This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “The Ribosome : The Cell’s Decoding Machine – 1”.
1. How many polypeptides are required for the structural assembly of the ribosome?
a) 10
b) Less than 10
c) 50
d) More than 50
View Answer
Explanation: Single polypeptides can perform DNA or RNA synthesis. In contrast, the machinery for polymerizing amino acids is composed of atleast three RNA molecules and more than 50 different proteins.
2. Which of the following is the slowest process among the following?
a) Replication
b) Translation
c) Splicing
d) Transcription
View Answer
Explanation: The speed of DNA replication that is, 200 to 1000 nucleotides per second. Translation takes place at a rate of only 2 to 20 amino acids per second.
3. The ribosome is designed in such a way so as to keep up with the speed of the RNA polymerase.
a) True
b) False
View Answer
Explanation: The typical prokaryotic rate of translation of 20 amino acids per second corresponding to the translation of 20 amino acids per second corresponding to the translation of 60 nucleotides (20 codons) of mRNA per second. This is similar to the rate of 50 to 100 nucleotides per second synthesized by RNA polymerase.
4. Transcription and translation occur in the same compartment in the cases of both prokaryotes and eukaryotes.
a) True
b) False
View Answer
Explanation: In contrast to the situation in prokaryotes, translation in the eukaryotes is completely separate from transcription. Indeed, these events occur in separate compartments of the cell: transcription occurs in the nucleus, whereas translation occurs in the cytoplasm.
5. Transcriptional coupling ensures a fast rate f translation.
a) True
b) False
View Answer
Explanation: Due to transcriptional coupling prokaryotic translation occurs at a rate of 2 -20 amino acid per second. As eukaryotes lack transcriptional coupling translation proceeds at a more leisurely speed of 2 – 4 amino acid per second.
6. Ribosome has two subunits with 4 rRNA molecules. Which of the four rRNAs is found in the decoding center of the ribosome?
a) 5S
b) 23S
c) 28S
d) 16S
View Answer
Explanation: The ribosome is composed of two subunits the large subunit and the small subunit. The small subunit contains the decoding center and is composed of 16S rRNA and other proteinaceous components.
7. The large ribosomal subunit in prokaryotes has the sedimentation velocity of ___________
a) 30S
b) 40S
c) 50S
d) 60S
View Answer
Explanation: In bacteria the large subunit has a sedimentation velocity of 50 Svedberg units and is accordingly known as the 50S subunit whereas the small subunit is called the 30S subunit. The intact prokaryotic ribosome is referred to as the 70S subunit.
8. Svedberg unit used to distinguish among the rRNAs and proteins by measuring it’s ___________
a) moecular weight
b) mass
c) composition
d) sedimentation velocity
View Answer
Explanation: The ribosome is made up of two subunits comprising of both RNA and protein. Svedberg unit are once again used to distinguish among ribosomal RNAs and is done by measuring the sedimentation velocity during centrifugation.
9. Correct the order of occurrence of the following steps.
i. Binding of the large and small subunit ii. Binding of mettRNA iii. Binding of small subunit iv. mRNA scanning
a) ii, iii, i, iv
b) iii, i, ii, iv
c) iv, iii, i, ii
d) iii, iv, ii, i
View Answer
Explanation: The correct order of occurrence is as follows:
i. Binding of mettRNA
ii. Binding of small subunit
iii. Binding of the large and small subunit
iv. mRNA scanning.
10. Multiple proteins can be synthesized from an mRNA at a time.
a) True
b) False
View Answer
Explanation: Although a ribosome can synthesize only one polypeptide at a time, each mRNA can be translated simultaneously by multiple ribosomes. An mRNA bearing multiple ribosomes is known as a polyribosome or a polysome.
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