C485 Exam IV Fall ‘14
Name___________________
Legible please!
Do not use acronyms. Use structures whenever they are asked for, or appropriate. Your
explanations should be brief. Overly lengthy answers with irrelevant or erroneous
material will receive deductions. GOOD LUCK
1. (10 Pts) The compound shown below is an intermediate in the biosynthesis of
cholesterol that is derived from acetate. Using the numbering system shown below for
acetate, number this compound so it is obvious how it is derived from acetate. Please
draw and number a six carbon intermediate in this pathway.
2. (12pts) There are three pathways for the biosynthesis of phospholipids from
phosphatidic acid. Outline the reactions of these pathways (structures please) and give an
example of a lipid synthesized via each pathway.
3. 10. (8 Pts) How many electrons are involved in the oxidations shown below?
a)
b)
4. (10 pts) Draw the mechanism for thymidilate synthase. What molecule would
function as a useful suicide substrate for this enzyme? Explain how this inhibitor would
work.
5. (14 pts) Draw the mechanism for ribonucleotide reductase. Also, summarize how this
enzyme is regulated.
6. (16 pts) Starting with simple sugars, amino acids and one carbon donors, draw the
biosynthetic pathway for GMP biosynthesis. You must show all reactions and include all
reactants and products.
7. (12 pts) The carbon backbone of ceramide and sphingosines is assembled in a carboncarbon bond forming reaction. Show the precursors for this reaction, the cofactor
required for this conversion, and a mechanism for any C-C bond forming or C-C bond
making events that take place in this conversion. You must show the entire mechanism
starting from the resting state of the cofactor and regenerating it.
8. (12 Pts) Starting with cholesterol, outline the biosynthesis of the major sex hormones
(estrogen and testosterone). You must use structures. What are the actual sex hormones
that are most active in stimulating a receptor response? Explain how receptors might
differentiate between two molecules that are so similar.
9. (8pts) Explain the regulatory strategy used to control purine biosynthesis. Make sure
you specifically state which reaction is affected, and what is causing the effect. Explain
the rationale for this type of effect.
10. (5 pts total)
a. (1 pt.) Please name the key regulatory step in cholesterol biosynthesis. (may show
enzyme or reaction)
b. (3 pts) State three ways in which the concentration of this enzyme is regulated.
c. (1 pt) Please describe a way in which the specific activity of the enzyme is regulated.
11. (10 pts) Nandrolone (structure shown below) is widely used by strength athletes.
What steroid(s) does this molecule mimic? There is one very obvious difference between
this molecule and its natural congeners that gives nandrolone a property that the natural
steroids lack. What is this difference and what is the property? (Hint, identify one of the
structural differences between male and female sex hormones and this may help you.)
Point breakdown
Possible
actual
1)
10
________
2)
12
________
3)
10
________
4)
10
________
5)
14
________
6)
16
________
7)
12
________
8)
12
________
9)
8
________
10)
5
________
11)
10
________
TOTAL 119
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