CH 20: Anabolism (biosynthesis) of AA

Question 1

Source of Nitrogen

What is the original source of nitrogen for AA?

Answer 1

Atmospheric Nitrogen (N2)

Question 2

Source of Nitrogen

What process converts N2 to NH3?

Answer 2

Nitrogen Fixation

Question 3

Source of Nitrogen

What do microorganisms use to reduce N2 to NH3?

Answer 3

Nitrogenase and ATP

Question 4

Source of Nitrogen

How does NH3/NH4+ enter into AAs?

Answer 4

Through glutamate (by glutamate dehydrogenase) and gluteamine (through glutamine synthetase)

Question 5

Source of Nitrogen

What does the transamination reaction of glutamate establish in AAs?

Answer 5

their stereochemisty and the a-carbon

Question 6

Source of Nitrogen

What does the side-chain nitrogen of Glutamine contribute to?

Answer 6

the N in the ring of Trp and His

Question 7

Source of Carbon Skeleton

Which intermediates make up the carbon skeletons used to synthesize AAs?

Answer 7

Glycolysis (pyruvate, phosphoenolpyruvate, and 3-phosphoglycerate)

Pentose Phosphate Pathway/Sugar Metabolism (ribose-5-phosphate, erythrose-4-phosphate)

Citric Acid Cycle (oxaloacetate, a-ketoglutarate)

Question 8

Source of Carbon Skeleton

What AAs come from a-ketoglutarate?

Answer 8

Glu- derives frmo a-ketoglutarate
Gln- derives from Glu
Pro- cyclized reduced derivative of Glu
Arg- synthesized from Glu via ornithine

Question 9

Source of Carbon Skeleton

What AAs come from 3-phosphoglycerate?

Answer 9

Ser- derives from glycolysis
Gly- derives from Ser
Cys- Derives from Ser

Question 10

Source of Carbon Skeleton

What AAs come from Oxaloacetate?

Answer 10

Asp
Met, Lys, and Thr - derived from Asp
Ile - derived from Thr

Question 11

Source of Carbon Skeleton

What AAs come from Pyruvate?

Answer 11

Ala
Val
Leu

Question 12

Source of Carbon Skeleton

What AAs come from phosphoenolpyruvate and erythrose-4-phosphate?

Answer 12

Phe, Tyr, Trp (rings must be synthesized and closed then oxydized to create double bonds, chorismate is common intermediate)

Tyr can also be derived from Phe

Question 13

Source of Carbon Skeleton

What AAs come from ribose-5-phosphate?

Answer 13

His (precursor of purine biosynthesis)

Question 14

Essential and nonessential AAs

What is the difference between essential and nonessential AAs?

Answer 14

Essential: Must come frmo diet as they cannot be synthesized in mammals due to needing complex pathways
Nonessential: synthesized in simple reaction pathways

Question 15

Regulation of AA biosynthesis

What is AA synthesis regulated by?

Answer 15

Primarily: allosteric enzyme regulation
Secondarily: feedback inhibition