hey everyone way back mister basics here so today I'll be taking a lecture on DNA replication and this lecture is divided into five parts that is initiation of DNA replication structure of DNA polymerase enzyme elongation termination and the control of the energy application shann off DNA replication in prokaryotes requires the following proteins this includes DNA DNA be DNA C prime is SSB and DNA polymerase tree enzyme the initiation starts at or IC on the chromosome in the initial step DNA protein binds a specific 9-mer sequence within the or I see it is to be noted that only ATP bound DNA binds to DNA adp bound DNA cannot bind DNA sequence there's a 13 verse sequence repeat besides the nightmare sequence once the DNA protein binds to 9-mer sequence it causes strand separation within the 13 where repeat in the next step DNA be protein also known as hilly case and the NHC protein also known as helicase lauder are loaded to the Mantid DNA helicase loader interacts with DNA and loads the helicase in the melted region using energy from ATP the helicase starts unwinding of the DNA the DNA so form are quickly occupied by SSB also known as single-stranded DNA binding protein the SSB interacts with single-stranded DNA while ecto static interactions and nitrogenous bases while stacking interaction SSB shows cooperative binding that is one molecule of SSB helps the binding of other SSB after opening of the DNA strands Primus forms a short RNA primer on the template DNA finally DNA polymers tree hollow enzyme is loaded and the lady and the lagging strand synthesis starts so let's quickly go through the steps of initiation of DNA replication the DNA protein along with ATP binds the DNA at the 9-mer sequence DNA denatures the DNA at the 13 mer sequence the helicase and the DNA see that helices loader is loaded to the melted DNA with the help of ATP the helicase unwinds DNA the single-stranded DNA are occupied by SSB primase forms a short primer and finally ball three is loaded the structure of DNA polymerase resembles a closed hand it has a palm domain finger domain and a tongue domain a palm domain binds magnesium and zinc ions for catalysis the magnesium ions plays an important role and the phosphodiester bond formation between the OHA and the incoming dntp in this reaction the hydrogen of hydroxyl group is removed to form an oxy anion this oxy anion reacts with the alpha phosphoryl group of the incoming dntp to complete the reaction it should be noted at all for dntps act as a substrate for DNA polymerase enzyme when the correct dntp base pairs only one out of four nucleotide is added this phenomenon is known as kinetic selectivity of DNA polymerase enzyme the DNA polymerase enzyme also has a unique ability to distinguish between RN TPS and dntps the concentration of aren t piece is tenfold higher as compared to dntps in the cytoplasm but only dntps are incorporated into the DNA this occurs because the nucleotide binding pocket is too small to allow the presence of extra hydroxyl group of the our ntp anise phenomenon is known as steric exclusion of aren t piece okay now I like to talk about a finger domain the finger domain has alpha helical protein having arginine lysine and tiresome residues at the active site these residues binds to incoming nucleotides if correct nucleotide is added and base pairing forms there is a conformational change in the Alpha helix that brings the nucleotide close to the catalytic site in the pound domain the term domain has two roles it maintains correct position of RNA primer and maintains strong Association of DNA polymerase with a substrate let's quickly go through the structure of DNA polymerase enzyme and has three main domains known as the pam domain finger domain and the tum domain the pam domain is the main catalytic site which binds magnesium and zinc ions and play an important role in catalysis the finger domain has the alpha helical protein it binds the incoming nucleotide and brings the dntp close to the palme domain once a correct base bearing is formed and finally the time domain maintains the correct position of the primer let's talk about elongation elongation occurs after DNA polymerase tree is loaded during initiation during elongation there's the synthesis of leading strand and the lagging strand the synthesis of leading strand occurs in a continuous fashion and it's in the direction of the moment of DNA polymerase enzyme however the synthesis of lagging strands should occur in the opposite direction let's talk about lagging strand synthesis in the first step the primates forms a primer and this primer can be extended in five prime to three prime direction by the formation of Lu as the polymerase moves forward the loop is released early primates again forms a primer which is again extended in the form of loop finally when the RNA primers are degraded by the rnase enzyme it results in the formation of short fragments known as the Okazaki fragments are the lagging strand so during elongation as the helices continuously unwinds the DNA there is a positive supercoiling and the supercoiling is removed by DNA topoisomerase enzyme termination of DNA replication occurs by the Terr sequences present on the DNA and thus protein as the chromosome of bacteria is circular both the replication forks meet at the termination sequence where they are encountered by dust protein which halts the moment of replication fork this results in the formation of two detonated are linked circular DNA and finally topoisomerase du d catenate the two circular DNA resulting in two separate chromosomes let's talk about regulation of DNA replication only the Metallica strands undergo DNA replication the newly synthesized strand is not methylated and this structure is known as the Hemi methylated DNA that is parent strand is methylated while the daughter strand is not methylated these Hemi methylated regions are bound by a protein known as sec a sec a protein prevents the binding of DNA and then metallus and so reinitiation of replications prevented now what time set a dis associates during space for dermatology and DNA protein to bind that metallus enzyme metalitz to daughter DNA so that the reinitiation of replication can occur the DNA protein also has a role in regulation of replication only DNA a protein bound with the ATP can bind to the DNA the ADP Brown DNA fails to bind DNA replication occurs only when there is high nutrient for the generation of enough ATP for the DNA protein to be activated [Music]