biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5-12-smkf4y4gw4m

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> DNA replication </primary>
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- Objectives

- DNA Replication and its importance
 - Different models of replication
 - Meselson and Stahl Experiment
 - Types of DNA Replication
 - Various Enzymes/Proteins involve in DNA replication
 - Mechanism of DNA Replication

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<footer style = "font-size: 18px"> $\rightarrow$ Genetics and evolution $\rightarrow$ <span style = "color:blue"> DNA replication </span> $\rightarrow$ DNA replication $\rightarrow$ DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> DNA replication </primary>
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<footer style = "font-size: 18px">DNA replication $\rightarrow$ DNA replication $\rightarrow$ <span style = "color:blue"> DNA replication </span> $\rightarrow$ DNA replication $\rightarrow$ DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> DNA replication </primary>
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- **Why DNA replication is essential?**
 - Cell Division (Mitosis/Meiosis)

- Reproduction  
 
 - Synthesis of RNA and Protein

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### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> DNA replication </primary>
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<footer style = "font-size: 18px">DNA replication $\rightarrow$ DNA replication $\rightarrow$ <span style = "color:blue"> DNA replication </span> $\rightarrow$ Conservative model $\rightarrow$ Conservative model </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Semiconservative model </primary>
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- The two parental DNA strands separate and each

- Separated strands then serves as a template for the synthesis of a new DNA strand

- The result is two DNA double helices, both of which consist of one parental and one new strand

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<footer style = "font-size: 18px">Conservative model $\rightarrow$ Conservative model $\rightarrow$ <span style = "color:blue"> Semiconservative model </span> $\rightarrow$ Semiconservative model $\rightarrow$ Dispersive model </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Dispersive model </primary>
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- The parental double helix is broken into double-stranded DNA segments

- These fragments act as templates for the synthesis of new double helix molecules. The segments then reassemble into complete DNA double helices

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<footer style = "font-size: 18px">Semiconservative model $\rightarrow$ Semiconservative model $\rightarrow$ <span style = "color:blue"> Dispersive model </span> $\rightarrow$ Dispersive model $\rightarrow$ Model of replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Model of replication </primary>
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- A. Semiconservative model

- B. Conservative model

- C. Dispersive model

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<footer style = "font-size: 18px">Dispersive model $\rightarrow$ Dispersive model $\rightarrow$ <span style = "color:blue"> Model of replication </span> $\rightarrow$ Meselson and Stahl's Exprement $\rightarrow$ Semiconservative model </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Meselson and Stahl's Exprement </primary>
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- They cultured a bacteria in a N<sup>15</sup> medium

- They then shifted the bacteria to a N<sup>14</sup> medium

- DNA was isolated at different times correspondig to replication cycle 0, 1 and 2

- Then seprated the DNA with CsCI density gradient centrifugation

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<footer style = "font-size: 18px">Dispersive model $\rightarrow$ Model of replication $\rightarrow$ <span style = "color:blue"> Meselson and Stahl's Exprement </span> $\rightarrow$ Semiconservative model $\rightarrow$ Semiconservative model </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Semiconservative model </primary>
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<footer style = "font-size: 18px">Model of replication $\rightarrow$ Meselson and Stahl's Exprement $\rightarrow$ <span style = "color:blue"> Semiconservative model </span> $\rightarrow$ Semiconservative model $\rightarrow$ Types of DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Semiconservative model </primary>
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<footer style = "font-size: 18px">Meselson and Stahl's Exprement $\rightarrow$ Semiconservative model $\rightarrow$ <span style = "color:blue"> Semiconservative model </span> $\rightarrow$ Types of DNA replication $\rightarrow$ Types of DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Types of DNA replication </primary>
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<figcaption>Theta replication</figcaption>
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<footer style = "font-size: 18px">Semiconservative model $\rightarrow$ Types of DNA replication $\rightarrow$ <span style = "color:blue"> Types of DNA replication </span> $\rightarrow$ Types of DNA replication $\rightarrow$ Requirements of replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Types of DNA replication </primary>
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- Eukaryotic DNA replication
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<footer style = "font-size: 18px">Types of DNA replication $\rightarrow$ Types of DNA replication $\rightarrow$ <span style = "color:blue"> Types of DNA replication </span> $\rightarrow$ Requirements of replication $\rightarrow$ Enzymes involved in DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Requirements of replication </primary>
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- A template consisting of single-stranded DNA,

- Raw materials (substrates i.e. dNTPs) to be assembled into a new nucleotide strand, and

- Enzymes and other proteins that "read" the template and assemble the substrates into a DNA molecule.

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<footer style = "font-size: 18px">Types of DNA replication $\rightarrow$ Types of DNA replication $\rightarrow$ <span style = "color:blue"> Requirements of replication </span> $\rightarrow$ Enzymes involved in DNA replication $\rightarrow$ Direction of replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Direction of replication </primary>
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- DNA strands always elongate in the 5'to 3' direction (5'$\longrightarrow$ 3').

- **Why? (5'$\longrightarrow$ 3') Direction**

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<footer style = "font-size: 18px">Requirements of replication $\rightarrow$ Enzymes involved in DNA replication $\rightarrow$ <span style = "color:blue"> Direction of replication </span> $\rightarrow$ Direction of replication $\rightarrow$ The Mechanism of replication </footer>

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### <primary style="font-size:24px"> Direction of replication </primary>
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<footer style = "font-size: 18px">Enzymes involved in DNA replication $\rightarrow$ Direction of replication $\rightarrow$ <span style = "color:blue"> Direction of replication </span> $\rightarrow$ The Mechanism of replication $\rightarrow$ Initiation of replication </footer>

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### <primary style="font-size:24px"> Initiation of replication </primary>
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- _E. coli_ has a single replication origin (oriC)

- Initiator proteins bind to oric and cause a short section of DNA to unwind

- This unwinding allows helicase to separate the double strand of DNA

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<footer style = "font-size: 18px">Direction of replication $\rightarrow$ The Mechanism of replication $\rightarrow$ <span style = "color:blue"> Initiation of replication </span> $\rightarrow$ Initiation of replication $\rightarrow$ Initiation of replication </footer>

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### <primary style="font-size:24px"> Initiation of replication </primary>
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<footer style = "font-size: 18px">The Mechanism of replication $\rightarrow$ Initiation of replication $\rightarrow$ <span style = "color:blue"> Initiation of replication </span> $\rightarrow$ Initiation of replication $\rightarrow$ Initiation of replication </footer>

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- Topoisomerases control the supercoiling of DNA

- It reduces torque/tension by making a double-stranded break in one segment of the DNA helix, passing another segment of the helix through the break, and then resealing the broken ends of the DNA

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<footer style = "font-size: 18px">Initiation of replication $\rightarrow$ Initiation of replication $\rightarrow$ <span style = "color:blue"> Initiation of replication </span> $\rightarrow$ Initiation of replication $\rightarrow$ Initiation of replication </footer>

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- All DNA polymerases require a nucleotide with a 3-OH group to which a new nucleotide can be added.

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- Because of this requirement, DNA polymerases cannot initiate DNA synthesis on a bare template; rather, they require a primer-an existing 3-OH group-to get started.

- **How, then, does DNA synthesis begin?**

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<footer style = "font-size: 18px">Initiation of replication $\rightarrow$ Initiation of replication $\rightarrow$ <span style = "color:blue"> Initiation of replication </span> $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ Elongation of nucleotide chain </footer>

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### <primary style="font-size:24px"> Elongation of nucleotide chain </primary>
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- DNA polymerases elongate the polynucleotide strand by catalyzing DNA polymerization

- There are five different DNA polymerases

- Two of them, DNA polymerase I and DNA polymerase III, carry out DNA synthesis associated with replication; the other three have specialized functions in DNA repair

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<footer style = "font-size: 18px">Initiation of replication $\rightarrow$ Initiation of replication $\rightarrow$ <span style = "color:blue"> Elongation of nucleotide chain </span> $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ Elongation of nucleotide chain </footer>

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<footer style = "font-size: 18px">Initiation of replication $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ <span style = "color:blue"> Elongation of nucleotide chain </span> $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ Elongation of nucleotide chain </footer>

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- Its 5' $\rightarrow$ 3' polymerase activity allows it to add new nucleotides in the 5'$\rightarrow$ 3' direction

- Its 3'$\rightarrow$ 5' exonuclease activity allows it to remove nucleotides in the 3'$\rightarrow$ 5' direction, enabling it to correct errors

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<footer style = "font-size: 18px">Elongation of nucleotide chain $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ <span style = "color:blue"> Elongation of nucleotide chain </span> $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ DNA Polymerase of prokaryotes and their functions </footer>

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| DNA Polymerase | '5'$\rightarrow$'3' <br>Polymerization | '3'$\rightarrow$'5' <br> Exonuclease | '5'$\rightarrow$'3' <br> Exonuclease | Function |
| -------- | -------- | -------- | -------- | -------- |
| I    | Yes     | Yes   | yes  | Removes and replaces primers |
| II    | Yes     | Yes  | No  | DNA repair:restarts replication after damaged DNA halts synthesis  |

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<footer style = "font-size: 18px">Elongation of nucleotide chain $\rightarrow$ Elongation of nucleotide chain $\rightarrow$ <span style = "color:blue"> DNA Polymerase of prokaryotes and their functions </span> $\rightarrow$ DNA Polymerase of prokaryotes and their functions $\rightarrow$ DNA polymerase </footer>

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- Synthesize any sequence specified by the template strand

- Synthesize in the 5' $\rightarrow$ 3' direction by adding nucleotides to a '3'-OH group

- Use dNTPs to synthesize new DNA

- Require a primer to initiate synthesis

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<footer style = "font-size: 18px">DNA Polymerase of prokaryotes and their functions $\rightarrow$ DNA Polymerase of prokaryotes and their functions $\rightarrow$ <span style = "color:blue"> DNA polymerase </span> $\rightarrow$ DNA polymerase $\rightarrow$ Termination of DNA replication </footer>

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- Catalyze the formation of a phosphodiester bond by joining the 5' phosphate group of the incoming nucleotide to the '3'-OH group of the preceding nucleotide on the growing strand

- Produce newly synthesized strands that are complementary and antiparallel to the template strands

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<footer style = "font-size: 18px">DNA Polymerase of prokaryotes and their functions $\rightarrow$ DNA polymerase $\rightarrow$ <span style = "color:blue"> DNA polymerase </span> $\rightarrow$ Termination of DNA replication $\rightarrow$ Summary </footer>

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### <primary style="font-size:24px"> Termination of DNA replication </primary>
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- Termination In some DNA molecules, replication is terminated whenever two replication forks meet

- In others, specific termination sequences block further replication

- A termination protein, called Tus in _E. coli_, binds to these sequences

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<footer style = "font-size: 18px">DNA polymerase $\rightarrow$ DNA polymerase $\rightarrow$ <span style = "color:blue"> Termination of DNA replication </span> $\rightarrow$ Summary $\rightarrow$ Summary </footer>

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- Helicase to unwind the DNA

- Single-strand-binding proteins to keep the nucleotide strands separate long enough to allow replication

- The topoisomerase, gyrase to remove strain ahead of the replication fork

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<footer style = "font-size: 18px">DNA polymerase $\rightarrow$ Termination of DNA replication $\rightarrow$ <span style = "color:blue"> Summary </span> $\rightarrow$ Summary $\rightarrow$ Eukaryotic DNA replication </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Summary </primary>
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- Primase (RNA Polymerase) to synthesize primers with a '3'-OH group at the beginning of each DNA fragment

- DNA polymerase to synthesize the leading and lagging nucleotide strands and Also removes primers

- DNA Ligase seal the nick

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<footer style = "font-size: 18px">Termination of DNA replication $\rightarrow$ Summary $\rightarrow$ <span style = "color:blue"> Summary </span> $\rightarrow$ Eukaryotic DNA replication $\rightarrow$ Origin site in eukaryotes </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Origin site in eukaryotes </primary>
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- In Yeast, Autonomously replicating sequences (ARSs) enabled any DNA to which they were attached to replicate

- A multiprotein complex, the origin recognition complex (ORC), binds to the ARS and unwinds the DNA in this region

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![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-321-2992.8.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-48.jpg)

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<footer style = "font-size: 18px">Summary $\rightarrow$ Eukaryotic DNA replication $\rightarrow$ <span style = "color:blue"> Origin site in eukaryotes </span> $\rightarrow$ DNA polymerase of eukaryotes $\rightarrow$ DNA synthesis at the ends of chromosomes </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> DNA synthesis at the ends of chromosomes </primary>
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- A fundamental difference between eukaryotic and bacterial replication arises because eukaryotic chromosomes are linear and thus have ends

- The ends of chromosomes-the telomeres-possess several unique features, one of which is the presence of many copies of a short repeated sequence

- End of DNA is replicated with the help of telomerase enzyme

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![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-322-3067.2.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-50.jpg)

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<footer style = "font-size: 18px">Origin site in eukaryotes $\rightarrow$ DNA polymerase of eukaryotes $\rightarrow$ <span style = "color:blue"> DNA synthesis at the ends of chromosomes </span> $\rightarrow$ Summary $\rightarrow$ Summary </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Summary </primary>
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- Replication is always semiconservative

- Replication begins at sequences called origins

- DNA synthesis is initiated by short segments of RNA called primers

- The elongation of DNA strands is always in the 5' 3'direction

- New DNA is synthesized from dNTPs

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![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-323-3181.2.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-52.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-53.jpg)

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<footer style = "font-size: 18px">DNA polymerase of eukaryotes $\rightarrow$ DNA synthesis at the ends of chromosomes $\rightarrow$ <span style = "color:blue"> Summary </span> $\rightarrow$ Summary $\rightarrow$ Think it over </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-5 </Success>
### <primary style="font-size:24px"> Summary </primary>
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- Replication is continuous on the leading strand and discontinuous on the lagging strand

- New nucleotide strands are made complementary and antiparallel to their template strands

- Replication takes place at very high rates and is accurate, because of precise nucleotide selection, proofreading, and repair mechanisms

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![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-325-3250.8.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-06-chapter-05-genetics-and-evolution-molecular-basis-of-inheritance-l-5_12-smkf4y4gw4m-327-3301.2.jpg)

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<footer style = "font-size: 18px">DNA synthesis at the ends of chromosomes $\rightarrow$ Summary $\rightarrow$ <span style = "color:blue"> Summary </span> $\rightarrow$ Think it over $\rightarrow$ Thank you </footer>