There are 9 pages to this half of the examination. Write your name on each new page. Read every question so that you understand what is being asked. If you feel any question is unclear or ambiguous, clearly explain your answer or interpretation. Please call my attention to any errors you encounter.

You will be given a separate page which has many metabolic pathways written on it.

This examination will assess your learning, problem-solving skills, and ability to communicate clearly. It is intended to be challenging even to the best students in the class. Some of the questions will deal with material you have not seen before and is not in your text; however, they can be answered by applying basic principles discussed in the course.

Do not expose your answers to the scrutiny of your neighbors. Please fold under each page before you go on to the next.

Breakdown of the examination by sections:

__________________________ 1. Another name for biosynthesis.

__________________________ 2. Coenzyme involved in transamination reactions.

__________________________ 3. One letter symbol for tryptophan.

__________________________ 4. Dihydrofolate reductase is inhibited by this antitumor agent.

__________________________ 5. Number of carbon atoms in phosphoribosylpyrophosphate.

__________________________ 6. NAD is an abbreviation for.

__________________________ 7. Aspirin inhibits the synthesis of this class of compounds.

__________________________ 8. Element common in nucleic acids and infrequent in proteins.

__________________________ 9. Common abbreviation for adenylic acid..

__________________________ 10. Group of organisms that excrete nitrogen as uric acid.
 

Part II Structures (16 points)
1.    (8 Points) During protein synthesis, tRNAs go through a cycle in which they become aminoacylated at their 3' -CCA end with their cognate amino acid, bind to the A-site on the ribosome, undergo a transpeptidation reaction to form a peptidyl tRNA, translocate to the P-site, transfer the peptidyl moiety to the next aminoacyl tRNA, and then dissociate to repeat the cycle. Consider a tRNA^Tyr participating in normal protein synthesis and bearing a dipeptide on its 2’ hydroxyl group. Draw the complete structure of the expected dipeptide attached to the tRNA^Tyr.
 

2. (8 Points) Draw the structure of the terminal 3' dinucleotide (-CA) at the end of tRNA^Tyr and show where and how the dipeptide above is covalently attached to it.
 

            A.  G, C, L     B.  F, K, V   C.  E, T, H     D.  M, R, Q   E.  N, P, D     F. I, Y, S

_____ 2. Consider Question 1 again and the same set of choices. Which group of amino acids consists only of amino acid we can synthesize?

_____ 3. Consider the following isotopes some of which are used as metabolic tracers. Which group consists only of non-radioactive isotopes?

             A. ¹⁸O, ³⁵S, ³H    B. ¹⁴C, ¹⁶O, ¹⁴N   C. ¹³C, ³²P, ²H   D. ¹²C, ³H, ¹⁵N   E. ³¹P, ²H, ¹⁴N

_____ 4. The X and Y columns pair components of fatty acid synthesis with components of protein synthesis, respectively. Examine each pair. Which pair has the relationship, X is to fatty acid synthesis as Y is to protein synthesis?
 

_____ 5. Which statement is false?

A.    B-complex vitamins are precursors for a variety of coenzymes.
B.    Fatty acids found in plants and animals have predominantly 16 or 18 carbon atoms.
C.    Some coenzymes are also nucleotides.
D.    The a -helix is an important part of the structure of DNA.
E.    Galactose is the 4-epimer of glucose.
F.    Steriod biosynthesis from acetyl CoA starts in the cytosol .

A.    TPP stands for thymine pyrophosphate
B.    Humans can convert fatty acids into glucose.
C.    Adenylate Energy Charge can never be higher than 1.0.
D.    Both CO₂ molecules generated with each turn of the TCA cycle come directly from the
       acetyl group that enters the cycle.
E.    Mutated enzymes with impaired activity would have low sensitivity coefficients.
F.    Dehydration reactions use NAD.

A.     Pyruvate + Glyceraldehyde-3-Phosphate B.     Carbon Dioxide + Ribose-5-Phosphate  C.     3-Phosphoglycerate + Propionate D.     Glyceraldehyde-3-Phosphate + Dihydroxyacetone           Phosphate E.      Dihydroxyacetone + 3-Phosphoglycerate F.      Acetate + Erythrose-4-Phosphate

_____ 8. Considering all of the reactions and compounds that use or incorporate nucleotides in a cell, which of the following bases would be least concentrated in a total cell hydrolysate?

A.    It operates principally when muscle is actively working, not in the resting state.
B.    In muscle, glycolysis is occurring, while in liver gluconeogenesis is occurring.
C.    The blood transports glucose from muscle to liver. It then transports lactate
        from liver back to muscle.
D.    Lactate dehydrogenase operates in the direction, pyruvate to lactate, in muscle,
        whereas in liver this enzyme operates in the direction, lactate to pyruvate.
E.    The Cori Cycle operates at the expense of ATP in the liver.

____ ATP     ____ NAD(P)H	A.    (4 points) In this modified pathway for glucose oxidation, five, rather than six, glyceraldehyde-3-Ps (GAP) are produced per three glucoses. Calculate the net production of ATP and NAD(P)H per glucose in going from glucose to pyruvate in this pathway. (Use the back of this page as a work sheet if necessary for this and subsequent questions.)
	B. (6 points) If carbon 3 of glucose were labeled with 14C, how would the label be distributed in pyruvate?
	C. (3 points) How would the 14C label be distributed in pyruvate, if the normal glycolytic pathway were operating alone, i. e. phosphoglucose isomerase is fully functional and the pentose phosphate pathway were not involved.

2.    The biosynthesis of phenylalanine requires erythrose-4-P (E4P) and two moles of phosphoenol pyruvate (PEP) as precursors as is shown below. Return to Question 1 and the metabolism of [3-¹⁴C] glucose in the bacteria lacking phosphoglucose isomerase.
 

A.    (7 points) Trace the labeled carbons and show which carbons of phenylalanine would be labeled. (Because the answer here is dependent on your answer on 3B, I will give up to 6 points for an answer that is consistent with an incorrect answer to 1B.)

 






B.    Bonus Question (5 points) Do not do this until you have completed the rest of the examination. What would be the relative amounts of ¹⁴C in each of the labeled carbons of phenylalanine?

1.    Discuss the regulation of the branched purine biosynthetic pathway or the aspartate family of amino acids. Answer only one of the two choices.

2.    Explain the following: A man on a low protein – high carbohydrate excretes 6.2 grams of urea per day. Then, after a three-day fast, he excretes 26.3 grams of urea per day or the relation between metabolic energy sources and world record human running performance at various distances. Answer only one of the two choices.