THE DNA DNA structure Replication of DNA Enzymes involved in DNA Replication Replication process types of replication meselson and stahl experiment

THE DNA
DNA structure
Replication of DNA
Enzymes involved in DNA Replication
Replication process
types of replication
meselson and stahl experiment

1. REPLICATION OF DNA - Gitanjali Priya

2. THE DNA DNA is a long polymers of deoxyribonucleotides. The length of DNA is usually define as number of nucleotide (or a pair of nucleotide referred to as base pairs) present in it. This also is the characteristics of an organism. Watson and Cricket Most DNA is located in the cell nucleus called as nuclear DNA, but a small amount of DNA can be found in the mitochondria where it is called as mitochondrial DNA. DNA stores an organisms genetic information and controls the production of proteins and thus responsible for the biochemistry of an organism.

3. DNA STRUCTURE The structure of DNA is illustrated by right handed double helix with about 10 and nucleotide base pairs per helical turn Eat spiral stand composed off a figure phosphate that won an attached basis is connected with a complement tree brand by hydrogen bonding between paired bases adenine(A) with thymine(T) and guanine(G) with cytosine(C). Nitrogenous bases : Purines & Pyrimidine Purine Consist of 6 members and 5 members nitrogen ring fused together with Adenine and Guanine Pyrimidine consist of only 6 members nitrogen ring consists of Uracil, Thymine & Cytosine. Adenine forms 2 bonds with Thymine. Guanine forms three bonds with Cytosine.

4. REPLICATION OF DNA DNA replication is a biological process that occurs in all living organisms and copies the exact DNA. It is the basis for biological inheritance. Replication is the process of synthesis of daughter DNA from parental DNA by the enzyme DNA polymerase. In a cell, DNA replication begins at specific locations or origins of replication in the genome. Unwinding of DNA and synthesis of news trends takes place by an enzyme known as helicase which results in the formation of replication forks growing bidirectionally from the origin. DNA replication occurs during the S stage of Interphase.

5. ENZYMES INVOLVED IN DNA REPLICATION DNA HELICASE:- Unwind and separate double stranded as it moves along the DNA DNA PRIMASE:- A type of RNA polymerase that generates are any primer RNA molecule act as template for the starting point of DNA replication DNA POLYMERASE:- Synthesize new DNA molecules by adding nucleotides to leading and lagging DNA strands DNA LIGASE:- Joins DNA fragments together by forming phosphodiester bonds between nucleotides

6. ENZYMES INVOLVED IN DNA REPLICATION RNA PRIMERS:- RNA primers composed of multiple bases that attached to the template strands to initiate the DNA replication.

7. REPLICATION PROCESS DNA replication including all biological polymerization processes in 3 in thematically catalysed and coordinated steps: Initiation. Elongation. Termination

8. REPLICATION PROCESS Step1: Initiation i.e Replication fork formation Before DNA can be replicated the double stranded molecule must be unzipped into two single strands. DNA has 4 base gold adenine, thymine, cytosine, guanine that form pairs between the two strands. In order to unwind DNA these interaction between base pairs must be broken. These are performed by an enzyme known as DNA helicase DNA helicase separate the strands into Y-shape known as the replication forks.

9. REPLICATION PROCESS

10. REPLICATION PROCESS Step 2:- Primer Binding Once the DNA stands have been separated a short piece of the RNA called a primal binds to the 3’ and of the strands The primers always binds as the starting point for replication Primers are generated by the enzyme DNA primase.

11. REPLICATION PROCESS Step 3:- Elongation Enzymes known as DNA polymerase are responsible for creating the new strands by a process called elongation. In eukaryotic cells polymerases Alpha, delta and Epsilon are the primary polymerases involved in the DNA replication because replication proceeds in the 5’ to 3’ direction on the leading strand, the newly formed stands is continuous strands The lagging strands begins with replication by binding with multiple primer Each primer is only several bases apart DNA polymerases then add pieces of DNA called okazaki fragments to the stand between primers

12. REPLICATION PROCESS This process of replication is discontinuous as the newly created fragments are disjointed. Involves the addition of new nucleotides based on the complimentary of the templated stands. The daughter stands are elongated with the binding of more DNA nucleotides.

13. REPLICATION PROCESS Step 4:- Termination Once the both the continuous and this continuous strengths are formed then the enzyme called exonuclease removes all the RNA primers from the original strands. These primers are then replaced with appropriate bases Another enzyme for DNA ligase joins okazaki fragments together forming a single unified strands The ends of linear DNA presents of problem as DNA polymerase can only add nucleotides in 5’ to 3’ direction. Once completed the parents strands and its complementary DNA strands coils into familiar double helix shape.

14. REPLICATION PROCESS In the end replication produces the two DNA molecule each with one stand from the parent molecule and the one new strands.

15. TYPES OF REPLICATION Conservative Semiconservative Dispersive

16. Conservative Model Of Replication According to this hypothetical model of DNA replication old DNA molecule directs the synthesis of entirely new DNA molecules The entire parent DNA molecule directs the synthesis of new daughter DNA molecules.

17. Semiconservative Model Of Replication According to this model the parent DNA molecule is Semi conserved The DNA to be replicated undergoes a strand separation process. Each separated strand serves as a template strands for the synthesis of new DNA molecule i.e daughter DNA molecule. In the new synthesized two DNA molecules, one strand is newly synthesized and one strand is from old DNA molecule and this is conserved strand. This model is widely accepted. Watson and Cricket only hypothesized this model but they couldn’t prove it experimentally. This model was experimentally proved by two scientists Meselson and Stahl

18. Meselson and Stahl Experimental Proof Matthew Meselson and Franklin Stahl performed experiment to show that DNA replication is semi conservative They grew E coli cells in medium containing N¹⁵ heavy isotope of nitrogen, after few generations all Nitrogenous base will contain N¹⁵ isotope of DNA of E coli cells They transferred E Coli cells to medium containing N¹⁴ isotope and cell sample were analysed after every replication cycle with technique called Sedimentation Equilibrium Centrifugation In this technique samples are separated using gradient centrifugation performed with heavy metal salt like Cesium chloride

19. Meselson And Stahl Experimental Proof Observation After 1 st replication DNA was neither heavy like N¹⁵not light like N¹⁴ but in between showing the DNA molecule is formed by one old strand N¹⁵ and one new strands N¹⁴ confirming semiconservative replication After 2 nd generation two types of DNA detected After 3 rd generation similar results obtained but N¹⁴ frequency increased Thus the experiment proves that DNA replication is semiconservative.

20. Dispersive Model Of Replication In this model, the parent DNA strands are broken down into small pieces and they get dispersed. New DNA strands are synthesized in between these small broken DNA fragments As a result, we get a hybrid DNA made with small fragments of old DNA molecule and newly synthesized DNA molecule that get synthesized in between