Chapter 23. Protein Turnover and Amino Acid Catabolism

Question 1

A cycle that allows the use of branched chain amino acids by muscle as a fuel. The nitrogen removed from the branched chain amino acids is transferred to pyruvate to form alanine, which is released into the bloodstream. In the liver, alanine is taken up and converted into pyruvate for the subsequent synthesis of glucose.

Answer 1

Glucose-alanine cycle

Question 2

amino acids whose carbon skeletons, in toto or in part, are degraded into acetyl CoA or acetoacetyl CoA; only leucine and lysine are solely ketogenic.

Answer 2

Ketogenic amino acid

Question 3

an allosteric activator of the mammalian carbamoyl phosphate synthetase involved in the synthesis of urea.

Answer 3

N-acetylglutamate

Question 4

a class of enzymes that transfer an α-amino group from an α-amino acid to an α-keto acid.

Answer 4

Aminotransferase (transaminase)

Question 5

Large protein complexes that carry out routine degradation of ubiquitinated cellular proteins as well as of those from pathogens.

Answer 5

Proteasomes

Question 6

describing amino acids whose carbon skeleton, in toto or in part, can be converted into substrates for gluconeogenesis.

Answer 6

Glucogenic amino acid

Question 7

the enzyme that begins the urea cycle by catalyzing the synthesis of carbamoyl phosphate from bicarbonate, ammonium ion and ATP. The enzyme also catalyzes the initial reaction in pyrimidine biosynthesis.

Answer 7

Carbamoyl phosphate synthetase

Question 8

An aminated form of pyridoxal phosphate that is an intermediate in transamination reactions.

Answer 8

Pyridoxamine phosphate (PMP)

Question 9

prosthetic group derived from vitamin B6(pyridoxine) that plays a key role in transamination reactions.

Answer 9

Pyridoxal phosphate (PLP)

Question 10

A specific sequence of amino acids that is a signal for protein destruction.

Answer 10

Degron

Question 11

the enzyme that catalyzes the oxidative deamination of glutamate, yielding ammonium ion and α-ketoglutarate.

Answer 11

Glutamate dehydrogenase

Question 12

a cofactor from which the electron carrier tetrahydrobiopterin is derived.

Answer 12

Biopterin

Question 13

a disease caused by the inability to convert phenylalanine into tyrosine, which results in excess phenylalanine and its secondary metabolites; the disease is characterized by severe retardation.

Answer 13

Phenylketonuria

Question 14

cyclic pathway that converts excess ammonia into urea for secretion; it was the first metabolic pathway to be discovered.

Answer 14

Urea cycle

Question 15

a small, highly conserved protein present in all eukaryotes that, when attached to another protein, targets it for proteolytic destruction.

Answer 15

Ubiquitin