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Ribonucleic acid (RNA),type of RNA

Ribonucleic acid (RNA)
RNA is also a polymer of ribonucleotides.

Location in cell

RNA is present in the nucleolus, in the ribosomes, in the cytosol and in smaller amounts in other parts of the cell.

Structure

  • The RNA molecules occur as single strand, which may be folded back on it, to give double helical characteristics.
  • Nitrogenous bases, which are involved, are adenine (A), guanine (G), cytosine (C) and uracil (U).
  • RNA is synthesized by DNA in a process known as transcription.

Types of RNA

There are three main types of RNA i.e.
  1. Messenger RNA (mRNA)
  2. Transfer RNA (tRNA)
  3. Ribosomal RNA (rRNA)
All these types of RNAs are synthesized from DNA in the nucleus and then are moved out in cytoplasm to perform their specific functions.
(i) Messenger RNA (mRNA)
  • It takes genetic message from the nucleus to the ribosomes in the cytoplasm to form particular proteins. They carry the genetic information from DNA to ribosomes, where amino acids are arranged according to the information in mRNA to form specific protein molecules.
  • This type of RNA consists of a single strand of variable length. Its length depends upon the size of the gene as well as the protein for which it is taking the message. For example, for a protein molecule of 1,000 amino acids,mRNA will have the length of 3,000 nucleotides.
  • mRNA is about 3-4% of the total RNA in the cell.
(ii) Transfer RNA (tRNA)
  • It transfers amino acid molecules to the site where peptide chains are being synthesized. There is one specific tRNA for each amino acid. So the cell will have at least 20 kinds of tRNA molecules. It picks up amino acids and transfers them to ribosomes, where they are linked to each other to form proteins.
  • Their molecules are small, each with a chain length of 75 to 90amino acids.
  • It comprises about 10-20% of the cellular RNA.
(iii) Ribosomal RNA (rRNA)

  • It acts as machinery for the synthesis of proteins. On the surface of the ribosomes the mRNA and rRNA molecules interact to translate the information from genes into a specific protein.
  • It is strongly associated with the ribosomal protein where 40-50% of it is present.
  • It is the major portion of RNA in the cell, and may be upto 80% of the total RNA.
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