/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 29 The carboxylation of pyruvate by... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 16: Problem 29

The carboxylation of pyruvate by pyruvate carboxylase occurs at a very low rate unless acetyl-CoA, a positive allosteric modulator, is present, If you have just eaten a meal rich in fatty acids (triacylglycerols) but low in carbohydrates (glucose), how does this regulatory property shut down the oxidation of glucose to \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{3} \mathrm{O}\) but increase the oxidation of acetyl-CoA derived from fatty acids?

Short Answer

Expert verified
Acetyl-CoA from fatty acids activates gluconeogenesis and inhibits glycolysis, optimizing fatty acid oxidation over glucose oxidation.

Step by step solution

01

Understanding Pyruvate Carboxylase Activation

Pyruvate carboxylase is an enzyme that catalyzes the carboxylation of pyruvate to form oxaloacetate, a critical step in gluconeogenesis. This enzyme requires acetyl-CoA as a positive allosteric modulator to become active.
02

Effects of Fatty Acid-Rich Meal on Acetyl-CoA Production

When you consume a meal rich in fatty acids, these fats are broken down into acetyl-CoA through beta-oxidation. The increase in acetyl-CoA serves as a signal for pyruvate carboxylase activation.
03

Role of Acetyl-CoA in Gluconeogenesis vs Glycolysis

Acetyl-CoA helps activate pyruvate carboxylase, converting pyruvate to oxaloacetate, thus promoting gluconeogenesis. With acetyl-CoA available, there is less reliance on glucose, decreasing glycolysis and glucose oxidation.
04

Dual Effect: Shutting Down Glycolysis and Enhancing Fatty Acid Oxidation

As acetyl-CoA stimulates gluconeogenesis while inhibiting pyruvate dehydrogenase (the enzyme converting pyruvate to acetyl-CoA for tricarboxylic acid cycle), it effectively reduces glucose oxidation. At the same time, it boosts the oxidation of acetyl-CoA, primarily derived from fatty acids, enhancing energy production from fats.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Pyruvate Carboxylase
Pyruvate carboxylase is a crucial enzyme in the metabolic pathway. Its primary function is to convert pyruvate into oxaloacetate. This process is essential for gluconeogenesis, where the body generates glucose from non-carbohydrate sources.

This enzyme is unique because it requires acetyl-CoA to function efficiently. Without acetyl-CoA, pyruvate carboxylase operates at a minimal rate, making it an important control point in metabolism. This allows the body to regulate energy production based on different physiological needs.
Gluconeogenesis
Gluconeogenesis is the metabolic pathway through which glucose is synthesized from non-carbohydrate precursors. It is a vital process, especially during fasting or low-carbohydrate intake, ensuring a continuous supply of glucose when dietary intake is insufficient.

Pyruvate carboxylase plays a pivotal role in the initial steps of gluconeogenesis by forming oxaloacetate. Once oxaloacetate is produced, it enters a series of reactions that ultimately lead to glucose. This pathway is notably activated by high levels of acetyl-CoA, steering the body away from glucose consumption toward glucose production when it detects sufficient energy supply from fats.
Allosteric Modulation
Allosteric modulation refers to the regulation of an enzyme's activity through molecules binding at specific sites other than the active site. Acetyl-CoA acts as an allosteric modulator for pyruvate carboxylase. Instead of directly engaging in the reaction, it binds to the enzyme, altering its structure and increasing its catalytic activity.

This mechanism allows for nuanced metabolic control without needing changes in enzyme concentration. In the context of pyruvate carboxylase, acetyl-CoA's allosteric modulation ensures that gluconeogenesis can be rapidly activated in response to high acetyl-CoA levels from fatty acid metabolism.
Acetyl-CoA
Acetyl-CoA stands out as a central metabolic molecule, linking various biochemical pathways. It is produced from carbohydrates, fats, and possibly proteins, acting as a convergence point in metabolism.

When there is an abundance of acetyl-CoA, usually from fatty acid breakdown, pyruvate carboxylase activation occurs, guiding the cell to focus on gluconeogenesis. Simultaneously, acetyl-CoA inhibits pyruvate dehydrogenase, slowing glucose oxidation. This balance ensures that energy is derived from fatty acids, conserving glucose reserves.
Fatty Acid Metabolism
Fatty acid metabolism involves breaking down fatty acids to produce acetyl-CoA, which enters the Krebs cycle for energy production. This process, known as beta-oxidation, increases acetyl-CoA levels significantly.

A high-fat meal results in elevated acetyl-CoA, activating pyruvate carboxylase and enhancing gluconeogenesis. Thus, the body prioritizes fat over glucose, reducing the need for glucose oxidation. By upregulating fatty acid metabolism, the body efficiently utilizes dietary fats, storing glucose for circumstances where fats are less available.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Mammalian liver can carry out gluconeogenesis using oxaloacetate as the starting material (Chapter 14 ). Would the operation of the citric acid cycle be affected by extensive use of oxaloacetate for gluconeogenesis? Explain your answer.

Although oxygen does not participate directly in the citric acid cycle, the cycle operates only when \(\mathrm{O}_{2}\) is present. Why?

Write the net biochemical equation for the metabolism of a molecule of glucose by glycolysis and the citric acid cycle, including all cofactors.

Citrate is formed by the condensation of acetyl-CoA with oxaloacetate, catalyzed by citrate synthase: Oxaloacetate \(+\) acetyl-CoA \(+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons\) citrate \(+\mathrm{CoA}+\mathrm{H}^{+}\) In rat heart mitochondria at pH 7.0 and \(25^{\circ} \mathrm{C}\), the concentrations of reactants and products are: oxaloacetate, \(1 \mu\). CoA, \(1 \mu \mathrm{M} ;\) citrate, \(220 \mu \mathrm{M} ;\) and \(\mathrm{CoA}, 65 \mu \mathrm{M}\). The standard free-energy change for the citrate synthase reaction is \(-32.2 \mathrm{kJ} / \mathrm{mol} .\) What is the direction of metabolite flow through the citrate synthase reaction in rat heart cells? Explain.

The metabolic pathways of organic compounds have often been delineated by using a radioactively labeled substrate and following the fate of the label. (a) How can you determine whether glucose added to a suspension of isolated mitochondria is metabolized to \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O} ?\) (b) Suppose you add a brief pulse of \(\left[3-^{14} \mathrm{C}\right]\) pyruvate (labeled in the methyl position) to the mitochondria. After one turn of the citric acid cycle, what is the location of the \(^{14} \mathrm{C}\) in the oxaloacetate? Explain by tracing the \(^{14} \mathrm{C}\) label through the pathway. How many turns of the cycle are required to release all the \(\left[3^{-14} \mathrm{C}\right]\) pyruvate as \(\mathrm{CO}_{2} ?\)
See all solutions

Recommended explanations on Chemistry Textbooks

Kinetics

Read Explanation

Organic Chemistry

Read Explanation

Chemical Analysis

Read Explanation

Physical Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Making Measurements

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.