5.7.2

• glycolysis

  biochemical pathway that occurs in cytoplasm of all living organisms that respire, including many prokaryotes

  • the pathway involves a sequence of 10 reactions (only need to know 3), each catalysed by a different enzyme, some with the help of the coenzyme, NAD

  1. phosphorylation of glucose to hexose bisphosphate
  2. splitting each hexose bisphosphate into two triose phosphate molecules
  3. oxidation of triose phosphate to pyruvate

  A) phosphorylation

  B) oxidation

  
• NAD nicotinamide adenine dinucleotide

  coenzyme that accept hydrogen atoms removed during oxidation when enzyme catalyse oxidation + reductions reactions

  • non-protein molecule that helps dehydrogenase enzymes to carry out oxidation • synthesised in living cells from nicotinamide (Vitamin B3), 5-carbon sugar ritoe, adenine + 2 phosphoryl groups 1 nicotinamide ring can accept two hydrogen becoming reduced NAD
• NAD nicotinamide adenine dinucleotide 2

  • reduced NAD carries protons + electrons to cristae of mitochondria + delivers them to be used in oxidative phosphorylation for ADP+ Pi generation
  • when reduced NAD give up the protons + electrons that it accepted during on of the first three stages of respiration, it can be reused to oxidise more substrate, in the process becoming reduced again
• 3 main stages of glycolysis

  • phosphorylation
  • splitting the hexose bisphosphate
  • oxidation of triose phosphate + pyruvate
• Phosphorylation

  glucose is an organic compound of 6 carbons

  It is stable so it needs to be activated before they can split into two 3 carbons

  1. one molecule of ATP Is hydrolysed + One phosphoryl group is added to glucose to form hexose monophosphate
  2. another molecule of ATP is hydrolysed + one phosphoryl group is added to hexose bisphosphate

  • this sugar has one phosphate group at 1° carbon + another at 6° carbon

  → the energy from hydrolysed ATP activates, hexose sugar + prevents it from being transported out of cell
• Phosphorylation 2

  Splitting hexose bisphosphate

  • split into two 3-Carbon molecules, TP, each with a phosphate group attached

  Oxidation of TP to pyrinate

  1. dehydrogenase enzymes, aided by coenzyme NAD, remove hydrogens from TP
  2. the two molecules of NAD accept hydrogen atoms (protons + electrons) + become reduced
  3. At this stage, two molecules of NAD are reduced for every molecules of glucose undergoing this process

  • also, 4 molecules of ATP are made for every two triose phosphate undergoing oxidation
• Products of glycolysis

  from each molecule of glucose, at the end of glycolysis there are :

  • 2 molecules of ATP; 4 have been made, but two were used to ‘kick start’ the process, so net gain is 2 molecules of ATP
  • two molecules of reduced NAD
  • Two molecules of pyruvate
• The stages of respiration

  1. glycolysis
  2. the link reaction
  3. the Krels Cycle
  4. oxidative phosphorylation

  
• link reaction, Krebs Cycle + oxidative phosphorylation only take place under aerobic condition

  • under aerobic conditions, pyruvate molecules from glycolysis are actively transported into mitochondria for the link reaction
  • in the absence of oxygen (anaerobic condition), pyruvate is converted, in cytoplasm, to lactate or ethanol

  → In me process, reduced NAD molecules are reoxidised so that glycolysis can continue to run, generating 2 molecules of ATP for every glucose metabolised