C485 Exam IV Fall ‘10
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. (8 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. (8pts) Describe the general mechanism used by cells to replace a carbonyl group with
an amino group in nucleotide biosynthesis. Please use structures to illustrate your point.
What are the nitrogen donors used in nucleotide biosynthesis?
3. (6 pts) What are the carbon donors for synthesis of the purine base in nucleotide
biosynthesis? (name(s) or structure(s))
4. (6 pts) What are the carbon donors for synthesis of the pyrimidine base in nucleotide
biosynthesis? (Name(s) or structure(s))
5. (12 pts) Define suicide inhibitor and give an example from pyrmidine biosynthesis
(show the molecule and describe how it works- structures please). Why is such a
molecule useful for anti-cancer therapy?
6. (10 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.
7. (8 Pts) There are two disorders associated with defects or misfunctions of purine
degradation. What are these disorders, and indicate what the molecular basis of the
defect or misfunction is (i.e. show which reaction is defective, or draw the structure of the
molecule that is causing the problem).
8. (10 pts total)
(2 pts.) Please name the key regulatory step in cholesterol biosynthesis. (may show
enzyme or reaction)
(6 pts) State three ways in which the concentration of this enzyme is modified.
(2 pts) Please name a way in which the specific activity of the enzyme is modified.
9. (8 pts) Match the appropriate properties in the right column with the lipoproteins in the
left column.
(a) chylomicron ________________
(b) VLDL
___________________
(c) LDL
___________________
(d) HDL
___________________
(1) transports endogenous cholesterol
esters
(2) transports dietary triacylglycerols
(3) transports endogenous
triacylglycerols
(4) is degraded by lipoprotein lipase
(5) is taken up by cells via receptormediated mechanisms
(6) is a precursor of LDL
(7) may remove cholesterol from cells
10. (12 Pts) List the three major metabolic junction molecules. List or diagram the
possible fates of these molecules.
11. (6 Pts) Two metabolic pathways are tightly coupled to ATP synthesis. What are
these pathways? Explain how this control works, and why this makes sense from a
biochemical perspective.
12. (8 Pts) There are two related methods for the attachment of head groups in
phospholipid biosynthesis. Show these reactions and give an example of a lipid
synthesized via each pathway.
EC 13. (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.)
EC 14. (10 Pts) Estrogens play a key role in receptor positive breast cancer. Explain the
role of this hormone in promoting growth of tumor cells. Identify two different strategies
that are clinically employed to target the role of these hormones in growth of the disease.
EC15 (10pts) Pyrimidine biosynthesis contains a C-N bond-forming reaction that is
unusual in biosynthesis. What is this reaction and why is it so unusual? What enzymic
strategy is employed to make this reaction feasible?
Point breakdown
Possible
actual
1)
8
________
2)
8
________
3)
6
________
4)
6
________
5)
12
________
6)
10
________
7)
8
________
8)
10
________
9)
8
________
10)
12
________
11)
6
________
12)
8
________
13)
10
________
14)
10
________
15)
10
________
TOTAL 130
________