Krebs Cycle and Cellular Respiration Quiz

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Questions and Answers

What is the primary role of Acetyl CoA in the Krebs cycle?

To release carbon dioxide

To provide 2-carbon units to feed the cycle (correct)

To convert FAD to FADH2

To accept electrons from NADH

How many molecules of NADH are generated per molecule of Acetyl CoA in one turn of the Krebs Cycle?

One

Two

Four

Three (correct)

Besides NADH, which other electron carrier is produced during the Krebs Cycle?

NADPH

FADH2 (correct)

GTP

ATP

What is the final fate of carbon atoms from the acetyl group in the Krebs Cycle?

They are released as carbon dioxide (D) Signup and view all the answers

Which molecule directly accepts electrons stripped from nutrient substrates in the Krebs Cycle?

NAD+ (B) Signup and view all the answers

How many ATP molecules are produced per NADH molecule after oxidative phosphorylation?

2.5 (B) Signup and view all the answers

Which molecule is used to regenerate oxaloacetate in the Krebs cycle?

Malate (B) Signup and view all the answers

If the Krebs cycle is not functioning, what would be the direct consequence for both NADH and FADH2?

They cannot be generated (A) Signup and view all the answers

What is the change in Gibbs free energy (∆G) for an exergonic reaction?

∆G < 0 (C) Signup and view all the answers

Which of the following best describes an endergonic reaction?

Requires input of free energy (D) Signup and view all the answers

What role does ATP serve in cellular processes?

The universal energy carrier (B) Signup and view all the answers

What are the products of ATP hydrolysis?

ADP + Pi + H+ (D) Signup and view all the answers

What is the approximate daily turnover rate of ATP in a typical person?

40 kg (A) Signup and view all the answers

What is the role of NADH in redox reactions?

An electron donor (A) Signup and view all the answers

What is the oxidized form of NAD?

NAD+ (B) Signup and view all the answers

What is the function of Coenzyme A (CoA)?

A carrier of fatty acids and acetyl groups (A) Signup and view all the answers

Which vitamin is a precursor for the synthesis of FAD?

Vitamin B2 (A) Signup and view all the answers

What is the Gibbs free energy change (∆Go) for the hydrolysis of ATP?

-7.3 kcal mol-1 (B) Signup and view all the answers

What is the net ATP production in glycolysis?

2 ATP (A) Signup and view all the answers

Which of the following is a sugar alcohol form of galactose?

Galactitol (B) Signup and view all the answers

Which of these is a symptom of galactosemia?

Cataracts (C) Signup and view all the answers

What is the role of 2,3-bisphosphoglycerate (2,3-BPG)?

It promotes oxygen release from hemoglobin. (C) Signup and view all the answers

What two molecules combine to form lactose?

Glucose and galactose (C) Signup and view all the answers

Which of these correctly lists the intermediate products in glycolysis?

Glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate → 3-phosphoglycerate → 2-phosphoglycerate → phosphoenolpyruvate (B) Signup and view all the answers

In glycolysis, how many ATP molecules are directly produced from 1,3-bisphosphoglycerate (1,3BPG)?

1 ATP (D) Signup and view all the answers

What is the end product of glycolysis under anaerobic conditions?

Lactate (B) Signup and view all the answers

Which process primarily involves the breakdown of complex molecules?

Catabolism (D) Signup and view all the answers

What is primarily indicated by the term 'free energy' in the context of metabolic processes?

The energy available to perform cellular work (D) Signup and view all the answers

Which of the following best describes the role of ATP in cellular metabolism?

A renewable storage of immediate cellular energy (A) Signup and view all the answers

The regulation of what process within the body is a direct consequence of catabolic reactions?

The release of heat (C) Signup and view all the answers

The citric acid cycle is a common pathway for converting nutrients into energy. What else does this pathway allow for?

The deamination of amino acids and provision of intermediates for other metabolic processes (C) Signup and view all the answers

What effect does a lack of sufficient vitamin B1 (thiamine) have on pyruvate metabolism?

It causes pyruvate to be converted to lactate. (D) Signup and view all the answers

Under anaerobic conditions, which process provides energy during activities like sprinting?

Substrate level phosphorylation in glycolysis (B) Signup and view all the answers

Which of the following is NOT a necessary condition for mitochondrial metabolism of pyruvate?

Excessive concentrations of lactate (D) Signup and view all the answers

What is produced when pyruvate is converted in anaerobic conditions?

Lactate (A) Signup and view all the answers

Which role does thiamine play in pyruvate metabolism?

It serves as a precursor for a coenzyme. (B) Signup and view all the answers

What is a possible consequence of acidosis related to lactate production?

Impaired muscle function (A) Signup and view all the answers

Which of the following statements about NAD+ is accurate in relation to pyruvate metabolism?

NAD+ is required for efficient pyruvate oxidation. (D) Signup and view all the answers

What does pyruvate dehydrogenase link glycolysis to?

The citric acid cycle (D) Signup and view all the answers

What is the total ATP yield from one Acetyl CoA during the Krebs cycle?

10 ATP (D) Signup and view all the answers

Which of the following disaccharides is composed of glucose and fructose?

Sucrose (B) Signup and view all the answers

Galactosemia is primarily caused by a failure in the metabolism of which compound?

Galactose (A) Signup and view all the answers

What is the primary role of the pentose phosphate pathway?

Ribose synthesis and NADPH production (D) Signup and view all the answers

What product results from the combination of glucose and galactose?

Lactose (D) Signup and view all the answers

What effect does galactose-1-phosphate have on cells when not metabolized properly?

Becomes toxic to the cell (A) Signup and view all the answers

Which intermediate is formed directly from fructose-1-phosphate in glycolysis?

Glyceraldehyde (D) Signup and view all the answers

Which component is essential for the antioxidant synthesis mentioned in the context of carbohydrate metabolism?

NADPH (B) Signup and view all the answers

Study Notes

Metabolic Pathways for Energy Conversion

Major nutrients like carbohydrates, fats, and proteins are broken down to usable energy.

Learning Objectives

ATP, a crucial energy source, is renewable and stored in cells.
Cells absorb essential nutrients such as glucose, amino acids, fatty acids, triacylglycerols, and cholesterol.
Glucose metabolism occurs in both anaerobic and aerobic processes.
Fatty acid oxidation results in either ketone body formation or immediate ATP production.
The citric acid cycle is a combined pathway for nutrient breakdown into energy. It also provides intermediates for the glycolytic and citric acid pathways to function properly.
The citric acid cycle facilitates the breakdown of nutrients into energy and regulates the deamination of amino acids, delivering essential intermediates to support the glycolytic and citric acid cycles.

Metabolism = Anabolism and Catabolism

Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.
Anabolism: The synthesis of complex molecules from simpler ones, requiring energy.
Catabolic processes produce energy needed for anabolic reactions alongside producing heat regulation.

Energy

Free energy (ΔG): The energy available for work in a chemical reaction.
Exergonic reaction: A reaction releasing free energy (ΔG < 0).
Endergonic reaction: A reaction requiring free energy input (ΔG > 0).

Stages of Energy Extraction from Fuel Molecules

Stage I: Digestion, absorption, and transport of nutrients.
Stage II: Converting various molecules into smaller key components and metabolites.
Stage III: Complete energy transfer for cellular use.

Adenosine 5'-triphosphate (ATP)

ATP is the cellular energy currency.
ATP is constantly recycled, releasing the stored energy and converting itself into ADP and phosphate.
The conversion of ATP to ADP releases 7.3 kcal/mol of free energy.

ATP Turnover

ATP turnover rate is high, about 40 kg per day.
ATP is crucial for various cellular functions, making its continuous replenishment essential.

Nicotinamide Adenine Dinucleotide (NAD)

NAD acts as an electron donor and acceptor during crucial biochemical processes.
NAD exists in reduced (NADH) and oxidized (NAD+) states, facilitating electron transfer.
Nicotinamide is a part of Vitamin B3.

Flavine Adenine Dinucleotide (FAD)

FAD is an electron carrier involved in redox reactions.
FAD exists in reduced (FADH₂) and oxidized (FAD) forms.
Riboflavin is a part of Vitamin B2.

Coenzyme A

Coenzyme A is essential for the transport of fatty acids and acetyl groups.

Bioenergetics

The production of ATP from carbohydrates, fats, and proteins.

Major Nutrient Metabolism: Overview

Fats are broken down into fatty acids and glycerol.
Polysaccharides are broken down into glucose and other sugars.
Proteins are broken down into amino acids.
Each nutrient flows to their respective metabolic pathways for energy extraction.

Carbohydrate Metabolism: Glycolysis and Krebs Cycle

Glycolysis: The breakdown of glucose into pyruvate.
It is a series of enzymatic reactions in the cytoplasm.
Results in a small yield of ATP under anaerobic conditions.
Pyruvate: A crucial intermediate for glucose metabolism and is either converted into lactate under anaerobic conditions or into acetyl-CoA under aerobic conditions to enter the Krebs cycle.
Krebs cycle (Citric acid cycle): A crucial metabolic pathway for extracting energy from acetyl CoA.
The Krebs cycle occurs in the mitochondria.
Releases carbon dioxide, generating ATP, NADH, and FADH₂.

Features of Glycolysis

A multi-step, cytoplasmic process.
Breaks down 6-carbon glucose into 3-carbon compounds (pyruvate or lactate).
Provides considerable amounts of ATP without oxygen.
Intermediates can be used for other metabolic pathways.

The Overall Glycolysis Reaction

Glucose is converted to pyruvate, producing ATP, NADH, and hydrogen ions.

Krebs Cycle

The citric acid cycle, also known as the tricarboxylic acid cycle.
It occurs in the mitochondria.
Acetyl CoA enters the cycle.
The cycle results in CO₂, NADH, FADH₂, one GTP.

Krebs Cycle: The Net Reaction

Acetyl CoA, NAD⁺, FAD, GDP, P₁, and H₂O yield CoA, CO₂ , NADH, FADH₂, GTP, and H⁺.

Energy Yield via Glycolysis

Four ATPs are generated per glucose molecule.
Two ATPs are consumed during the initial glycolytic steps.
Two ATPs are net generated per glucose.

Pyruvate Dehydrogenase Links Glycolysis to the Citric Acid Cycle

Pyruvate, a product of glycolysis, is converted to acetyl CoA.
This conversion is mediated by the enzyme pyruvate dehydrogenase complex in the mitochondria.
Thiamine pyrophosphate is crucial for this conversion.

Thiamine (Vitamin B₁)

A precursor for the coenzyme thiamine pyrophosphate, important for the conversion of pyruvate to acetyl-CoA.

Conditions for Mitochondrial Pyruvate Metabolism

Oxygen availability
Adequate NAD+ levels
Adequate thiamine (Vitamin B₁) levels.

Clinical Features of Lactic Acidosis

Low blood pH
High serum lactate
Increased respiratory rate
Muscle pain

Causes of Lactic Acidosis

Low oxygen levels
Thiamine deficiency
Pyruvate dehydrogenase deficiency
Certain drugs

Carbohydrates: Simple and Complex Sugars

Monosaccharides: Simple sugars like glucose, galactose, and fructose.
Disaccharides: Two monosaccharides linked together (e.g., sucrose, lactose, maltose).

Glycolysis (for Galactose and Fructose Metabolism)

The metabolic pathways for converting galactose and fructose to glycolytic intermediates.

Metabolism of Galactose and Galactosemia

Galactosemia: A condition where galactose can't be converted to glucose. Galactose builds up in cells and it is converted into galactitol.
This inability causes serious issues.

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Description

Test your knowledge on the Krebs cycle and its essential role in cellular respiration. This quiz covers key concepts such as the function of Acetyl CoA, electron carriers, and the production of ATP and NADH. Perfect for students of biochemistry looking to reinforce their understanding.