Krebs Cycle Overview and Functions

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

How many ATP are produced from the complete oxidation of one acetyl CoA in the Krebs Cycle?

15 ATP

12 ATP

8 ATP

10 ATP (correct)

Which of the following molecules is a stimulator of citrate synthase in the Krebs Cycle?

Citrate

ATP

NADH

ADP (correct)

Which inhibitor regulates isocitrate dehydrogenase (ICDH) in the Krebs Cycle?

Ca+2

NADH (correct)

ADP

AMP

From glucose degradation via glycolysis and the Krebs Cycle, how much ATP is produced from complete oxidation of one glucose?

32 ATP Signup and view all the answers

What effect does ATP concentration have on the energy level in cells affecting the Krebs Cycle?

Slows down the cycle Signup and view all the answers

Which reaction converts pyruvate to oxaloacetate in the context of anaplerosis?

Pyruvate Carboxylase reaction Signup and view all the answers

Which of the following molecules stimulates the α-ketoglutarate dehydrogenase complex?

ADP Signup and view all the answers

What is the main regulatory factor for the Krebs Cycle concerning energy levels?

NADH concentration Signup and view all the answers

What happens to pyruvate when aerobic conditions are present?

It is oxidized to CO2 and H2O. Signup and view all the answers

Which of the following best describes the purpose of the TCA cycle?

To oxidize Acetyl-CoA to CO2 and produce ATP. Signup and view all the answers

Which coenzymes are reduced during the TCA cycle?

NADH and FADH2 Signup and view all the answers

What distinguishes the TCA cycle from glycolysis?

Glycolysis is a linear pathway while the TCA cycle is cyclic. Signup and view all the answers

Which of the following is a result of each turn of the TCA cycle for one acetyl-CoA?

Two molecules of CO2 are released. Signup and view all the answers

Which molecules serve as electron acceptors in the TCA cycle?

NAD+ and FAD Signup and view all the answers

What is one of the roles of intermediates in the TCA cycle?

They are used for nucleic acid synthesis. Signup and view all the answers

What happens under anaerobic conditions regarding energy production?

Energy production is significantly reduced. Signup and view all the answers

Study Notes

Krebs Cycle Overview

The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a crucial metabolic process.
It's named after Hans Krebs, who received a Nobel Prize in 1953 for his work on it.
The cycle is aerobic, meaning it requires oxygen.
Pyruvate from glycolysis is oxidized completely to CO2 and H2O.
Oxygen acts as the final electron acceptor.
If the cell is under anaerobic conditions, energy production is less efficient (6%).

Krebs Cycle Energy Production

The cycle produces reduced coenzymes (NADH and FADH2).
Oxidative phosphorylation utilizes these coenzymes to create ATP (adenosine triphosphate).
The cycle is amphibolic, meaning it has both catabolic and anabolic functions.

Krebs Cycle Two Purposes

Oxidize acetyl-CoA: To CO2 releasing energy (ATP/GTP).
Produce reducing power: (NADH, FADH2).
Involved in the aerobic degradation of carbohydrates, lipids, and amino acids.

Krebs Cycle Intermediates

The cycle's intermediates can be used for biosynthetic reactions.
- Supply precursors for the synthesis of carbohydrates, lipids, amino acids, nucleotides, and porphyrins.
Intermediates can be shared with other metabolic pathways.
Reactions feeding into the cycle replenish the cycle's intermediates.

Glycolysis vs. Krebs Cycle

Glycolysis is a linear pathway occurring in the cytosol that doesn't require oxygen.
The Krebs cycle is a cyclic pathway located in the mitochondrial matrix that requires oxygen.

Krebs Cycle Summary

For each acetyl-CoA entering, two CO2 molecules are released.
Coenzymes NAD+ and FAD are reduced.
One GDP (or ADP) is phosphorylated.
The initial acceptor (oxaloacetate) is reformed.

Krebs Cycle Energy Yield

Each acetyl CoA entering the cycle produces 3 NADH, 1 FADH2 and 1 GTP (or ATP).

ATP Calculation

Oxidation of one NADH yields 2.5 ATP.
Oxidation of one FADH2 yields 1.5 ATP.
Complete oxidation of one acetyl CoA yields 10 ATP.
Complete oxidation of one glucose yields 32 ATP.

Krebs Cycle Regulation

Regulation depends on the energy level of the cell (ATP, NADH, FADH2).
High energy levels slow down the Krebs cycle.
The reverse is also true; low energy levels increase activity.

Pathway Control Mechanisms

Control mechanisms include:

Small molecule modulators (cycle products can inhibit).
Covalent modification of cycle enzymes.
Supply of acetyl-CoA.

Regulation of specific Krebs enzymes

Citrate synthase
- Inhibitors: NADH, ATP, succinyl-CoA, citrate
- Stimulators: ADP
Isocitrate dehydrogenase
- Inhibitors: NADH, ATP
- Stimulators: NAD+, ADP and Ca2+
α-ketoglutarate dehydrogenase complex
- Inhibitors: NADH, ATP and succinyl-CoA
- Stimulators: NAD+, ADP, AMP

Anaplerotic Reactions

Anaplerotic reactions replenish the Krebs cycle intermediates.
- Pyruvate carboxylase converts pyruvate to oxaloacetate, activated by acetyl-CoA.
- Degradation of odd-numbered fatty acids produces succinyl-CoA.
- Degradation of amino acids produces other intermediates.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the intricacies of the Krebs cycle, or citric acid cycle, a fundamental metabolic pathway that plays a vital role in energy production. Learn about its aerobic nature, its importance in oxidizing acetyl-CoA, and the production of key coenzymes like NADH and FADH2. This overview includes the cycle's catabolic and anabolic functions, and its intermediates.