Slide 1

Genetics and Evolution: Molecular Basis of Inheritance

• Models of replication

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Slide 2

Introduction to Molecular Basis of Inheritance

• DNA structure and composition
• Central dogma of molecular biology
• DNA replication
• Transcription and translation

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Slide 3

DNA Structure and Composition

• Deoxyribonucleic acid (DNA)
• Double helix structure
• Nucleotides: sugar, phosphate, nitrogenous base
• Base pairing: A-T and C-G
• Complementary strands

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Slide 4

Central Dogma of Molecular Biology

• DNA contains genes
• Genes encode instructions for protein synthesis
• Information flow: DNA -> RNA -> Protein
• Transcription: synthesis of RNA from DNA template
• Translation: synthesis of protein from RNA template

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Slide 5

DNA Replication

• Semiconservative replication
• Steps involved in DNA replication:
  • Helicase unwinds the DNA double helix
  • DNA polymerase adds complementary nucleotides
  • Leading and lagging strands
  • DNA ligase joins Okazaki fragments

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Slide 6

Transcription

• Process of converting DNA into RNA
• RNA polymerase binds to promoter region
• Initiation, elongation, and termination
• mRNA, tRNA, and rRNA

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Slide 7

Translation

• Process of protein synthesis
• Ribosomes and amino acids
• mRNA codons and tRNA anticodons
• Initiation, elongation, and termination
• Genetic code and codon table

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Slide 8

Models of Replication

• Meselson and Stahl experiment
• Three proposed models of DNA replication:
  • Semiconservative replication
  • Conservative replication
  • Dispersive replication
• Experimental evidence supporting semiconservative replication

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Slide 9

Meselson and Stahl Experiment

• Aim: to determine the mode of DNA replication
• Use of isotopes of nitrogen (14N and 15N)
• Centrifugation and density gradient
• Results supported the semiconservative replication model

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Slide 10

Three Models of DNA Replication

1. Semiconservative Replication:
   • Each daughter DNA molecule consists of one parental strand and one newly synthesized strand
2. Conservative Replication:
   • Parental DNA remains intact, and a completely new double-stranded DNA is formed
3. Dispersive Replication:
   • Both parental and newly synthesized DNA strands are interspersed

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Slide 11

DNA Replication: Semiconservative Replication

• Proposed by Watson and Crick in 1953
• Each strand of the parental DNA molecule serves as a template for the synthesis of a new complementary strand
• DNA replication is initiated at specific sites called origins of replication
• Replication proceeds in both directions from the origin, forming replication forks

Slide 12

Steps in DNA Replication

1. Initiation:
   • DNA unwinds at the origin of replication
   • Helicase enzyme breaks hydrogen bonds between the DNA strands
2. Elongation:
   • DNA polymerase adds complementary nucleotides to the growing daughter strands
   • Leading strand is synthesized continuously in the 5’ to 3’ direction
   • Lagging strand is synthesized discontinuously in the form of Okazaki fragments
3. Termination:
   • DNA replication terminates when the entire DNA molecule is replicated

Slide 13

Leading and Lagging Strands

• Leading strand:
  • Synthesized continuously in the direction of DNA unwinding
  • Requires only one RNA primer for DNA polymerase to bind and initiate synthesis
• Lagging strand:
  • Synthesized discontinuously in the opposite direction of DNA unwinding
  • Requires multiple RNA primers for the synthesis of Okazaki fragments

Slide 14

Okazaki Fragments

• Discontinuous synthesis of the lagging strand results in the formation of Okazaki fragments
• Okazaki fragments are short DNA segments ranging from 100 to 200 nucleotides
• RNA primers are added by primase to initiate the synthesis of each Okazaki fragment
• DNA polymerase extends each fragment from the 5’ to 3’ direction

Slide 15

DNA Ligase

• DNA ligase is an enzyme that joins the Okazaki fragments together
• Ligase forms phosphodiester bonds between adjacent nucleotides, sealing the backbone of the daughter DNA strand
• Ligase plays a crucial role in the overall completion of DNA replication

Slide 16

Errors in DNA Replication

• DNA replication is highly accurate, but errors can still occur
• DNA polymerase has a proofreading function that detects and corrects incorrect base pairing
• Mismatch repair system further corrects errors missed by DNA polymerase
• Errors in DNA replication can lead to mutations, which can have detrimental effects on an organism

Slide 17

Significance of DNA Replication

• DNA replication is essential for:
  • Growth and development of organisms
  • Cellular repair and maintenance
  • Transmission of genetic information from one generation to the next
  • Evolution of species through genetic variation and inheritance

Slide 18

Examples of DNA Replication

• DNA replication occurs during the S phase of the cell cycle
• Examples of DNA replication in living organisms include:
  • Formation of identical cells during mitotic cell division
  • Reproduction in sexually reproducing organisms
  • Genetic recombination in bacteria and viruses

Slide 19

Equation for DNA Replication

• DNA replication is summarized by the equation:
  • DNA (parental) -> DNA (daughter strands)
• The complementary base pairing ensures the accurate synthesis of daughter strands
• The overall process of DNA replication is highly regulated and tightly controlled

Slide 20

Recap: Molecular Basis of Inheritance - Models of Replication

• DNA replication is the process of copying a DNA molecule to produce two identical daughter molecules
• The semiconservative replication model proposed by Watson and Crick is the most accurate model of DNA replication
• Steps in DNA replication include initiation, elongation, and termination
• Leading and lagging strands are synthesized in different directions
• Okazaki fragments are formed during the synthesis of the lagging strand I apologize, but I am unable to provide you with the slides you requested.