Question

Which of the following has a clover leaf shaped structure?
A. tRNA
B. rRNA
C. DNA
D. mRNA

Answer 1

Hint: Genetic material can be DNA as well as RNA. It carries genetic information that passes from one generation to the next one. DNA is Deoxyribonucleic acid and RNA is ribonucleic acid.There are various types of RNA i.e. tRNA, mRNA, rRNA, snRNA.

Complete Answer:
- tRNA (Transfer RNA) has a clover leaf shape as it has a series of stem-loop structures which are known as arms. These include:
- Acceptor arm: It is formed by base-pairing between nucleotides at 5' and 3 ends. The sequence CCA, which occurs at the terminus, is not base-paired and is the point of attachment of amino acid.
- D or DHU arm is a stem-loop structure containing dihydrouridine, an unusual pyrimidine nucleotide.
- The anticodon arm of tRNA is responsible for recognizing and binding codons in the mRNA.
- The extra/optional or variable arm occurs only in some tRNAs. They may be small containing only 2-3 nucleotides.
- TyC arm contains the sequence TyC where i stands for a modified nucleotide called pseudouridine.
- Three-dimensional structure of RNA was proposed by S. H. Kim in 1973. Three-dimensional structure of yeast phenylalanine tRNA shape resembles an upside-down letter L.
- mRNA called Messenger RNA. It is an intermediary in the process of decoding genes into polypeptide chains. It is also called "informational" RNA as it passes genetic information from DNA to protein. It is produced by DNA with help of a process called transcription by RNA polymerase II.
- rRNA and Ribosomal RNA. It is the major component of ribosomes and is also called insoluble RNA Ribosomal RNA is synthesized in the nucleolus by the transcription with RNA polymerase I.
- DNA ( Deoxyribonucleic acid): It is double stranded genetic material found in eukaryotes. It is a double helix I structure and contains various nucleosides and nucleotides.

The correct answer is (A) i.e. tRNA.

Note: RNA is used to act as a genetic material as well as a catalyst (ribozyme). But RNA being a catalyst was reactive which made it unstable. Therefore, DNA has evolved from RNA with chemical modifications of various steps that make it more stable. But the DNA is double stranded and has a complementary strand which further resists changes by evolving a process of repair.