tRNA Structure
tRNA molecule has two ends 5’ and 3’ ends. The 5’ end consists of a phosphate group which is attached to the 5th carbon atom of ribose sugar while the other 3’ end has a free OH group on the 3-carbon atom. So, there are two types of structure of tRNA- 2D clover leaf model and 3D, L shape model.
Cloverleaf Model
tRNA molecule consists of 70-80 nucleotides that fold like a clover leaf. A 2D t-RNA molecule appears like a cloverleaf. As clove has the following ends, the t-RNA molecule also has four ends:
- Acceptor end: It is called the acceptor end as it accepts the specific amino acid. It is made up of 7-9 nucleotides. It has two ends- 3′ and 5′. It is the 3’ end that consists of a base triplet CCA with OH group whereas the 5′ end consists of a phosphate group. At this OH at the 3′ end, the COOH group of amino acids joins.
- Anti-codon end: It is made up of 5 base pairs and consists of codons that are complementary to the codon present on mRNA, therefore known as an anticodon. Anticodon is the triplet base sequence in tRNA which binds with the codon at the time of translation. There is specific tRNA for a particular amino acid. Base pairing between the codon and anticodon helps in the synthesis of proteins. There are no tRNAs for stop codons but have specific tRNAs for initiate codons.
- Enzyme site/DHU end: It is present on the lateral side of the molecule that recognizes aminoacyl-tRNA synthetase that activates the amino acids and catalyzes the binding of a specific amino acid to a tRNA molecule. It consists of 3- 4 base pairs and is called a D loop because it consists of a modified nucleotide called dihydrouridine.
- Ribosome recognition end: It is on the other lateral side of the molecule. It is meant for attachment to a ribosome.
- TΨC Loop end: It is known as T arm. It consists of 4-5 base pairs and a loop consisting of modified uridine called pseudouridine.
- Variable Loop: This loop is of variable size and ranges from 3-21 base pairs. It is present between the anticodon and TΨC loop. It recognizes tRNA molecules.
L-shaped model
3D tRNA looks like an L-shaped molecule that has two functional ends:
- The acceptor stem: Site of attachment of specific amino acid (3’ end of the molecule)
- Anticodon loop: Site where codons are read on mRNA (5’ end of the molecule)
tRNA – the Adapter Molecule
tRNA is also known as transfer RNA is a subtype of RNA, tRNA help in the protein synthesis process. tRNA carries the amino acid to the ribosome, which is the molecular machine that assembles the protein, and ensures that the amino acid is incorporated into the growing protein chain in the correct order. Different types of tRNA present, each with a different sequence and structure allow it to recognize a specific amino acid. Specific amino acids are incorporated in the protein sequence via specific tRNA.
What is RNA?
Ribonucleic acid (RNA) is a single-stranded, non-hereditary (except-retroviruses) molecule that helps in the synthesis of proteins. The nitrogenous bases present in RNA are A (Adenine), U (Uracil), G (Guanine), and C (Cytosine), in which A pairs with U and G with C. The function of ribonucleic acid is to convert genetic information from genes into amino acid sequences of protein. It is classified into three types- messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA) on the basis of the function and molecular size of the nucleic acids.
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