Glycolysis

• Glycolysis


  Sugar splitting
• Glucose is a very adaptable metabolite that is able to meet both the material and energy requirements of the cell. Unlike fats which mostly only meet energy requirements
• The complete oxidation of glucose has a ΔGo ՚ = -2834 kJ/mol of free energy that can be used to meet the cells energy requirements
• In theory we could make 2834/30 (per ATP) ≈ 95 ATP molecules from 1 glucose. This does not happen as a lot of the energy is used to keep driving the formation of products rather than reaching equilibrium
• Biological systems cannot utilise heat as a source of energy
• No single reaction of metabolism requires the full 2834 kJ/mol of energy to be released in one step
• Always need to overcome the activation energy. Enzymes are capable of effecting only small changes when they catalyse biological reactions, releasing the energy in steps
• During the catabolism of glucose the molecule is broken down in small steps and the energy is released in usable amounts (~ -30 kJ/mol) in the form of chemical energy, with ATP being the energy carrier
• Glucose metabolism


  1. Glucose 2 Pyruvate

  2. 2 ATP

  3. 2 NADH + 2H+
• Coenzymes


  ATP/ADP for phosphate transfer

  NADH/NAD+ for oxidation/reduction reactions

  ATP for transferring energy between reactions
• Enzyme naming convention


  Named after substrate plus enzymatic activity

  Kinases phosphorylate

  Phosphatases dephosphorylate
• Glycolysis - Step 1

  Glucose 2 Glucose-6-phosphate

  Hexokinase

  ATP 2 ADP

  Irreversible
• Glucose transport


  • Glucose cannot cross membrane alone, uses transport proteins (e.g. GLUT2)

  Facilitated diffusion, no energy required

  Phosphorylation prevents glucose from returning
• Glycolysis - Step 2

  Glucose-6-phosphate 2 Fructose-6-phosphate

  Phosphoglucose isomerase

  Reversible
• Glycolysis - Step 3

  Fructose-6-phosphate 2 Fructose-1,6-bisphosphate

  Phosphofructokinase

  ATP 2 ADP

  Irreversible
• Glycolysis - Step 4

  Fructose-1,6-bisphosphate 2 Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate

  Aldolase

  Reversible
• Glycolysis - Step 5

  Dihydroxyacetone phosphate 2 Glyceraldehyde-3-phosphate

  Triose phosphate isomerase

  Reversible
• Glycolysis - Step 6


  Glyceraldehyde-3-phosphate 2 1,3-bisphosphoglycerate

  Glyceraldehyde-3-phosphate dehydrogenase

  NAD+ 2 NADH + H+

  Reversible
• Glycolysis - Step 7

  1,3-bisphosphoglycerate 2 3-phosphoglycerate

  Phosphoglycerate kinase

  ADP 2 ATP

  Reversible
• Glycolysis - Step 8

  1. phosphoglycerate 2 2-phosphoglycerate

  Phosphoglycerate mutase

  Reversible
• Glycolysis - Step 9

  1. phosphoglycerate 2 Phosphoenolpyruvate

  Enolase

  Reversible
• Glycolysis - Step 10

  Phosphoenolpyruvate 2 Pyruvate

  Pyruvate kinase

  ADP 2 ATP

  Irreversible
• Glycolysis


  • 3 irreversible steps

  Hexose sugar phosphorylated at both ends before splitting

  Conversation to GAP, followed by oxidation and phosphorylation with Pi

  4 ATPs produced from substrate level phosphorylation

  2 NADHs generated (equivalent to 3 ATPs per NADH)
• Glycolysis is an ancient process, believed to be around before oxygen was introduced into the atmosphere
• Glycolysis occurs in plants, animal cells, fungi and microbes
• Glycolysis

  Series of 10 reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates

  Includes an energy investment/preparatory phase and an energy generation/payoff phase
• From the structure of glucose you can derive carboxylate, carbonyl, and methyl groups
• From the structure of glycerol you can derive carboxylate, carbonyl, and methyl groups
• From the structure of pyruvate you can derive carboxylate, carbonyl, and methyl groups
• From the structure of acetone you can derive two methyl groups