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Essential Biochemistry - Protein Metabolism (Section 1)

1
Which enzyme catalyzes the committed step in the biosynthesis of serotonin?
Answer
(A)
Tryptophan hydroxylase
2
In the context of melanin synthesis, what role does DOPA (dihydroxyphenylalanine) play?
Answer
(A)
Precursor
3
All of the following statements are true in the transamination of amino acids, except:
Answer
(D)
All amino acids can undergo transamination
4
What is the deficiency in alkaptonuria?
Answer
(C)
Homogentisate dioxygenase
5
Which amino acid is formed from ketoglutarate?
Answer
(A)
Glutamate
6
What are the clinical implications of hyperammonemia?
Answer
A
B
C
7
Which of the following amino acids is required for the formation of serine from glycine?
Answer
(D)
Folate
8
What is the role of glutamate dehydrogenase?
Answer
(A)
To remove the amino group from glutamate.
9
In alkaptonuria, which of the following accumulates abnormally in the urine?
Answer
(C)
Homogentisate
10
Which of the following amino acids is the precursor for the synthesis of cysteine?
Answer
(A)
Methionine
11
What is the main function of serine in the body?
Answer
(C)
Precursor for cysteine synthesis
12
Which of the following conditions is associated with a deficiency in the enzymes of the urea cycle?
Answer
A
D
13
What are the two major sources of one-carbon units?
Answer
A
B
14
Which vitamin is essential in the metabolism of methionine and homocysteine?
Answer
(A)
Vitamin B12
15
What is the role of arginase in the urea cycle?
Answer
(C)
To produce urea and ornithine from arginine.
16
Which of the following is a precursor for serotonin?
Answer
(A)
Tryptophan
17
The methylene group, transferred to glycine in converting it to serine, comes from:
Answer
(D)
N5,N10-methylene-THF
18
Which of the following enzymes is responsible for converting glutamate to alpha-ketoglutarate?
Answer
(A)
Glutamate Dehydrogenase
19
Which enzyme is involved in the conversion of phenylalanine to tyrosine?
Answer
(A)
Phenylalanine hydroxylase
20
What is a characteristic of a negative nitrogen balance?
Answer
(C)
Nitrogen excretion exceeds nitrogen intake.
21
Which of the following is the metabolic precursor of cysteine?
Answer
(B)
Homocysteine
22
What are the possible outcomes of defects in the urea cycle?
Answer
A
B
23
Which of the following is a precursor for the synthesis of carnitine?
Answer
A
B
24
What is the role of tetrahydrobiopterin (BH4)?
Answer
A
B
25
What is the role of transamination reactions in amino acid metabolism?
Answer
(B)
To transfer amino groups between amino acids.
26
What is the role of carbamoyl phosphate synthetase I?
Answer
(A)
Synthesizing carbamoyl phosphate in the urea cycle.
27
Which of the following amino acids is most closely associated with the urea cycle?
Answer
(C)
Ornithine
28
What is the first step in the degradation of threonine?
Answer
(D)
Transamination
29
Which of the following conditions is caused by the deficiency of homogentisate dioxygenase?
Answer
(B)
Alkaptonuria
30
Which of the following is a precursor for carbamoyl phosphate?
Answer
(A)
Ammonia and CO2
31
Glycine is synthesized from serine by removal of which group?
Answer
(B)
Hydroxymethyl group
32
What are the key metabolic fates of the carbon skeletons of amino acids?
Answer
A
B
33
Which molecule links the urea cycle to the citric acid cycle?
Answer
(A)
Fumarate
34
The degradation of proline yields which of the following intermediate compounds?
Answer
(C)
Glutamate
35
Which of the following is not used in the synthesis of cysteine?
Answer
(D)
Pyruvate
36
Which organ plays a crucial role in regulating blood ammonia levels?
Answer
(C)
Liver
37
Which of the following are ketogenic amino acids?
Answer
A
B
38
Which of the following are involved in the urea cycle?
Answer
A
B
C
D
39
Following enzymes are endopeptidase, except:
Answer
(D)
Aminopeptidase
40
Which of the following is a major characteristic of the branched-chain amino acids (BCAAs)?
Answer
(C)
They are essential amino acids
41
Which of the following amino acids is synthesized from methionine?
Answer
(A)
Cysteine
42
Which of the following amino acids is primarily ketogenic?
Answer
(B)
Leucine
43
Which of the following is the precursor for the synthesis of dopamine?
Answer
B
C
44
The condition known as phenylketonuria is due to a deficiency in which enzyme?
Answer
(A)
Phenylalanine hydroxylase
45
What is the role of transamination reactions in amino acid metabolism?
Answer
(B)
To transfer an amino group from an amino acid to a keto acid.
46
Which organ is primarily responsible for the synthesis of urea?
Answer
(A)
Liver
47
Which of the following molecules is an essential intermediate in the urea cycle?
Answer
(C)
Ornithine
48
What amino acid accumulates in the urine in cystinuria?
Answer
A
B
C
D
49
Which of the following is a key function of cysteine?
Answer
(B)
Important for detoxification processes
50
What is the role of S-adenosylmethionine (SAM) in the metabolism of amino acids?
Answer
(B)
It is a methyl donor