Describe brifly about the process of translation in procaryotes??
Answers
Answer:
Introduction to Translation in Prokaryotes:
The process by which proteins are produced with amino acid sequences specified by the sequence of codons in messenger RNA is called translation. Translation is the first stage of protein biosynthesis.
The main points about translation in prokaryotes are given below:
Explanation:
1. Site:
Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA. In prokaryotic translation 70S ribosomes with 30S and 50S subunits are used. The mRNA is synthesized from DNA only. In prokaryotes, there are several initiation and termination sites.
2. Template:
In translation, messenger RNA (mRNA) is decoded to produce a specific polypeptide according to the rules specified by the genetic code. This uses an mRNA sequence as a template to guide the synthesis of a chain of amino acids that form a protein. Many types of transcribed RNA, such as transfer RNA, ribosomal RNA, and small nuclear RNA are not necessarily translated into an amino acid sequence.
3. Requirements:
The translation process requires mRNA, rRNA, ribosomes, 20 kinds of amino acids and their specific tRNAs.
4. Factors Involved:
In prokaryotes, three factors are involved in the initiation of translation [IF 1, IF 2 and IF 3], one factor in the elongation of polypeptide chain and three factors in chain termination [RF1, RF2 and RF3],
5. Enzymes Involved:
Two types of enzymes are used in translation. Aminoacyl tRNA synthetase (an enzyme) catalyzes the bonding between specific tRNAs and the amino acids. The enzyme peptidyl transferase connects A site and P site by forming a peptide bond [the nitrogen carbon bond] during elongation phase.
6. Codons Involved:
In the process of translation two types of codons, viz., start codon and stop codons are involved. The codon, AUG, initiates the process of translation and one of three stop codons i.e. UAA, UAG or UGA is used for chain termination.
7. Starting Amino Acid:
In prokaryotes, starting amino acid is N-formyl methionine. Moreover, there is overlapping of transcription and translation.
Mechanism of Translation in Prokaryotes:
Translation process consists of three major phases or stages, viz:
(1) Initiation,
(2) Elongation and
(3) Termination.
These are briefly discussed below:
1. Initiation:
This is the first phase of translation. Start or initiation codon [AUG] is responsible for initiation of translation process.
Initiation of translation in prokaryotes involves the assembly of the components of the translation system which are: the two ribosomal subunits (small and large), the mRNA to be translated, the first (formyl) aminoacyl tRNA (the tRNA charged with the first amino acid), GTP (as a source of energy), and three initiation factors (IF 1, IF 2 and IF 3) which help the assembly of the initiation complex.
The ribosome consists of three sites, the A site, the P site, and the E site. The A site is the point of entry for the aminoacyl tRNA (except for the first aminoacyl tRNA, fMet-tRNAfMet, which enters at the P site). The P site is where the peptidyl tRNA is formed in the ribosome. And the E site which is the exit site of the now uncharged tRNA after it gives its amino acid to the growing peptide chain.
Initiation
Translation begins with the binding of the small ribosomal subunit to a specific sequence on the mRNA chain. Initiation of translation begins with the 50S and 30S ribosomal subunits. IF1 (initiation factor 1) blocks the A site to ensure that the IMet-tRNA can bind only to the P site and that no other aminoacyl-tRNA can bind in the A site during initiation, while IF3 blocks the E site and prevents the two subunits from associating.