Characteristics of RNA
> Like DNA (or deoxyribonucleic acid), RNA (or ribonucleic acid) is also a type of nucleic acid.
> RNA is also made up of polynucleotide chain (i.e., a polymer of nucleotides) where large number of nucleotides are joined with one another by 3’-5’ phosphodiester bond.
> Nucleotide in RNA is made up of a ribose sugar (which is a pentose sugar), a phosphate group, and nitrogenous base.
> Nitrogenous bases in RNA are adenine, guanine, cytosine and uracil (instead of thymine).
> RNA consists of a single polynucleotide chain.
> OH group in RNA is present in the second carbon atom of a ribose sugar ring.
> It is less stable and more reactive in nature.
> The length of RNA is much shorter than that of DNA.
> RNA originates in the nucleus and then travels to the cytoplasm of the cell.
> The rate of mutation in RNA is much higher than that of DNA.
Functions of RNA
> It serves as the genetic material of large number of viruses.
> It is responsible for the formation of proteins in almost all organisms.
> It is very essential for performing various biological roles such as: coding, decoding, regulation, and expression of genes.
> It also sometimes acts as a catalyst in many biological reactions.
> It is more resistant to damage from UV rays than that of DNA.
> The rate of mutation is higher in RNA, which results in rapid evolution of an organism whose genetic material is RNA (such as: Virus).
Types of RNA
There are several different types of RNA present among these the three most important types of RNA, these are:
- rRNA (or ribosomal RNA)
- tRNA (or transfer RNA)
- mRNA (or messenger RNA)
A. Messenger RNA (mRNA)
1. For about 5% of the total RNA in the cell are mRNA.
2. It is the most heterogenous type of RNA in the cell.
3. It carries the genetic information from the DNA in the nucleus to ribosome in the cytoplasm of the cell
4. It carries genetic information in the form of triplets of nucleotides called codons.
5. It is the dominant RNA present in the cell as it acts as a template to assemble different amino acids in an ordered sequence to synthesize protein.
6. It undergoes modifications after completing the transcription process in the nucleus of the cell in order to reach to the cytoplasm of the cell, and this is called as the post-transcriptional processing.
7. This post-transcriptional processing involves many events, such as: capping at the 5’ end of mRNA with a guanosine triphosphate nucleotide, which helps mRNA in recognition during translation (or protein synthesis).
8. Similarly, at the 3’ end of an mRNA, tailing process is done, where poly Adenylate tail (or multiple adenylate residues) are added to it, which protects the mRNA from enzymatic degradation.
9. Also, the post-transcriptional process involves splicing of mRNA, where the unwanted part of mRNA called introns are removed.
B. Ribosomal RNA (rRNA)
1. They are found in the ribosomes (also called as protein factory of the cell), a cell organelle present in the cytoplasm of the cell and hence are called ribosomal RNA (or rRNA).
2. For about 80% of the total RNA present in the cell are rRNA.
3. They plays an important role in deriving information from the mRNA to synthesize desired protein.
4. Ribosomes contains two major subunits: a smaller subunit, which reads the information present in the mRNA, and a larger subunit, which joins amino acids one by one with a peptide bond to form a polypeptide chain.
5. Each ribosomal subunit comprises one or more rRNA (or ribosomal RNA).
6. These ribosomal RNAs (or rRNAs) combines with certain proteins in the cytoplasm of the cell to form ribosomes.
7. These ribosomes travel along mRNA during translation mechanism (or protein synthesis mechanism) and gradually assembles suitable amino acids to form a polypeptide chain.
8. They binds to tRNAs (or transfer RNAs) and certain other molecules essential for protein synthesis.
9. Thus, rRNAs directs the process of translation of mRNA into proteins.
C. Transfer RNA (tRNA)
1. tRNA (or transfer RNA) is the smallest of the 3 types of RNAs.
2. It consists of about 75-95 nucleotides.
3. They possess cloverleaf-like structure, which is formed by folding their chain and forming hydrogen bonds in between with three hairpin loops.
4. One of these three hairpin loops is the anticodon loop which recognizes and decodes specific codon in the mRNA sequence.
5. The 3’ end of upper region of tRNA (called as acceptor stem) provides a site for the attachment of suitable amino acid.
6. tRNA brings amino acids on the basis of the information (or codon) present in the mRNA which is decoded by its anticodon loop.
7. Thus, tRNAs play an important role in the transfer of amino acids during protein synthesis. Hence, they are called transfer RNAs.
8. Each amino acids has its own specific tRNA that binds with it and transfers it to form a polypeptide chain.
9. They are also called adapter molecules, since they act as adapters in the process of translation of genetic information of mRNA into proteins.