protein synthesis, processing, and regulation Flashcards
1
Q
- The amount of a protein in a cell is regulated by the rate of
a. transcription of its gene.
b. translation of its mRNA.
c. degradation of the protein.
d. All of the above
A
d. all of the above
2
Q
2. In translation, mRNAs are read in the \_\_\_\_\_\_\_ direction, and polypeptide chains are synthesized from the \_\_\_\_\_\_\_ends. a. 5′ to 3′; carboxyl to the amino b. 5′ to 3′; amino to the carboxyl c. 3′ to 5′; carboxyl to the amino d. 3′ to 5′; amino to the carboxyl
A
b. 5′ to 3′; amino to the carboxyl
3
Q
- Translation always occurs on which one of the following structures?
a. Ribosomes
b. Endoplasmic reticulum
c. Nuclear envelope
d. Transfer RNAs
A
a. Ribosomes
4
Q
4. During translation, the codons on the mRNA are recognized by complementary base pairing to the anticodon on the a. ribosome. b. transfer RNA. c. small cytoplasmic RNA. d. aminoacyl tRNA synthetase.
A
b. transfer RNA.
5
Q
- Aminoacyl tRNA synthetases are enzymes that
a. synthesize transfer RNAs.
b. attach amino acids to specific transfer RNAs.
c. connect amino acids together while they are held in place on ribosomes by transfer
RNAs.
d. attach the terminal CCA sequence to transfer RNAs.
A
b. attach amino acids to specific transfer RNAs.
6
Q
6. E. coli contains about \_\_\_\_\_\_\_ different tRNAs that code for \_\_\_\_\_\_\_ different amino acids. a. 62; 40 b. 62; 20 c. 40; 20 d. 20; 16
A
c. 40; 20
7
Q
7. The capacity for some tRNAs to recognize more than one codon in mRNA is explained by a phenomenon called a. a reading mistake. b. redundancy. c. wobble. d. a reading frameshift.
A
c. wobble
8
Q
- Prokaryotic and eukaryotic ribosomes are
a. the same size.
b. 30S and 50S, respectively.
c. 40S and 60S, respectively.
d. 70S and 80S, respectively
A
d. 70S and 80S, respectively
9
Q
- Translation of mRNAs starts at
a. the 3′ end of the mRNA.
b. a site downstream of a 3′ untranslated region.
c. the 5′ end of the mRNA.
d. a site downstream of a 5′ untranslated region.
A
d. a site downstream of a 5′ untranslated region.
10
Q
- Eukaryotic ribosomes recognize and initially bind to what structure on the mRNA?
a. A Shine-Dalgarno sequence
b. The 7-methylguanosine cap
c. A TATA sequence
d. An AUG initiation codon
A
b. The 7-methylguanosine cap
11
Q
- The factor that escorts the amionacyl tRNA to the prokaryotic ribosome and then
releases it with GTP hydrolysis following the correct codon–anticodon base pairing is
a. IF-1.
b. EF-1
c. EF-Tu.
d. EF-G.
A
a. IF-1
12
Q
- snRNAs act primarily to inhibit
a. transcription by binding to specific genes
b. transcription, by formation of heterochromatin
c. translation, by blocking abnormal attachment
d. translation, by binding to an mRNA
A
d. translation, by binding to an mRNA
13
Q
- processing of RNA transcripts occurs
a. only in eurkaryotic cells
b. only with mRNA transcripts
c. only with tRNA and mRNA transcripts
d. with tRNA, RNA, and mRNA transcripts
A
d. with tRNA, RNA, and mRNA transcripts
14
Q
- DNA sequences that prevent enhancers from acting on promoters located on adjacent domains are called
a. Insulators
b. Molators
c. Repressors
d. Boundaries
A
a. Insulators
15
Q
- The formation of peptide bonds is catalyzed by which portion of the bacterial ribosome?
a. Proteins of the small subunit
b. 16S rRNA
c. proteins of the large subunit
d. 23S rRNA
A
d. 23S rRNA
16
Q
- Which of the following statements is evidence that a certain component of the ribosome catalyzes protein synthesis?
a. Ribosomes are inactive after protease digestion
b. Ribosomes are inactive after RNase digestion
c. Structural analysis shows that proteins occupy the catalytic site where peptide bonds are formed
d. Structural anaylsis shows that rRNA occupies the catalytic site where peptide bonds are formed
e. Both b and d
A
e. Both b and d
17
Q
- The first amino acid that initiates the eukaryotic polypeptide is which of the following?
a. Any amino acid
b. Glutamine
c. Methionine
d. N-formylmethionine
A
c. Methionine
18
Q
- The first step in the initiation of protein synthesis is the binding of ___ to the ___
a. Initiation factors; initiation codon
b. Initiation factors; small ribosomal subunit
c. The small ribosomal subunit; initiation codon
d. The initiator tRNA; initiation codon
A
b. Initiation factors; small ribosomal subunit
19
Q
- Termination of translation and release of the polypeptide chain occurs when
a. tRNA binds to a termination codon via a complementary anticodon but lacks an amino acid
b. a protein release factor binds to the termination codon
c. a trNA with a complementary anticodon binds to a termination codon, and a release factor bound to the CCA end releases the chain
d. a small molecule shaped like puromycin binds to the termination codon
A
a. tRNA binds to a termination codon via a complementary anticodon but lacks an amino acid
20
Q
- Which of the following antibiotics does not inhibit protein synthesis
a. Erythromycin
b. Streptomycin
c. Tetracycline
d. Penicillin
A
d. Penicillin
21
Q
- Which of the following antibiotics inhibits protein synthesis only in eukaryotic cells
a. Erythromycin
b. Cycloheximide
c. Puromycin
d. Chloramphenicol
A
b. Cycloheximide
22
Q
- To function as a repressor-binding site, the iron response element (IRE) must be in the first 70 nucleotides of the ferritin mrNA. This suggests that protein binding to this IRE
a. Regulates message degradation
b. Interferes with the 5’ cap binding to the ribosome
c. Blocks the translation start site
d. Inhibits the binding of EF-Tu
A
b. Interferes with the 5’ cap binding to the ribosome
23
Q
- Activation of translation after fertilization occurs by
a. Synthesis of new mRNAs
b. Uptake of amino acids into the fertilized egg
c. Binding of an activator protein to the 5’ untranslated region
d. Elongation of poly-A tails on mRNAs
A
a. Synthesis of new mRNAs
24
Q
- Phosphorylation of elongation factors 2 and 2B
a. Allows them to be recycled back to the ribosome
b. Allows them to initiate translation
c. Blocks their exchange of bound GDP for GTP
d. Blocks the addition of a terminal phosphate to the bound GDP
A
a. Allows them to initiate translation
25
Q
- Proteins that facilitate the folding of other proteins are called
a. Foldases
b. Binding proteins
c. Chaperones
d. Escorts
A
c. Chaperones
26
Q
- Many chaperones are called heat-shock proteins because they
a. Are expressed at higher levels after a heat shock than at normal growth conditions
b. Cause fever in mammals
c. Misfold during a heat shock
d. All of the above
A
a. Are expressed at higher levels after a heat shock than at normal growth conditions
27
Q
- The enzyme protein disulfide isomerase, which facilitates breakage and reformation of disulfide bonds, is located primarily in the
a. Cytosol
b. Lumen of the endoplasmic reticulum
c. Matrix of mitochondria
d. Lumen of lysosomes
A
b. Lumen of the endoplasmic reticulum
28
Q
- The signal sequence of a protein being translocated into the endoplasmic reticulum is cleaved off by a signal peptidase located
a. On the outer surface of the ER membrane
b. On the inner surface of the ER membrane
c. In the lumen of the ER
d. On the amino terminal of the polypeptide being translocated
A
b. On the inner surface of the ER membrane
29
Q
- The correctly folded three-dimensional configuration of a protein is determined primarily by the
a. Sequence of nucleotides of its gene
b. Primary sequence of its amino acids
c. Chaperones with which it interacts
d. Pathway by which it folds
A
b. Primary sequence of its amino acids
30
Q
- A signal peptidase
a. Removes a signal sequence from a polypeptide chain after it passes through a channel into the rough ER
b. Attaches a signal sequence to a growing polypeptide chain before it passes into the rough ER
c. Attaches an acetyl group the to the 5’ end of a polypeptide after removal of the initial methionine
d. Removes the initial methionine from a polypeptide chain
A
a. Removes a signal sequence from a polypeptide chain after it passes through a channel into the rough ER
31
Q
- N-linked glycosylation attaches a complex carbohydrate onto the
a. Free amino group at the amino terminal end of the polypeptide
b. Amino group of asparagine
c. Amino group of lysine
d. Hydroxyl group of serine
A
b. Amino group of asparagine
32
Q
- Which of the following groups anchor proteins to the outer surface of the plasma membrane?
a. Myristate
b. Farnesyl
c. Palmitate
d. Glycolipid
A
d. Glycolipid
33
Q
- Prior to N-linked glycosylation of a protein, a complex oligosaccharide is assembled in the endoplasmic reticulum on a lipid carrier called
a. A prenyl group
b. Myristic acid
c. Dolichol phosphate
d. Phosphatidylinositol
A
c. Dolichol phosphate
34
Q
- Inhibitors of the synthesis or transfer of which of the following groups to the Ras oncogene proteins interfere with the growth of many cancer cells
a. Myristate
b. Farnesyl
c. Palmitate
d. Glycolipid
A
b. Farnesyl
35
Q
- Feedback inhibition is a type of allosteric regulation in which a molecule binds to ___ and inhibits its ___
a. a site on an enzyme distinct from the catalytic site; activity
b. the catalytic site on an enzyme; activity
c. the mRNA for an enzyme; synthesis
d. the gene for an enzyme; synthesis
A
a. a site on an enzyme distinct from the catalytic site; activity
36
Q
- in feedback inhibition, the inhibiting molecule is often the
a. substrate of the inhibited enzyme
b. product of the inhibited enzyme
c. first unique molecule in the pathway
d. end product of the pathway
A
d. end product of the pathway
37
Q
- Which of the following is a hormone that regulates genes by binding directly to transcription factor proteins?
a. Growth hormone
b. Insulin
c. Estrogen
d. Epinephrine
A
c. Estrogen
38
Q
- Monomeric G proteins like Ras and several elongation factors are usually in the active state when a molecule of which of the following of binds to them?
a. GDP
b. GTP
c. ADP
d. ATP
A
b. GTP
39
Q
- Binding of the activating nucleotide di-or triphosphate causes the Ras protein to (first)
a. Separate into subunits
b. Split the terminal phosphate from the nucleotide-phosphate
c. Undergo a configurational change
d. Attach a farnesyl tail
A
c. Undergo a configurational change
40
Q
- Proteins are often regulated by phosphorylation by enzymes called
a. Protein phosphatases
b. Phosphoproteases
c. Protein phosphorylases
d. Protein kinases
A
d. Protein kinases
41
Q
- Which of the following amino acids is not commonly phosphorylated to regulate protein activity
a. Serine
b. Threonine
c. Tryptophan
d. Tyrosine
A
c. Tryptophan
42
Q
- Proteins can be regulated by the removal of phosphates by
a. Protein phosphatases
b. Phosphoproteases
c. Protein phosphorylases
d. Protein kinases
A
a. Protein phosphatases
43
Q
- Which of the following is an example of a protein that is inhibited when bound to its regulatory subunit(s) but becomes active when free
a. Adenylyl cylase
b. cAMP-dependent protein kinase
c. Protein kinase C
d. Phosphorylase kinase
A
b. cAMP-dependent protein kinase
44
Q
- Nitrosylation (addition of NO groups to proteins) occurs on the side chain of which amino acid(s)
a. Lysine
b. Cysteine
c. Tyrosine
d. Serine or threonine
A
b. Cysteine
45
Q
- In a major protein degradation pathway, a short polypeptide called ___ is attached to a protein to target it for destruction
a. Glutathione
b. Ubiquinone
c. Ubiquitin
d. KDEL
A
c. Ubiquitin
46
Q
- A proteasome is a
a. Vesicle containing proteolytic enzymes
b. Precursor to lysosomes
c. Complex of a proteolytic enzyme and the protein that is being degraded
d. Multisubunit protease complex that degrades proteins marked for destruction
A
d. Multisubunit protease complex that degrades proteins marked for destruction
47
Q
- What happens to ubiquitin in proteasomes
a. It is degraded
b. It is released and recycled
c. It is phosphorylated
d. It has an AMP group added
A
b. It is released and recycled
48
Q
- A protein that becomes marked in a sequence called the destruction box and is degraded by proteasomes is
a. Tubulin
b. Cyclin
c. Ras
d. Cdk1 protein kinase
A
b. Cyclin
49
Q
- Degradation of cytoplasmic organelles occurs by fusion of lysosomes with structures called
a. Secondary lysosomes
b. Phagolysosomes
c. Autophagosomes
d. Mitochondria
A
c. Autophagosomes
50
Q
- The function of aminoacyl tRNA synthetases is
a. To covalently attach amino acids to their corresponding tRNA molecules
b. To synthesize tRNA molecules
c. To catalyze the formation of the aminoacyl-ATP intermediate during amino acid attachment to tRNAs
d. To catalyze the formation of a peptide bond between amino acids
A
c. To catalyze the formation of the aminoacyl-ATP intermediate during amino acid attachment to tRNAs
51
Q
- The primary function of rRNAs in the ribosome is
a. To serve as a scaffold for the ribosomal proteins
b. To assist in the proper positioning of tRNAs along the mRNA template
c. To catalyze peptide bond formation
d. To assist in the proper folding of ribosomal proteins
A
c. To catalyze peptide bond formation
52
Q
- The initiator codon in prokayrotes is
a. The first codon located at the 5’ end of the mRNA
b. Recognized by scanning of the ribosome downstream of the 5’ methylguanosine cap
c. Recognized via the Shine-Delgarno sequence
d. The most 5’ AUG of the mRNA
A
c. Recognized via the Shine-Delgarno sequence
53
Q
- Ferritin expression is stimulated by iron because
a. Iron stimulates a protein to bind the ferritin mRNA and inhibit its degradation
b. Iron stimulates the dissociation of a translational inhibitor from the ferritin mRNA
c. Iron binding stabilizes the ferritin protein
d. Iron stimulates the extension of poly-A tails of ferritin mRNAs
A
a. Iron stimulates a protein to bind the ferritin mRNA and inhibit its degradation
54
Q
- Chaperones are required for all of the following processes except
a. Protein transport into the nucleus
b. Protein transport into the ER
c. Folding during protein synthesis
d. Assembly of proteins consisting of multiple polypeptide chains
A
a. Protein transport into the nucleus
55
Q
- The proteins shaped like “double doughnuts” that are involved in protein folding are called
a. The Hsp70 proteins
b. Protein disulfide isomerases
c. The Hsp60 (chaperonin) proteins
d. Peptidyl prolyl isomerases
A
a. The Hsp70 proteins
56
Q
- All of the following are common lipid modifications to proteins except
a. N-myristoylation
b. Prenylation
c. GPI anchor addition
d. Glycosylation
A
d. Glycosylation
57
Q
- Protein phosphatases
a. Catalyze the addition of phosphate residues to proteins
b. Catalyze the removal of phosphate residues from proteins
c. Catalyze the addition of glycosylphosphatidylinositol to proteins
d. Are proteins that specifically bind phosphorylated proteins
A
b. Catalyze the removal of phosphate residues from proteins
58
Q
- cAMP activated cAMP-dependent protein kinase by
a. stimulating its phosphorylation
b. stimulating the dimerization of kinase subunits
c. stimulating the release of a translational inhibitory protein bound to its mRNA
d. binding regulatory subunits and inducing their release from the catalytic subunits
A
d. binding regulatory subunits and inducing their release from the catalytic subunits
59
Q
- the half-lives of proteins in the cell vary widely, ranging from
a. milliseconds to seconds
b. minutes to days
c. days to weeks
d. three to seven minutes
A
b. minutes to days
60
Q
- which of the following statements regarding tRNAs is false
a. tRNAs are approximately 70-80 bases long and form a cloverleaf structure
b. all tRNAs have a CCA sequence at their 3’ terminus
c. tRNAs differ in sequence only at the anticodon
d. there are several modified bases present in mature tRNAs
A
c. tRNAs differ in sequence only at the anticodon
61
Q
- which of the following is not associated with the attachment of amino acids to tRNAs
a. the amino acid is first joined to AMP, forming an aminoacyl AMP intermediate
b. the amino acid is transferred to the 3’ end of the tRNA
c. aminoacyl tRNA synthetases catalyze the reaction
d. two molecules of ATP are required for the process, one at each step
A
d. two molecules of ATP are required for the process, one at each step
62
Q
- which of the following statements about translational initiation is false
a. initiation codons in prokaryotic cells are preceded by Shine-Dalgarno sequences
b. viral mRNAs contain internal ribosome entry sites that allow ribosomes to bind to an internal site of the mRNA
c. in prokaryotes, ribosomes often bind the mRNA and can scan 5’ or 3’ until recognizing a Shine-Dalgarno sequence
d. 4 5’ 7-methyl caps serve as the point of recognition and binding for ribosomes in eukaryotic cells
A
c. in prokaryotes, ribosomes often bind the mRNA and can scan 5’ or 3’ until recognizing a Shine-Dalgarno sequence
63
Q
- antibiotics are powerful medications that inhibit the growth of bacteria. They work at a variety of levels, but many target the process of protein synthesis in the bacterial cell. In developing an antibiotic, which of the following would be an effective strategy or target for the drug
a. inhibition of translational initiation
b. induction of premature polypeptide chain termination
c. inhibition of aminoacyl tRNA binding
d. all of the above
A
d. all of the above
64
Q
- which of the following statements about translational regulation of ferritin is false
a. the iron response element is a unique sequence of amino acids near the amino terminal end of the growing polypeptide
b. in the absence of iron, an iron regulatory protein binds the IRE, preventing translation
c. in the presence of iron, the ferritin protein is translated
d. the iron binding protein must bind the mRNA within about 70 bases of the 5’ mRNA cap
A
a. the iron response element is a unique sequence of amino acids near the amino terminal end of the growing polypeptide
65
Q
- which of the following is not associated with translational regulation
a. dephosphorylation of 4E-BPs that bind eIF4E and prevent its interaction with eIF4G
b. phosphorylation of eIF2 that inhibits GDP/GTP exchange
c. cleavage of mRNA by miRNA/RISC complexes
d. autolytic degradation of the mRNA by folding back on itself
A
d. autolytic degradation of the mRNA by folding back on itself
66
Q
- signal sequences are sequences of hydrophobic amino acids that target membrane translocation. Signal sequences are found
a. in the amino terminal end of the secreted protein
b. in the carboxyl terminus of the secreted protein
c. on the cytoplasmic side of the membrane channel proteins
d. on the amino terminus of the 28S of certain ribosomal complexes associated with secretion
A
a. in the amino terminal end of the secreted protein
67
Q
- which of the following is an example of posttranslational modification
a. glycosylation
b. proteolysis
c. palmitoylation
d. all of the above
A
d. all of the above
