Structure of RNA

C i.e. t – RNA

B i.e. Clover leaf pattern

t-RNA molecule gets folded into a structure that appears like a cloverleaf.

There are four arms.

1. Acceptor arm: It consists of a base-paired stem that terminates in the sequence CCA at the 3′ end. This is the attachment site for amino acids.
2. D arm – It contains the base dihydrouridine (D).
3.  Anticodon arm – It contains anticodon that base pairs with the codon of coming mRNA. Anticodon has a nucleotide sequence complementary to the codon of mRNA and is responsible for the specificity of the t RNA.
4. Tyr C arm: It contains both ribothymidine (T) and pseudouridine.

Ans. is ‘c’ i.e., m RNA

The m RNA carries genetic information in the form of codons.

• Codons are a group of three adjacent nucleotides that code for the amino acids of protein.
• Each mRNA molecule is a transcript of antisense or template strand of a particular gene.
• Its nucleotide sequence is complementary to that of antisense or template strand of the gene, i.e. adenine for thyamine, guanine for cytosine, uracil for adenine (as RNA does not contain thymine) and cytosine for guanine.
• For example, if antisense strand of DNA has a gene with sequence 5′-TTACGTAC-3′, its complementary RNA transcript will be 5 ‘-GUACGUAA-3’.

Ans.D. tRNA

• Modified bases found in tRNA are –

1. Dihydrouridine (D) in which one of the double bonds of the base is reduced.
2. Ribothymidine (T) in which methyl group is added to uracil to form thymine. Thus, tRNA is the only RNA that can contain thymine though only some times.
3. Pseudouridine (yr) in which uracil is attached to ribose by a carbon-carbon bond rather than a nitrogen bond.

Ans: A. tRNA of alanine

• • Small nuclear RNAs contain a unique 5′-caps. Sm-class snRNAs are found with 5′-trimethylguanosine caps, while Lsm-class snRNAs are found with S’-monomethyl phosphate caps.
  • mRNAs do have a 7-methyl guanylate cap(m7G).
  • tRNAs and rRNAs don’t require 5′ capping. They have other modifications.