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Question 1

How is de novo purine biosynthesis distinguished from de novo pyrimidine biosynthesis?

Answer 1

By inhibition by azaserine (a glutamine analog).

Question 2

Roles of the reductase and nitrogenase in regard to nitrogen fixation.

Answer 2

Reductase: provides electrons with high reducing power
Nitrogenase: Vanadium cofactor
High reducing power needed to break triple bond.

Question 3

What are the three ways to make glutamate?

Answer 3

Branch chain amino acid transaminase
Glutamate synthase
Glutamate dehydrogenase (not common)

Question 4

What is meant when we say that an amino acid is conditionally essential?

Answer 4

They are usually only essential during illness, stress, or other physiological condition that could perturb normal biosynthetic processes.

Question 5

From an evolutionary perspective, what is the major reason why we do not synthesize our essential amino acids?

Answer 5

Evolution has allowed for enzyme consideration. Since 8-10 enzymes are usually involved in amino acid synthesis, the balance of obtaining essential amino acids from diet conserves energy that would otherwise be used to make them.

Question 6

Identify the major difference between aminotransferases and amidotransferases in regard to nonessential amino acid synthesis.

Answer 6

Amino: The enzyme that catalyzes the transfer of an amino group to a molecule.

Amido: The enzyme catalyzes transfer of amino group that replaces a carbonyl group on a molecule.

Question 7

What is the major precursor for proline synthesis in the liver?

Answer 7

Liver can synthesize all nonessential amino acids, but proline must be synthesized a different route via arginine because the lack of a certain enzyme.

Question 8

Identify the role of the intestine and kidneys in arginine synthesis.

Answer 8

Arginine contains guanadino group, NH4+ needed. If glutamine and glutamate are ultimate precursors for amino acid synthesis, the nitrogen must be obtained via pathways of glutamine and glutamate synthesis.

Question 9

What role does S-adenosyl methionine play in polyamine synthesis?

Answer 9

S-AM: The sulfur serves as a good facilitator of ammonia transfer while also carrying the methyl group from products.

Question 10

List three of the amino acid families identifies in class other than the “other amino acids” family.

Answer 10

TCA cycle: Oxaloacetate, a-ketoglutarate
Glycolysis: Pyruvate, PEP, 3-phosphoglycerate
PPP: Ribose-5P

Question 11

What makes an essential amino acid essential?

Answer 11

Our metabolic ability to produce it’s a-ketoacid.

Question 12

List three functions of nucleotides aside from genetics.

Answer 12

Glycogen, energy, coenzymes, regulation, group transfers (S-AM)

Question 13

What two amino acids play a role in making purines and pyrimidines?

Answer 13

Aspartate & glutamine

Question 14

Describe the mechanism involved in replacing a carbonyl group with an amino group.

Answer 14

Tautomerization then nitrogen attacks intermediate followed by removal of Pi.

Question 15

Describe 3 methods of regulating purine synthesis in mammals.

Answer 15

Feedback inhibition
PRPP synthesis
Ribose-5P synthesis
IMP–> AMP or GMP

Question 16

What nucleotide that we discussed could not be made if we were deficient in tetrahydrofolate?

Answer 16

Thymine. THF is the preferred methyl carrier and is made from folic acid. Used in both purine and pyrimidine synthesis.

Question 17

Describe substrate channeling with regard to PRPP and purine/pyrimidine synthesis.

Answer 17

PRPP synthesis allows for subsequent synthesis of other things such as histidine and pyrimidines and also resulting in a cumulative effect on regulation.

Question 18

What amino acids can undergo direct deamination and why can these types of amino acids do this?

Answer 18

Serine & threonine because of OH groups

Question 19

What are the two sources of nitrogen in the urea compound?

Answer 19

Aspartate and ammonium ion from glutamate or glutamine.

Question 20

What effect does dietary nitrogen have on the enzymes in the urea cycle?

Answer 20

The more dietary nitrogen present, the higher the production of urea.

Question 21

Diagram (explain) the glucose-alanine cycle.

Answer 21

Muscle: Glucose —–> Pyruvate—>alanine–…
Liver: …—>alanine —-> Pyruvate (also urea out) —> glucose —> (back to muscle)

Question 22

What role does pyridoxal phosphate play in amino acid metabolism?

Answer 22

Aminotransferases & helping to generate other amino acids.

PLP is a prosthetic group of aminotransferases and is an intermediate carrier of amino groups at the active site of aminotransferases.