Biochemistry TCA Cycle Quiz

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Questions and Answers

What is the primary role of NADPH in cellular processes?

It functions solely to detoxify reactive oxygen species.

It is exclusively used for energy production.

It serves as an electron donor in reductive biosynthesis. (correct)

It is involved only in the synthesis of nucleotides.

Which enzyme is responsible for converting superoxide to hydrogen peroxide in antioxidant mechanisms?

Glutathione reductase

Glutathione peroxidase

Superoxide dismutase (correct)

Catalase

Glucose-6-phosphate dehydrogenase (G6PD) deficiency primarily affects which cellular mechanism?

Production of ATP in glycolysis

Detoxification of reactive oxygen species (correct)

Synthesis of fatty acids

Regulation of the TCA cycle

In the context of antioxidant mechanisms in red blood cells, what is the role of glutathione peroxidase?

It converts hydrogen peroxide into water and oxygen. Signup and view all the answers

Which of the following statements regarding reactive oxygen species (ROS) is correct?

ROS can damage macromolecules in cells. Signup and view all the answers

What role does coenzyme Q (ubiquinone) play in the electron transport chain?

It receives electrons from complex I and II, transferring them to complex III. Signup and view all the answers

Which complex does not pump protons across the mitochondrial membrane?

Complex II Signup and view all the answers

Which of the following toxins inhibits the electron flow from complex IV to oxygen?

Cyanide Signup and view all the answers

What is the primary function of the H+ gradient generated during electron transport?

To provide energy for ATP synthase to produce ATP. Signup and view all the answers

Which of the following vitamins is NOT involved in the proper function of the electron transport chain?

Vitamin C Signup and view all the answers

What is the outcome of the absence of oxygen in the electron transport chain?

The entire electron transport system will stop. Signup and view all the answers

What type of enzymes are complexes I-IV in the electron transport chain classified as?

Oxidoreductases Signup and view all the answers

Which mineral is vital for the proper function of the electron transport chain?

Iron Signup and view all the answers

Which process, associated with oxidative phosphorylation, occurs after electron transport?

ATP synthesis via ATP synthase Signup and view all the answers

In what way does complex IV contribute to the electron transport chain?

It reduces oxygen to form water. Signup and view all the answers

Which enzyme is responsible for converting glucose to glucose-6-phosphate during glycolysis?

Hexokinase Signup and view all the answers

What is the primary function of phosphofructokinase 1 in glycolysis?

To phosphorylate fructose-6-phosphate to fructose-1,6-bisphosphate Signup and view all the answers

During glycolysis, the conversion of fructose-1,6-bisphosphate produces which two molecules?

Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate Signup and view all the answers

What happens to dihydroxyacetone phosphate (DHAP) in glycolysis?

It can be converted to glyceraldehyde-3-phosphate (GAP). Signup and view all the answers

Which phase of glycolysis is characterized by the generation of ATP and NADH?

Payoff phase Signup and view all the answers

Which organ primarily relies on anaerobic glycolysis for energy due to a lack of mitochondria?

Red blood cells Signup and view all the answers

What is true about the reaction catalyzed by hexokinase in glycolysis?

It uses one ATP to convert glucose to glucose-6-phosphate. Signup and view all the answers

Which substance is generated as a final product in anaerobic glycolysis?

Lactate Signup and view all the answers

Which statement is most accurate regarding glycolysis in muscles during strenuous exercise?

Glycolysis primarily operates under anaerobic conditions. Signup and view all the answers

What is the role of the enzyme triose phosphate isomerase in glycolysis?

To convert dihydroxyacetone phosphate into glyceraldehyde-3-phosphate. Signup and view all the answers

Which molecule is known to inhibit citrate synthase during the TCA cycle?

Citrate Signup and view all the answers

What role does isocitrate dehydrogenase play in the TCA cycle?

It serves as a rate-limiting enzyme. Signup and view all the answers

How does ATP influence the TCA cycle?

It inhibits the cycle by signaling high energy levels. Signup and view all the answers

Which of the following components is a product of the TCA cycle used in gluconeogenesis?

Oxaloacetate Signup and view all the answers

What is the consequence of arsenic binding to lipoic acid in relation to the TCA cycle?

Inhibition of the TCA cycle. Signup and view all the answers

Which cofactor is involved in the dehydrogenase reactions within the TCA cycle?

Lipoic acid Signup and view all the answers

Which of the following is TRUE regarding the production of NADH and FADH2 in the TCA cycle?

Both NADH and FADH2 are generated through redox reactions. Signup and view all the answers

Which enzyme catalyzes the conversion of pyruvate to oxaloacetate, thus replenishing the TCA cycle?

Pyruvate carboxylase Signup and view all the answers

Which enzyme is responsible for converting 1,3-bisphosphoglycerate to 3-phosphoglycerate in glycolysis?

Phosphoglycerate kinase Signup and view all the answers

What is the primary function of lactate dehydrogenase during anaerobic glycolysis?

To regenerate NAD+ from NADH Signup and view all the answers

Which hormones primarily regulate glycolysis by acting on hexokinase/glucokinase, PFK-1, and pyruvate kinase?

Insulin and glucagon Signup and view all the answers

In the irreversible reaction converting phosphoenolpyruvate to pyruvate, which molecule is produced alongside ATP?

Pi Signup and view all the answers

Which statement best describes the fate of pyruvate under anaerobic conditions?

It is converted to lactate, generating NAD+. Signup and view all the answers

Identify the steps of glycolysis that are reversible.

Reactions 6 to 9 Signup and view all the answers

What role does NAD+ play in glycolysis, especially under anaerobic conditions?

It is reduced to NADH during glycolysis. Signup and view all the answers

Which of the following reactions occurs first in the glycolytic pathway?

Glucose to glucose-6-phosphate Signup and view all the answers

What represents the overall reaction of glycolysis under aerobic conditions?

1 Glucose + 2 Pi + 2 ADP + 2 NAD+ → 2 Pyruvate + 2 H+ + 2 ATP + 2 NADH + 2 H2O Signup and view all the answers

What effect does insulin have on glycolysis?

It promotes the synthesis of glycolytic enzymes. Signup and view all the answers

Study Notes

Citric Acid Cycle (TCA/Krebs Cycle)

Occurs in mitochondria and oxidizes Acetyl CoA (2 carbons) to 2 CO2, maintaining a net input-output balance.
Produces NADH, FADH2, and GTP (ATP equivalent) as key energy carriers for the electron transport chain (ETC).
Net reaction: Acetyl CoA + 3 NAD+ + FAD + GDP + Pi → 2 CO2 + 3 NADH + FADH2 + GTP.
Contains four redox reactions generating high-energy molecules; regulated by energy levels in the cell.

Key Enzymes and Regulation

Citrate synthase catalyzes the first step (Acetyl CoA + Oxaloacetate → Citrate) and is inhibited by high citrate levels.
Isocitrate dehydrogenase is the rate-limiting enzyme, activated by ADP and Ca++, and crucial for TCA regulation.
Alpha-ketoglutarate dehydrogenase is inhibited by its own product, succinyl CoA, and NADH.
Arsenic poisoning affects TCA by inhibiting dehydrogenase enzymes.

Anabolic Functions of TCA Cycle

TCA intermediates are vital for synthesizing biomolecules:
- Citrate: Precursor for fatty acids and steroids.
- Alpha-ketoglutarate: Intermediate for amino acids.
- Succinyl CoA: Essential for heme synthesis.
- Oxaloacetate and malate: Precursor for gluconeogenesis.
Anaplerotic reactions replenish intermediates, with oxaloacetate derived from pyruvate via pyruvate carboxylase.

Electron Transport Chain (ETC) and Oxidative Phosphorylation

ETC is the final stage of oxidation, dependent on oxygen as the final electron acceptor to form water.
NADH and FADH2 from TCA transfer electrons through complexes in the inner mitochondrial membrane.
Proton (H+) pumping by complexes I, III, and IV creates a proton gradient to drive ATP synthesis via ATP synthase.
Complex II (succinate dehydrogenase) does not pump protons.
Vitamins (NAD+, FAD, FMN) and minerals (iron, copper) are essential for ETC function.

Complexes in the ETC

Complex I: NADH dehydrogenase, pumps H+ while reducing Coenzyme Q.
Complex II: Succinate dehydrogenase, utilizes FADH2 without H+ pumping.
Coenzyme Q transfers electrons to complex III.
Complex III: Cytochrome b-c1, receives electrons from Coenzyme Q and pumps H+.
Complex IV: Cytochrome oxidase transfers electrons to O2, producing H2O and pumping H+.

Glycolysis Overview

Stage I: Investment phase consumes 2 ATP; hexokinase/glucokinase phosphorylates glucose.
Stage II: Payoff phase generates ATP and NADH, converting glucose to pyruvate or lactate.
Anaerobic conditions lead to lactate production via lactate dehydrogenase, regenerating NAD+.

Regulation of Glycolysis

Major regulatory enzymes: hexokinase/glucokinase, phosphofructokinase (PFK-1), and pyruvate kinase.
Insulin promotes glycolysis, while glucagon inhibits it to maintain blood glucose levels.

Non-Oxidative Reactions of Pentose Phosphate Pathway

Converts ribulose-5-phosphate to ribose-5-phosphate (for nucleotide synthesis) or to glycolytic intermediates.

NADPH Functions

Crucial for reductive biosynthesis, antioxidant defense, and nitric oxide synthesis, particularly in fatty acid biosynthesis.

Reactive Oxygen Species (ROS) and Cellular Damage

ROS are highly reactive; can damage lipids, proteins, and nucleic acids.
Superoxide dismutase (SOD) and catalase are key enzymes in detoxifying superoxide and H2O2.

G6PD Deficiency

An X-linked recessive disease causing hemolytic anemia due to inadequate NADPH production.
Reduced NADPH levels impair antioxidant mechanisms in red blood cells, leading to oxidative damage.

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Description

Test your knowledge of the Citric Acid Cycle, also known as the TCA or Krebs cycle. This quiz covers the oxidation of Acetyl CoA, redox reactions, and the production of key electron carriers like NADH and FADH2. Perfect for students studying biochemistry and genetics.