krebs cycle

where does the krebs cycle take place?

• in the matrix of the mitochondria

what are the products of the krebs cycle?

• 2 coenzymes (NADH and FADH2)

• ATP

• CO2

what is the first step of the krebs cycle?

• acetyl coenzyme A from the link reaction combines with a 4 carbon molecule (oxaloacetate) to form a 6 carbon molecule (nitrate)

• coenzyme A goes back to the link reaction to be used again

what is the 2nd step of the krebs cycle?

• the 6 carbon citrate molecule is converted to a 5 carbon molecule

• decarboxylation occurs, where carbon dioxide is released

• dehydrogenation also occurs, where hydrogen is removed

• the hydrogen is used to produce reduced NAD from NAD

3rd step of the krebs cycle?

• the 5 carbon molecule is then converted to a 4 carbon molecule

• decarboxylation and dehydrogenation occur, producing 1 molecule of reduced NAD and release of CO2

regeneration of oxaloacetate (4th step)?

• the 4 carbon molecule is then dehydrogenated again to produce another molecule of reduced NAD.

• ATP is produced by substrate-level phosphorylation

• the 4 carbon molecule is dehydrogenated, so, FAD is also reduced to FADH2

• no decarboxylation takes place at this stage

• these intermediate reactions regenerate oxaloacetate, which allows the cycle to continue again

what is substrate-level phosphorylation?

• when a phosphate group is directly transferred from one molecule to another

what is the net gain of the krebs cycle?

• 2 CO2 molecules

• 3 NADH molecules

• 1 ATP molecule

• 1 FADH2 molecules

for every molecule of glucose, how many cycles are there?

• 2 cycles

  • this is because 2 molecules of pyruvate are produced in glycolysis

• so this means: 1 glucose produces 2 acetyl coenzyme A, so the krebs cycle happens twice per glucose

• so the overall net gain is:

  • 6 NADH

  • 2 FADH

  • 4 CO2

  • 2 ATP

what else can be used as respiratory substrates in aerobic respiration?

• fatty acids and amino acids

  • the substrates are converted to molecules that can easily enter the krebs cycle