Review Problems (Amino acid Biosynthesis) Week 10
1) The carbons of phenylalanine and tyrosine are derived from what glucogenic
molecules?
2) The branchpoint for aromatic amino acid biosynthesis is chorismate. What is the
structure of chorismate? What are the three immediate products derived from chorismate
that constitute the first unique steps in the synthesis of the three aromatic amino acids?
3) From where are the two carbons of the five-membered ring of tryptophan derived? Be
specific. (Show the molecule and highlight the carbons that are used.) The carbons that
are not used are converted into what compound?
4) The nonaromatic carbons of tryptophan are derived from what precursor? What
cofactor is involved in this reaction? Show the mechanism of this transformation.
5) Roundup (glyphosate) inhibits biosynthesis of aromatic amino acids. Which step does
it inhibit? Why does this inhibitor have little effect on humans? Considering that
glyphosate is an incredibly effective herbicide, can you give a likely reason for why this
compound is not an effective antibiotic.
6) Which transformation in aromatic amino acid biosynthesis requires NAD+, but does
not yield NADH as a product. Explain the role of this cofactor. (Hint: this is similar to
the reaction catalyzed by S-adenosylhomocysteine hydrolase).
7) What are the carbon-containing precursors used for the synthesis of valine and
isoleucine? What cofactor is common to both these biosynthetic pathways? Explain its
role and draw a mechanism for the transformation.
8) The biosynthesis of valine and isoleucine have a rearrangement step that is very
similar. Draw this rearrangement (curly arrows please).
9) Leucine is derived from the same pathway that generates valine. What additional
carbon source is used in this synthesis? The later stages of leucine’s biosynthetic
pathway are similar to what other pathway? Explain.
10) Threonine is derived from what non-proteinacious amino acid? Which common
amino acid is the ultimate source of this molecule?
11) The methyl group of methionine is derived from what common amino acids? What is
the byproduct of this one carbon transfer in each case? What cofactor catalyzes this
carbon cleavage? What is the acceptor of this carbon? The actual agent that ultimately
transfers the carbon is which cofactor?
12) In what way are the biosynthesis of methionine and cysteine related? Give a general
outline of the biosynthesis of these amino acids. What cofactor plays a central role?
What is that role?
13) What are the starting materials for the biosynthesis of lysine? What “protecting
group” is employed in this synthesis?
14) What molecules provide the carbon and nitrogen sources for histidine. Please
delineate which atoms in the starting materials wind up in which places in histidine.
15) What is remarkable about the architecture of tryptophan synthase?
16) Show how the starting carbons sources used in the shikimate pathway map onto the
three aromatic amino acids.
17) The indole nitrogen of tryptophan is derived from what source? What is unusual
about this transformation? Comment on the thermodynamics of the reaction that
generates this nitrogen source.