CELLULAR RESPIRATION

Cards (80)

  • Cellular respiration
    1. Glycolysis
    2. Krebs Cycle
    3. Electron Transport Chain
  • Cellular respiration
    • Vital to all living organisms
    • Purpose is to transfer chemical energy stored in glucose (C6H12O6) into ATP which is used to power cellular reactions
  • Why use ATP to provide energy for living organisms
    • Energy can be easily released in a single step: ATP → ADP + Pi + Energy
    • ATP has a fast turn over rate (it only takes a few seconds to covert ATP to ADP and then back from ADP to ATP)
  • Why not just use glucose
    • Release of energy from glucose occurs via a complex multistep pathway which is much slower
    • Energy in glucose is high (3000kJ) compared to ATP (30kJ)
  • Types of cellular respiration
    • Aerobic Cellular Respiration
    • Anaerobic Fermentation
  • Aerobic Cellular Respiration
    • Requires oxygen
    • Produces 30-32 ATP molecules per one glucose molecule
  • Anaerobic Fermentation
    • Does not require oxygen
    • Produces 2 ATP molecules per one glucose molecule
    • Produces harmful by-products (lactic acid or ethanol)
  • Aerobic cellular respiration
    1. Glycolysis
    2. Krebs Cycle
    3. Electron Transport Chain
  • Mitochondria
    • Crucial to aerobic cellular respiration as they are the site at which Krebs Cycle and Electron Transport Chain occur
    • Complex organelles made up of many different structures
  • Mitochondrial structures
    • Inner and outer membrane
    • Mitochondrial matrix
    • Cristae
    • Intermembrane Space
  • Glycolysis
    1. Occurs in Cytosol of cells
    2. Involves the breakdown of 6-carbon glucose into two 3-carbon pyruvate molecules via a sequence of 10 enzyme-regulated reactions
    3. Results in net production of 2 ATP molecules
  • As glucose is broken down into pyruvate
    Energy is released
  • The Link Reaction
    Pyruvate moves from cytosol to matrix of mitochondria and combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl-CoA)
  • The Krebs Cycle (also known as the Citric Acid Cycle)
    1. Takes place in mitochondrial matrix
    2. Consists of 8 reactions that break down acetyl CoA
    3. Breaking down of acetyl CoA results in the release of protons and high-energy electrons which are loaded onto NAD+ and FAD to generate high-energy coenzymes NADH and FADH2
    4. Produces 2 ATP
  • During formation of acetyl-CoA from pyruvate – 1 CO2 molecule is produced
  • During one full turn of the Krebs Cycle – 2 CO2 molecules are produced (totaling 3 CO2 molecules)
  • In ONE turn of the Krebs Cycle, acetyl-CoA is metabolised into: 2 CO2 molecules, 1 ATP molecule, 3 NADH molecules, 1 FADH2 molecule
  • High Energy
    NADH, FADH2 and ATP
  • Low Energy
    NAD+, FAD and ADP
  • The Electron Transport Chain (ETC)
    1. Takes place on inner membrane of mitochondria (Cristae)
    2. Place where majority of ATP is produced
    3. Converts high-energy coenzymes NADH and FADH2 back to NAD+ and FAD forms which are then recycled for continued use in glycolysis and the Krebs cycle
  • 26 or 28 ATP produced in the Electron Transport Chain
  • Steps involved in making ATP at Electron Transport Chain
    1. NADH and FADH unload protons (H+) and electrons at first and second protein of ETC
    2. Excited electrons power active transport of protons (H+) from mitochondrial matrix into narrow intermembrane space
    3. Concentration of protons (H+) increases
    4. To move down concentration gradient, protons (H+) need to move through protein channel (ATP synthase) – ADP + Pi → ATP
    5. Large amounts of ATP are made
    6. Unbound protons (H+) and electrons bind with oxygen to produce water
  • In total, for every glucose molecule metabolised, 30 – 32 ATP molecules are formed: 2 ATP (from glycolysis), 2 ATP (from Krebs Cycle), 26-28 ATP (from ETC)
  • Enzymes and coenzymes in cellular respiration
    • Enzymes, with the help of their coenzymes, catalyse the reactions of cellular respiration to allow them to proceed at a fast rate
    • Cells can breakdown and extract energy from glucose at a rate fast enough to sustain energy-dependent processes
    • Each enzyme is only capable of catalysing one specific reaction, so there is a wide range of enzymes involved in cellular respiration
  • Anaerobic fermentation
    1. Glycolysis to generate ATP
    2. Lactic Acid Fermentation (occurs in bacteria and animals)
    3. Alcoholic Fermentation (occurs in yeast and plants)
  • Lactic Acid Fermentation
    Occurs in skeletal muscle cells when supply of oxygen to cells cannot keep up with their energy demands
  • During strenuous exercise, lactic acid levels rise
  • Lactic acid dissociates – forming lactate and H+ ions which lowers the pH of muscle tissue causing pain and fatigue (can be toxic in high amounts)
  • Lactic acid is metabolised back into pyruvate when oxygen is present
  • Anaerobic fermentation in yeasts
    1. Glycolysis
    2. Pyruvate is converted to ethanol and carbon dioxide
  • Yeasts are used in bread making and in the production of alcoholic beverages (predominantly wine and beer)
  • Yeasts are unable to metabolise ethanol into any useful products
  • Ethanol diffuses out of cells
  • If concentration of ethanol rises within a confined area – it can become toxic
  • Temperature and pH
    They have a large effect on the rate at which cellular respiration occurs due to their effect on enzymes
  • Respiration rate and ATP production are greatest when temperature aligns to enzymes optimal temperature
  • Below optimal temperature, enzymes and substrates have less kinetic energy so there are fewer reaction-inducing collisions = lower rate of cellular respiration
  • When temperature rises above optimum, enzymes denature and respiration rate drops significantly due to loss of enzyme function
  • Above or below optimal pH, enzymes begin to denature and the rate of cellular respiration slows
  • Glucose availability

    Increasing glucose availability increases the rate of cellular respiration until enzymes reach saturation point