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12 Cards in this Set

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  • Back
What are the branched chain amino acids (BCAA)?

-hydrophobic, major component of body protein
Which BCAA are ketogenic and which are ketogenic?

What component do they produce?
Valine --> purely glucogenic
Isoleucine --> both
Leucine --> purely ketogenic

Valine and Isoleucine glucogenic through SUCCINYL CoA (PROPIONYL-CoA)
Isoleucine ketogenic through ACETYL CoA
Leucine ketogenic through HMG CoA (ACETYL CoA)
What are the first two steps of BCAA metabolism?
1. Transamination by a specific amino-transferase to make an alpha-keto-BCAA
2. Oxidative Decarboxylation, shortening chain of BCAA by one C, using a decarboxylating dehydrogenase (same for all three)--site of defect in maple syrup urine disease

*occurs largely in muscle
Describe the modified Cori Cycle using BCAA?
Used to take off Nitrogen from BCAA. First put N onto glutamte then alanine through transamination. Export the N from muscle tothe liver using alanine. Take alanine back to glutamate so that the N can be excreted in urea. The C-skeleton is taken to pyruvate. (Alanine is the same oxidation level as lactate) The cycle lets us do BCAA metabolism in muscle and export N group to liver for excretion. This way couples amino group transport with gluconeogenesis in liver to supply muscle with glucose.
What are the main transaminase reactions?
*Glutamate --> @-KG
*Alanine --> Pyruvate
*Aspartate --> Oxaloacetate
Where does amino acid metabolism take place?
Mainly in the liver where there is an abundance of Branched Chain Dehydrogenase, but for BCAA this mainly takes place in the muscle.
What cofactors do @-KG dehydrogenase and pyruvate dehydrogenase require?
TLC for Nancy
If you have a defect in Branched Chain Dehydrogenase, what disease do you have?

Maple Syrup Urine Disease

S-failure to thrive, feeding difficulties, presents after first protein meal, mental development severely affected, convulsions, characteristic odor
P-low incidence, but 1/200 births among PA Mennonites
T-low protein meal, low in BCAA
How is Propionyl CoA glucogenic? and what BCAAs produce it?
*Propionyl CoA is carboxylated using using biotin as a cofactor to form Methlmalonyl CoA
*Methylmalonyl CoA is rearranged ot succinyl CoA using Methylmalonyl CoA Mutase that requires B12 to straighten the 4 C chain to form Succinyl CoA.
*Succinyl CoA feeds TCA to form new Malate, and Glucose
What aa are ketogenic?
What is the role of B12 in BCAA metabolism?
It is a cofactor of Methylmalonyl CoA Mutase.

It straightens out the 4 C chain of methylmalonyl CoA.

You can get it from animal sources such as meat and eggs.
What two reactions use B12?
1. Homocysteine --> Methionine
2. Methylmalonyl CoA --> Succinyl CoA

*both reactions have toxic substrates, methylmalonate (from MMCoA) causes demyelination