Glycolysis

Cards (44)

  • 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.
  • Reasons why the whole 2834 kJ/mol (from the complete oxidation of glucose) is not released as heat

    • Biological systems cannot utilise heat as a source of energy
    • No single reaction of metabolism requires this amount 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.
  • Ten steps to glycolysis

    1. Glucose
    2. 2 Pyruvate
    3. 2 ATP
    4. 2 NADH + 2H+
    5. Energy investment
    6. Energy payoff
  • Glycolysis occurs in the cytosol
  • Coenzymes in glucose catabolism

    • ATP/ADP deliver/receive phosphates
    • NADH/NAD+ involved in oxidation/reduction reactions
  • ATP is also involved in transferring energy between reactions.
  • Aldehyde
    • Carboxylate
    • A ketone with 2 methyls = acetone
  • General Enzyme Naming Convention
    • Enzymes named after their substrate plus the enzymatic activity
    • Kinases phosphorylate substrates
    • Phosphatases dephosphorylate substrates
    • Not all enzymes follow this convention because of how their functions were originally discovered
  • Knowing the substrates and the steps involved, allows you to also name the enzymes.
  • Glycolysis - STEP 1
    1. ATP
    2. ADP
    3. Hexokinase
    4. Mg2+
    5. GLUCOSE
    6. GLUCOSE-6-PHOSPHATE (G6P)
  • Glucose-6-phosphate (G6P)
    • Aldehyde at top
    • 6 carbon compound
    • Hydroxyl groups on the same side except for third carbon from top
  • Glucose by itself cannot cross a membrane. Uses transport proteins e.g., GLUT2 to move from a high to a low concentration. This process does not require energy.
  • Phosphorylation prevents the glucose from Returning. Remember G -> G6P is irreversible, powered by the energy from ATP hydrolysis using this enzyme hexokinase. Can be reversed but using a different enzyme.
  • Glycolysis - STEP 2

    1. GLUCOSE-6-PHOSPHATE (G6P)
    2. FRUCTOSE-6-PHOSPHATE (F6P)
    3. Phosphoglucose isomerase
  • Glycolysis - STEP 3

    1. FRUCTOSE-6-PHOSPHATE (F6P)
    2. FRUCTOSE-1,6-BISPHOSPHATE (F1,6P)
    3. ATP
    4. ADP
    5. Phosphofructokinase
  • Fructose-1,6-bisphosphate (F1,6P)

    Bisphosphate means two phosphate groups added to different places
  • Glycolysis - STEP 4

    1. FRUCTOSE-1,6-BISPHOSPHATE (F1,6P)
    2. Dihydroxyacetone phosphate (DHAP)
    3. Glyceraldehyde-3-phosphate (GAP)
    4. Aldolase
  • This reaction is readily reversible and is catalysed by aldolase. The enzyme derives its name from the reverse reaction, an aldol condensation (reaction between an aldehyde and a alcohol).
  • Glycolysis - STEP 5

    1. DHAP
    2. GAP
    3. Triose phosphate isomerase
  • Glycolysis - STEP 6

    1. Glyceraldehyde-3-phosphate (GAP)
    2. 1,3-bisphosphoglycerate
    3. NAD+
    4. NADH + H+
    5. GAP dehydrogenase
  • Dehydrogenase means it is an oxidation step in which an aldehyde is converted to a carboxylic acid.
  • An usual phosphorylation step as the Pi comes from solution and NOT from ATP. What is driving this reaction is the oxidation step which is exergonic.
  • Glycolysis - STEP 7

    1. 1,3-bisphosphoglycerate
    2. 3-phosphoglycerate
    3. ADP
    4. ATP
    5. Phosphoglycerate kinase
  • 1,3-bisphosphoglycerate
    A carboxylic acid linked to a phosphate = phospho-anhydride
  • An acid from the phosphate and an acid from the carboxylic acid results in a greater negative deltaG. Phosphoester bond as a result of the reaction between an acid and an alcohol. This has a negative deltaG.
  • Glycolysis - STEP 8
    1. 3-phosphoglycerate
    2. 2-phosphoglycerate
    3. Phosphoglycerate mutase
  • The phosphoester is not sufficiently exergonic to produce ATP from ADP but this rearrangement allows, in the next step, for such a compound to be formed.
  • Glycolysis - STEP 9

    1. 2-phosphoglycerate
    2. Phosphoenol-pyruvate
    3. Enolase
  • Phosphoenol-pyruvate
    Enol is an alkene with a hydroxyl group
  • Donation of the phosphate group allows the enol to convert into the mores stable ketone (pyruvate).
  • Glycolysis - STEP 10
    1. Phosphoenol-pyruvate
    2. Pyruvate
    3. ADP
    4. ATP
    5. Pyruvate kinase
  • Glycolysis
    • Three irreversible steps
    • The hexose sugar is first phosphorylated at both ends before splitting
    • Conversation to GAP, followed by oxidation and phosphorylation with Pi results in the triose phosphorylated at both ends
    • The four phosphates are used to generate 4 ATP
  • 2 ATPs used to prime glycolysis.
  • 4 ATPs produced from the glycolytic pathway as a result of substrate level phosphorylation 2x(step 7 & 10).
  • 2 NADHs generated (equivalent to 3 ATPs per NADH through oxidation via the electron transport chain).
  • 8 ATPs net gained from the conversion of glucose to pyruvate and the re-oxidation of the 2 NADHs produced.
  • Acetone
    A ketone with 2 methyls
  • Glycolysis occurs in plants, animal cells, fungi and microbes.