2. krebs cycle

KREBS CYCLE- DIAGRAM

KREBS CYCLE- 1

• acetylcoenzyme A (2C) combines w/ a 4C compound in mitochondrial matrix

• 6C compound called citrate is formed

KREBS CYCLE- 2

• citrate is decarboxylated by removal of CO2

KREBS CYCLE- 3

• citrate is oxidised by removal of hydrogen

• hydrogen is accepted by NAD to form reduced NAD

KREBS CYCLE- 4

• 5C compound (acid) is formed

• 5C compound is decarboxylated by removal of CO2

KREBS CYCLE- 5

• during conversion of 5C compound into 4C compound, 1 molecule of ATP is synthesized by combining ADP + Pi- substrate level phosphorylation

KREBS CYCLE- 6

• 5C compound is oxidised by removal of hydrogen

• hydrogen accepted by coenzymes NAD and FAD and are reduced

• 4C compound regenerated and cycle restarts

KREBS CYCLE- PRODUCTS

• 2 turns of cycle for every glucose molecule broken down in glycolysis

• so for every glucose molecule, Krebs cycle produces:

  • 2 ATP

  • 4 CO2

  • 6 reduced NAD

  • 2 reduced FAD

DEVELOPING KREBS CYCLE-1

• before Krebs discovery, experiments by Thunberg, Batelli and Stern showed that minced animal tissues contained substances transfered H atoms from specific intracellular organic acids (including citrate) to methylene blue dye, reducing it to a colourless form

• now know these substances are dehydrogenases

DEVELOPING KREBS CYCLE-2

• Albert Szent-Gyorgyi extended studies by describing sequence of enzymic reactions involving oxidation of organic acids which are part of cycle

• krebs then worked out cyclic nature of reactions by realising the 2C molecule combined with 4C to form citrate (6C)

• used different inhibitors that brought about halt of specific reactions to work out which compounds were involved

• also realised that series of reactions he proposed could take place at a fast enough rate to account for the known pyruvate and O2 use of tissues