate

2 acetyl CoA + 2 CO2 + 2 NADH

2 pyruvate

2 acetyl CoA + 2 CO2 + 6 ATP

17

ATP Energy from Citric Acid Cycle One turn of the citric acid cycle 3 NADH x 3 ATP = 9 ATP 1 FADH2 x 2 ATP = 2 ATP 1 GTP

x 1 ATP = 1 ATP Total = 12 ATP Glucose provides two acetyl COA molecules for two turns of citric acid cycle 2 acetyl CoA 24 ATP + 4 CO2 18

ATP from Glucose For 1 glucose molecule undergoing complete oxidation Glycolysis 6 ATP 2 Pyruvate to 2 Acetyl CoA 6 ATP 2 Acetyl CoA to 4 CO2 24 ATP Glucose + 6 O2

6 CO2 + 6 H2O + 36 ATP 19