Genetics and Evolution - Molecular Basis of Inheritance - Bacterial DNA Replication

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Slide 1

• Definition of DNA replication
• Significance of DNA replication in cells
• Key players involved in bacterial DNA replication:
  • DNA polymerase
  • Helicase
  • Primase
  • Single-strand binding proteins
  • DNA ligase

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Slide 2

• DNA polymerase:
  • Catalyzes polymerization of new DNA strand
  • Requires a template strand and primer
  • Ensures accuracy of replication through proofreading
• Three different DNA polymerases are involved in bacterial DNA replication:
  • DNA polymerase I
  • DNA polymerase II
  • DNA polymerase III

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Slide 3

• Helicase:
  • Unwinds the double-stranded DNA helix
  • Breaks hydrogen bonds between base pairs
• Helicase forms the replication fork, where DNA synthesis occurs

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Slide 4

• Primase:
  • Synthesizes short RNA primers
  • Provides a starting point for DNA polymerase
  • Primers are later replaced by DNA

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Slide 5

• Single-strand binding proteins (SSB):
  • Stabilize and protect single-stranded DNA during replication
  • Prevent reannealing of the separated DNA strands

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Slide 6

• DNA ligase:
  • Joins Okazaki fragments on the lagging strand of DNA
  • Seals nicks in the sugar-phosphate backbone
  • Catalyzes the formation of phosphodiester bonds between adjacent nucleotides

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Slide 7

• DNA replication is a semiconservative process:
  • Each new DNA molecule consists of one original (template) strand and one newly synthesized strand
• Meselson-Stahl experiment provided evidence for semiconservative replication

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Slide 8

• Initiation of DNA replication:
  • DNA helicase binds to the origin of replication
  • Helicase unwinds the DNA helix
  • Single-stranded binding proteins stabilize the unwound DNA strands

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Slide 9

• Elongation of DNA strand:
  • Leading strand synthesized continuously in the 5’ to 3’ direction
  • Lagging strand synthesized discontinuously as Okazaki fragments
• RNA primers are added by primase to initiate DNA synthesis

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Slide 10

• Termination of DNA replication:
  • DNA replication machinery reaches the termination site
  • DNA polymerase synthesizes to the end of the template strand
  • RNA primers are removed and replaced with DNA
• Two DNA molecules are formed, each consisting of an original strand and a newly synthesized strand

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Slide 11

• DNA replication in eukaryotes:

  • More complex process compared to prokaryotes
  • Multiple origins of replication
  • Involves larger and more specialized replication proteins

• Replication forks:

  • The areas where the replication machinery is actively synthesizing DNA
  • Move bidirectionally along the DNA molecule

• Telomeres:

  • Repeated nucleotide sequences at the ends of linear chromosomes
  • Prevent the loss of genetic information during replication
  • Problematic area for replication due to the nature of DNA synthesis

• Telomerase enzyme:

  • Adds telomeric DNA sequences to the ends of chromosomes
  • Prevents the shortening of telomeres

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Slide 12

• DNA proofreading and repair mechanisms:

  • DNA polymerase performs proofreading during DNA synthesis
  • Incorrect base pairings can be detected and corrected
  • Mismatch repair system fixes errors after replication

• Nucleotide excision repair:

  • Corrects DNA damage caused by UV light and certain chemicals
  • Removes damaged DNA and replaces it with newly synthesized DNA

• Examples of mutations:

  • Substitutions: one base pair is replaced with another
  • Insertions: extra nucleotides are added into the DNA sequence
  • Deletions: nucleotides are missing from the DNA sequence

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Slide 13

• Mutagens:

  • Factors that increase the rate of mutations
  • Examples: UV radiation, chemicals, certain drugs

• Effects of mutations:

  • Silent mutations: no change in the amino acid sequence
  • Missense mutations: change in the amino acid sequence
  • Nonsense mutations: premature stop codon formation
  • Frameshift mutations: insertion or deletion of nucleotides, altering the reading frame

• Mutations can have different effects on an organism depending on their location and impact on protein function

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Slide 14

• DNA repair mechanisms:

  • Base excision repair (BER): repairs single-base lesions
  • Nucleotide excision repair (NER): repairs larger DNA lesions
  • Mismatch repair (MMR): corrects mispaired bases that escape proofreading
  • Homologous recombination repair (HRR): repairs double-strand breaks

• Importance of DNA repair in maintaining genetic stability and preventing diseases

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Slide 15

• DNA replication errors:

  • Can occur naturally due to the inherent imperfections of DNA replication
  • Environmental factors can increase the error rate

• Consequences of DNA replication errors:

  • Changes in DNA sequence
  • Mutations
  • Genetic diseases

• Role of DNA repair mechanisms in minimizing the impact of replication errors

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Slide 16

• Replicative DNA damage:

  • Errors that occur during normal DNA replication
  • Can result in base mispairings
  • Can be corrected by DNA repair mechanisms

• Non-replicative DNA damage:

  • Caused by environmental factors and chemical agents
  • Examples include oxidative damage, UV radiation, and chemical modifications

• DNA repair mechanisms are important for maintaining the integrity of the genome and preventing diseases

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Slide 17

• Variations in DNA repair mechanisms can contribute to genetic diversity

• Different DNA repair pathways exist to address different types of DNA damage

• Genetic variations in DNA repair genes can affect an individual’s susceptibility to certain diseases

• Importance of studying DNA repair mechanisms in understanding genetic diseases and developing targeted therapies

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Slide 18

• Recombinant DNA technology:

  • Manipulation of DNA to create new combinations of genetic material
  • Important tool in genetic engineering, biotechnology, and medical research

• Techniques used in recombinant DNA technology:

  • DNA cloning
  • Polymerase chain reaction (PCR)
  • DNA sequencing
  • DNA fingerprinting

• Applications of recombinant DNA technology:

  • Production of recombinant proteins
  • Genetic modification of organisms
  • Gene therapy

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Slide 19

• DNA cloning:

  • Process of creating multiple copies of a specific DNA fragment
  • Involves inserting the DNA fragment into a vector (such as a plasmid or a virus)
  • The recombinant DNA is then transferred into host cells for replication

• Polymerase chain reaction (PCR):

  • Technique for amplifying specific DNA sequences
  • Uses heat-resistant DNA polymerase to repeatedly copy the target DNA

• DNA sequencing:

  • Determining the order of nucleotides in a DNA molecule
  • Important for understanding the structure and function of genes

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Slide 20

• DNA fingerprinting:

  • Analyzing unique patterns in an individual’s DNA to identify them
  • Uses regions of the genome that vary between individuals (such as microsatellites)
  • Applications: forensic science, paternity testing, identifying genetic diseases

• Ethical considerations in the use of recombinant DNA technology:

  • Safety precautions
  • Potential misuse
  • Regulation and oversight

Slide 21

• Role of DNA replication in inheritance and passing of genetic information to offspring
• Replication of DNA ensures that each new cell or organism receives an identical copy of the genetic material
• Without accurate DNA replication, genetic information may be lost or altered

Slide 22

• Importance of fidelity in DNA replication
• High degree of accuracy is maintained during replication due to the proofreading ability of DNA polymerase
• DNA polymerase can detect and correct errors in base pairing
• Fidelity in DNA replication ensures that genetic information is faithfully transmitted from one generation to the next

Slide 23

• Replication of DNA in prokaryotes vs. eukaryotes
• Prokaryotes have a single circular chromosome, whereas eukaryotes have multiple linear chromosomes
• Replication in prokaryotes occurs in the cytoplasm, while in eukaryotes, it occurs in the nucleus
• Differences in the mechanisms and regulation of DNA replication between prokaryotes and eukaryotes

Slide 24

• Replication bubbles and replication forks
• Replication bubbles form at the origin of replication, where DNA replication initiates
• Replication forks are the Y-shaped structures formed at the ends of replication bubbles
• Two replication forks move in opposite directions, synthesizing new DNA strands

Slide 25

• Leading and lagging strands in DNA replication
• Leading strand is synthesized continuously in the 5’ to 3’ direction
• Lagging strand is synthesized discontinuously as Okazaki fragments in the 5’ to 3’ direction away from the replication fork
• Primase synthesizes RNA primers on the lagging strand, serving as starting points for DNA synthesis

Slide 26

• Okazaki fragments and their synthesis
• Okazaki fragments are short DNA strands on the lagging strand
• Primase synthesizes RNA primers on the lagging strand, which are later replaced by DNA
• DNA polymerase III extends the leading strand and synthesizes Okazaki fragments on the lagging strand
• DNA ligase joins the Okazaki fragments together to create a continuous DNA strand

Slide 27

• Telomeres and their role in DNA replication
• Telomeres are repeated nucleotide sequences at the ends of linear chromosomes
• They prevent the loss of genetic information during DNA replication
• Telomerase enzyme adds telomeric DNA sequences to the ends of chromosomes to counteract their shortening during replication

Slide 28

• Replication errors and mutations
• Replication errors can lead to mutations in the DNA sequence
• Mutations can have different effects on an organism, such as changes in protein structure or function
• Mutations can be beneficial, neutral, or harmful, depending on the context

Slide 29

• DNA repair mechanisms
• Cells have various DNA repair mechanisms to correct errors and damage in the DNA sequence
• These mechanisms include base excision repair, nucleotide excision repair, mismatch repair, and homologous recombination repair
• Failure to repair DNA damage can lead to genetic disorders and diseases

Slide 30

• Importance of DNA replication and repair in maintaining genetic stability
• Accurate DNA replication ensures that genetic information is transmitted faithfully from one generation to the next
• DNA repair mechanisms prevent the accumulation of DNA damage and maintain the integrity of the genome
• Understanding the molecular basis of DNA replication and repair is crucial for various fields, including medicine and biotechnology