Carbohydrate Metabolism Overview
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Questions and Answers

What substance can change into 5, 4, 7, 3 carbon sugars?

Glucose

Only 5 molecules of glucose can be resynthesized for every 6 molecules of glucose.

True

What pathway does H can enter to form ATP?

Oxidative phosphorylation pathway

Which molecule does H combine with to form NADPH?

<p>NADP+</p> Signup and view all the answers

When glucose is not immediately required for energy, what is it stored as?

<p>Glycogen or fat</p> Signup and view all the answers

What hormone is important in the regulation of gluconeogenesis?

<p>Cortisol</p> Signup and view all the answers

ATP promotes the activity of phosphofructokinase.

<p>False</p> Signup and view all the answers

What is produced when there is a buildup of pyruvic acid and H atoms under anaerobic conditions?

<p>Lactic acid</p> Signup and view all the answers

What happens to lactic acid when oxygen becomes available again?

<p>Converted back to pyruvic acid</p> Signup and view all the answers

What is the normal blood glucose concentration of a person who has fasted for 3-4 hours?

<p>90 mg/dl</p> Signup and view all the answers

Which hormone increases blood glucose levels?

<p>Glucagon</p> Signup and view all the answers

What is the central role of glucose in carbohydrate metabolism?

<p>Glucose is the final common pathway for transport of almost all carbohydrates to the tissue cells.</p> Signup and view all the answers

What are the final products of carbohydrate digestion?

<p>Glucose, fructose, and galactose.</p> Signup and view all the answers

Fructose and galactose can be used directly by cells for energy.

<p>False</p> Signup and view all the answers

What is glycogenesis?

<p>The formation of glucose from glucose-6-phosphate.</p> Signup and view all the answers

What happens during glycolysis?

<p>Glucose is split to form 2 molecules of pyruvic acid.</p> Signup and view all the answers

Which of the following statements is true about the Krebs cycle?

<p>It releases CO2.</p> Signup and view all the answers

Glycogenolysis breaks down glycogen to form glucose.

<p>True</p> Signup and view all the answers

What is oxidative phosphorylation?

<p>The process that forms ATP by oxidation of hydrogen ions released in earlier glycolysis and Krebs cycle stages.</p> Signup and view all the answers

The oxidation of hydrogen atoms during metabolism primarily occurs in the __________.

<p>mitochondria</p> Signup and view all the answers

What role does insulin play in glucose transport?

<p>Insulin increases during the facilitated diffusion of glucose.</p> Signup and view all the answers

What is the total net gain of ATP from one molecule of glucose metabolism?

<p>38 ATP</p> Signup and view all the answers

Study Notes

Carbohydrate Metabolism Overview

  • Central to energy production in cells through oxidation of carbohydrates, fats, and proteins.
  • Free energy from the complete oxidation of 1 mole of glucose: 686,000 calories.
  • ATP serves as the energy currency of the body, continuously converted from ADP via energy from food oxidation.

Formation and Storage of Glycogen

  • Glucose enters cells, phosphorylated by enzymes like glucokinase (in the liver) and hexokinase (in other cells) to capture glucose inside.
  • Phosphorylation is irreversible except in liver, renal, and intestinal cells due to glucose phosphatase.
  • Glycogenesis: conversion of glucose-6-phosphate to glucose-1-phosphate, which is polymerized to form glycogen for storage in liver and muscle.
  • Glycogenolysis: breakdown of glycogen to release glucose while phosphorylated by the enzyme phosphorylase.

Hormonal Regulation

  • Glucagon, secreted by alpha cells of the pancreas, stimulates glycogenolysis when blood glucose is low.
  • Epinephrine increases glucose availability during sympathetic activation by stimulating glycogen breakdown in liver and muscles.

Metabolic Pathways

  • Glycolysis: Splitting glucose into 2 pyruvic acid molecules through a series of enzyme-catalyzed reactions, yielding a net gain of 2 ATP.
  • Conversion to Acetyl-CoA: Pyruvic acid is converted to Acetyl-CoA, releasing CO2 and producing no ATP.
  • Krebs Cycle: Acetyl-CoA enters the cycle, resulting in the degradation of acetyl into CO2 and H+; produces 2 ATP per molecule of glucose metabolized.
  • Oxidative Phosphorylation: Majority of ATP (approximately 90%) is synthesized here from H+ released in earlier steps through electron transport and chemiosmotic mechanisms.

Pentose Pathway

  • Operates as an alternative pathway for glucose oxidation primarily in liver and fat cells, crucial when Krebs cycle enzymes are deficient.
  • Converts glucose into 5-carbon sugars, facilitating the resynthesis of glucose and fat synthesis via NADPH production.

Control of Glycolysis

  • Regulated by the concentrations of ATP and ADP; high ATP inhibits the enzyme phosphofructokinase, slowing glycolysis when energy is abundant.
  • This mechanism ensures the energy needs of cells dictate the rate of carbohydrate oxidation.

Glucose Storage

  • Excess glucose not needed immediately is stored as glycogen in cells, providing energy for 12-24 hours.
  • Surplus glucose beyond storage capacity is converted into fat, stored in adipose tissues for long-term energy needs.### Glycolysis Regulation
  • Excess ATP slows or stops glycolysis, halting carbohydrate metabolism.
  • Increased ADP concentration from ATP usage boosts phosphofructokinase activity, initiating glycolysis.
  • Citrate, a product of the citric acid cycle, inhibits phosphofructokinase and glycolytic processes.

Anaerobic Metabolism

  • Oxygen deficiency halts oxidative phosphorylation, but glycolysis can still occur.
  • Glycolysis converts glucose to pyruvic acid without oxygen, albeit inefficiently, providing crucial energy.
  • Lactic acid is produced under anaerobic conditions when pyruvic acid and hydrogen ions accumulate.

Lactic Acid Formation and Effects

  • Excess pyruvic acid and hydrogen ions slow glycolysis; their reaction forms lactic acid.
  • Lactic acid diffuses to less active cells, allowing continued glycolysis in active ones.
  • Upon oxygen reintroduction, lactic acid converts back to pyruvic acid and contributes to ATP production.

Utilization of Lactic Acid

  • The heart can metabolize lactic acid into pyruvic acid for energy during heavy exercise.
  • Muscle activity produces lactic acid, which is used as an additional energy source by the heart.

Gluconeogenesis

  • Gluconeogenesis converts amino acids and glycerol into glucose when carbohydrate stores are low, especially during fasting.
  • Ensures stable blood glucose levels, critical for brain energy needs, provided largely by the liver.
  • The liver can synthesize glucose from lactate and amino acids, with 25% of liver glucose production derived from gluconeogenesis.

Amino Acid Conversion to Glucose

  • Different amino acids undergo distinct chemical processes to convert to glucose, e.g., alanine through deamination to pyruvic acid.
  • More complex amino acids can be converted to simple sugars, entering the phosphogluconate pathway to form glucose.

Regulation of Gluconeogenesis

  • Stimulated by low carbohydrate availability and decreased blood sugar levels.
  • Diminished carbohydrates enable conversion of amino acids and glycerol into carbohydrates, regulated by cortisol.

Hormonal Regulation

  • Low carbohydrate availability triggers increased secretion of adrenocorticotropic hormone (ACTH) from the adenohypophysis.
  • ACTH stimulates cortisol release from the adrenal cortex, mobilizing proteins for amino acid availability.
  • Cortisol promotes gluconeogenesis by providing substrates for glucose conversion in the liver.

Blood Glucose Levels

  • Normal fasting blood glucose is approximately 90 mg/dl. After high carbohydrate meals, levels can exceed 140 mg/dl.
  • Regulation of blood glucose involves insulin (lowers levels) and glucagon (raises levels), managed by pancreatic hormones.

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Description

This quiz covers key aspects of carbohydrate metabolism, including the formation and storage of glycogen, and an in-depth comparison of metabolic pathways like glycolysis and the Krebs cycle. Learn about the regulatory mechanisms that control these processes, essential for understanding energy production in the body.

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