18.3 The Krebs Cycle

Question 1

Where does the kerbs cycle take place

Answer 1

matrix of mitochondria

Question 2

What are the steps of the Krebs cycle

Answer 2

1. Acetyl coA delivers an acetyl group to the Krebs cycle. The 2 carbon acetyl group combines with four carbon oxaloacetate to form 6 carbon citrate
2. Citrate molecule undergoes decarboxylation and dehydrogenation, NAD is reduced to NADH by removal of a hydrogen atoms and CO2 is removed to form a 5 carbon compound
3. The five carbon compound undergoes further decarboxylation and dehydrogenation into produce another CO2 and reduce another NAD to NADH to form a 4 carbon molecule
4. The 4C compound is dehydrogenated again to reduce NAD and FAD to NADH and FADH. ATP is also produced by substrate-level phosphorylation. Oxaloacetate is regenerated and the cycle continues

Question 3

What is the importance of coenzymes in respiration

Answer 3

-required to transfer protons, electrons and functional groups between enzyme-catalysed reaction
-without coenzymes redox reaction would not be able to take place which play an important role in respiration
-derived from vitamins so are an essential micronutrient

Question 4

What is the difference between NAD and FAD

Answer 4

-both coenzymes that accept protons and electrons
-NAD accepts one hydrogen, FAD accepts two
-NAD takes part in all stages of respiration, FAD only accepts hydrogen in the Krebs cycle
-NADH is oxidised at the start of the electron transport chain, FADG is oxidised further along the transport chain
-NADH results in the synthesis of 3 ATP molecules, FADH results in synthesis of 2 ATP molecules

Question 5

What are the overall products of the Krebs cycle

Answer 5

4 CO2
2 FASH
2 ATP
6 NADH