Synthesis And Degradation Of Amino Acids 2

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1

Serine biosynthesis

-3-phosphoglycerate is oxidized to 3-phosphohydroxypyruvate which is then transaminated to form phosphoserine. Phosphoserine phosphatase removes the phosphate, forming serine

-major sites of synthesis are liver and kidney

2

Serine is generally degraded by ____ to ____, followed by reduction and phosphorylation to form ____, an intermediate of glycolysis that forms ____ and subsequently ____.

-transamination
-hydroxypyruvate
-2-phosphoglycerate
-PEP
-pyruvate

3

When serine levels, serine synthesis is increased by induction of ____ and by release of feedback inhibition of ____

-3-phosphoglycerate dehydrogenase
-phosphoserine phosphatase

4

Glycine can be synthesized from ___ and to a minor extent ___

-serine
-threonine (threonine degradation)

5

____ produced from glycine or obtained from the diet, forms precipitates w/ calcium. (kidney stones) A lack of the transaminase that can convert glyoxyate back to glycine --->_____

-Oxalate (glycine is converted to glyoxylate by the enzyme D-amino acid oxidase. Glyoxylate is then oxidized to oxalate which is sparingly soluble)
-primary oxaluria type I; renal failure

6

Generation of energy from glycine occurs through a ____ that oxidizes glycine to ____

-dehydrogenase
-CO2, ammonia, a carbon that is donated to FH4

7

Serine reacts with homocysteine (produced from methionine) to produce ___, catalyzed by ___

-cystathionine
-cystathionine B-synthase

8

Cleavage of cystathionine by ____, produces ____ and ____, which forms ____

-cystathionase
-cysteine and a-ketobutyrate
-succinyl CoA (via propionyl CoA)

*cysteine inhibits cystathionine B synthase, and therefore regulates its own production to adjust for the dietary supply of cysteine

9

Both cytathionine B-synthase and cystathionase require ____

-pyridoxal phosphate (PLP)

10

2 causes of homocystinemia

-vit. B6 deficiency and congenital cystathionine B-synthase deficiency
-it is associated w/ cardiovascular disease

11

Cystathionuria

-the presence of cystathionine in the urine
-common in premature infants until cystathionase levels rise
**In adults a genetic deficiency of cystathionase or from dietary deficiency of pyridoxine (vit. B6), because cystathionase requires the cofactor pyridoxal phosphate.
-benign