Metabolism of Pyruvate and Krebs Cycle

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Questions and Answers

Under aerobic conditions, what is the primary product of pyruvate conversion?

Glycogen

Ethanol

Acetyl-CoA (correct)

Lactate

Which of the following is an end product of alcoholic fermentation?

Lactate

Ethanol (correct)

Carbon dioxide

Pyruvate

What type of fermentation occurs when pyruvate is converted to lactate?

Acidic fermentation (correct)

Lactic acid fermentation

Aerobic fermentation

Alcoholic fermentation

Which of the following statements about pyruvate metabolism is correct?

Lactate is produced in acidic fermentation. (D) Signup and view all the answers

What role do glucose transporters (GLUTs) play in carbohydrate metabolism?

They transport absorbed glucose into body cells. (D) Signup and view all the answers

What is the main purpose of the catabolic reactions described in the content?

To completely oxidize substances for energy (B) Signup and view all the answers

Which reaction in the Krebs cycle produces ATP through substrate-level phosphorylation?

Succinyl CoA to succinate (D) Signup and view all the answers

How much ATP is produced from the complete oxidation of two acetyl CoA during two cycles of the Krebs cycle?

24 ATP (C) Signup and view all the answers

What is the total ATP yield from glucose oxidation, considering both glycolysis and the Krebs cycle?

36 or 38 (C) Signup and view all the answers

Which shuttle is responsible for transferring electrons from cytosolic NADH to complex II in the electron transport chain?

Glycerol Phosphate Shuttle (D) Signup and view all the answers

What is the primary function of the malate-aspartate shuttle?

To regenerate NADH in the mitochondria (A) Signup and view all the answers

What type of energy conversion occurs in the Krebs cycle?

Oxidation of substrates to release energy (A) Signup and view all the answers

Which component's oxidation leads to the generation of NADH in the Krebs cycle?

α-ketoglutarate (A) Signup and view all the answers

What is the primary role of the Krebs cycle in cellular respiration?

To facilitate the transfer of reducing equivalents to the respiratory chain (A) Signup and view all the answers

Which of the following correctly describes the type of phosphorylation that occurs during the Krebs cycle?

Both substrate-level and oxidative phosphorylation occur (C) Signup and view all the answers

What is the product formed from carbohydrates, lipids, and proteins that enters the Krebs cycle?

Acetyl CoA (B) Signup and view all the answers

How many ATP molecules are produced directly from one molecule of glucose during glycolysis and the Krebs cycle combined?

4 ATP (B) Signup and view all the answers

What distinguishes the amphibolic nature of the Krebs cycle?

It is involved in both oxidation and synthetic processes (A) Signup and view all the answers

Which molecule serves as an important high-energy substrate in substrate-level phosphorylation during the Krebs cycle?

GTP (A) Signup and view all the answers

Why is the location of enzymes in the mitochondria significant for ATP production in the Krebs cycle?

It facilitates the transfer of reducing equivalents to the ETC (B) Signup and view all the answers

What is the significance of NADH and FADH2 generated during the Krebs cycle?

They transfer electrons to the respiratory chain for ATP synthesis (A) Signup and view all the answers

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

Hexokinase (A) Signup and view all the answers

Which of the following enzymes is absent from muscle and adipose tissue?

Glucose-6-phosphatase (C) Signup and view all the answers

What is the primary role of the Cori cycle?

To link gluconeogenesis with anaerobic glycolysis (A) Signup and view all the answers

Which of the following best describes glycogen?

A branching glucose polymer with (1→4) and (1→6) glycosidic bonds (A) Signup and view all the answers

Which enzyme is primarily responsible for the synthesis of glycogen from glucose?

Glycogenin (C) Signup and view all the answers

What process describes the breakdown of glycogen back into glucose?

Glycogenolysis (A) Signup and view all the answers

Which metabolic pathway is involved in synthesizing glucose from non-carbohydrate precursors?

Gluconeogenesis (B) Signup and view all the answers

What is a consequence of the Cori cycle during intense exercise?

Recycling of lactate into glucose (C) Signup and view all the answers

What process occurs when glucose is synthesized in the liver and kidneys from non-carbohydrate precursors?

Gluconeogenesis (C) Signup and view all the answers

Which metabolic process is primarily responsible for lowering blood glucose levels?

Glycogenesis (B) Signup and view all the answers

When blood glucose concentration exceeds the kidney threshold, what occurs?

Glucose appears in urine (B) Signup and view all the answers

Which of the following processes is stimulated during fasting to increase blood glucose levels?

Glycogenolysis (D) Signup and view all the answers

What happens to lipids stored in adipose tissues in humans?

They cannot be converted into glucose (D) Signup and view all the answers

In the fed state, which process is NOT stimulated to increase glucose utilization?

Glycogenolysis (B) Signup and view all the answers

What is the primary effect of glycogen storage in the liver and muscles?

Decrease glucose levels in the bloodstream (A) Signup and view all the answers

Which hormone-related response occurs when blood glucose levels drop?

Stimulation of gluconeogenesis (B) Signup and view all the answers

Study Notes

Pyruvate Metabolism

Acetyl-CoA is the primary product of pyruvate conversion under aerobic conditions.
Ethanol is an end product of alcoholic fermentation.
Lactic acid fermentation occurs when pyruvate is converted to lactate.
Pyruvate is a key intermediate in carbohydrate metabolism, linking glycolysis to the Krebs cycle.
Glucose transporters (GLUTs) facilitate the movement of glucose across cell membranes, allowing cells to take up glucose for energy production.

Krebs Cycle & Energy Production

Catabolic reactions break down complex molecules into simpler ones, releasing energy.
The succinyl CoA synthetase reaction in the Krebs cycle produces ATP through substrate-level phosphorylation.
Two cycles of the Krebs cycle yield 24 ATP molecules from the complete oxidation of two acetyl CoA.
The complete oxidation of glucose yields a total of 38 ATP molecules, considering both glycolysis and the Krebs cycle.
The glycerol 3-phosphate shuttle transfers electrons from cytosolic NADH to complex II in the electron transport chain.
The malate-aspartate shuttle is responsible for transferring electrons from cytosolic NADH to complex I in the electron transport chain, increasing ATP yield.
The Krebs cycle mainly involves energy conversion from chemical bonds to electron carriers, generating reducing power.
The Krebs cycle's oxidation of isocitrate, α-ketoglutarate, and malate leads to the generation of NADH.
The Krebs cycle plays a central role in cellular respiration by oxidizing acetyl CoA and producing ATP, electron carriers, and precursor metabolites for biosynthesis.
The Krebs cycle involves substrate-level phosphorylation, where ATP is directly produced from the breakdown of a high-energy substrate.
Acetyl CoA, derived from carbohydrates, lipids, and proteins, enters the Krebs cycle.
Glycolysis and the Krebs cycle combined directly produce 4 ATP molecules from one molecule of glucose.
The Krebs cycle is amphibolic because it participates in both catabolism (breakdown) and anabolism (synthesis) by providing intermediates for other metabolic pathways.
Succinyl CoA acts as an important high-energy substrate in substrate-level phosphorylation during the Krebs cycle.
Enzymes are located in the mitochondria, enabling efficient ATP production in the Krebs cycle due to the close proximity of electron transport chain components.
NADH and FADH2, generated during the Krebs cycle, carry electrons to the electron transport chain for oxidative phosphorylation.

Glycolysis & Glycogen Metabolism

Hexokinase converts glucose into glucose-6-phosphate during glycolysis.
Glycogen phosphorylase is absent from muscle and adipose tissue.
The Cori cycle involves lactate produced in muscles being transported to the liver, where it's converted back to glucose and released into the bloodstream.
Glycogen is a branched polymer of glucose that serves as a storage form of glucose in animals.
Glycogen synthase is primarily responsible for the synthesis of glycogen from glucose.
Glycogenolysis is the process of breaking down glycogen back into glucose.
Gluconeogenesis is the metabolic pathway involved in synthesizing glucose from non-carbohydrate precursors.
During intense exercise, muscles utilize glucose faster than they can receive it from the bloodstream, leading to lactate production and its conversion to glucose in the liver through the Cori cycle, recycling glucose for muscle use.
Gluconeogenesis occurs when the liver and kidneys synthesize glucose from non-carbohydrate precursors, like amino acids and glycerol.
Insulin is the primary hormone involved in lowering blood glucose levels.
When blood glucose concentration exceeds the kidney threshold, excess glucose is excreted in urine.
Gluconeogenesis is stimulated during fasting to increase blood glucose levels.
Lipids stored in adipose tissues are broken down into fatty acids and glycerol, which can be used for energy or converted to glucose.
In the fed state, glycogen synthesis is stimulated to store excess glucose.
Glycogen storage in the liver and muscles provides a readily available source of glucose for energy needs.
When blood glucose levels drop, glucagon is released, stimulating glycogenolysis and gluconeogenesis to increase blood glucose levels.

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Description

Explore the biochemical processes of aerobic and anaerobic metabolism of pyruvate, including its conversion to Acetyl-CoA and fermentation types. Learn how the Krebs cycle functions as the final common pathway for energy production from carbohydrates, lipids, and proteins, along with ATP generation mechanisms.