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Exam 21: Amino Acid Metabolism

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Question 1

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Which of the following statements about tryptophan synthase is FALSE?

A) Indole can pass between active sites via a channel in the enzyme.
B) Tryptophan synthase catalyzes two distinct reaction steps to form tryptophan.
C) The enzyme is a tetramer of four identical subunits.
D) The enzyme has two states,an "open" and "closed",to ensure that bound indole is not lost to solvent.
E) The indole group is produced following release of glyceraldehyde-3-phosphate from the indole-glycerol-3-phosphate.

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Question 2

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The neurotransmitters,dopamine,epinephrine,and norepinephrine are synthesized from the amino acid

A) tryptophan
B) tyrosine
C) glutamate
D) aspartate
E) lysine

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Question 3

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In which cellular location listed below does the following reaction take place? Arginine → urea + ornithine

The synthesis of which of the following uses an aminotransferase in the first step of the synthesis?

The total cost of nitrogen reduction is ____ and ___ transferred electrons.

Individuals with an alanine to valine mutation in N⁵,N¹⁰ - methylenetetrahydrofolate reductase (MTHFR) (I) typically have higher levels of homocysteine. (II) have increased risk for cardiovascular disease. (III) typically have increased incidence of oxidative damage to the walls of blood vessels. (IV) are at increased risk,if female,of giving birth to a child with a neural tube defect.

In which cellular location listed below does the following reaction take place? Ornithine + carbamoyl-phosphate → citrulline

Heme biosynthesis

Matching Choose the correct answer from the list.Not all the answers will be used. -The cofactor ______ is used to transfer C₁ units such as methyl,formyl,and methenyl groups.

Which of the following are essential amino acids for adult humans?

The pictured compound,glutamate-5-semialdehyde,is an intermediate in the biosynthesis of which of the following amino acids?

Matching Choose the correct answer from the list.Not all the answers will be used. -The amino acid ______ has been thought to act as a transfer system for NH₃,safely allowing the toxic molecule to be transported from the liver to the kidneys.

What are KFERQ proteins? (I) Proteins that contain the KFERQ pentapeptide sequence (or a similar sequence) . (II) Proteins that are selectively degraded in tissues that atrophy after a prolonged fast (starvation) . (III) A special set of enzymes that are activated in response to starvation.

Which of the following statements about maple syrup urine disease is FALSE? (I) It is caused by a genetic deficiency in the enzyme BCKDH. (II) The disease is fatal unless promptly treated. (III) There is a buildup of the branched-chain $\alpha$ -keto acids. (IV) Patients with the disease excrete urine that smells like maple syrup.

What species are combined to produce carbamoyl phosphate?

Which of the following describes the steps required prior to ATP-dependent degradation of proteins? (I) Ubiquitin is transferred to cysteine on a ubiquitin-conjugating enzyme. (II) The protein is linked to at least four tandemly linked ubiquitin units. (III) Activated ubiquitin is transferred to a lysine of the previously bound protein. (IV) Ubiquitin is attached via a thioester to a unbiquitin-activiating enzyme.

Matching Choose the correct answer from the list.Not all the answers will be used. -ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

Matching Choose the correct answer from the list.Not all the answers will be used. -Aminotransferases utilize a coenzyme synthesized from ______.

Which of the following amino acids is NOT synthesized from aspartate?

Which enzyme catalyses a reaction via an enzyme-bound adenylated intermediate?