The anticodon of a particular tRNA molecule is
(A) complementary to the corresponding mRNA codon.
(B) complementary to the corresponding triplet in rRNA.
(C) the part of tRNA that bonds to a specific amino acid.
(D) catalytic, making the tRNA a ribozyme.
Which of the following is not true of RNA processing?
(A) Exons are cut out before mRNA leaves the nucleus.
(B) Nucleotides may be added at both ends of the RNA.
(C) Ribozymes may function in RNA splicing.
(D) RNA splicing can be catalyzed by spliceosomes.
The Correct Answer and Explanation is :
Let’s address each multiple-choice question one by one:
Question 1:
The anticodon of a particular tRNA molecule is:
Correct Answer: (A) complementary to the corresponding mRNA codon.
Explanation:
Transfer RNA (tRNA) plays a crucial role in translating the genetic code carried by messenger RNA (mRNA) into a specific sequence of amino acids to form a protein. Each tRNA molecule contains a specific anticodon, which is a sequence of three nucleotides. This anticodon is complementary to a codon on the mRNA strand.
For example, if the mRNA codon is AUG (which codes for methionine), the corresponding tRNA anticodon would be UAC. This ensures that the correct amino acid (methionine, in this case) is brought to the ribosome during protein synthesis.
- Option B is incorrect because tRNA anticodons interact with mRNA, not rRNA.
- Option C is incorrect because the amino acid binding site is on the opposite end of the anticodon loop.
- Option D is incorrect because tRNAs are not ribozymes (although some RNAs, like rRNA, can have catalytic activity).
Question 2:
Which of the following is not true of RNA processing?
Correct Answer: (A) Exons are cut out before mRNA leaves the nucleus.
Explanation:
During RNA processing in eukaryotic cells, the initial RNA transcript (pre-mRNA) undergoes several modifications before it becomes mature mRNA ready for translation:
- Introns, which are non-coding regions, are removed.
- Exons, which are coding regions, are spliced together and retained.
- A 5′ cap is added to the beginning of the RNA.
- A poly-A tail is added to the 3′ end.
The incorrect statement is (A) because exons are not cut out. Instead, introns are the parts that are removed, and exons remain in the final processed mRNA.
- Option B is true: Nucleotides are added at both ends (5′ cap and poly-A tail).
- Option C is true: Some ribozymes (RNA molecules with catalytic activity) can catalyze RNA splicing.
- Option D is true: Spliceosomes, large RNA-protein complexes, carry out RNA splicing.
Summary:
- The anticodon of tRNA is complementary to the mRNA codon.
- During RNA processing, exons are not removed—they are preserved; introns are removed.