Biochemistry ATP Generation Mechanisms

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Questions and Answers

What is the primary role of ATP synthase in the process of chemiosmosis?

To oxidize NADH and FADH2

To pump electrons into the intermembrane space

To facilitate the diffusion of H+ back into the matrix (correct)

To synthesize FADH2 from NADH

How many ATP molecules are generated from the complete oxidation of one NADH molecule during aerobic respiration?

3 ATP

1.5 ATP

2.5 ATP (correct)

2 ATP

During glycolysis, what is the total ATP gain through substrate-level phosphorylation?

2 ATP (correct)

3 ATP

4 ATP

2 NADH

What happens to the H+ ions that are pumped into the intermembrane space during the electron transport chain?

They accumulate and decrease the pH of the intermembrane space Signup and view all the answers

In the citric acid cycle, what is the total contribution of FADH2 to ATP production when one glucose molecule is fully oxidized?

3 ATP Signup and view all the answers

What is the net gain of ATP molecules produced during glycolysis?

2 ATP molecules Signup and view all the answers

Which of the following describes the conversion of pyruvic acid into acetyl CoA?

CO2 and NADH are released Signup and view all the answers

In each turn of the Krebs cycle, how many molecules of carbon dioxide (CO2) are released?

2 CO2 molecules Signup and view all the answers

Which mechanism is primarily responsible for ATP production during glycolysis?

Substrate level phosphorylation Signup and view all the answers

How many NADH molecules are produced from each glucose molecule during the Krebs cycle?

8 NADH molecules Signup and view all the answers

What are the two key processes involved in oxidative phosphorylation?

Electron Transport Chain and Chemiosmosis Signup and view all the answers

What happens to NADH in the absence of oxygen during fermentation?

It reduces pyruvic acid to lactic acid or ethanol Signup and view all the answers

What is formed when acetyl CoA combines with oxaloacetic acid in the Krebs cycle?

Citrate Signup and view all the answers

What process is responsible for generating ATP during glycolysis and the Krebs cycle?

Substrate-level Phosphorylation Signup and view all the answers

Which of the following correctly describes Oxidative Phosphorylation?

Utilizes coenzymes and requires a sequence of reactions in the mitochondria. Signup and view all the answers

What is the main role of the Electron Transport Chain in cellular respiration?

To generate a proton gradient for ATP synthesis. Signup and view all the answers

Which coenzyme is formed when FAD accepts electrons during the Krebs cycle?

FADH2 Signup and view all the answers

What is a consequence of high energy electrons in the cellular environment?

They can form reactive oxygen species such as superoxides. Signup and view all the answers

What is the outcome when glucose is oxidized during cellular respiration?

It loses electrons and serves as the electron donor. Signup and view all the answers

Chemiosmosis in oxidative phosphorylation involves which of the following?

The flow of H+ ions back across the membrane through protein channels. Signup and view all the answers

Which statement about ATP production mechanisms is accurate?

Oxidative phosphorylation relies on a proton gradient created by the Electron Transport Chain. Signup and view all the answers

Study Notes

Generating ATP

Two Mechanisms:
- Substrate-level Phosphorylation:
  - Occurs during glycolysis and citric acid cycle.
  - Uses enzyme/substrate interaction.
  - ADP + P → ATP
- Oxidative Phosphorylation:
  - Takes place within the mitochondria.
  - Requires coenzymes, electrons (H), and oxygen.
  - Electron Transport Chain (ETC):
    - Electrons are shuttled, releasing energy to pump H+ ions.
    - Creates an electrical gradient across the inner mitochondrial membrane.
  - Chemiosmosis:
    - H+ ions are allowed back across the membrane, generating energy for ATP synthesis.
    - The number of H+ ions used determines the total ATP production.

Oxidation-Reduction Reactions

Oxidation: Loss of electrons from an atom or molecule.
- Glucose is oxidized, losing H and its electrons.
Reduction: Gain of electrons.
- Electron recipient is reduced.
- Oxygen is reduced, gaining electrons to form water.
Coenzymes:
- FAD (Flavin Adenine Dinucleotide):
  - Derivative of Vitamin B2.
  - Accepts two hydrogen atoms from the TCA cycle.
  - Gains two electrons to become FADH2.
- NAD (Nicotinamide Adenine Dinucleotide):
  - Derivative of Vitamin B3.
  - Accepts two hydrogen atoms.
  - Gains two electrons to become NADH.

Forming ATP

Oxidative Phosphorylation:
- Allows slow, gradual release of ATP to prevent cell "explosion."
- Uses energy from electrons in the electron transport chain to form protons (H+).
Reactive Oxygen Species (ROS):
- High energy electrons are dangerous.
- Form superoxides and hydrogen peroxide.
- Contribute to aging, disease, and cancer.
- Antioxidants bind electrons to decrease these effects.
- Cells utilize oxygen to bind electrons to form the O2- ion, which combines with 2H+ to form H2O.

Glycolysis

Location: Cytoplasm
Final Products:
- 2 molecules of pyruvic acid.
- 2 molecules of NADH (go to mitochondria for OXPHOS).
- 4 molecules of ATP (net gain of 2) via substrate-level phosphorylation.
Pyruvic Acid:
- With oxygen: continues to the Citric Acid (Krebs) Cycle.
- Without oxygen: NADH "dumps" H+ onto pyruvic acid, forming lactic acid or ethyl alcohol.

Transition Step (Reaction)

Location: Mitochondrial matrix.
Converts pyruvic acid into acetyl CoA.
Steps:
- Removal of C and 2 O forming CO2.
- Removal of H forming NADH.
- Acetic acid + coenzyme A = acetyl CoA.

Citric Acid (Krebs) Cycle (CAC)

Location: Mitochondrial matrix.
Begins with the formation of citric acid from acetyl CoA (derived from pantothenic acid).
Steps:
- Acetyl CoA + oxaloacetic acid → citric acid (citrate).
- Citric acid continues through the cycle, removing carbons to form CO2.
- One ATP molecule is formed via substrate-level phosphorylation.
- Each acetyl CoA produces:
  - 2 CO2 molecules
  - 3 NADH2 molecules
  - 1 FADH2 molecules
  - 1 ATP molecule.
Per Glucose Molecule:
- 6 CO2 molecules
- 8 NADH molecules
- 2 FADH2 molecules
- 2 ATP molecules.

Oxidative Phosphorylation

Location: Inner mitochondrial membrane.
Directly uses oxygen.
Consists of two processes:
- Electron Transport Chain (ETC).
- Chemiosmosis.

Electron Transport Chain (ETC)

Location: Inner mitochondrial membrane.
NADH and FADH2 deliver H+ and electrons.
Electrons are split and shuttled, generating energy used for H+ pumping into the intermembrane space.
Creates an H+ gradient.
Components:
- Cytochromes: proteins with a heme group and Fe (cyt b, cyt a).
- Coenzyme Q: non-protein carrier.
Energy from the electrons is used to pump H+ into the intermembrane space.

Chemiosmosis

Location: Inner mitochondrial membrane.
ATP synthesis occurs when H+ diffuses back into the matrix through ATP synthase.
ATP synthase uses the energy of protons to make ATP.
ATP Yield:
- Each NADH provides energy to pump 10 H+ into the intermembrane space.
- Every 4 H+ traversing ATP synthase generates 1 ATP.
Efficiency:
- Oxidation of each NADH = 2.5 ATP.
- Oxidation of each FADH2 = 1.5 ATP.

Aerobic Cellular Respiration - Summary

Total ATP Production from one glucose molecule:
- Glycolysis:
  - 2 ATP via substrate-level phosphorylation............. 2
  - 2 NADH (ETC: X 2.5)............................. 5
- Transition Reaction:
  - 2 NADH (ETC: X 2.5)............................. 5
- Citric Acid Cycle:
  - 3 NADH X 2 = 6 NADH2 (ETS: X 2.5 in ETC)........... 15
  - 1 FADH2 X 2 = 2 FADH2 (ETS: X 1.5 in ETC)........... 3
  - 1 ATP X 2 via substrate-level phosphorylation)....... 2
- Total: 32-38 ATP

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Description

This quiz covers the mechanisms of ATP generation, including substrate-level phosphorylation and oxidative phosphorylation. It focuses on the electron transport chain, chemiosmosis, and the principles of oxidation and reduction. Test your knowledge on these essential biochemical processes!