Question

Acetyl COA + H2O Coo- o coo- Citrate synthase CH2 -OH -ooc— CH2 CH2 NADH + H+ COO- Oxaloacetate Coo- Citrate Aconitase Malate dehydrogenase NAD+ - Çoo- Çoo- ---OH -O00—-H HO-CH CH2 CH2 Coo- Malate Coo- Isocitrate Isocitrate lyase Malate synthase COO- COO- Coh CH2 Acetyl COA + H2O Ho Glyoxylate coo Succinate Figure 17.23 Biochemistry, Seventh Edition 2012 W. H. Freeman and Company Question 1 (10 pts) Using diagrams show the pathway that is used to convert succinate to phosphoenol-pyruvate, which can be used to make glucose through gluconeogenesis. Be sure to show the structure of all of the intermediates along the pathway and show the name of each enzyme over the arrow. Also be sure to indicate other co-substrates or cofactors required (ie. ATP, NAD+, FAD, etc...) Question 2 (5 pts) A key enzyme in the glyoxylate cycle is isocitrate lyase. Draw out the mechanism of Isocitrate lyase and briefly explain why isocitrate is used as the substrate for this reaction and not citrate.

Answer 1

question 2.Second part Citrate is isomerized to isocitrate, which is then decarboxylated to a-ketoglutarate. If citrate had not been isomerized to isocitrate, this decarboxylation would yield a branched carbon compound which is harder to metabolize.