Biochemistry Week 9: Citric Acid Cycle

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Questions and Answers

What is the primary outcome of the electron transport chain and chemiosmosis?

Formation of an electrochemical gradient (correct)

Production of NADH and FADH2

Conversion of ADP to pyruvate

Direct synthesis of glucose

Where do NADH and FADH2 primarily arrive at the electron transport chain from?

Glycolysis and Krebs cycle (correct)

Light reactions of photosynthesis

Fatty acid oxidation

DNA replication processes

What role does ATP synthase play in the process of ATP formation?

It utilizes the proton gradient to synthesize ATP (correct)

It transports protons into the inner mitochondrial membrane

It generates NADH from FADH2

It directly produces glucose from ADP

Which of the following best describes the function of the intermembrane space in mitochondria during cellular respiration?

It accumulates protons to create a gradient Signup and view all the answers

How do electrons from FADH2 compare to those from NADH when they enter the electron transport chain?

Electrons from FADH2 enter at a lower energy level than NADH Signup and view all the answers

What molecule initiates the citric acid cycle?

Acetyl-CoA Signup and view all the answers

Which enzyme is responsible for converting citrate into isocitrate?

Aconitase Signup and view all the answers

How many total dehydrogenases are involved in the citric acid cycle?

4 Signup and view all the answers

What is the product of the conversion of α-Ketoglutarate in the citric acid cycle?

Succinyl-CoA Signup and view all the answers

Which molecule is generated alongside NADH during the conversion of malate to oxaloacetate?

GTP Signup and view all the answers

What is the role of Coenzyme A (CoA) in the citric acid cycle?

Participate in the formation of acetyl-CoA Signup and view all the answers

What is FAD converted to in the citric acid cycle?

FADH2 Signup and view all the answers

Which citric acid cycle enzyme does NOT catalyze a decarboxylation reaction?

Aconitase Signup and view all the answers

Which of the following compounds is produced as a byproduct during the conversion of pyruvate to acetyl-CoA?

NADH + H+ Signup and view all the answers

What is the total ATP yield from one molecule of glucose during glycolysis?

2 ATP Signup and view all the answers

How many ATP can be generated from one NADH during cellular respiration?

2.5 ATP Signup and view all the answers

What percentage efficiency is achieved in ATP production from glucose in cellular respiration?

32% Signup and view all the answers

What is the ATP yield from FADH2 during cellular respiration?

1.5 ATP Signup and view all the answers

Which metabolic process directly produces pyruvate from glucose?

Glycolysis Signup and view all the answers

What is the total amount of NADH produced during the Krebs cycle per glucose molecule?

6 NADH Signup and view all the answers

Which type of molecule is glucose when considering its energy content measured in kcal/mol?

686 kcal/mol Signup and view all the answers

What role does ATP play in relation to glucose during cellular respiration?

It stores energy. Signup and view all the answers

What is the principal function of the Pyruvate Dehydrogenase complex?

To catalyze the reaction of pyruvate to acetyl-CoA Signup and view all the answers

Which enzyme is NOT part of the Pyruvate Dehydrogenase complex?

Lactate dehydrogenase Signup and view all the answers

What are the cofactors required by the Pyruvate Dehydrogenase complex?

TPP, FAD, NAD, CoA, and lipoic acid Signup and view all the answers

Which condition activates the Pyruvate Dehydrogenase complex?

Increased NAD+/NADH ratio Signup and view all the answers

What is produced when oxygen is absent during pyruvate metabolism in bacteria?

Acetaldehyde Signup and view all the answers

Which metabolic pathway is directly linked to the production of lactate from pyruvate?

Anaerobic glycolysis Signup and view all the answers

Which product is formed alongside NADH during the conversion of pyruvate to acetyl-CoA?

CO2 Signup and view all the answers

What role does lipoic acid play in the Pyruvate Dehydrogenase complex?

It helps in the transfer of acyl groups. Signup and view all the answers

Under which metabolic state is the Pyruvate Dehydrogenase complex primarily active?

Fed state Signup and view all the answers

Which enzyme in the Pyruvate Dehydrogenase complex is responsible for decarboxylation?

E1 Signup and view all the answers

What disease is caused by thiamine deficiency?

Beriberi Signup and view all the answers

What are the characteristic symptoms of pellagra?

Diarrhea, dermatitis, dementia, and death Signup and view all the answers

What does the glyoxylate cycle primarily produce?

Glucose Signup and view all the answers

Which enzyme is responsible for converting isocitrate to α-ketoglutarate?

Isocitrate dehydrogenase Signup and view all the answers

How many times does the glyoxylate cycle turn to produce one molecule of glucose?

Two turns Signup and view all the answers

Which product is formed from the conversion of succinyl-CoA in the glyoxylate cycle?

ATP Signup and view all the answers

What is the primary role of the glyoxylate cycle in plants?

Converting fats into carbohydrates Signup and view all the answers

Which coenzyme is involved in the conversion of isocitrate to oxalosuccinate?

NAD+ Signup and view all the answers

What compound reacts with acetyl-CoA at the beginning of the glyoxylate cycle?

Oxaloacetate Signup and view all the answers

What is the significance of the glyoxylate cycle in organisms that cannot convert fatty acids into glucose?

Provides an alternative energy source Signup and view all the answers

What is the main function of Acetyl-CoA in the citric acid cycle?

To combine with oxaloacetate to form citrate Signup and view all the answers

Which enzyme catalyzes the conversion of succinate to fumarate?

Succinate dehydrogenase Signup and view all the answers

How many GTP molecules are produced per turn of the citric acid cycle?

1 Signup and view all the answers

Which component of the citric acid cycle is involved in amino acid metabolism?

α-ketoglutarate Signup and view all the answers

What major product is released during the oxidative decarboxylation of isocitrate?

NADH Signup and view all the answers

Which is the only substrate-level phosphorylation event in the citric acid cycle?

From succinyl-CoA to succinate Signup and view all the answers

What is the role of citrate synthase in the citric acid cycle?

To condense Acetyl-CoA and oxaloacetate into citrate Signup and view all the answers

What is the significance of FADH2 produced in the cycle?

It is used to generate ATP in the electron transport chain. Signup and view all the answers

Which of the following is NOT a product of one turn of the citric acid cycle?

2 pyruvate Signup and view all the answers

In which part of the cell does succinate dehydrogenase operate?

Inner mitochondrial membrane Signup and view all the answers

Which intermediate in the citric acid cycle is an allosteric effector?

Citrate Signup and view all the answers

Which reaction in the citric acid cycle is the first oxidative decarboxylation?

From isocitrate to α-ketoglutarate Signup and view all the answers

What type of metabolism are succinate and fumarate involved in besides the TCA cycle?

Glyoxylate metabolism Signup and view all the answers

Study Notes

Certificate in Health Professions Preparation

FIMS Biochemistry - PBC9400 Week 9
Topic: Citric Acid Cycle and Electron Transport Chain
Instructor: Thomas A. Panavelil, Ph.D., M.S., M.B.A.

Learning Objectives

Describe the citric acid cycle and the pathways of electrons and carbons.
Describe how electrochemical gradients are produced.
Explain how ATP is generated during chemiosmosis.
Describe the theoretical energy yield for cellular respiration.
Identify entry points of fats and proteins in cellular respiration.
Describe key intermediates, key regulators, and negative feedback mechanisms of cellular respiration.

Respiration

Conversion of nutrients into usable energy for the cell
Carbohydrates (sugars)
Proteins (amino acids)
Fats (fatty acids & glycerol)

Acetyl-CoA Metabolism

Fats, polysaccharides, and proteins are metabolized into Acetyl-CoA
Acetyl-CoA enters the citric acid cycle
Electrons and protons are transferred to the electron transport chain
Oxidative phosphorylation produces ATP

Electron Transport Chain (ETC) and Chemiosmosis

Diagram of electron and carbon flow.
Description of gradient production in the ETC.
Explanation of ATP production in chemiosmosis.

Anaplerotic/Cataplerotic Reactions of the Citric Acid Cycle

Diagram showing incoming and outgoing molecules in the citric acid cycle
Key molecules: Citrate, a-Ketoglutarate, Succinyl-CoA, Oxaloacetate, Acetoacetate , Pyruvate
Important molecules for entry points and regulation

Pyruvate Pathways

Pyruvate metabolism pathways
Key molecules: Glucose, Alanine, Cahill cycle, CO2, ATP, Lactate, Cori cycle, Oxaloacetate, Acetyl-CoA

Pyruvate Dehydrogenase Complex (PDH)

Mitochondrial enzyme complex linking glycolysis and the TCA cycle
Regulation of PDH is regulated in fed or fasting states
Complex contains 3 enzymes and 5 cofactors
Cofactors derived from vitamins (B1, B2, B3, B5)
Oxidative decarboxylation reaction

Metabolic Fates of Pyruvate

Metabolic pathways of pyruvate
Pyruvate can be converted to lactate in animals (oxygen absent)
Pyruvate can be converted to ethanol in bacteria and yeast (oxygen absent)
Pyruvate can be converted to Acetyl-CoA in animals (oxygen present)

Pyruvate Dehydrogenase Mechanism

Detailed diagram outlining the mechanism, steps and enzymes involved
Key intermediates: TPP-Acetaldehyde, Acetyl-Lipoamide, COA-SH, NAD+, FADH2, Acetyl-CoA

Making acetyl-CoA

Pyruvate dehydrogenase snatches CO2 from pyruvate and adds coenzyme A, making acetyl-CoA
Two electrons are transferred to a nearby NAD+, making NADH
Links glycolysis to the citric acid cycle, but not considered part of either pathway
Coenzyme A has a reactive thiol group which carries acyl groups.
This forms thioesters.

Lipoamide Oxidized/Reduced

Chemical structure of lipoamide
Lipoic acid component oxidized and reduced

Acetyl-CoA

Chemical structure of Acetyl-CoA

Citric Acid Cycle

Pyruvate enters as two carbons (Acetyl-CoA)
Eight enzymatic reactions converting Acetyl-CoA to CO2.
Key enzymes and their roles in catalysis.
Energy production is in the form of ATP, NADH, FADH2, and GTP.

Krebs Cycle

8 enzymatic reactions
Acetyl-CoA to CO2
Citric Acid Cycle and Krebs cycle are interchangeable terms.
Reactions occur in the mitochondrial matrix

Krebs Cycle Consumes Remaining Carbons of Glucose

Potential energy of glucose is captured by electron carriers

Clinical Correlation

Adequate intake of vitamins, B1, B5, B2, and B3 is essential for functioning of the TCA cycle.
Thiamine deficiency - disease called beriberi, problems with the central nervous system
Niacin deficiency - disease called pellagra (4 D's).

Glyoxylate Cycle

Key enzymes and their functions in the cycle
Two Acetyl-CoA enter per turn of the cycle
Net synthesis of glucose form acetyl-CoA

Isocitrate Lyase

Product of the isocitrate reaction
Succinate and Glyoxylate produced

Malate Synthase

Enzyme that catalyzes malate production

Glyoxylate Cycle Summary

Input of 4 carbons (2 Acetyl-CoA)
Release of 0 carbon dioxide molecules
Production of one extra oxaloacetate molecule
Two oxidations result in 1 NADH, 1 FADH2 and a net extra oxaloacetate
Synthesis from Acetyl-CoA

Citric Acid Cycle Summary

Input of two carbons (Acetyl-CoA)
Release of two carbon dioxide molecules
Four oxidations of carbon atoms
Production of 3 NADH, 1 FADH2, and 1 GTP per turn of the cycle.
No net synthesis of glucose from acetyl-CoA.

Each Citric Acid Cycle Intermediate Functions in Other Pathways

Shows how each intermediate plays a vital role in other metabolic pathways.
Showing how intermediates are important in processes other than just the citric acid cycle

Electron Transport Chain (ETC)

Explains electron transport processes
Role of proton pumps
Explanation of the hydrogen gradient
Description of ATP synthase and its function

Chemiosmosis

Explains how ATP is produced during chemiosmosis

Oxidative Phosphorylation

How oxidative phosphorylation is regulated by cellular energy demands.
Explains the importance of the intracellular ADP and ATP/ADP/Pi ratio.

Many Poisons Inhibit Respiratory Chain, Inhibited by ETC

Several substances inhibit the electron transport chain or oxidative phosphorylation.

Clinical Correlation: Inherited Defects in OxPhos

Defects that occur in the genetic material of mitochondria
Issues with a variety of organs and symptoms.

Formation of HMG-CoA

Enzyme catalyzed reactions
Molecules involved in reactions

Cellular Respiration

Four stages of cellular respiration

Putting it Together, forming Lots of ATP

Summary of the process

Theoretical Energy Yields for Cell Respiration

Explanation of theoretical energy yields and variations in actual yields.

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Description

This quiz covers the essential concepts of the citric acid cycle and the electron transport chain, focusing on the pathways of electrons and carbon. You'll learn about ATP generation through chemiosmosis and the role of Acetyl-CoA in metabolism. Test your understanding of cellular respiration and its energy yield.