Protein synthesis : Transcription & Translation  (Nucleic Acid Replication by semi - conservative)
Channel: BioEng
Date: 01/05/2022

Protein synthesis is the core biological procedure which occurs inside a cell in order to produce cellular protein molecules via 03 steps : Initiation, Elongation and Termination.
Protein synthesis occurs in ribosomal site of the cells.

This process is further sub divided into 05 steps : 
Activation of amino acids
Transfer of amino acid to tRNA
Initiation of polypeptide chain
Chain Termination
Protein translocation

---------------  RULES OF REPLICATION ---------------

01.Semi conservative : 03 types of replications have been suggested 01. conservative : where parent DNA is fully conserved & 02. Dispersive :where parent DNA is scattered to both daughter cells where the daughter DNA is high in percentage but finally, they discovered replication
takes place as per the 03. Semi-conservative way where parent DNA is passed into both daughter cells equally where each half strand of
parent acts as template strand. 

02. Starts at origin
Initiator protein identifies specific base sequence on DNA as the site of origin to Helicase to commence the replication.
Prokaryotic : one start origin site
Eukaryotic : multiple sites of origin

03. Synthesis of 5’-3’ direction
Free nucleotides base pairs on template strand in direction of 5 – 3’ starting from 5’

04. Uni / Bidirectional
Replication forks starts replication in one direction or by both of the sides of the bubble unwinding the helix in opposite direction

05. Semi Discontinuous replication
Anti parallel strands replicate from 5 ‘ to 3 ‘ in both lagging and leading strands;
In Leading strand continuous synthesis of nucleotide occurs
In Lagging strand discontinuous synthesis of Okazaki fragments occurs

MECHANISM OF REPLICATION

Takes place in 3 steps :
Initiation
Elongation
Termination

Initiator protein in cell identifies the site of origin
Topoisomerase (DNA gyrase) acts on the origin where DNA helix starts to unwinds by mechanism of Gyrase:

Tyrosine aa has a OH group which binds with the strand making the DNA to split and rotate around the turns at 3’
Phosphate atom binds with Tyrosine amino acid changing the structure of DNA and Topoisomerase disassociates

DNA Helicase further unwinds the helix by breaking the hydrogen bons in between the complementary bases
Process forms a bubble at the origin of replication, then forms a Y shape structure and replication forms starts to unwind the strands
completely forming leading and lagging strands.
Single strand binding proteins stabilize the new Template strands preventing from rejoining of strands
DNA polymerase do proofreading and Polymerase I activates the lagging strand filling up DNA between Okazaki fragments, then DNA
polymerase III acts on leading strand joining the nucleotides together.
DNA Ligase acts on lagging strand adding the Okazaki Fragments and joins the both the template strand and daughter strand bind together
forming the double helix

#Protein #synthesis #Transcription #DNA #RNA #Translation #Ligase #Gyrase #mRNA #Ribosome #Nucleic Acids #Replication