biochemistry

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I have three questions. I don't even know where to begin.

1.
a) If an in vitro fatty acid synthesizing system is supplied with [2-14C]-acetyl CoA as the only source of radioactive label along with all other necessary cofactors/reactants for net fatty acid synthesis, in what position(s) will the label appear in newly synthesized palmitic acid? (Note that the in vitro system lacks acetyl CoA carboxylase)
b) If instead 2,2-dideuteromalonyl CoA was supplied as the only source of label, how many deuterium atoms would be incorporated into palmitate and where would they appear?
c) If [3-14C]-malonyl CoA were used in the above reaction, which atom(s) in palmitate would be labeled?
d) Describe the pathway by which some of the carbons in an odd-chain fatty acid can undergo net conversion to carbohydrate.

2. A mammal on a particular diet expends 10,000 kJ of energy per day while excreting 40g of urea. Assuming that protein is 16% N by weight and that its catabolism yields 18kJ of energy per gram, what percentage of the mammal's energy needs are met by the degradation of protein?

3. [3-14C]-Pyruvate was administered to isolated liver cells in the presence of sufficient malonate to completely block succinate dehydrogenase. After a 30-minute incubation period, isocitrate was isolated from the reaction mixture and was found to contain 14C at both C2 and C4: Explain the presence of isotopic label at the indicated positions.

Any help would be appreciated! Thanks!

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