Deck 10: Protein Synthesis, Processing, and Regulation

Question 1

Aminoacyl tRNA synthetases are enzymes that

A) synthesize transfer RNAs.
B) attach amino acids to specific transfer RNAs.
C) connect amino acids while they are held in place on ribosomes by transfer RNAs.
D) attach the terminal CCA sequence to transfer RNAs.

Answer 1

B

Question 2

E. coli contains about _______ different tRNAs that code for _______ different amino acids.

A) 62; 40
B) 62; 20
C) 50; 20
D) 40; 20

Answer 2

D

Question 3

The capacity for some tRNAs to recognize more than one codon in mRNA is explained by a phenomenon called

A) redundancy.
B) wobble.
C) reading frameshift.
D) degeneracy.

Answer 3

B

Question 4

Translation always occurs on which of the following structures?

A) Ribosomes
B) Endoplasmic reticulum
C) Nuclear envelope
D) Mitochondria

Question 5

The combined sizes of prokaryotic and eukaryotic ribosomes are

A) the same.
B) 30S and 50S, respectively.
C) 40S and 60S, respectively.
D) 70S and 80S, respectively.

Question 6

Which statement is true and provides 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 analysis shows that mRNA occupies the catalytic site where peptide bonds are formed.

Question 7

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

Question 8

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) A CCAAT sequence

Question 9

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

Question 10

The first amino acid that initiates the eukaryotic polypeptide is

A) any amino acid.
B) glutamine.
C) methionine.
D) N-formylmethionine.

Question 11

In translation, mRNAs are read in the _______ direction, and polypeptide chains are synthesized from the _______ ends.

A) 5ʹ to 3ʹ; carboxyl to the amino
B) 5ʹ to 3ʹ; amino to the carboxyl
C) 3ʹ to 5ʹ; carboxyl to the amino
D) 3ʹ to 5ʹ; amino to the carboxyl

Question 12

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.

Question 13

Translation of mRNAs starts at

A) the 3ʹ end of the mRNA.
B) a site downstream of a 3ʹ untranslated region.
C) the 5ʹ end of the mRNA.
D) a site downstream of a 5ʹ untranslated region.

Question 14

The factor that escorts the aminoacyl tRNA to the eukaryotic ribosome and then releases it with GTP hydrolysis following the correct codon-anticodon base pairing is

A) eIF1.
B) eRF1.
C) eIF2.
D) eE $\alpha$ .

Question 15

Termination of translation and release of the polypeptide chain occur 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.

Question 16

To function as a repressor-binding site, the iron response element (IRE) must be within the first 70 nucleotides of the ferritin mRNA. This suggests that protein binding to this IRE

A) regulates message degradation.
B) interferes with the 5ʹ cap binding to the ribosome.
C) blocks the translation start site.
D) inhibits the binding of eEF2.

Question 17

The amount of a protein in a cell is regulated by the rate of

A) translation of its mRNA only.
B) transcription of its gene and translation of its mRNA only.
C) translation of its mRNA and degradation of the protein only.
D) transcription of its gene, translation of its mRNA, and degradation of the protein.

Question 18

Oocytes store mRNAs with _______ and activate them by _______.

A) no cap; adding a cap
B) long poly-A tails; shortening the tails
C) short poly-A tails; lengthening the tails
D) bound siRNA; removing the siRNA

Question 19

Peptide bond formation in translation occurs by

A) an enzyme catalyzed reaction.
B) a tRNA catalyzed reaction.
C) a tRNA synthase catalyzed reaction.
D) an rRNA catalyzed reaction.

Question 20

siRNAs act primarily to inhibit

A) transcription, by binding to specific genes.
B) transcription, by formation of heterochromatin.
C) translation, by blocking ribosomal attachment.
D) translation, by binding to an mRNA.

Question 21

Phosphorylation of eukaryotic initiation factors 2 and 2B (eIF2 and eIF2B)

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.

Question 22

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.

Question 23

Many chaperones are called heat-shock proteins because they

A) are expressed at higher levels after a heat shock than under normal growth conditions.
B) cause fever in mammals.
C) misfold during a heat shock.
D) denature at high temperatures.

Question 24

Transmissible spongiform encephalopathies, such as scrapie, mad cow disease, Creutzfeldt Jakob disease, and kuru, are caused by an infectious agent known as a prion. Prions are composed of

A) protein only.
B) protein and RNA.
C) protein and DNA.
D) RNA surrounded by a lipid-protein coat.

Question 25

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.

Question 26

In cystic fibrosis patients, deletion of an amino acid (phenylalanine 508) in the CFTR protein

A) disrupts the normal interactions of CFTR with chaperones in the endoplasmic reticulum, leading to defective protein folding and reduced levels of functional CFTR in the plasma membranes of affected cells.
B) leads to misfolded proteins, which aggregate to form insoluble amyloid fibrils characterized by β-sheet structures.
C) precludes CFTR phosphorylation by a protein kinase, which is necessary for activation of this protein.
D) prevents ATP hydrolysis required for the active transport of Cl^- by CFTR.

Question 27

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.

Question 28

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) carboxyl group of aspartic acid.

Question 29

Which of the following groups anchors proteins to the outer surface of the plasma membrane?

A) Myristate
B) Farnesyl
C) Palmitate
D) Glycolipid

Question 30

Monomeric G proteins, such as Ras and several elongation factors, are usually in the active state when a molecule of _______ is bound to them.

A) GDP
B) GTP
C) ADP
D) ATP

Question 31

Nitrosylation occurs on the side chain of

A) lysine.
B) cysteine.
C) tyrosine.
D) serine and threonine.

Question 32

Proteins are often regulated by phosphorylation, which is catalyzed by enzymes called

A) protein phosphatases.
B) phosphoproteases.
C) protein phosphorylases.
D) protein kinases.

Question 33

Which of the following amino acids is not commonly phosphorylated to regulate protein activity?

A) Serine
B) Threonine
C) Tryptophan
D) Tyrosine

Question 34

Receptor tyrosine kinases catalyze the transfer of a phosphate group from _______ to the side chains of tyrosine residues.

A) cAMP
B) the plasma membrane
C) ATP
D) GTP

Question 35

Which of the following regulates genes by binding directly to transcription factor proteins?

A) Growth hormone
B) Insulin
C) Steroid hormones
D) Epinephrine

Question 36

Which protein is inhibited when bound to its regulatory subunit(s) but becomes active when free?

A) Adenylyl cyclase
B) cAMP-dependent protein kinase
C) Protein kinase C
D) Phosphorylase kinase

Question 37

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

Question 38

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.

Question 39

In proteasomes, ubiquitin

A) is degraded.
B) is released and recycled.
C) is phosphorylated.
D) has a GTP group added.

Question 40

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) cAMP-dependent protein kinase.

Question 41

The adapters that align amino acids in a sequence determined by the mRNAs are called _______.

Question 42

Of the 64 possible codons, _______ (number) are usually stop codons and the others code for amino acids.

Question 43

Protein synthesis occurs on RNA-protein complexes called _______.

Question 44

Prokaryotic ribosomes differ from eukaryotic ribosomes in that their large and small subunits are _______ and _______, respectively, rather than 60S and 40S.

Question 45

Translation starts at a particular start codon near the _______ end of the mRNA.

Question 46

Initiation sequences in bacterial mRNAs are preceded by a specific sequence called a _______ sequence.

Question 47

Translation is initiated by the binding of the methionyl tRNA and the mRNA to the _______ subunit, after which the other subunit joins the complex.

Question 48

Elongation requires _______ GTP per amino acid.

Question 49

Two human diseases caused by aggregates of misfolded proteins are _______ and _______.

Question 50

The enzyme that catalyzes the breakage and reformation of disulfide bonds between cysteine residues of proteins is _______.

Question 51

Many cellular proteins are regulated by the level of phosphorylation of certain amino acids. The level of phosphorylation results from the opposing actions of two types of enzymes, protein _______ and protein _______.

Question 52

A protein kinase transfers a phosphate group from _______ to a protein.

Question 53

Cells contain 64 tRNAs, with one anticodon for each codon.

Question 54

An 80S eukaryotic ribosome is made up of one large 50S subunit and one small 30S subunit.

Question 55

Eukaryotic mRNAs have a 7-methylguanosine cap on their 3ʹ end.

Question 56

A single mRNA can code for more than one polypeptide chain.

Question 57

One molecule of GTP is split in the process of loading one amino acid onto its tRNA.

Question 58

Ferritin levels can be regulated by IRE binding proteins that bind to a site near the 5ʹ end of ferritin mRNAs and block translation of the RNA.

Question 59

Translation can be regulated by proteins that bind to the 3ʹ untranslated regions of mRNAs.

Question 60

MicroRNAs can regulate translation by targeting proteins that can either cleave an mRNA or repress its translation.

Question 61

Chaperones determine the folded conformation of many proteins.

Question 62

Some chaperones were originally known as heat-shock proteins because they are expressed in cells subjected to high temperatures and facilitate the refolding of denatured proteins.

Question 63

One unique feature of prokaryotes is that their mRNAs are often polycistronic. What does this mean?

Question 64

Experimentally you measure the number of mRNAs being processed from a single gene at 40 copies per minute, yet based on the rate at which ribosomes scan, there should only be about three copies per minute. How might this be explained?

Question 65

What would happen in a bacterium in which the Shine-Dalgarno sequence was mutated?

Question 66

Why do chaperones bind to nascent polypeptide chains while they are still being translated?

Question 67

Why are disulfide bonds, which form between proteins in the endoplasmic reticulum, unable to form between proteins in the cytosol?

Question 68

What would be the likely result of a mutation in the enzyme protein disulfide isomerase (PDI)?

Question 69

By what mechanism is proinsulin converted to insulin?

Question 70

To what do glycosylphosphatidylinositol (GPI) anchor target proteins?

Question 71

What function does covalent modification of proteins serve in the cell that proteolysis cannot?

Question 72

Which statement 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 3ʹ terminus.
C) tRNAs differ in sequence only at the anticodon.
D) There are several modified bases present in mature tRNAs.

Question 73

The function of aminoacyl tRNA synthetases is to

A) covalently attach amino acids to their corresponding tRNA molecules.
B) synthesize tRNA molecules.
C) catalyze the formation of the aminoacyl ATP intermediate during amino acid attachment to tRNAs.
D) catalyze the formation of a peptide bond between amino acids.

Question 74

Which statement about the attachment of amino acids to tRNAs is false?

A) The amino acid is first joined to AMP, forming an aminoacyl AMP intermediate.
B) Two molecules of ATP are required for the process, one at each step.
C) Aminoacyl tRNA synthetases catalyze the reaction.
D) The amino acid is transferred to the 3ʹ end of the tRNA.

Question 75

The first amino acid of eukaryotic polypeptides is

A) the amino acid encoded by the first 5ʹ codon.
B) valine.
C) N-formylmethionine.
D) methionine.

Question 76

The initiator codon in prokaryotes is

A) the first codon located at the 5ʹ end of the mRNA.
B) recognized by scanning of the ribosome downstream of the 5ʹ 7-methylguanosine cap.
C) recognized via the Shine-Dalgarno sequence.
D) the first 5ʹ AUG of the mRNA.

Question 77

Which statement about translational initiation is false?

A) In prokaryotes, ribosomes often bind the mRNA and can scan 5ʹ or 3ʹ until recognizing a Shine-Dalgarno sequence.
B) Viral mRNAs contain internal ribosome entry sites that allow ribosomes to bind to an internal site of the mRNA.
C) Initiation codons in prokaryotic cells are preceded by Shine-Dalgarno sequences.
D) 5ʹ 7-methylguanosine caps serve as the point of recognition and binding for ribosomes in eukaryotic cells.

Question 78

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 the developing of an antibiotic, which of the following would be an effective strategy or target for the drug?

A) Inhibiting translational initiation
B) Inducing premature polypeptide chain termination
C) Inhibiting aminoacyl tRNA binding
D) All of the above

Question 79

The primary function of rRNAs in the ribosome is to

A) serve as a scaffold for the ribosomal proteins.
B) assist in the proper positioning of tRNAs along the mRNA template.
C) catalyze peptide bond formation.
D) assist in the proper folding of ribosomal proteins.

Question 80

Ferritin expression is stimulated by iron because iron

A) stimulates a protein to bind the ferritin mRNA and inhibit its degradation.
B) stimulates the dissociation of a translational inhibitor from the ferritin mRNA.
C) binding stabilizes the ferritin protein.
D) stimulates the extension of poly-A tails of ferritin mRNAs.