MCG - Gene products and protein synthesis Flashcards
from teachmed booklet 22-23
72) What does it mean to describe the genetic code as degenerate?
a) In the event of a mutation, a change in two bases in a codon will still likely encode the same amino acid.
b) Any one amino acid can be coded by one of 60 permutations of the possible triplet combinations
c) In the event of a mutation, a change in one base in a codon will still likely encode the same amino acid.
d) The genetic code loses information in the conversion between mRNA to protein as part of translation
e) Any one amino acid can be coded by one of 16 permutations of the possible pair combinations
c
73) Nierenberg’s experiment included:
a) Making synthetic mRNA of unknown sequences but known nucleotide concentrations, using a single specific radioactively labelled amino acid per assay in a cell free system to then assess the proportions of amino acid sequences generated to assess the likelihood that the mRNA sequence incorporates the labelled amino acid
b) Making synthetic mRNA of known sequences, using a single specific radioactively labelled amino acid per assay in bacterial expression system to then assess the proportions of amino acid sequences generated to account for the degeneracy of the genetic code
c) Making radioactively labelled mRNAs of unknown sequences, using a known amino acid per assay in bacterial expression system to then assess the yield of that amino acid generated by the labelled mRNA accounting for the lack of a defined reading frame for the ribosome
d) Making radioactively labelled mRNAs of known sequences, using a known amino acid per assay in bacterial expression system to then assess the yield of that amino acid generated by the labelled mRNA accounting for the lack of a defined reading frame for the ribosome
e) Making synthetic mRNA of known sequences, using a single specific radioactively labelled amino acids per assay in a cell free system to then assess the proportions of amino acid sequences generated to account for the lack of a defined reading frame for the ribosome
a
75) What is the reading frame of an mRNA sequence set by?
a) The length of the mRNA sequence
b) The presence of the first start codon in the mRNA sequence
c) Based on whether the mRNA sequence is even or odd numbered
d) The Shine-Dalgarno sequence of the ribosome
e) The Shine-Dalgarno sequence of the mRNA
b
76) Translation requires the following:
a) mRNA, uncharged tRNA, rRNA, protein cofactors and ATP
b) mRNA, charged tRNA, ribosome subunits, cofactors and ATP
c) mRNA, uncharged tRNA, ribosome subunits and ATP
d) mRNA, charged tRNA, rRNA, protein cofactors and ATP
e) mRNA, charged tRNA, ribosome subunits, cofactors
d
79) What is the correct statement in relation to the wobble mechanism?
a) Usually it is the first base that varies.
b) One tRNA molecule can bind to different codons.
c) Only tryptophan and histamine are encoded by a single codon.
d) There is variation in the tRNA anticodon.
e) There are more tRNA molecules than amino acid codons.
b
80) Which of the following codon could pair with a tRNA anticodon 5’ GAC 3’?
a) 5’ GTC 3’
b) 5’ GUU 3’
c) 5’ CUU 3’
d) 5’ CUG 3’
e) 5’ CUC 3’
b
In RNA, adenine (A) pairs with uracil (U), cytosine (C) pairs with guanine (G), and guanine (G) pairs with cytosine (C).
Given the tRNA anticodon 5’ GAC 3’, the complementary mRNA codon would be:
5’ GAC 3’ (tRNA anticodon)
3’ CUG 5’ (mRNA codon)
Now, let’s compare this mRNA codon with the options:
a) 5’ GTC 3’ - This does not match the mRNA codon.
b) 5’ GUU 3’ - This matches the mRNA codon (complementary to the tRNA anticodon).
c) 5’ CUU 3’ - This does not match the mRNA codon.
d) 5’ CUG 3’ - This does not match the mRNA codon.
e) 5’ CUC 3’ - This does not match the mRNA codon.
So, the correct answer is b) 5’ GUU 3’, which pairs with the tRNA anticodon 5’ GAC 3’.
86) Which initiation factors (IFs) bind to the ribosome at the start of translation?
A) IF1 and IF3
b) IF1, IF3 and IF2.
c) IF2 and IF3.
d) IF2, IF3 and IF4.
e) IF1, IF3 and IF4.
b
remember IF2 is involved, its brought by Fmet trna
87) During prokaryotic translation in ribosomes, which hydrolysis reaction occurs with translocation of the ribosome?
a) EF-G-GTP -> EF-G-GDP + Pi
b) EF-G-ATP -> EF-G-ADP + Pi
c) EF-Tu-GTP -> EF-G-GDP + Pi
d) EF-Tu-ATP -> EF-G-ADP + Pi
e) EF-G-ATP -> EF-G-AMP + PPi
a
89)Select the incorrect difference between prokaryotic and eukaryotic translation.
a) In prokaryotes, the initiator tRNA is fmet-tRNAfmet whilst for eukaryotes the initiator tRNA is met-tRNAmet
b) In eukaryotes, it is the 5’cap that interacts with the ribosome whilst in prokaryotes the ribosome is positioned at the start codon by interaction of 16S rRNA with the ShineDalgarno sequence.
c) Prokaryotes have polycistronic mRNA which needs to be modified before translation whilst eukaryotes have monocistronic mRNA that doesn’t need to be modified before translation.
d) In prokaryotes, polyribosomes are free in the cytoplasm whilst in eukaryotes polyribosomes can be free in the cytoplasm or can be bound to rough endoplasmic reticulum
e) Prokaryotes have 70S ribosomes whilst eukaryotes have 80S ribosomes.
c
90) Which of the following combinations of events would result in termination of prokaryotic translation?
a) Codon CAG on the mRNA is presented in the A site and release factor enters the A site with a H2O molecule
b) Codon AUG is presented in the A site and release factor enters the A site with EF-G-
GTP
c) Codon UAG presented in the P site and release factor enters the A site with H2O
d) Codon UCG presented in the A site and release factor enters the A site with EF-G-
GTP
e) Codon UAA presented in the A site and release factor enters the A site with H2O
e
91) Which statement incorrectly describes a ribosome?
a) They release uncharged tRNA
b) 16S rRNA is part of the large subunit of the E.coli ribosome.
c) They are made of 2 subunits
d) They have 3 sites involved in accommodating tRNAs.
e) They have 4 binding sites.
b
Cells have been extracted from patient X, in order to centrifuge isolating the cytoplasm. Within patient X’s cytoplasm are tRNAs. Analysis of this tRNA would indicate that all the statements below are correct except?
a) It is composed of 75-90 nucleotides.
b) It is single stranded.
c) Where the amino acid binds at the 5’ end, it has a CCA-OH sequence.
d) The anticodon is on a central loop.
e) The anticodon binds to mRNA codon.
C
the CCA-OH sequence is at the 3’ end
In a patient with a genetic disorder, which step of protein synthesis is most likely to be affected?
a) Initiation of transcription
b) Elongation of the polypeptide chain
c) Termination of transcription
d) Attachment of the ribosome to the endoplasmic reticulum
e) Translocation of the ribosome along the mRNA molecule
b
