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biochem 2 > protein turnover and amino acid catabolism > Flashcards

protein turnover and amino acid catabolism Flashcards

1
Q

What happens to excess amino acids in the body?
a) They are stored in the liver for future use.
b) They are excreted through urine.
c) They are converted into carbohydrates.
d) They are used as metabolic fuel.

A

d) They are used as metabolic fuel.

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1
Q

Which of the following statements about essential amino acids is true?
a) They can be synthesized by the human body.
b) They are only obtained from dietary sources.
c) They can be stored for later use.
d) They are primarily involved in cellular energy production.

A

b) They are only obtained from dietary sources.

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2
Q

Which of the following amino acids must be acquired through the diet?
a) Glycine
b) Alanine
c) Methionine
d) Aspartic acid

A

c) Methionine

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3
Q

Where does protein digestion primarily begin in the human body?
a) Small intestine
b) Large intestine
c) Stomach
d) Liver

A

c) Stomach

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4
Q

What is the primary proteolytic enzyme of the stomach?
a) Trypsin
b) Amylase
c) Pepsin
d) Lipase

A

c) Pepsin

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5
Q

How are absorbed amino acids released into the bloodstream?
a) Through passive diffusion
b) Via facilitated diffusion
c) By active transport using Na+–amino acid cotransporters
d) Through osmosis

A

c) By active transport using Na+–amino acid cotransporters

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6
Q

What stimulates the secretion of sodium bicarbonate and proteolytic enzymes from the pancreas during protein digestion?
a) Gastric acid
b) Presence of fatty acids
c) Partially digested proteins in the duodenum
d) Absorption of carbohydrates

A

c) Partially digested proteins in the duodenum

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7
Q

How are free amino acids, dipeptides, and tripeptides transported into intestinal cells during protein digestion?
a) Simple diffusion
b) Facilitated diffusion
c) Active transport using specific transporters
d) Osmosis

A

c) Active transport using specific transporters

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8
Q

What is the primary purpose of protein turnover in cells?
a) To increase protein synthesis
b) To remove long-lived proteins
c) To degrade and resynthesize proteins
d) To decrease cellular metabolism

A

c) To degrade and resynthesize proteins

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9
Q

Which enzyme catalyzes the synthesis of polyamines and has a half-life of approximately 11 minutes?
a) Hemoglobin
b) Ornithine decarboxylase
c) Crystallin
d) Pepsin

A

b) Ornithine decarboxylase

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10
Q

What is the role of ubiquitin in protein turnover?
a) It promotes protein synthesis
b) It stabilizes proteins within the cell
c) It tags proteins for destruction
d) It facilitates protein transport

A

c) It tags proteins for destruction

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11
Q

How does ubiquitin attach to target proteins?
a) Through its N-terminal Gly residue
b) Through its C-terminal Gly residue
c) Through its N-terminal Lys residue
d) Through its C-terminal Lys residue

A

b) Through its C-terminal Gly residue

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12
Q

Which process is essential for ubiquitin to attach to target proteins?
a) Hydrolysis of ATP
b) Dehydration synthesis
c) Reduction-oxidation reaction
d) Glycosylation

A

a) Hydrolysis of ATP

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13
Q

What is the role of ubiquitin-conjugating enzyme (E2) in ubiquitin conjugation?
a) Adenylates ubiquitin and transfers it to a sulfhydryl group
b) Transfers ubiquitin to the target protein
c) Transfers ubiquitin to one of its own sulfhydryl groups
d) Transfers ubiquitin from E2 to an ε-amino group on the target protein

A

c) Transfers ubiquitin to one of its own sulfhydryl groups

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14
Q

Which enzyme in the ubiquitin conjugation process transfers ubiquitin from E2 to the target protein?
a) Ubiquitin-activating enzyme (E1)
b) Ubiquitin-conjugating enzyme (E2)
c) Ubiquitin-protein ligase (E3)
d) Protease

A

c) Ubiquitin-protein ligase (E3)

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15
Q

What is the initial step in the process of ubiquitin conjugation?
a) Transfer of ubiquitin from E2 to the target protein
b) Adenylation of ubiquitin by E1
c) Transfer of ubiquitin from E1 to E2
d) Transfer of ubiquitin from E3 to the target protein

A

b) Adenylation of ubiquitin by E1

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16
Q

How are ubiquitin molecules linked in a tetraubiquitin chain?
a) Via disulfide bonds
b) Via hydrogen bonds
c) Via peptide bonds
d) Via isopeptide bonds

A

d) Via isopeptide bonds

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17
Q

What is the role of the E3 enzyme in the addition of multiple ubiquitin molecules?
a) It generates a chain of ubiquitin molecules
b) It dissociates after the first ubiquitin addition
c) It remains bound to the target protein throughout the process
d) It catalyzes the adenylation of ubiquitin by E1

A

a) It generates a chain of ubiquitin molecules

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18
Q

Which type of ubiquitin chain is particularly effective as a signal for protein degradation?
a) Tetraubiquitin chain
b) Monoubiquitin chain
c) Polyubiquitin chain linked via Lys 48
d) Polyubiquitin chain linked via Lys 63

A

c) Polyubiquitin chain linked via Lys 48

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19
Q

What is a degron?
a) A sequence of DNA nucleotides
b) A specific sequence of amino acids indicating a protein should be degraded
c) A protein complex involved in DNA replication
d) A structural motif found in ribosomes

A

b) A specific sequence of amino acids indicating a protein should be degraded

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20
Q

Which type of degron is often an important degradation signal for E3 enzymes?
a) C-degron
b) Z-degron
c) N-degron
d) M-degron

A

c) N-degron

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21
Q

What is a characteristic feature of the N-degron?
a) It is always located at the C-terminus of a protein.
b) It is resistant to proteolytic cleavage.
c) It is added to the protein after synthesis.
d) It is dependent on the identity of the protein’s carboxyl-terminal residues.

A

c) It may only be exposed after proteolytic cleavage or may be added after protein synthesis

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22
Q

Which factor determines the half-lives of cytoplasmic yeast proteins according to the information provided?
a) The sequence of DNA nucleotides
b) The presence of specific amino acids in the protein sequence
c) The presence of specific lipids in the cell membrane
d) The type of RNA molecules associated with the protein

A

b) The presence of specific amino acids in the protein sequence

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23
Q

Which amino acid types are considered primary destabilizing residues for protein degradation according to the N-terminal rule?
a) Acidic and amide amino acids
b) Basic and acidic amino acids
c) Basic and large hydrophobic amino acids
d) Acidic and large hydrophobic amino acids

A

c) Basic and large hydrophobic amino acids

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24
Q

What modification occurs to acidic residues (D, E) according to the N-terminal rule to render them secondary destabilizing residues?
a) Addition of an amine group
b) Addition of a phosphate group
c) Modification by addition of Arg to the N-terminus
d) Modification by deamidation to yield D, E

A

c) Modification by addition of Arg to the N-terminus

25
Q

Which amino acids undergo deamidation to yield D, E, thus becoming tertiary destabilizing residues as per the N-terminal rule?
a) Basic amino acids
b) Acidic amino acids
c) Amide amino acids (N, Q)
d) Hydrophobic amino acids

A

c) Amide amino acids (N, Q)

26
Q

In mammals, what modification occurs to cysteine residues to render them tertiary destabilizing residues according to the N-terminal rule?
a) Reduction to form disulfide bonds
b) Oxidation to sulfonic acid (C*)
c) Acetylation
d) Phosphorylation

A

b) Oxidation to sulfonic acid (C)*

27
Q

Which enzyme is responsible for recognizing the acidic side chain of oxidized cysteine residues in mammals according to the N-terminal rule?
a) Arginase
b) Arg-transferase
c) Oxidoreductase
d) Amidease

A

b) Arg-transferase

28
Q

How does human papillomavirus (HPV) contribute to cervical cancer development?
a) By directly causing mutations in the DNA of cervical cells
b) By activating the expression of oncogenes in cervical cells
c) By inducing the degradation of the tumor suppressor protein p53
d) By stimulating abnormal cell division in cervical tissue

A

c) By inducing the degradation of the tumor suppressor protein p53

29
Q

Which protein produced by HPV is involved in the degradation of the tumor suppressor protein p53?
a) E2
b) E3
c) E6
d) E7

A

c) E6

30
Q

What role does the E3 protein (E6-AP) play in the mechanism of cervical cancer caused by HPV?
a) It directly binds to p53 and promotes its degradation
b) It activates the expression of oncogenes in cervical cells
c) It recruits ubiquitinated E2 protein to degrade p53
d) It binds to the E6 protein produced by HPV, enabling it to target p53 for degradation

A

d) It binds to the E6 protein produced by HPV, enabling it to target p53 for degradation

31
Q

What is the primary function of the proteasome in cellular processes?
a) Synthesizing new proteins
b) Transporting proteins across cellular membranes
c) Degradation of ubiquitinated proteins
d) Storing excess proteins for future use

A

c) Degradation of ubiquitinated proteins

32
Q

Which component of the proteasome controls access to the interior of the catalytic subunit?
a) α-subunits
b) β-subunits
c) 19S regulatory units
d) Ubiquitin molecules

A

c) 19S regulatory units

33
Q

How many subunits does the 20S catalytic unit of the proteasome consist of?
a) 20
b) 26
c) 28
d) 30

A

b) 26

34
Q

What is the primary function of the ubiquitin receptors within the 19S regulatory unit?
a) Binding to ATP molecules
b) Recognizing specific protein substrates
c) Unfolding polyubiquitinated chains
d) Cleaving off intact ubiquitin molecules

A

b) Recognizing specific protein substrates

35
Q

Which cellular energy source is utilized by the 19S regulatory unit to unfold polyubiquitinated chains?
a) Glucose
b) ATP
c) NADH
d) GTP

A

b) ATP

36
Q

What role does the isopeptidase within the 19S regulatory unit play in the ubiquitin-proteasome pathway?
a) Cleaving off intact ubiquitin molecules for reuse
b) Breaking down protein substrates into amino acids
c) Generating polyubiquitin chains
d) Binding to protein substrates for degradation

A

a) Cleaving off intact ubiquitin molecules for reuse

37
Q

Which class of enzymes are the key ATPases within the 19S regulatory unit associated with?
a) DNA polymerases
b) RNA polymerases
c) AAA+
d) Proteases

A

c) AAA+

38
Q

What type of residue is found at the N-terminal of the active sites in the β subunits of the 20S proteasome barrel?
a) Aspartic acid
b) Glutamic acid
c) Threonine
d) Serine

A

c) Threonine

39
Q

How do the active sites within the β subunits initiate degradation of substrates?
a) The hydroxyl group of a Ser residue attacks peptide bonds
b) The hydroxyl group of a Thr residue attacks peptide bonds
c) The carboxyl group of an Asp residue attacks peptide bonds
d) The amino group of a Lys residue attacks peptide bonds

A

b) The hydroxyl group of a Thr residue attacks peptide bonds

40
Q

What type of intermediates are formed during substrate degradation by the active sites of the 20S proteasome barrel?
a) Ester-enzyme intermediates
b) Glycosyl-enzyme intermediates
c) Acyl-enzyme intermediates
d) Peptidyl-enzyme intermediates

A

c) Acyl-enzyme intermediates

41
Q

How are substrates degraded within the 20S proteasome barrel?
a) Non-processive manner with intermediate release
b) Processive manner with intermediate release
c) Non-processive manner without intermediate release
d) Processive manner without intermediate release

A

d) Processive manner without intermediate release

42
Q

Which pathway is primarily responsible for protein degradation in biological processes?
a) Ubiquitin-lysosome pathway
b) Autophagy pathway
c) Ubiquitin-proteasome pathway
d) Endocytosis pathway

A

c) Ubiquitin-proteasome pathway

43
Q

What is the therapeutic application of Bortezomib (Velcade)?
a) Treatment of Alzheimer’s disease
b) Therapy for multiple sclerosis
c) Management of Parkinson’s disease
d) Treatment for multiple myeloma

A

d) Treatment for multiple myeloma

44
Q

What role do degrons play in protein expression regulation?
a) Initiating translation of mRNA
b) Initiating protein folding
c) Targeting proteins for degradation
d) Activating protein kinases

A

c) Targeting proteins for degradation

45
Q

Which inhibitor specifically targets the proteasome of M. tuberculosis without affecting human proteasomes?
a) Velcade
b) HT1171
c) Autophagin
d) Proteolysin

A

b) HT1171

46
Q

Which enzyme is responsible for converting the α-amino group of amino acids to glutamate?
a) Glutamate synthase
b) Glutamine synthetase
c) Glutamate dehydrogenase
d) Glutamic acid decarboxylase

A

c) Glutamate dehydrogenase

47
Q

What type of reaction does glutamate dehydrogenase catalyze?
a) Reductive amination
b) Transamination
c) Oxidative deamination
d) Decarboxylation

A

c) Oxidative deamination

48
Q

Which molecule is formed by the conversion of the nitrogen atom in glutamate by oxidative deamination?
a) Ammonia
b) Urea
c) Glutamine
d) Ammonium ion

A

a) Ammonia

49
Q

In most terrestrial vertebrates, what is NH4+ converted into before excretion?
a) Glutamate
b) Urea
c) Ammonium ion
d) Glutamine

A

b) Urea

50
Q

What is the primary function of aminotransferases (transaminases) in biochemical reactions?
a) Catalyzing the transfer of a keto group from an α-ketoacid to an amino acid
b) Catalyzing the transfer of an amino group from an α-amino acid to an α-ketoacid
c) Catalyzing the transfer of a phosphate group from ATP to an amino acid
d) Catalyzing the transfer of a methyl group from S-adenosylmethionine to an amino acid

A

b) Catalyzing the transfer of an amino group from an α-amino acid to an α-ketoacid

51
Q

What type of reactions can aminotransferases catalyze?
a) Irreversible reactions
b) Redox reactions
c) Hydrolysis reactions
d) Reversible reactions

A

d) Reversible reactions

52
Q

In what direction can aminotransferase reactions proceed?
a) Only from amino acids to α-ketoacids
b) Only from α-ketoacids to amino acids
c) Both from amino acids to α-ketoacids and vice versa
d) None of the above

A

c) Both from amino acids to α-ketoacids and vice versa

53
Q

What can aminotransferases be utilized for in biochemical pathways?
a) Only for breaking down amino acids into α-ketoacids
b) Only for converting α-ketoacids into amino acids
c) Only for synthesizing amino acids from α-ketoacids
d) Both for synthesizing amino acids from α-ketoacids and for converting amino acids into α-ketoacids

A

d) Both for synthesizing amino acids from α-ketoacids and for converting amino acids into α-ketoacid

54
Q

Which coenzyme is required by aminotransferases for their catalytic activity?
a) NAD+
b) FAD
c) Pyridoxal phosphate (PLP)
d) Coenzyme A (CoA)

A

c) Pyridoxal phosphate (PLP)

55
Q

What type of linkage does PLP form with amino acid substrates in aminotransferase reactions?
a) Hydrogen bond
b) Ionic bond
c) Disulfide bond
d) Schiff-base linkage

A

d) Schiff-base linkage

56
Q

How many steps are involved in the transamination process to form pyridoxamine phosphate (PMP)?
a) One
b) Two
c) Three
d) Four

A

c) Three

57
Q

In the absence of substrate, with what group does PLP form a Schiff-base linkage?
a) Carboxyl group of an amino acid
b) Hydroxyl group of an amino acid
c) α-amino group of a specific Lys residue
d) Thiol group of a specific Cys residue

A

c) α-amino group of a specific Lys residue

58
Q

Which subunit structure does aspartate aminotransferase exhibit?
a) Monomer with two distinct domains
b) Dimer with identical subunits
c) Trimer with variable subunits
d) Tetramer with alternating subunits

A

b) Dimer with identical subunits

59
Q

Where does pyridoxal phosphate (PLP) bind within the structure of aspartate aminotransferase?
a) Small domain of each subunit
b) Active site of the enzyme
c) Large domain of each subunit
d) Interface between subunits

A

c) Large domain of each subunit

60
Q

Which amino acid residue within the large domain forms a Schiff-base linkage with PLP?
a) Serine 128
b) Glutamine 172
c) Lysine 258
d) Tyrosine 305

A

c) Lysine 258

61
Q

What is the quaternary structure of aspartate aminotransferase?
a) Tertiary
b) Dimeric
c) Monomeric
d) Tetrameric

A

b) Dimeric

biochem 2 (6 decks)

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