This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “The Ribosome : The Cell’s Decoding Machine – 2”.
1. How many charged tRNA substrate is used for the polypeptide formation at a time?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Both the growing chain and the incoming amino acid are attached to tRNAs; as a result, during peptide bond formation, the growing polypeptide is continuously attached to a tRNA. The actual substrates for each round of amino acid addition are two charged species of tRNAs – an aminoacyl-tRNA and a peptidyl tRNA.
2. The peptidyl transferase reaction is a result of ____________ consecutive steps.
a) 2
b) 3
c) 4
d) 1
View Answer
Explanation: The peptidyl transferase reaction is a result of 2 consecutive steps. First, the N-terminus of the protein is synthesized followed by the transfer of the growing polypeptide from the peptidyl-tRNA to the aminoacyl tRNA.
3. The polypeptide bond formation is an ATP dependent process.
a) True
b) False
View Answer
Explanation: Peptide bond formation takes place without the simultaneous hydrolysis of a nucleoside triphosphate. This is because peptide bond formation is driven by breaking the high energy acyl bond that joins the growing polypeptide chain to the tRNA.
4. During the addition of amino acid, the codon on the mRNA is identified by the direct interaction of the anticodon loop of the tRNA.
a) True
b) False
View Answer
Explanation: The 16S rRNA of the small subunit also plays a critical role in the addition of amino acid in the growing polypeptide chain. The anticodon loops of the charged tRNAs and the codons of the mRNA contact the 16S rRNA, not the ribosomal proteins of the small subunit.
5. The peptidyl transferase reaction center of the ribosome contains ___________ sites.
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: The peptidyl transferase reaction center of the ribosome contains 3 sites. The A site for the addition of the aminoacyl-tRNA. The P site is the binding site for the peptidyl tRNA.
6. How many channels are observed in a ribosome molecule?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Three channels are observed in a ribosome molecule. The first two are found in the small subunit that serves as the entry and exit channels for the mRNA. The third channel is found in the large subunit and provides an exit path for the newly synthesized polypeptide chain.
7. The channel for the entry of the mRNA into the decoding center is a crucial feature for the proper decoding of them RNA.
a) True
b) False
View Answer
Explanation: This is because the entry channel is only wide enough for unpaired RNA to pass through. This feature ensures that the mRNA is in an extended form as it enters the decoding center by removing any intramolecular base-pairing interactions that may have formed in the mRNA.
8. The polypeptide elongation channel allows the formation of which of the following structures?
a) α – helix
b) β – sheet
c) Turns
d) Loops
View Answer
Explanation: The channel found in the large subunit, provides an exit path for the newly synthesized polypeptide chain. The size of this channel limits the formation of all secondary structures except the α – helix. For this reason, the final 3D form of the newly synthesized protein is not attained until after it is released from the ribosome.
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