C485 Exam III Fall ‘12

Name______

Legible please!

Do not use acronyms unless instructed to do so. 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. Use the back of the page if you need room. GOOD LUCK

1. (8 Pts) What are the requirements for biological nitrogen fixation in terms of electrons/nitrogen molecule and ATP consumed /nitrogen molecule fixed. Does the reaction require the same amount of electrons as chemical fixation? If not, how do these numbers differ and why are they different?

2. (12pts) The urea cycle is fairly intensive in its use of ATP. Diagram (structures and equations) the steps of the cycle that use ATP. Make sure you show the fate of the ATP.

3. (6pts)What are the two major (multicarbon) degradation products of tyrosine? (structure or name acceptable)

4. (6 pts) Which of the following are intermediates in the pathway for the biosyntheiss of both phenylalanine and tryptophan? circle your answer(s)

(a) Indole (b) chorismate(c)dehydroquinate(d) prephenate

5. (12 Pts) Unlike most organs, muscle uses three specific amino acids as energy sources. What are these amino acids (structures)? Choose one and draw its degradation pathway.

6. (14 pts) The biosynthetic pathwaysfor tryptophan and cystathionineutilize a beta-elimination/beta addition process for their synthesis.

1- What is the amino acid that undergoes elimination in each case?

2- What is the component that adds in each case?

3- Pick one of these processes and draw the mechanism of elimination, starting from the relevant PLP-adduct. You do not have to show cleavage of the final product from PLP.

7. (10 pts) By what two reactions is ammonia assimilated into amino acids? (Structures and equations please).

8. (12 Pts) Draw the pathway used for the biosynthesis of valine. Show starting molecule(s) and all stable intermediates. Note the participation of any cofactors in specific steps. Show the mechanism (curly arrows and structures please) of the first step of the pathway.

9. (10 Pts). Draw the structure of tryptophan and itemize the source of each heavy atom.

10. (10Pts) Match the amino acid with its breakdown product (breakdown may be used more than once).

Threonine _____A Acetyl CoA

Glycine______B Pyruvate

Alanine______C alpha-keto glutarate

Histidine______D alpha-keto butyrate

Lysine______E N5,N10-methylene THF

11. (10 pts) The biosynthesis of cysteine employs a gamma-elimination from cystathionine. Draw this reaction and draw the mechanism of all relevant steps starting from the cytasthionine-pyridoxal adduct.

Point breakdown

Possibleactual

1)8______

2)12______

3)6______

4)6______

5)12______

6)14______

7)10______

8)12______

9)10______

10)10______

11) 10______

TOTAL 110______