Practice Exam #2 (Modules 8 & 9) - Unit 2

Question 1

The genetic code is said to be “degenerate” because:

a) There are more amino acids than codons.
b) There are more codons than amino acids.
c) Some codons specify more than one amino acid.
d) Different organisms use different codons to encode the same amino acid.
e) There are more tRNAs than amino acids.

Question 2

Which of the following statements about the genetic code and its degeneracy is TRUE?

a) Isoaccepting tRNAs carry different amino acids that have similar chemical properties.
b) Due to the wobble effect codons can pair with different tRNAs that are isoaccepting.
c) There are more tRNAs than amino acids and more tRNAs than codons.
d) Due to the wobble effect some tRNAs can pair with two or three different codons.

Answer 2

d) Due to the wobble effect some tRNAs can pair with two or three different codons.

Question 3

Which of the codon pairs represent partially degenerate codons?

a) AAA and AAC
b) UGU and GGU
c) GAA and GAG
d) GGU and GAU
e) GAA and GAC

Question 4

Fill in the blanks: There are _______ codons, _____ are sense codons and _____ are stops codons.

a) 64; 60; 3
b) 61; 60; 3
c) 64; 61; 3
d) 61; 60; 1
e) 63; 60; 3

Answer 4

c) 64; 61; 3

Question 5

A tRNA anticodon is 5’-AUC-3’. What amino acid does it carry?

a) Asp
b) stop
c) Ala
d) Leu
e) Ile

Question 6

An mRNA has the codon 5’-UAC-3’. What tRNA anticodon will bind to it?

a) 5’-AUG-3’
b) 5’-GUA-3’
c) 5’-CTA-3’
d) 5’-ATC-3’
e) 5’-CAU-3’

Answer 6

b) 5’-GUA-3’

Question 7

Which of the following mRNA codon(s) would be recognized by the anticodon 3’-UCG-5’?

a) 3’-AGC-5’
b) 5’-AGC-3’
c) 5’-AGC-3’ and 5’-AGU-3’
d) 5’-AGC-3’, 5’-AGU-3’ and 5’-AGI-3’
e) 3’-AGC-5’ and 3’-AGU-5’

Question 8

Determine the amino acid sequence encoded by the ature mRNA sequence shown below. Use the start codon to determine the reading frame.

5’-ACCAUGCCUUGUACGCUCUAAGCA-3’

a) (amino end) Met Pro Cys Thr Leu (carboxyl end)
b) (carboxyl end) Met Pro Cys Thr Leu (amino end)
c) (carboxyl end) Thr Met Pro Cys Thr Leu (amino end)
d) (amino end) Thr Met Pro Cys Thr Leu Ala (carboxyl end)
e) (amino end) Met Pro Cys Thr Leu Ala (carboxyl end)

Answer 8

a) (amino end) Met Pro Cys Thr Leu (carboxyl end)

Question 9

The DNA sequence shown below represents the nontemplate strand of a prokaryotic gene (for the sake of this question, it is a very short gene). The transcription start site is in italics and underlined and the transcription termination site is underlined. Based on the information how many amino acids will the encoded protein contain?

5’-CATGCACTACCGGTGCATGGGCAAACTATAACCC
TAACGGTCCCTA-3’

a) 4 amino acids
b) 13 amino acids
c) 3 amino acids
d) 9 amino acids
e) 7 amino acids

Question 10

The following strand of non-template DNA is part of a prokaryotic gene that codes for a polypeptide. As you know, each DNA strand has three reading frames. For this DNA strand, which of the three reading frame(s) would produce an open reading frame?

3’-GATTAACTAATCATG-5’

a) Second frame
b) First and second frame
c) Third frame
d) First frame
e) Second and third frame

Question 11

Consider the following mRNA molecule. The deletion of the first nucleotide of the second codon would result in what type of mutation?

5’-AUG CCU GCG GCU UAA-3’

a) Missense mutation
b) Deletion
c) Frameshift mutation
d) Nonsense mutation
e) Silent mutation

Answer 11

c) Frameshift mutation

Question 12

The function of aminoacyl-tRNA synthetases is to:

a) attach appropriate amino acids to corresponding tRNAs.
b) form the peptide bond between amino acids at the ribosome.
c) transcribe tRNA genes.
d) transport amino acids to the ribosomes.
e) match tRNA anticodons and mRNA codons at the ribosome.

Answer 12

a) attach appropriate amino acids to corresponding tRNAs.

Question 13

Complete the sentence: During initiation of prokaryotic translation_________.

a) both the 50S and 30S ribosome subunits must simultaneously recognize an mRNA to bind.
b) initiation factors must remain bound to the 30S ribosome in order for the 70S initiation complex to assemble.
c) any amino acid can be attached to the initiator tRNA.
d) the initiator tRNA binds to the A site of a ribosome.
e) specific rRNA base pairs with a sequence in mRNA to position a ribosome at the start codon.

Answer 13

e) specific rRNA base pairs with a sequence in mRNA to position a ribosome at the start codon.

Question 14

Translation in prokaryotes and eukaryotes has some similarities but differs in important ways. Which of the following statements about similarities and differences in prokaryotic and eukaryotic translation is FALSE?

a) Transcription and translation routinely occur simultaneously in prokaryotes but not in eukaryotes.
b) Initiation in prokaryotes, but not in eukaryotes, begins with a formylmethionine.
c) Prokaryotic and eukaryotic large ribosomal subunits contain two rRNAs.
d) Prokaryotic and eukaryotic ribosomes are different sizes.
e) Initiation in eukaryotes, but not in prokaryotes, requires the 5’ cap and the 3’ poly(A) tail of the mRNA.

Question 15

Fill in the blank: During elongation, an incoming charged tRNA enters at the _____ of the ribosome.

a) exit (E) site
b) peptidyl (P) site
c) small subunit
d) mRNA exit channel
e) aminoacyl (A) site

Answer 15

e) aminoacyl (A) site

Question 16

This question addresses concepts like tRNA binding sites, codon-anticodon matching, wobble effect, and polypeptide orientation. Shown below is a snapshot of a prokaryotic mRNA transcript that is undergoing translation. Which statement is incorrect?

a) The tRNA occupies the A-site.
b) The next tRNA to enter the ribosome and pair with a codon could have the anticodon 3’-GUG-5’.
c) The Arg amino acid is at the carboxyl end of the growing polypeptide.
d) Translation is currently in the elongation phase.
e) The amino acid that will be added next to the chain is His.

Answer 16

a) The tRNA occupies the A-site.

Question 17

Which of the following statement(s) about gene regulation concerning operons is INCORRECT?

a) A negative repressible operon is controlled by a regulatory protein that inhibits transcription.
b) For an operon under negative repressible control, interaction with a small molecule is required to prevent the repressor from binding to operator.
c) For an operon under positive repressible control, the operon is usually on due to the presence of an activator.
d) A regulator gene has its own promoter and is expressed independently from the operon.
e) All of the above, a) to d), are incorrect.

Question 18

Determine if and when the Lac operon of the partial diploid shown below would produce a functional (active) β-galactosidase enzyme. Note: only consider the effects of lactose on transcription.

LacI- LacP+ LacO+ LacZ+ / LacI+ LacP- LacO+ LacZ-

a) A functional enzyme will be produced only in the absence of lactose.
b) A functional enzyme will NOT be produced in the presence or absence of lactose.
c) A functional enzyme will be produced only in the presence of lactose.
d) A functional enzyme will be produced in the presence and absence of lactose.

Answer 18

c) A functional enzyme will be produced only in the presence of lactose.

Question 19

Determine if and when the Lac operon of the partial diploid shown below would produce a functional (active) β-galactosidase enzyme. Note: only consider the effects of lactose on transcription.

LacI+ LacP+ LacOC LacZ- / LacI+ LacP- LacO+ LacZ+

a) A functional enzyme will be produced only in the absence of lactose.
b) A functional enzyme will NOT be produced in the presence or absence of lactose.
c) A functional enzyme will be produced in the presence and absence of lactose.
d) A functional enzyme will be produced only in the presence of lactose.

Question 20

In the presence of high levels of both lactose and glucose, which of the following occurs with the E. coli lac operon?

a) The lacI gene does not produce repressor.
b) The cAMP-CAP complex is available to bind near or at the lac promoter.
c) The lacZ gene is not expressed.
d) Lactose is converted to glucose and galactose.
e) Lactose binds to the operator.

Answer 20

c) The lacZ gene is not expressed.

Question 21

Which of the following statements concerning the concept of “colinearity” is INCORRECT?

a) Colinearity generally holds true for the coding regions of prokaryotic viral genes.
b) The vast majority of eukaryotic genes follow the concept of colinearity.
c) Colinearity means that the linear nucleotide sequence of a given gene corresponds directly to the linear amino acid sequence in the corresponding polypeptide.
d) The exception to colinearity between genes and polypeptides is the presence of sequences that are not transcribed or translated.
e) The number of nucleotides in a gene should be precisely proportional to the number of amino acids present in the corresponding polypeptide.

Question 22

Which of the following statements about the control of gene expression is FALSE?

a) Enhancers are regulatory elements that contain binding sites for transcriptional activator proteins.
b) miRNAs methylate histones or DNA to inhibit transcription.
c) Due to alternative splicing, different proteins can be produced from the same mRNA transcript in different tissues or at different times.
d) The RNA Polymerase and other transcription factors make up the basal transcripton apparatus which binds to the core promoter region.
e) Acetylation of histone tails loosens tightly packed nucleosomes and allows the expression of the associated genes.

Answer 22

b) miRNAs methylate histones or DNA to inhibit transcription.