Lecture 04, 5

• What is another name for the Pentose Phosphate Pathway?

  Hexose monophosphate pathway
• What is the primary product generated by the Pentose Phosphate Pathway?

  NADPH
• Which organ does not have the Pentose Phosphate Pathway?

  Muscles
• What does the Pentose Phosphate Pathway mediate?

  Catabolism and synthesis of pentose sugars
• What are the two stages of the Pentose Phosphate Pathway?

  1. Oxidation/reduction to yield NADPH
  2. Interconversion of sugars
• What are the three steps of glycolysis in the Pentose Phosphate Pathway?

  1. Oxidation
  2. Hydrolysis
  3. Oxidation and decarboxylation
• How many NADPH are yielded in Stage 1 of the Pentose Phosphate Pathway?

  2 NADPH
• What is produced alongside ribulose-5-phosphate in Stage 1?

  CO2
• What enzyme is responsible for the first step of the Pentose Phosphate Pathway?

  Glucose-6-phosphate dehydrogenase
• What happens during the second step of Stage 1?

  Hydrolysis opens up the ring
• What is the result of the oxidative decarboxylation in Step 3?

  1 NADPH and CO2
• What are the biosynthetic roles of NADPH?

  • Fatty acids
  • Cholesterol
  • Nucleotides
  • Neurotransmitters
• What are the steps involved in the interconversion of sugars in Stage 2?

  1. Isomerisation to ribose-5-phosphate
  2. Epimerisation to xylulose-5-phosphate
• What is produced during the interconversion of sugars in Stage 2?

  2 hexoses and 1 triose
• What cofactor is used during the transfer of a two-carbon unit in Stage 2?

  Thiamine pyrophosphate
• How is a three-carbon unit transferred in Stage 2?

  Via formation of a Schiff base
• What is the net result of Stage 2 of the Pentose Phosphate Pathway?

  Conversion of 3 pentoses to 2 hexoses and 1 triose
• What combats oxidative stress in cells?

  Reduced glutathione
• What is the role of NADPH in red blood cells?

  Regenerate glutathione
• What is the primary energy source for red blood cells?

  Anaerobic glycolysis
• What happens to Fe2+ when oxidised by oxygen?

  It forms Fe3+ and superoxide
• What is methaemoglobin unable to do?

  Bind to O2
• What happens to methaemoglobin when water is added?

  It becomes irreversibly degraded
• How is NADPH generated in red blood cells?

  Only via the Pentose Phosphate Pathway
• What is the significance of glucose-6-phosphate dehydrogenase in the Pentose Phosphate Pathway?

  • First enzyme in the pathway
  • Deficiency leads to metabolic disorder
  • Gene located on the X chromosome
  • Significant under oxidative stress
  • Deficiency causes haemolytic anaemia
• What happens to excess amino acids from the diet?

  Converted to fat for storage
• When are muscle proteins broken down for energy?

  During fasting, starvation, endurance exercise
• Where does most deamination occur?

  Liver
• Which amino acids are deaminated in skeletal muscle?

  Leucine, isoleucine, valine
• What happens to carbon skeletons after deamination?

  • Fed into glycolysis
  • Enter the citric acid cycle
  • Used in gluconeogenesis
  • Used in fatty acid synthesis
• What is the fate of nitrogen during transamination?

  Amino group transferred to another amino acid
• What occurs during deamination?

  Amino group removed as ammonium ion
• What is formed as a result of deamination?

  Urea
• What is the role of α-ketoglutarate in transamination?

  It forms glutamate
• What cofactor do transferases use?

  Pyridoxal phosphate
• What enzyme is responsible for oxidative deamination of glutamate?

  Glutamate dehydrogenase
• Where does deamination of serine and threonine occur?

  Via a dehydration step
• How is nitrogen transported to the liver?

  As alanine or glutamine
• What is the glucose-alanine cycle?

  • Transports nitrogen to the liver
  • Involves conversion of pyruvate to alanine
  • Helps in gluconeogenesis
• What is the Urea Cycle?

  • First cyclic metabolic pathway elucidated
  • Takes place in mitochondria and cytosol
  • Combines nitrogen from aspartate and ammonium
  • Requires ATP for energy