Respiration: An Overview (Edexcel A (SNAB) A Level Biology)

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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

C6H1206 + 6 O2 →  6 CO2 + 6 H20 + 2870kJ

  • 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

Mitochondria Structure

The structure of a mitochondrion

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Marlene

Author: Marlene

Expertise: Biology

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.