Energy Releasing Pathways:Cellular Respiration and Glycolysis

Biology 1010 -Chapter 8

Introduction

A. Unity of Life

1. all organisms use energy

2. byproducts of metabolism

a. carbon dioxide

b. water

c. heat

3. at the biochemical level, all life is united

Process of ATP Synthesis

A. Comparison of Pathways

1. ATP is the energy currency of all cells

2. glycolysis

a. common to all pathways

b. splitting of glucose forms ATP

c. occurs in the cytoplasm of the cell

2. Fermentation and anaerobic electron transport

a. occur in the absence of oxygen

b. release small amounts of ATP

3. Aerobic respiration

a. main pathway for converting CHO to ATP

b. occurs in the mitochondria

c. requires oxygen

d. efficient

4. chemical formula

H2O +C6H12O6 + O2 = CO2 + H2O

5. similarities to photosynthesis

Glycolysis

A. First stage of all energy-releasing pathways

1. occurs in the cytoplasm of the cell

2. does not require oxygen

3. evolutionary considerations

B. Stages

1. energy investment phase

a. glucose is phosphorylated by 2 ATP molecules

2. energy releasing phase

a. glucose is split to form 4 ATP and 2 pyruvate molecules.

b. electrons captured by NAD+ to form NADH (to ETS)

c. ATP is produced by substrate-level phosphorylation.

C. Inputs and Outputs

1. Inputs

a. glucose

b. NAD+

c. ADP

2. Outputs

a. 2 pyruvate

b. 2 NADH

c. 2 ATP (net)

Krebs Cycle: Aerobic Respiration

A. General

1. occurs in the mitochondria (inner membrane space)

2. requires oxygen

3. input is the pyruvate (3-C)from glycolysis, which is modified to form acetyl-CoA

4. carbon leaves the cycle as CO2

B. Stages

1. pyruvate is converted to acetyl-CoA

2. oxygen is used to break C-C bonds

3. broken bonds release energy and electrons.

4. energy is used to form ATP by oxidative phosphorylation

5. electrons captured by NAD+ and FAD+ to form NADH and FADH2 (to ETS)

6. carbon leaves as CO2

7. cyclic pathway - intermediates are recycled

8. 1 glucose = 2 pyruvate. Two complete turns of the pathway per glucose

molecule

9. 2 ATP produced per glucose

C. Inputs and Outputs

1. Inputs

a. pyruvate

b. NAD+ and FAD+

c. ADP

d. O2

2. Outputs (per glucose)

a. CO2

b. NADH and FADH2

c. 2 ATP

Electron Transport System (ETS)

A. General

1. inputs are the NADH and FADH2 from glycolysis and the Krebs cycle

a. processes electrons, not carbon

2. located on the inner membrane of the mitochondria (integral proteins)

3. uses oxygen as a terminal electron receptor

4. ATP is produced by chemiosmosis or electron-level phosphorylation

B. Stages of chemiosmosis

1. NADH and FADH2 transfer electrons to integral proteins on the inner membrane

a. electrons are high energy

2. passage of energy between proteins pumps H+ ions out of the inner space

a. generates an electrical gradient

3. channels are opened, allowing the H+ ions to reenter, generating ATP.

4. oxygen is used to gather the spent electrons, generating water

5. high amounts of ATP are produced, typically 32 ATP per glucose.

6. NAD+ and FAD+ are recycled

C. Inputs and Outputs

1. Inputs

a NADH and FADH2

b. ADP

c. O2

2. Outputs (per glucose)

a. H2O

b. NAD+ and FAD+

c. 32 ATP

Summary of Energy Harvest

A. ATP per glucose

1. glycolysis 2 ATP

2. Krebs 2 ATP

3. ETS 32 ATP

B. Variations

1. yield per glucose may be 32-38 ATP depending on cell type

ATP Yields

2 2

32

Glyco

Kreb

ETS

Anaerobic Respiration

A. General

1. occur in the absence of oxygen or oxygen-poor environments

2. after glycolysis, pyruvate is converted to other molecules than acetyl-CoA.

3. many bacteria are completely anaerobic

B. Fermentation Pathways

1. Lactate fermentation

a. pyruvate is converted to lactate

b. process regenerates NAD+

c. occurs in bacteria and muscle cells

2. Alcohol fermentation

a. pyruvate is converted to acetaldehyde and then alcohol

b. NAD+ is regenerated

C. Anaerobic electron transport

1. some bacteria have modified electron transport systems.

2. types

a. convert SO4 to H2S

b. convert NO3 to NO2

3. evolutionary significance