Lecture 3

• Where does glycolysis occur?


  Cytosol of cytoplasm
• How many enzyme-catalysed reactions make up glycolysis?


  Ten
• How does glucose change in glycolysis?


  • Starts as glucose
  • Fructose 1,6-bisphosphate
  • 2 molecules of glyceraldehyde 3-phosphate
  • 2 molecules of pyruvate (3C)
• Extracting electrons from food is energetically...


  Favourable- energy released can be coupled to ATP production
• What type of reaction is glycolysis?

  Oxidation
• How much ATP is produced from glycolysis?


  Net production of 2 ATP per glucose molecule

  (Make 4 at end but used 2 at start)
• How much NADH is made per glucose molecule in glycolysis?


  2 NADH (4 electrons released in total & each NAD+ accepts 2 electrons)
• What happens during anaerobic conditions (fermentation)?


  Can't pass electrons onto oxygen so electrons in NADH passed onto pyruvate. Reduces 2 pyruvate to 2 lactate molecules. NAD+ regenerated.
• Where does pyruvate go after glycolysis?


  Mitochondrial matrix
• When is lactate fermentation important?


  Intense exercise as muscles quickly run out of oxygen. Must rely on glycolysis & fermentation to lactate to produce ATP. Lactic acid builds up in muscles causing pain.
• Alcoholic fermentation:


  • Yeast & other microorganisms carry this out
  • Electrons passed onto ethanol
  • Pyruvate decarboxylated (loses a C as CO2)

  2 C product from that accepts electrons from NADH to be reduced into ethanol

  (Can make alcoholic drinks)
• Why is glycolysis inefficient?

  Converts less than 5% of energy available

  (less energy released than conserved)
• What happens during aerobic respiration?


  • Pyruvate enters mitochondrial matrix & forms acetyl CoA (with CoA)
  • Acetyl CoA enters citric acid cycle
  • Carbons from acetyl group fully oxidised to CO2 (leaves cell and is exhaled)
  • Electrons passed onto NAD+ to make NADH
• Where does NADH pass its electrons after the citric acid cycle?


  Electron Transport Chain (part of oxidative phosphorylation)

  Happens in inner mitochondrial membrane

  Proteins pass electrons on via series of intermediates onto oxygen to make water (energetically favourable reaction)- drives forward pumping of H+ from matrix into intermembrane space (creates gradient)

  H+ flow down gradient back into matrix (energy from this used to make ATP)

  
• What does ATP synthase do?


  Allows H+ to flow down conc. gradient into matrix

  Energy released used to drive ATP synthesis from ADP & Pi
• How much ATP does each NADH produce in oxidative phosphorylation?


  2.5 ATP molecules
• How much ATP is made in the citric acid cycle?


  2 per glucose (2 turns of cycle)
• How much ATP is made during oxidative phosphorylation?


  26 per glucose
• How much ATP is made in total per glucose molecule?


  30 (aerobic)
• Why are metabolic pathways regulated?

  To prevent wasteful cycles of anabolic & catabolic pathways

  (Key steps in pathways catalysed by regulatory enzymes)
• How are catabolic & anabolic pathways often controlled?


  Reciprocally (When 1 switched on, other switched off)

  Catabolic activated when energy supply in cell is low

  Anabolic activated when energy supply in cell is high
• What does glycogen synthase do?

  Regulatory enzyme that controls glucose conversion into glycogen

  Activated by glucose-6-phosphate (signal for high glucose levels in cell) allosteric activator
• What does glycogen phosphorylase do?

  Regulatory enzyme that controls glycogen breakdown into glucose

  (activated by AMP allosteric activator adenosine monophosphate (signal for low energy in cell))

  Inhibited by ATP (signal for high energy in cell) & glucose-6-phosphate