Glycolysis and Glucose Transport

Jun 21, 2024

Review flashcards

Lecture on Glycolysis

Definition and Overview

  • Glycolysis: Metabolic pathway breaking down glucose into two molecules of pyruvate.
  • During glycolysis, energy is released and captured as ATP and NADH.
  • Glycolysis involves multiple steps and enzymes.
  • End products: ATP, NADH, and pyruvate.
  • Takes place in the cytosol of cells.

Types of Glycolysis

  1. Aerobic Glycolysis: Occurs when oxygen and mitochondria are available.
    • End product, pyruvate, enters the Krebs cycle.
    • Large amount of energy released.
  2. Anaerobic Glycolysis: Occurs when oxygen or mitochondria are unavailable.
    • Pyruvate is converted into lactic acid.
    • Less energy is released compared to aerobic glycolysis.

Cellular Occurrence

  • Glycolysis can occur in all cells and tissues.
  • Cells without mitochondria (e.g., red blood cells) perform anaerobic glycolysis.

Glycolysis Process

  1. First step: Glucose uptake from extracellular environment and blood into the cell.
    • Transported into the cell via transport mechanisms.

Glucose Transport Mechanisms

  1. Facilitated Diffusion: High to low concentration diffusion via glucose transporters.
    • Glucose transporters (GLUT) aid in cellular uptake.
    • Different GLUT types (e.g., GLUT1, GLUT2, GLUT4) for various tissues/functions.

Types of Glucose Transporters

  1. GLUT1 & GLUT3: Present in most tissues, especially CNS and RBCs. Responsible for basal glucose uptake.
    • High affinity transporters.
  2. GLUT2: Allows bidirectional movement of glucose. Found in liver, kidney, and beta cells of the pancreas.
    • Relevant in glucose storage and release mechanisms. Important for gluconeogenesis and glycogenolysis.
  3. GLUT4: Insulin-dependent transporter in skeletal muscles and adipose tissue.
    • Insulin binds to receptors, signaling the translocation of GLUT4 to cell membrane, increasing glucose uptake.
  4. GLUT5: Fructose transporter rather than glucose. Found in jejunum cells and testicular cells.
  5. GLUT7: Located in the endoplasmic reticulum, involved in gluconeogenesis.

Specific Functions and Importance

  • Liver Function: Acts as a glucose bank—stores glucose as glycogen and releases it during fasting.
  • Pancreas Beta Cells: Use GLUT2 to sense blood glucose levels and regulate insulin secretion.
  • RBCs: Perform anaerobic glycolysis due to the absence of mitochondria.
  • Skeletal Muscles and Adipose Tissue: Depend on insulin for glucose uptake via GLUT4.
  • Gluconeogenesis: Formation of glucose from non-carbohydrate sources (e.g., fatty acids, amino acids).

Key Concepts

  • Facilitated Diffusion: Glucose moves from high to low concentration via transporters without using energy.
  • Insulin Action: Facilitates glucose uptake in muscle and adipose tissues by promoting GLUT4 expression.
  • Glycogenesis and Glycogenolysis: Storage and breakdown of glycogen within the liver.
  • Types of Transporters: Different transporters are specialized for various functions and tissue requirements.

Summary

  • Glycolysis is a fundamental metabolic process occurring in all cells, playing a crucial role in energy production.
  • The transport of glucose into cells involves specific mechanisms and transporter proteins, crucial for homeostasis and energy balance.

Keywords to Remember: Glycolysis, Aerobic, Anaerobic, Pyruvate, ATP, NADH, Glucose Transporters (GLUT), Facilitated Diffusion, Insulin, Liver, RBCs, Skeletal Muscles, Adipose Tissue, Gluconeogenesis.