lec 4

• Replication, Maintenance and Rearrangement of genome

  The process by which the genome's DNA is copied, maintained, and organised in cells

  
• DNA replication


  The biological polymerization reaction for making multiple copies of DNA in cells

  
• Eukaryotic genome


  • Consists of several double-stranded linear DNA molecules packaged into chromosomes
  • Human body cells have 46 chromosomes, while human gametes have 23 chromosomes each
• DNA replication


  1. Initiation

  2. Elongation

  3. Termination

  
• Initiation


  Dissociation of the two DNA strands, recruitment of proteins like DNA helicase, primase, and DNA polymerase to form replication forks

  
• Elongation


  DNA polymerase synthesises new DNA strands complementary to the template strands, leading strand and lagging strand synthesis

  
• Termination


  Completion of DNA synthesis when replication forks meet or reach the end of the chromosome, stabilisation of newly synthesised strands

  
• Compaction


  The process of organising and condensing the genetic material after replication

  
• Compaction of eukaryotic DNA

  • DNA forms a complex with proteins called chromatin
  • Chromatin is condensed into a smaller volume, forming nucleosomes and chromosomes

  
• DNA repair


  Mechanisms to correct mistakes during DNA replication and repair DNA damage

  
• DNA repair mechanisms


  1. Direct reversal of DNA damage

  2. Excision repair (base excision repair, nucleotide excision repair)

  3. Post-replication repair (recombinational repair, error-prone repair)

  
• Direct reversal of DNA damage

  Repair of specific types of DNA damage, such as pyrimidine dimers, without removing the damaged bases
• Excision repair


  Removal of the damaged bases followed by replacement with newly synthesised DNA
• Post-replication repair


  Repair mechanisms that act after DNA replication to ensure accurate genetic information is restored and maintain genomic stability

  
• Abnormalities in DNA repair processes can have disastrous consequences, such as cancer
• Osmosis is the passage of water from a region of high concentration to a region of lower concentration through a semi-permeable membrane
• Vesicular transport


  • Endocytosis (pinocytosis, phagocytosis, receptor-mediated endocytosis)
  • Exocytosis - fusion of membrane-bound vesicles with the plasma membrane to release their contents