Review Problems For week 9.
We will definitely not get through all of these, but it is useful to have them in one place.
1) Draw the structure of S-adenosylmethionine. How is this molecule formed? What is
its biological function?
2) Methionine is degraded to a four carbon molecule- outline the steps in this conversion.
What other amino acid is required for this transformation? What amino acid is
synthesized in this process?
3) The four carbon molecule derived from methionine is coverted into a Krebs cycle
intermediate. What is this molecule? What cofactors are involved in this transformation?
4) Name the cofactor required for hydroxylation of phenylalanine. Draw the structures of
the three commonly observed forms of this cofactor. How are they related?
5) What is the consequence of a deficiency in phenylalanine hydroxylase?
6) What is the major difference(s) between monooxygenases and dioxygenases?
7) Why is hydroxylation of an aromatic ring a necessary precursor to its cleavage?
8) Draw the mechanism of the cofactor employed by phenylalanine hydroxylase.
9) What are the two major degradation products of phenylalanine/tyrosine?
10) What are the two major degradation products of tryptophan?
11) Show how the carbons of tryptophan map onto the products described in the answer
to question 10.
12) Draw mechanisms for the following reactions:
a) Conversion of threonine to acetaldehyde and glycine
b) Conversion of threonine to glycine and acetyl CoA
c) Conversion of threonine to a compound that is converted to succinyl CoA
d) Conversion of cysteine sulfinate to pyruvate and sulfur dioxide. How is cysteine
sulfinate synthesized?
e) Conversion of glycine to formaldehyde and carbon dioxide
13) Formaldehyde is formed in the degradation of two amino acids. Which are these?
How is formaldehyde trapped and carried in biochemistry? (structures please)
14) Which amino acids are essential? What is meant by an essential amino acid?
15) What is meant by a conditionally essential amino acid? What amino acids qualify?
16) Why are both cysteine and methionine often combined together when estimating the
content of essential amino acids?
17) What is mean by an protein-digestability corrected amino acid score? Why is it
possible to rate over 100 on such a score? Why is this typically reduced to 100 for
evaluation purposes?
18) What does it mean when a food has a score of 0 in protein-degestability aa score?
How can this be corrected for? What is the benefit of using foods with low scores?
Comment on nutritional benefits as well as other possible benefits?
19) What are the “best” sources of protein from a PDAAS perspective?
20) What enzyme is responsible for the fixation of nitrogen? What are the energetic
requirements for this reaction?
21) How many electrons are required to reduce nitrogen gas to ammonia? How many
electrons are required in the biological reduction? If these are not the same, explain why.
22) What are the ultimate biological molecules that act as acceptors of ammonia in higher
organisms? What enzymes mediate this(ese) transformation(s)? What are the energetic
requirements for this(ese) reaction(s)?