Glycolysis

Glycolysis: From Glucose (6 carbon) to 2 Pyruvate (2, 3 carbon sugars)

  1. Prepatory Phase:

  2. Payoff Phase: Harvest of energy through ATP

  1. Hexokinase Reaction: adds a phosphate to glucose (coming from ATP to be energetically favorable aka. coupling)

    1. Coupling a reaction is just to add positive free energy change and negative free energy change

  2. 2. Phosphohexose Isomerase changes the structure without changing the molecule- glucose is converted to fructose (isomer)

    1. Enables cleavage between C3 and C4 instead of C2 and C3 resulting in two 3C sugars at aldolase step

  3. Phosphofructokinase (PFK-1)

    1. Fruc-6-P + ATP → Fru-1,6-bisP + ADP (DeltaG = -14.2 kJ/mol)

    2. ATP is a substrate for this, yet inhibits enzyme activity:

    3. this is bc ATP binds to both the active sit of the enzyme and to a separate allosteric site

      1. Levels of ATP that inhibit are much higher than levels needed for reaction at the enzyme active site

  4. Aldolase: Hexose → 2 Trioses

    1. (Dihydroxyacetone-P, Glyceraldehyde-3-phosphate)

      1. When a pathway is operating, all DGs are negative

  5. Triose Phosphate Isomerase (TPI): makes interconversion of the phosphate in order to complete the payoff phase

Payoff Stage

  1. Oxidation of Glyveraldehyde-3-P: Dehydrogenase Reaction

    1. This is the only redox reaction in glycolysis

    2. Energy of oxidation is preserved a phosphate bond and an NADH

NAD: Nicotinaminde-Adenine-Dinucleotide

  • Reduced by two electrons

Dehydrogenation

  1. Phosphosglycerate Kinase: First Payoff, coupled to substrate level phosphorylation

  2. Phosphoglycerate Mutaste: re-arrange the molecule so phosphate is in a high energy state

  3. Formation of Phosphoenolpyruvate: lose an H2O

  4. ATP from PEP: Pyruvate Kinase - second payoff

Energy Changes:

  • Glucose → 2 Pyruvate coupled to:

    • 2 ADP + 2 Pi → 2 ATP; DG ~=+61 kj/mol

    • 2 NAD+ → 2 NADH; DG ~=+440 kj/mol

Regulation - half are inhibited are others are active

Quiz Questions:

  1. What molecules allosterically inhibits phosphofructokinase (the third enzyme in glycolysis)? Think about what makes metabolic sense: ATP

  2. Steps 1, 3 and 10 of glycolysis are irreversible.What is also true about these steps? :

    1. Cellular conditions do not exist that allow for steps 1, 3 and 10 to proceed in the reverse direction.

      Steps 1, 3 and 10 are catalyzed by kinases

  3. How many pyruvate molecules are formed from one molecule of glucose?: 2

  4. How many net ATP are formed in glycolysis per glucose molecule?: 2