3 - DNA Replication.pdf

DNA Replication Biotechnology  Basis for inheritance A fundamental process occurs in all cells to copy DNA to transfer the genetic information to daughter cells. The process of DNA replication is vital for cell growth, repair, and reproduction in organisms. Location...

DNA Replication Biotechnology  Basis for inheritance A fundamental process occurs in all cells to copy DNA to transfer the genetic information to daughter cells. The process of DNA replication is vital for cell growth, repair, and reproduction in organisms. Location - Nucleus Semi conservative Parental strands are not degraded Base pairing allows each stand to serve as a template strand. Biotechnology  Replication begins at an origin and usually proceeds bi-directionally. DNA Synthesis Proceeds in a 5' -3' direction and is semi-discontinuous. A new strand of DNA is always synthesized in the 5' -3' direction, with the free 3' OH as the point at which the DNA is elongated. Biotechnology  Enzymes DNA helicase - unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen bonds between nucleotide pairs in DNA. DNA primase - a type of RNA polymerase that generates RNA primers. Primers are short RNA molecules that act as templates for the starting point of DNA replication. DNA polymerases - synthesize new DNA molecules by adding nucleotides to leading and lagging DNA strands. Biotechnology Topoisomerase or DNA Grase - unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled. Exonucleases - group of enzymes that remove nucleotide bases from the end of a DNA chain. DNA ligase - joins DNA fragments together by forming phosphodiester bonds between nucleotides. Biotechnology  DNA Replication steps Initiation Identification of the origins of replication Unwinding (denaturation) of dsDNA to provide an SSDNA template Formation of the replication fork Elongation Initiation of DNA synthesis and elongation Termination Primer removal and ligation of the newly synthesized DNA segments Biotechnology  DNA Replication steps - Initiation First, the origins of replication has to be identified. Then to DNA to be replicated, the double-stranded molecule must be "unzipped" into two single strands. In order to unwind DNA, these interactions between base pairs must be broken. This is performed by an enzyme known as DNA helicase. DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork. This area will be the template for replication to begin. Biotechnology  DNA Replication steps - Initiation However, the replication fork is bi-directional; one strand is oriented in the 3' to 5' direction leading strand) while the other is oriented 5' to 3' (lagging strand). Primer Binding. Once the DNA strands have been separated, a short piece of RNA called a primer binds to the 3' end of the strand. The primer always binds as the starting point for replication. Primers are generated by the enzyme DNA primase. Biotechnology  DNA Replication steps - Elongation Enzymes known as DNA polymerases are responsible for creating the new strand by a process called elongation. In prokaryotes such as E. coli, polymerase III is the main replication enzyme, while polymerase I, II, IV, and V are responsible for error checking and repair. DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication. In eukaryotic cells, polymerases alpha, delta, and epsilon are the primary polymerases involved in DNA replication. Biotechnology  DNA Replication steps - Elongation Since replication proceeds in the 5' to 3' direction on the leading strand, the newly formed strand is continuous. The lagging strand begins replication by binding with multiple primers. Each primer is only several bases apart. DNA polymerase then adds pieces of DNA, called Okazaki fragments, to the strand between primers. This process of replication is discontinuous as the newly created fragments are disjointed. Biotechnology  DNA Replication steps - Termination Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. Another exonuclease "proofreads" the newly formed DNA to check, remove, and replace any errors. Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand. Once completed, the parent strand and its complementary DNA strand coils into the familiar double helix shape. In the end, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand. Biotechnology https://www.youtube.com/watch?v=TNKWgcFPHqw Biotechnology Thank You ! Biotechnology