respiration

• Examples of microorganisms that undergo anaerobic respiration:

  • Yeast (Saccharomyces cerevisiae) (facultative anaerobe)
  • Clostridium perfringens (obligate anaerobe)
• Examples of animal tissues that may undergo anaerobic respiration:

  • Muscle
• In the absence of oxygen, only glycolysis will occur because the link reaction and the Krebs cycle cannot occur due to the reduced NAD not being reoxidised
• Number of ATP molecules produced by anaerobic respiration: Gross 4, Net gain of 2 (2 used up to phosphorylate glucose)
• Anaerobic respiration allows the reoxidation of NAD to occur in the absence of oxygen after glycolysis, which then allows glycolysis to begin again
• In animal cells, pyruvate becomes reduced and accepts the hydrogen from reduced NAD forming lactate. In yeast and higher plants, ethanal becomes reduced and accepts the hydrogen from reduced NAD to form ethanol
• During vigorous exercise, when the human body cannot get sufficient oxygen to the muscle cells, they can only produce ATP by glycolysis, converting pyruvate into lactate. Net gain of ATP = 4
• Lactate pathway is most likely to occur in skeletal muscle cells during vigorous exercise when oxygen supply is insufficient. Lactate can build up in muscle cells, diffuse into the blood, causing symptoms like muscle cramping, disorientation, and nausea
• Cells most likely to use the lactate pathway: Skeletal muscle cells

  How is lactate transported around the body: Dissolves in the plasma and is carried around the body

  Symptoms due to lactic acid build up: Muscle cramping, disorientation, nausea

  Cells requiring oxygen for the removal of lactate: Hepatocytes (liver cells)

  What is the oxygen debt: Extra oxygen taken in through heavy breathing to introduce oxygen to the hepatocytes which can then metabolise lactate
• Respiratory substrate: A molecule that can be oxidised through respiration to fuel the synthesis of ATP

  Roles of lipids in living organisms:

  • Energy storage
  • Thermal insulation under the skin
  • Protection of vital organs

  Roles of proteins in living organisms:

  • Globular proteins: enzymes, hormones, antibodies, carrier proteins
  • Fibrous proteins: keratin, collagen
• When lipids are used as a respiratory substrate, they must be hydrolysed, producing glycerol and fatty acid chains that can enter glycolysis and the Krebs cycle, respectively
• Proteins are rarely used as a respiratory substrate and are usually used after reserves of carbohydrates and lipids have been used up. Proteins are hydrolysed into amino acids, and in the liver, the amine group is removed through deamination, forming keto acids that can enter glycolysis or the Krebs cycle
• Net gain of ATP for one molecule of palmitic acid, oxidised via β-oxidation and Krebs cycle: 115 ATP
• Respiration is a catabolic process involving a series of enzyme-catalysed reactions in cells
• Energy-rich substrates like glucose and fatty acids are hydrolysed to release energy
• Some energy is trapped as chemical energy in ATP and some is released as heat energy
• During respiration, high energy C-C, C-H and C-OH bonds are broken by enzymes in small steps to produce ATP
• Aerobic respiration releases large quantities of ATP energy from glucose or another organic substrate in the presence of oxygen
• Carbon dioxide is produced in aerobic respiration
• Anaerobic respiration takes place in the absence of oxygen and produces lactate in animal cells and carbon dioxide and ethanol in yeast cells
• ATP stands for Adenosine triphosphate
• ATP is a nucleotide found in all living organisms
• ATP is not an energy store but an energy source
• ATP is involved in energy changes by carrying the energy to where it is needed and releasing the energy when ATP is broken down
• Role of ATP
• ATP is required for protein synthesis, active transport, secretion/bulk transport/exocytosis, nerve transmission, muscle contraction, and DNA replication
• Formation of ATP
• ATP Synthase combines ADP and Pi in a condensation reaction to form ATP
• Hydrolysis of ATP by ATPase releases a small packet of energy and forms ADP and Pi
• Redox reactions
• During respiration, hydrogen atoms are removed from intermediate compounds and split into protons and electrons
• Oxidation is the loss of electrons/hydrogen, while reduction is the gain of electrons/hydrogen
• NAD+ is reduced to form reduced NAD (NADH/H+) and FAD is reduced to form reduced FAD (FADH2)
• Glycolysis
• Glycolysis is the initial biochemical pathway in both aerobic and anaerobic respiration
• Glucose is phosphorylated to form hexose phosphate, which splits into two triose phosphate molecules
• Each triose phosphate molecule is oxidised to pyruvate, resulting in the production of 2 ATP through substrate level phosphorylation
• Overall in glycolysis, 2 reduced NAD and 2 pyruvate are produced, along with a net gain of 2 ATP molecules
• Link Reaction
• Pyruvate diffuses into the mitochondrial matrix where the link reaction occurs