Edexcel A (SNAB) A Level Biology:复习笔记7.2.1 Respiration: An Overview

Respiration: An Overview

  • Glucose is the main respiratory substrate used by cells
  • Aerobic respiration is the process of breaking down a respiratory substrate in order to produce ATP using oxygen
  • The equation for aerobic respiration:

glucose + oxygen →  carbon dioxide + water + energy

  • The energy that is released during the process is used to phosphorylate (add a phosphate) ADP to form ATP
  • The ATP provides energy for other biological processes in cells
  • The process of aerobic respiration using glucose can be split into four stages:
    • Glycolysis
    • The Link reaction
    • The Krebs cycle
    • Oxidative phosphorylation
  • Glycolysis occurs in the cytoplasm of the cell, while the other three stages all occur within different parts of the mitochondria
  • The reactions in each stage of respiration are controlled by enzymes found inside the cell
  • The enzyme that catalyses these reactions the slowest will determine the overall rate of aerobic respiration
  • Several coenzymes are required during respiration to transfer various molecules involved in the process
    • NAD and FAD are the coenzymes responsible for transferring hydrogen between molecules
    • Depending on whether they give or take hydrogen, they are able to reduce or oxidise a molecule
    • Coenzyme A is responsible for the transfer of acetate (also known as acetic acid) from one molecule to another
  • Although glucose is the main fuel for respiration, organisms can also break down other molecules (such as fatty acids or amino acids) to be respired

Structure of mitochondria

  • Mitochondria have two phospholipid membranes
  • The outer membrane is:
    • Smooth
    • Permeable to several small molecules
  • The inner membrane is:
    • Folded (cristae)
    • Less permeable
    • The site of the electron transport chain (used in oxidative phosphorylation)
    • Location of ATP synthase enzymes (used in oxidative phosphorylation)
  • The intermembrane space:
    • Has a low pH due to the high concentration of protons
    • The concentration gradient across the inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis
  • The matrix:
    • Is an aqueous solution within the inner membranes of the mitochondrion
    • Contains ribosomes, enzymes and circular mitochondrial DNA necessary for mitochondria to function

The structure of a mitochondrion