What Is RNA
Ribonucleic Acid (abbreviated as RNA) is present in all living organisms. It is a nucleic acid similar to DNA (the genetic material of Humans.) It is most often single-stranded. It is a helical strand of bases. The Primary role of RNA is the conversion of instructions given by DNA into a functional protein. Molecular biology states that “DNA makes RNA and RNA make protein”.
RNA is responsible for protein synthesis in the human body as it is involved in the transcription, decoding and translation of the genetic code to produce protein. RNA is usually obtained from DNA. RNA also helps in chemical reactions in the body, also known as an enzyme.
Structure Of RNA
RNA is single-stranded and contains three elements: 1)A nitrogenous base, 2) A five-carbon sugar- Ribose 3) A Phosphate group. It includes Adenine, Uracil, Guanine and Cytosine. RNA molecules are polymers of nucleotides. In the RNA molecule nucleotide is joined together by a covalent bond between the phosphate of one nucleotide and the sugar of another.
- Nitrogenous bases are categorised into purine and pyrimidine:
Purine- Adenine & Guanine
Pyrimidine- Uracil, Thymine and Cytosine
- In the RNA molecule, Uracil is attached to the Adenine with two hydrogen bonds and Guanine is attached to Cytosine with three hydrogen bonds.
- A nucleotide comprises Nitrogenous base+ Sugar molecule+ Phosphate groups ( Ribose).
RNA folds into complex three-dimensional shapes and forms hairpin loops.
Types Of RNA
RNA molecules are produced in the nucleus of human cells and they can also be found in the cytoplasm. In both prokaryotes and eukaryotes there are mainly three types of RNA found:
- Transfer RNA (tRNA)
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
t RNA stands for transfer RNA and is the most minor RNA among the three types of RNA.t RNA especially play a role in the synthesis of a protein with the help of mRNA. tRNA acts as an adapter in the translation of the genetic sequence of m RNA into proteins. Thus they are called transfer RNA.
tRNA is synthesized in the nucleus by DNA. It is also known as soluble RNA (sRNA) and adapter RNA due to its adapter activity. t RNA is made RNA polymerase IIII t RNA process about 75-95 nucleotides. tRNA has a cloverleaf structure with three hairpin loops and the tertiary structure has an inverted L shape structure. The folded structure of t RNA is formed due to hydrogen bonding between complementary bases.
It has three-leafed clover and the main constituent are:
Acceptor Arm: It is formed by the base-pairing of 7-9 nucleotides of 5′ and 3′ terminal. It is concerned with the recognizing and binding site of amino acids. Hence Acceptor arm of t RNA is often called the binding site.
DHU Loop: It is also known as the D arm consisting of 3-4 base pairs in its stem. It contains a modified nucleotide called dihydroxyuracil. D loop recognizes amino acids.
It consists of 5 base pairs in its stems. It has a complementary codon present on the mRNA for the amino acid it carries. The unpaired base of the anticodon loop pairs with the mRNA codon and each codon is identified by a specific tRNA.
This T arm has 4-5 base pairs. It is also known as the GTPCG loop. Here P is pseudouracil, a modified uracil after enzymatic activity on uracil. It recognizes ribosomes.
Variable loop presents between the T ψ C loop and anticodon loop. Its size varies from 3-21 bases. Variable helps in the recognition of the tRNA molecule.
Messenger RNA (mRNA):
Messenger RNA is abbreviated as mRNA. Messenger ribonucleic acid transfer the genetic information from DNA in the nucleus to the cytoplasm. mRNA is a single-stranded structure. In 1961, French scientists Francois Jacob and Jacques Monod hypothesized the existence of an intermediary between DNA and its protein product, they called it messenger RNA.
mRNA can take part in the translation for protein synthesis. Prokaryotes contain an mRNA-transcribed copy of the DNA. mRNA is a long, single-stranded molecule. It consists of nucleotides attached by phosphodiester bonds. It contains adenine, guanine, cytosine and uracil nitrogenous base.
The mRNA consists of the following regions:
Coding region: It is made up of a triplet of nucleotides i.e. codon. Each codon codes to specific amino acids and codons in m RNA get translated by the ribosome to amino acids in a polypeptide chain. This coding region starts with the start codon i.e. AUG and ends with the stop codon i.e. UAG, UGA, and UAA.
Untranslated regions or UTRs: They present at 5’and 3′ regions before and after the coding region respectively. Untranslated regions are present before the start codon and after the stop codon. They take participate in gene expression. They are involved in the stability of the RNA, efficiency of translation and mRNA localisation.
5’Cap: 5’Cap of methyl guanosine presents at 5’end.
Poly A tail: This tail is present at 3’end.
It is abbreviated as rRNA. The RNA found in the ribosome is known as Ribosomal RNA. rRNA is responsible for catalytic protein synthesis. Approx 60-80% of the weight of the ribosome is composed of ribosomal RNA. rRNA has a three-dimensional structure and it influences the structure of ribosomes. The primary function of rRNA is in protein synthesis.
In prokaryotes 16s ribosomal RNA resides in the compact 30s ribosomal subunit. In a large 50s ribosomal unit, two rRNA species are present i.e. 23S and 5S ribosomal RNAs. A single rRNA gene in archaea and bacteria codes for three rRNA types: 16S, 23S, and 5S.ψ
In eukaryotes, the ribosome is composed of the 40S and 60S subunits. There are two short rRNA molecules with less than two hundred nucleotides in length (5S and 5.8S). The eukaryotic ribosome has a Svedberg coefficient of the 80S.
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