Jun 3, 2015

Protein Synthesis Steps: Transcription and Translation

Transcription

The genetic information housed in DNA undergoes transcription, leading to the generation of a single-stranded mRNA. This pivotal process, explored in prior blog posts, is dubbed transcription. The resulting mRNA, aptly named for its role in carrying the genetic message from DNA, contains codons mirroring the DNA's codes.

Translation

This intricate mechanism involves the translation of mRNA's triplet bases into a specific sequence of amino acids, constituting a polypeptide chain. The translation process encompasses essential stages:

Ribosome-MRNA Binding: mRNA aligns with a 30S ribosome, followed by the joining of the 50S subunit, culminating in the formation of an 80S ribosome. Within this assembly, distinct sites exist:

A site (Amino-acyl site)

P site (Peptidyl site)
Binding of mRNA with the ribosome


Amino Acid Activation: Enzymatic activation of amino acids occurs via attachment to AMP, inducing higher energy states. This activation process is catalyzed by activation enzymes, yielding Enzyme-Amino Acid-AMP+PP.

Amino Acid-tRNA Attachment: Amino acids form connections with specific tRNA molecules at the 3' end (A-C-C) through recognition by the D loop of the tRNA.

Amino Acid Activation

Chain Initiation: The initiation codon AUG primes the ribosome. A tRNA carrying methionine binds to the ribosome's P site, facilitated by the UAC anticodon matching the AUG codon. Adjacent codons are exposed, allowing tRNA with a matching anticodon to engage the A site. Subsequent peptide bond formation and methionine tRNA release ensue.

Chain Elongation: Ribosomal movement commences, progressing along mRNA by three nucleotides. Additional tRNAs, each transporting specific amino acids, align with codons, contributing to polypeptide growth. Sequential peptide bond formation and the release of tRNA from the P site continue this elongation process.

Chain Termination: Recognition of stop codons (UAA, UAG, UGA) halts amino acid joining, preventing tRNA engagement. This cessation prompts the release of the polypeptide chain from the ribosome, culminating in translation completion.

 
Chain initiation


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