Deck 12: Protein Synthesis Translation of the Genetic Message

Question 1

Wobble allows each codon to interact with more than one tRNA.

Answer 1

True

Question 2

At which position on tRNA is the wobble base of the triplet anticodon?

A) 1^st position (5' letter)
B) 2^nd position
C) 3^rd position (3' letter)
D) Wobble can occur at any position.

Answer 2

1^st position (5' letter)

Question 3

How many codons are known for each amino acid?

A) 1 only
B) 2 only
C) 2 to 4 depending on the nature of the amino acid
D) 1 to 6 depending on the nature of the amino acid

Answer 3

1 to 6 depending on the nature of the amino acid

Question 4

As in RNA and DNA synthesis, the synthesis of proteins follows the following steps, except :

A) Activation of monomers
B) Initiation
C) Elongation
D) Termination
E) All of these are involved in all polymer synthesis

Question 5

Aminoacyl-tRNA Synthetases are involved in which step of translation?

A) activation
B) initiation
C) elongation
D) termination
E) none of these

Question 6

Inosine or hypoxanthine can wobble with all the following bases, except :

A) A
B) C
C) T
D) U
E) Inosine can wobble with all of these bases.

Question 7

Wobble allows a single codon to code for more than one amino acid.

Question 8

The majority of protein synthesis occurs in the

A) nucleus
B) mitochondrion
C) cytoplasm
D) nucleolus

Question 9

Which category of RNA carries amino acids for the process of translation?

A) mRNA
B) rRNA
C) snRNA
D) tRNA

Question 10

Which of the following statements concerning the genetic code is false ?

A) It is based on triplets.
B) It is non-overlapping.
C) Commas are used.
D) It is degenerate.

Question 11

The template for protein synthesis is:

A) a mRNA strand
B) the DNA coding strand
C) the DNA template strand
D) a protein primer
E) none of these

Question 12

At which position on the mRNA is the wobble base of the triplet codon?

A) first position (5' letter)
B) second position
C) third position (3' letter)
D) the wobble base can be at any position

Question 13

What is the maximum number of amino acids that can be specified by a codon consisting of a sequence of two bases?

A) 4
B) 8
C) 16
D) 20

Question 14

Transfer RNAs contain an anti-codon loop meant to match (base pair) with a codon on an mRNA.

Question 15

Which of the following is not an advantage of degeneracy in the genetic code?

A) More than one amino acid can bind to a tRNA.
B) Each tRNA can bind to more than one codon.
C) Most codons can bind to more than one tRNA.
D) Fewer tRNA molecules are needed.

Question 16

What type of assay using tRNAs and ribosomes enabled complete determination of the genetic code?

A) filter binding assays
B) high performance chromatography
C) electrophoresis
D) density gradient centrifugation

Question 17

In the wobble phenomenon, the base that wobbles is found in

A) the tRNA.
B) the mRNA
C) either the tRNA or the mRNA.

Question 18

Which of the following codons does not code for an amino acid?

A) AUG
B) UAA
C) CAU
D) GUU
E) All of these code for an amino acid

Question 19

Which of the following is not a key advantage of wobble in the codon-anticodon reaction?

A) It allows for fewer tRNAs in the cell.
B) It allows for making more than one protein from the same coding sequence.
C) It allows for a certain amount of mutation in the mRNA without affecting the protein sequence.
D) All of these are advantages of wobble.

Question 20

Exceptions to the universality of the genetic code have been observed in

A) viruses
B) prokaryotes
C) eukaryotes
D) mitochondria and 16 other organisms, including some algae and fungae

Question 21

A tRNA was determined to have the following anticodon sequence:
3' − GAI − 5' (I represents the base hypoxanthine)
Which of the following codons can form base pairs with this anticodon?

A) 5' − CUA − 3'
B) 5' − CUC − 3'
C) 5' − CUU − 3'
D) all of these

Question 22

An aminoacyl-adenylate contains

A) an ester bond
B) an acid anhydride bond
C) an amide bond
D) an ether bond

Question 23

The genetic code is said to be degenerate. This means that

A) each codon codes for more than one amino acid.
B) each anticodon can interact with many different triplet sequences in the mRNA, which may differ in any or all of the three nucleotides.
C) many of the amino acids are coded for by different codons.
D) the code is universally used by virtually all species.

Question 24

The amino acids are initially attached to either the 2' or 3' hydroxyl group of the tRNA.

Question 25

Amino acids linked to the 2'-end of a tRNA

A) are regular substrates for protein synthesis.
B) are transferred to the 3' position prior to their use in protein synthesis.
C) are prompted hydrolysed off as part of a proofreading mechanism.
D) never occur.

Question 26

Activation of amino acids always takes place

A) on the ribosomes
B) on a ribosomal subunit
C) on the rough endoplasmic reticulum
D) in the cytoplasm

Question 27

The initial step in the formation of an aminoacyl-tRNA is

A) esterification of the tRNA
B) activation of the amino acid by reaction with ATP
C) activation of the tRNA by reaction with ATP
D) interaction of the mRNA with the tRNA

Question 28

Which of following best describes the two-step process for adding amino acids to tRNAs?
AA = amino acid, P_i = phosphate, PP_i = pyrophosphate

A) AA + ATP → AA − P + ADP; AA − P + tRNA → AA − tRNA + P_i
B) AA + ATP → AA − AMP + PP_i; AA − AMP + tRNA → AA − tRNA + AMP
C) tRNA + ATP → tRNA − P + ADP; tRNA − P + AA → AA − tRNA + P_i
D) tRNA + ATP → tRNA − AMP + PP_i; tRNA − AMP + AA → AA − tRNA + AMP

Question 29

Using the genetic code, indicate which polypeptides would be synthesized if poly (UGG) were used as a synthetic mRNA?

A) poly(gly)
B) poly(trp)
C) poly(trp-val-gly)
D) poly(trp), poly(val), poly(gly)

Question 30

Specificity of aminoacyl-tRNA synthetases is always based on the anticodon.

Question 31

Ribosomal frameshifting in Influenza Virus A is caused by the fact that

A) the virus has a modified genetic code
B) the virus attacks the mRNA
C) the ribosome reaches a rare arginine codon and stalls out
D) none of these

Question 32

Which of the following is not true?

A) A single activating enzyme can interact with all the tRNAs for its corresponding amino acid
B) The selectivity of the aminoacyl-tRNA synthetases for their tRNA molecules is often called the second genetic code
C) There are two major classes of aminoacyl-tRNA synthetases
D) aminoacyl-tRNA synthetases link amino acids to tRNA molecules without the need for an energy source

Question 33

Which linkage best describes the covalent bond between an amino acid (AA) and its tRNA?

A) Amino group of AA linked to 5' − OH of tRNA.
B) Amino group of AA linked to 5' phosphate of tRNA.
C) Carboxyl group of AA linked to 3' − OH of tRNA.
D) Carboxyl group of AA linked to 3' phosphate of tRNA.

Question 34

How many codons are possible in a system in which a sequence of three bases specifies a single amino acid?

A) 20
B) 24
C) 27
D) 64

Question 35

Activation of amino acids

A) produces a pyrophosphate byproduct.
B) produces an inorganic phosphate.
C) produces a cyclic AMP.
D) does not involve the release of energy.

Question 36

The standard free energy change for the following reaction is about zero.
Amino acid + ATP + tRNA → aminoacyl-tRNA + AMP + PP_i
The driving force for this reaction in the cell is

A) the relatively low concentrations of the reactants
B) the subsequent reaction of peptide bond formation, which is energetically favorable
C) the subsequent hydrolysis of pyrophosphate, which releases energy
D) the increased resonance stability of the acyl group on aminoacyl-tRNA

Question 37

Which amino acids have unique codons?

A) met, gly
B) trp, met
C) tyr, met
D) stop, his

Question 38

Which of the following statements concerning tRNAs is false ?

A) They have distinctive cloverleaf tertiary structures
B) They are unique in that they are transcribed by DNA polymerases
C) They contain many modified nucleobases
D) They contain the anticodon sequence

Question 39

The activating enzymes can actually remove wrong amino acids attached to a tRNA.

Question 40

The process of amino acid activation

A) involves the formation of a peptide bond between the amino acid and tRNA
B) takes place by formation of a mixed anhydride of the amino acid and tRNA
C) involves the formation of an ester bond between the amino acid and tRNA
D) none of these

Question 41

Each tRNA molecule has a separate activating enzyme.

Question 42

In bacteria, each mRNA will bind to only one ribosome at a time.

Question 43

At what point does the formylation reaction take place to produce N -formylmethionine?

A) On the free amino acid prior to its addition to a tRNA.
B) After methionine has been added to a specific tRNA.
C) After the methionine-tRNA adduct has complexed with the ribosome.
D) After the first peptide bond is formed on the ribosome.

Question 44

What is the mode of action of puromycin in the inhibition of protein synthesis?

A) inhibition of peptidyl transferase
B) inactivation of EF − G
C) termination of the growing polypeptide chain
D) dissociation of mRNA from the ribosome

Question 45

Which of the following is not a function of elongation factors in E. coli ?

A) Keep the ribosomal subunits bound together.
B) Lead the incoming tRNA to its correct position on the ribosome.
C) Carry GTP to provide energy for certain steps in the elongation process.
D) Regenerate the elongation factors by replacing GTP for GDP.
E) The elongation factors do all of these.

Question 46

Which of the following is not a prokaryotic elongation factor?

A) EF-Tu
B) EF-Ts
C) EF-G
D) EF-P
E) all of these are prokaryotic elognation factors

Question 47

Which of the following is not required for the elongation phase of protein synthesis?

A) GTP
B) fmet-tRNA^fmet
C) peptidyl transferase
D) mRNA

Question 48

The mRNA must contain the following to allow for initiation of protein synthesis in E. coli .

A) A purine rich sequence to bind to the ribosome.
B) A pyrimidine rich sequence to bind to the ribosome.
C) A Shine-Delgarno sequence.
D) A purine rich sequence to bind to the ribosome and a Shine-Delgarno sequence.
E) A pyrimidine rich sequence to bind to the ribosome and a Shine-Delgarno sequence.

Question 49

After peptide bond formation takes place, what step is necessary for continuation of protein synthesis?

A) binding of uncharged tRNA to the ribosome
B) binding of EF − Tu
C) binding of EF − Ts
D) translocation of the ribosome

Question 50

Which of the following best describes the assembly process to initiate translation in prokaryotes?

A) small ribosome subunit associates with large subunit; mRNA associates next; IFs bring in first f-Met-tRNA; bound NTP hydrolyzed.
B) IF binds f-Met-tRNA; small ribosome subunit associates next; mRNA associates next; then large subunit; bound NTP hydrolyzed.
C) IF w\ bound NTP binds f-Met-tRNA; mRNA associates next; small subunit associates next; bound NTP hydrolyzed; large subunit associates.
D) small subunit associates with mRNA; IF w\ bound NTP brings in first f-Met-tRNA; IF then hydrolyses bound NTP; large subunit associates

Question 51

What happens when a stop codon is reached by a ribosome (in the A site)?

A) A termination tRNA^ter binds to the codon and is used to release the growing peptide from the P site tRNA. The ribosome then dissociates.
B) A termination tRNA^ter binds to the codon and the growing peptide is transferred to it. When the peptidyl-tRNA^ter reaches the P site, the ribosome is signaled to release the protein. The ribosome then dissociates.
C) A termination protein binds to the codon and is used to release the growing peptide from the P site tRNA. The ribosome then is likely to dissociate.
D) A termination protein binds to the codon and the ribosome dissociates. A separate peptidyl transferase then releases the protein from the last tRNA to which was attached.

Question 52

The tRNAs may bind to the standard stop codons

A) in cellular organelles which use a modified genetic code.
B) to accommodate the tRNA for the unusual amino acid selenocysteine.
C) when the anticodon in a tRNA mutates to a sequence which can bind.
D) All of these

Question 53

In protein synthesis formation of new peptide bonds is catalyzed by

A) elongation factor EF − Tu
B) elongation factor EF − Ts
C) elongation factor EF − G
D) peptidyl transferase

Question 54

The formylation of methionine in prokaryotes

A) depends on two different tRNAs, where methionine can be formylated when bound to one form and not the other.
B) depends on two different tRNAs, where methionine can be formylated when bound to either one.
C) depends on one tRNA, where methionine is formylated after binding.
D) takes place before methionine is bound to tRNA.

Question 55

Which antibiotic confirmed that the growing peptide chain is transferred to the amino group of the incoming tRNA?

A) Puromycin
B) Streptomycin
C) Cyclohexamide
D) None of these antibiotics was useful for studying the mechanism of protein synthesis.
E) None of these antibiotics actually interferes with peptide transfer.

Question 56

What is the start codon on the mRNA for prokaryotic translation?

A) AUG
B) UAA
C) UAG
D) UGA

Question 57

Which of the following is not a function of termination factors in E. coli ?

A) Cause the ribosomal subunits to dissociate.
B) Bind to the stop codons on the mRNA.
C) Carry GTP to provide energy for certain steps in the termination process.
D) Release the new peptide from the ribosome.
E) The termination factors do all of these.

Question 58

N-formyl methionine

A) can be found attached to every protein in E. coli.
B) can be found attached to some proteins in E. coli.
C) is never found on proteins in E. coli.

Question 59

Which of the following is not a function of initiation factors in E. coli ?

A) Prevent the ribosomal subunits from binding together.
B) Lead the initial tRNA to its correct position on the large subunit of the ribosome.
C) Help the mRNA to bind to the tRNA.
D) Carry GTP to provide energy for certain steps in the initiation process.
E) The initiation factors do all of these.

Question 60

An aminoacyl-tRNA is initially bound to the ribosome

A) at the A site on the 50S subunit
B) at the P site on the 50S subunit
C) at the A site on the 30S subunit
D) at the P site on the 30S subunit

Question 61

Which of the following is necessary for chain termination in protein synthesis?

A) termination codons of mRNA
B) release factors
C) GTP
D) all of these
E) none of these

Question 62

Which of the following is associated with post-translational processing of proteins?

A) Folding into the 3-dimensional shape
B) Breaking large proteins into several components with differing functions
C) Forming disulfide bonds
D) Modification of specific amino acids
E) All of these

Question 63

During elongation, tRNA binds initially to the

A) "A" site on the ribosome.
B) "P" site on the ribosome.
C) "E" site on the ribosome.

Question 64

Leader sequences for protein transport to specific organelles are removed by proteases associated with the:

A) endoplasmic reticulum
B) golgi apparatus
C) nucleus
D) mitochondra
E) none of these

Question 65

Chaperones assist in protein folding by preventing aggregation of proteins before folding is completed.

Question 66

A Shine-Dalgarno Sequence is a

A) sequence of nucleotides in the DNA that interacts with the σ -subunit of RNA polymerase to begin transcription.
B) sequence of nucleotides in an mRNA that interacts with the small subunit of a ribosome to begin translation.
C) sequence of nucleotides in the DNA that interacts with ρ -protein to terminate transcription.
D) sequence of nucleotides in an mRNA that functions to terminate translation.

Question 67

Protein synthesis in prokaryotes always starts with

A) a methionine residue
B) a formylmethionine residue
C) a cysteine residue
D) no specific residue

Question 68

The final form of mRNA in eukaryotes has all these features, except :

A) There will be a special nucleotide cap on the 5' end of the mRNA.
B) There is usually a poly A tail on the 3' end of the mRNA.
C) The mature, active mRNA contains introns.
D) Only a single protein is made from any mature mRNA molecule.
E) All of these are true.

Question 69

Which of the following is true concerning protein synthesis and memory?

A) Animals that cannot make new proteins have no memories
B) Inhibition of protein synthesis in eukaryotes leads to lack of long term memory
C) Production of CREB is inhibited when strong memories are made
D) none of these is true

Question 70

It was recently discovered that AUG is not always the start codon in which of the following systems?

A) viruses
B) mammalian immune system proteins
C) mitochondria
D) all of these

Question 71

A polysome is

A) a complex consisting of one mRNA to which several ribosomes are attached
B) a polypeptide chain in the process of being formed
C) an intermediate stage in the self-assembly of ribosomes
D) an aggregate of ribosomal proteins

Question 72

Why do scientists believe the ribosome is a ribozyme?

A) because there are no proteins in ribosomes
B) because only RNA can catalyze reactions
C) because protein inhibitors have no effect on ribosomes
D) because x-ray crystallography showed that there is no protein in the vicinity of the active site of the peptidyl transferase reaction

Question 73

The first tRNA (bearing fmet) binds to the

A) "A" site of the ribosome.
B) "P" site on the ribosome.
C) "E" site on the ribosome.

Question 74

Under certain conditions, tRNAs can bind to the standard stop codons.

Question 75

In bacteria, translation of the mRNA begins

A) during the synthesis of the mRNA.
B) after synthesis of the mRNA has been completed.
C) after 5' capping of the mRNA.
D) after all processing (capping, polyadenylation, and removal of introns) has taken place.

Question 76

How do eukaryotic ribosomes prevent false starts at inappropriate parts of the mRNA?

A) There is a consensus sequence, called the Kozak sequence, surrounding the start codon in eukaryotes.
B) The Shine-Dalgarno sequence positions the ribosome properly, just as in prokaryotes.
C) Only one start codon ever appears in eukaryotic mRNA, so false starts are not a problem.
D) Nothing; false starts are quite common in eukaryotic translation.

Question 77

The ribosome is actually a ribozyme.

Question 78

The initiation of eukaryotic translation can be a control point in overall gene expression?

Question 79

How do eukaryotic and prokaryotic translation compare?

A) There is little to no difference between them; all the factors are homologous.
B) Eukaryotes utilize very different protein factors during the process but the ribosomes are homologous.
C) Eukaryotic ribosomes are very different, but the protein factors used during the process are homologous.
D) Both eukaryotic ribosomes and the protein factors used during the process are very different.

Question 80

The actual functions of the factors in eukaryotes are similar to the functions of these factors in bacteria.