Chapter 15 Flashcards by Davesh Purohit

Which of the following statements about proteins is incorrect?

a. All proteins are made up of some combination of 20 essential amino acids.
b. Like nucleic acids, polypeptides have polarity.
c. A single polypeptide has primary, secondary and tertiary structures.
d. α-helix and β-pleated sheets do not require specific sequence of amino acids to form.
e. Some proteins contain more than one polypeptide chain.

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During initiation of translation, ________.

a. the initiator tRNAmet binds to the A site of a ribosome.
b. specific rRNA base pairs with a sequence in mRNA to position a ribosome at the start codon.
c. IF-3 must be recruited to the 30S ribosome in order for the 70S initiation complex to assemble.
d. there is no energy expenditure as the tRNA binding to mRNA is via complementary base pairing.
e. Both 70S and 30S ribosome subunits must simultaneously recognize an mRNA to bind.

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Which of the following statements about translation is correct?

a. A special tRNA that does not have an attached amino acid binds to stop codons to terminate translation.
b. The first three bases at the 5 end of an mRNA are the AUG at which translation begins.
c. The codon for methionine appears only at the beginning of the mRNA for a protein, not in the middle or in the end.
d. In eukaryotes, the 5 cap and the 3 poly(A) tail are involved in translation initiation.
e. Ribosomes move along an mRNA in the 3 to 5 direction.

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Which of the following is observed in prokaryotes but not in eukaryotes?

a. UGG is an example of a stop codon only found in prokaryotes.
b. An mRNA can be translated by only one ribosome at a time in prokaryotes.
c. The 5’ end of a prokaryotic mRNA can be translated while the 3 end is still being transcribed.
d. Translation does not require any protein factors in prokaryotes.
e. In prokaryotes, ribosomes move along an mRNA in the 3’ to 5’ direction.

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Which of the following codon codes different amino acid from the rest?

a. CUU
b. CUC
c. UUA
d. UUU
e. CUA

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Which of the following statement describes the ‘wobble’ rules correctly?

a. There is a flexible pairing between tRNA and amino acid as there are more tRNAs than the number of amino acids.
b. The number of genetic code exceeds the number of amino acids available in the cell.
c. There are multiple tRNA that may bind to the same amino acids.
d. There are multiple codons that may code for the same amino acids.
e. The third base pairing between the tRNA and mRNA is relaxed.

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For a sequence of nucleotide, how many reading frame is possible?

a. One
b. Two
c. Three
d. Five
e. Ten

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Which amino acid is coded by the stop codons in most organisms?

a. met
b. pro
c. trp
d. cys
e. none

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Which of the following is not required during the process of tRNA charging?

a. amino acid
b. tRNA
c. GTP
d. ATP
e. aminoacyl-tRNA synthetase

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Which of the following does not enhance the biding of the ribosome to the 5’ end of the mRNA?

a. 5’ cap
b. 3’ poly-A tail
c. cap binding proteins
d. poly(A) proteins
e. enhancer

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Process 2 represents ___________.

a. replication
b. transcription
c. translation
d. RNA processing
e. RNA interference

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If the bottom strand of the DNA from the diagram above serves as the template strand, the RNA sequence, left to right 5 to 3, is

a. AUAGGCAGU
b. UCCCAGGUG
c. CACCUGGGA
d. AGGGUCCAC
e. GACAUUAGA

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If the bottom strand of the DNA serves as the template, the amino acid sequence of the protein produced from the RNA would be

a. met-leu-ser.
b. arg-val-his.
c. thr-ile-phe
d. pro-gly-trp
e. lys-val-his

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If the bottom strand of the DNA is the template, the tRNA anticodon sequence, left to right 5 to 3, for the first RNA codon is

a. GGA
b. AUG
c. CAC
d. UCC
e. CCU

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During initiation, the _____subunit is the first part of the ribosome to associate with the mRNA.

a. small
b. large
c. intermediary
d. secondary
e. tertiary

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During elongation, an incoming charged tRNA enters at the __ site of the ribosome.

a. peptidyl (P)
b. aminoacyl (A)
c. Exit (E)
d. Shine-Delgarno
e. Kozak

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Codons that specify the same amino acid are said to be

a. wobbly
b. isoaccepting
c. hypothetical
d. synonymous
e. anonymous

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The amino acid sequence of a polypeptide is referred to as the ______ sequence of the polypeptide.

a. primary
b. secondary
c. tertiary
d. quarternary

There are __ different codons, which encode 20 amino acids and 3 stop codons.

a. 16
b. 20
c. 23
d. 61
e. 64

Which of the following statement about the formation of the peptide bond between amino acids is incorrect?

a. The formation of peptide bond results in formation of a water molecule.
b. The amino group of the first amino acid and the carboxyl group of the second amino group are involved in forming a peptide bond.
c. Carboxyl group of the first amino acid reacts with the amino group of the second amino group to form a peptide bond.
d. A polypeptide formed by a series of peptide bonds will result in two distinct free ends, one with a free amino group and the other with a free carboxyl group.
e. The number of peptide bond formed in a polypeptide varies from protein to protein.

The next step in the translation of this mRNA will be the formation of a peptide bond between which two amino acids?

a. amino acid 2 and amino acid 3
b. amino acid 2 and amino acid 4
c. amino acid 1 and amino acid 3
d. amino acid 1 and amino acid 2
e. amino acid 3 and amino acid 4

After the peptide bond forms, what will happen?

a. tRNA A will be carrying the polypeptide and it will shift to the P site.
b. tRNA A will be carrying the polypeptide and it will shift to the A site.
c. tRNA B will be carrying the polypeptide and it will shift to the P site.
d. tRNA B will be carrying the polypeptide and it will shift to the A site.
e. Ribosome disassembles to release the tRNAs and allow new tRNA to enter.

What is the function of peptidyl transferase activity?

a. it charges tRNAs
b. it acetylates the end of a protein after translation
c. it cleaves the polypeptide from the last tRNA during termination
d. it moves ribosomes along mRNA during translation
e. it forms peptide bonds

A tRNA anticodon is 5GCU3. What amino acid does it carry?

a. ala
b. arg
c. ser
d. pro
e. thr

A bacterial protein is encoded by the following mRNA sequence: 5’-AUGGUGCUCAUGCCCTAA-3’. The second methionine codon (AUG) in this mRNA sequence will: a. serve as the initiation codon. b. encode N-formylmethionine. c. encode methionine that will eventually be removed. d. encode unformylated methionine. be skipped as the translation progresses.

To translate an mRNA requires two other types of RNA. These are: a. tRNA and mRNA. b. tRNA and miRNA. c. tRNA and rRNA. d. rRNA and siRNA. e. snRNA and snoRNA

The genetic code is said to be “degenerate” because: a. there are more codons than amino acids. b. there are more amino acids than codons. c. different organisms use different codons to encode the same amino acid. d. some codons specify more than one amino acid. e. there are more tRNAs than amino acids.

The genetic code is universal except for: a. prokaryotes, which use a different genetic code than eukaryotes. b. a few mitochondrial genes, which substitute one sense codon for another. c. viruses, which use an entirely different genetic code. d. archaebacteria, which have their own genetic code. e. animal species whose cells are more advanced and complex.

The function of aminoacyl-tRNA synthetases is to: a. transcribe tRNA genes. b. match tRNA anticodons and mRNA codons at the ribosome. c. attach appropriate amino acids to corresponding tRNAs. d. form the peptide bond between amino acids at the ribosome. e. synthesize and transport amino acids to the ribosomes.

What is the minimum number of different aminoacyl-tRNA synthetases required by a cell? a. 64, one for each codon b. 61, one for each sense codon c. 30, one for each different tRNA d. 50, one for each different tRNA e. 20, one for each amino acid

When codons that code for the same amino acid differ in their ________, a single tRNA might bind both of them through wobble base pairing. a. 5 base b. middle base c. 3 base

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 ATC 3 d. 5 CTA 3 e. 5’ CAU 3’

An mRNA has the stop codon 5' UAA 3'. What tRNA anticodon will bind to it? a. 5 ATT 3 b. 5 AUC 3’ c. 5’ ACU 3 d. 5’ UUA 3’ e. None

Mechanisms that exist to detect and deal with errors in mRNA in order to ensure the accurate transfer of genetic information are collectively referred to as a. mRNA surveillance b. Proofreading function c. RNA interference d. Alternative processing e. RNA transition

Which of the following mechanisms specifically allows detection and rapid degradation of mRNA containing premature termination codon? a. RNA interference b. no-go decay c. nonsense-mediated mRNA decay d. transfer-messenger RNA mediated ribosomal removal e. nonstop mRNA decay

Which molecule allows the release of mRNA from a stalled ribosome? a. miRNA b. snoRNA c. incRNA d. tmRNA e. siRNA

Which of the following statements about protein folding and post translational modifications of proteins is correct? a. All nascent polypeptide chains have intrinsic ability to fold into the active conformation based on the primary structure. b. Only eukaryotic proteins undergo alterations following translation. c. Amino acids within a protein may be modified by molecular chaperones. d. Signal sequence of a protein helps direct a protein to a specific location within the cell. e. Attachment of a protein called ubiquitin directs proteins to enter into the nucleus.

The genetic code uses three bases to encode one amino acid. Why can’t the code use only two bases to encode each amino acid?

Answer: With four bases in RNA, there are only 16 combinations of two bases. There are 20 different amino acids, so this would not be enough to encode all amino acids.

Write the anticodon, with correct polarity, of all tRNAs that will bind to the mRNA codon 5 UCG 3, considering wobblebase pairing rules.

Answer: 5 CGA 3

Write the codon, with correct polarity, of all mRNA codons that will bind to the tRNA anticodon 5 GCU 3, considering wobblebase pairing rules.

Answer: 5 AGU 3 | 5 AGC 3

A yeast strain was exposed to chemical mutagen. As expected, exposure to mutagen resulted in DNA sequence change in an essential gene you examined. Yet, this mutation did not result in any lethal phenotype. How could you explain this apparent discrepancy?

Answer: The DNA sequence change occurred in a synonymous nucleotide position of an amino acid and as a result the protein sequence remained unaltered. Since the protein sequence was not affected, no lethal phenotype manifested. Another possibility is that the DNA sequence change resulted in an amino acid change, but that amino acid change had no negative effect on protein function (i.e., was a neutral change).

Is the below sequence RNA or DNA? How can you tell? 5 ...GGAGCUCGUUGUAUU... 3

Answer: It is RNA because it contains Us (uracil) and no Ts (thymine).

Which amino acids are encoded, if the reading frame is as shown below, starting from the correct end? 5 ...GGAGCUCGUUGUAUU... 3

Answer: gly-ala-arg-cys-ile...