Slide 1

• Topic: Molecular Basis of Inheritance - Initiation of Replication
• Introduction to the process of DNA replication
• Importance of replication in cell division
• Understanding the concept of initiation of replication

Slide 2

• DNA Replication: The process of duplicating DNA molecules
• Occurs during the S phase of interphase in cell cycle
• Ensures accurate transmission of genetic information to daughter cells

Slide 3

• Semiconservative replication: Each DNA strand serves as a template for the synthesis of a new complementary strand
• Meselson and Stahl’s experiment that demonstrated semiconservative replication
• Conservation of one parent and one newly synthesized strand in each DNA molecule

Slide 4

• Enzymes involved in the initiation of DNA replication
• Roles of DNA helicase and DNA topoisomerase
• Unwinding of DNA strands and prevention of supercoiling

Slide 5

• Initiation of Replication Complex (ORC): A protein complex responsible for initiating DNA replication
• Binding of ORC to specific sites called origin of replication (ori)
• Recognition of origins in eukaryotic and prokaryotic cells

Slide 6

• Licensing of DNA replication: Ensures that DNA replication occurs only once per cell cycle
• Cdc6 and Cdt1 proteins prevent re-replication
• Activation and inactivation of licensing proteins at different stages of the cell cycle

Slide 7

• Assembly of the pre-replication complex (pre-RC)
• Recruitment of other proteins required for DNA replication
• Formation of a stable complex at the origin of replication

Slide 8

• Initiation of replication forks at each origin of replication
• Formation of replication bubbles in eukaryotes
• Multiple replication origins in eukaryotic cells

Slide 9

• DNA polymerase enzyme: The main enzyme involved in DNA replication
• Synthesis of new DNA strands in the 5’ to 3’ direction
• Leading and lagging strands during replication

Slide 10

• Replication fork movement and progression of DNA synthesis
• Primase enzyme and synthesis of RNA primers
• Continuous DNA synthesis on the leading strand and discontinuous synthesis on the lagging strand

Slide 11

• DNA polymerase III: Main enzyme for DNA replication in prokaryotes
  • High processivity, able to synthesize long stretches of DNA
  • Proofreading activity to correct any errors in replication
• DNA polymerase alpha: Main enzyme for DNA replication in eukaryotes
  • Synthesizes RNA primers on both leading and lagging strands
• DNA polymerase delta and DNA polymerase epsilon: Synthesize DNA on the lagging and leading strands, respectively

Slide 12

• Role of DNA ligase in DNA replication
  • Joins Okazaki fragments on the lagging strand
  • Forms phosphodiester bonds between adjacent nucleotides
• DNA ligase uses ATP to catalyze the ligation reaction
• Formation of a continuous, double-stranded DNA molecule after completion of replication

Slide 13

• Origin of replication complex and replication licensing factors ensure replication occurs only once per cell cycle
  • Dysregulation of replication licensing can lead to genomic instability
• Defects in DNA replication machinery can cause genetic diseases, such as Bloom syndrome and Werner syndrome
• Importance of DNA replication fidelity for maintaining genetic information

Slide 14

• Replication-associated diseases and disorders
  • DNA replication stress and its association with cancer
  • Microsatellite instability in DNA replication disorders like Huntington’s disease
• Therapeutic applications of understanding DNA replication
  • Targeting DNA replication in cancer therapy
  • Developing anti-viral drugs that inhibit viral DNA replication

Slide 15

• Regulation of DNA replication initiation
  • Checkpoints and cell cycle control to ensure replication occurs at the right time
  • Protein kinases and checkpoint proteins involved in replication regulation
• Coordination between replication and other cellular processes, such as transcription and DNA repair

Slide 16

• Examples of DNA replication in different organisms
  • Bacteria: Circular genome, bidirectional replication from a single origin
  • Eukaryotes: Multiple origins, replication bubbles, coordination with nuclear organization
• Conservation of DNA replication machinery across different species

Slide 17

• Replication of mitochondrial DNA (mtDNA)
  • Replication occurs independently of the nuclear DNA replication
  • Inherited maternally, with mutations in mtDNA associated with various diseases
• Challenges in studying mtDNA replication and its implications

Slide 18

• Replication timing and replication origins in the genome
  • Differences in replication timing between different cell types and during development
  • Importance of replication timing for genome stability and gene expression
• Replication domain organization in the genome

Slide 19

• Replication fork dynamics and challenges
  • Stalling and collapse of replication forks
  • Fork restart and repair mechanisms
• Impact of DNA damage on replication fork progression

Slide 20

• Summary of initiation of DNA replication
  • Initiation complex formation at origins of replication
  • Licensing of replication to ensure fidelity and prevent re-replication
  • DNA synthesis by DNA polymerase enzymes
  • Role of other proteins, such as DNA helicase, ligase, and topoisomerase in replication

Slide 21

• Features of DNA replication:
  • Semi-conservative
  • Bidirectional
  • Highly accurate
• Replication bubble and replication forks
  • Formation and movement of the replication forks
• Leading and lagging strands
  • Synthesis in opposite directions and their coordination

Slide 22

• DNA replication in prokaryotes
  • Circular genome
  • Single origin of replication (oriC)
• DNA replication in eukaryotes
  • Linear genome
  • Multiple origins of replication
• Licensing and activation of replication origins

Slide 23

• DNA polymerase I: Role in DNA replication in prokaryotes
  • Removes RNA primers
  • Fills the gaps with DNA nucleotides
  • Role in DNA repair
• DNA polymerase alpha: Role in DNA replication in eukaryotes
  • Initiates synthesis of RNA primers
  • Interaction with other DNA polymerases

Slide 24

• Telomeres: Repeated DNA sequences at the ends of linear chromosomes
  • Role in protecting the integrity of chromosomes
  • Telomerase enzyme and its role in maintaining telomere length
• Telomere shortening and its implications in aging and cancer

Slide 25

• DNA replication errors and repair:
  • Proofreading activity of DNA polymerases
  • Mismatch repair system
  • Base-excision repair and nucleotide excision repair
• Importance of DNA repair mechanisms to maintain genome stability

Slide 26

• DNA replication and cell cycle checkpoints
  • G1/S checkpoint and initiation of DNA replication
  • S phase checkpoint to monitor DNA synthesis
• Role of cyclin-dependent kinases (CDKs) in regulating DNA replication

Slide 27

• Regulation of DNA replication by cell signaling pathways
  • Cyclins and cyclin-dependent kinases (CDKs)
  • Checkpoint kinases (ATR and ATM)
  • Tumor suppressor proteins (p53)
• Importance of proper regulation for preventing genetic diseases and cancer

Slide 28

• DNA replication and epigenetic modifications
  • DNA methylation and histone modifications
  • Impact on DNA replication timing and replication origins
• Epigenetic inheritance and its implications in development and disease

Slide 29

• Techniques to study DNA replication
  • DNA fiber assay
  • Labeling and pulse-chase experiments
  • Microscopy techniques
• Advances in understanding DNA replication dynamics using next-generation sequencing (NGS) technologies

Slide 30

• Conclusion
  • DNA replication is a crucial process for the transmission of genetic information
  • Initiation of replication involves the assembly of a complex machinery at replication origins
  • Multiple enzymes and proteins coordinate to ensure accurate and efficient replication
  • Regulation of replication is important for maintaining genome stability and preventing diseases
• Questions and discussion.