3.2 Fatty acid biosynthesis

Question 1

Why is ATP hydrolysis used as an E source?

Answer 1

ATP hydrolysis - high ΔG<0 - phosphate transfer very favourable - due to ADP resonance stabilisation

Question 2

Is nuc addition the same in phosphates as carbonyls?

Answer 2

No, in carbonyls nuc addition only through tetrahedral intermediate (addition -> elimination) - in phosphates nuc direct through direct elimination (through tetrahedral intermediate could also occur but not as often)

Question 3

What is additionally required by all ATP using enzymes?

Answer 3

Metal ions

Question 4

Why is thioester Acetyl-CoA hydrolysis used instead of ester Acetyl-CoA?

Answer 4

Thioester Acetyl-CoA hydrolysis - higher ΔG<0 - due to stronger resonance stabilisation (orbitals overlap better) - S provides more stabilisation for C+ than O -> C more susceptible for nuc attacks

Question 5

Explain Acetyl-CoA formation from fatty acid oxidation

Answer 5

• β-oxidation pathway connverts fatty acids into Acetyl-CoA
• ATP, FAD+, NAD+, H2O used

Question 6

Explain Acetyl-CoA formation from acetate

Answer 6

• acetate and CoA reaction - unfavourable (ΔG>0) because of unlikely mechanism -> ATP-coupled recacion used for the reaction to occur

Question 7

What is a Claisen condensation reaction?

Answer 7

• C-C bond forming reaction that occurs between two esters / ester + carbonyl compound in strong B presence => results in β-keto ester / β-diketone

Question 8

Explain biological Claisen condensation reaction

Answer 8

• protein side chains act as B or acids
• thioesters used instead of esters

Question 9

How are fatty acid chains extended in synthesis?

Answer 9

By addition on acetyl-CoA - adds 2C units -> by decarboxylative condensation reactions