Lecture 5: DNA discovery and replication

• chemical composition of DNA: polymer of four nucleotides (AGCT)
• polarity defined by the sugar backbone, 3’ OH and 5’ phosphatee
• the hydrogen bonds between A/T and G/C are the moststable and 2) by always pairing a purine and a pyrimidine, the distance between the two strands
• Semiconservative Replication of DNA: each old DNA strand serves as a template for a new strand.
• • NA replication starts at the origins of replication, with helicase unwinding the DNA and primase adding primers (short stretches of complementary RNA → act as ragged ends → stretches of DNA that are partially double stranded and partially single stranded). 
  • As the helicases unwind the DNA in each direction from the origin of replication, a bubble forms with so-called replication forks on either end where the old double stranded DNA is being split to act as the template for the formation of two new strands.
• DNA replication starts at the origins of replication, with helicase unwinding the DNA and primase adding primers (short stretches of complementary RNA → act as ragged ends → stretches of DNA that are partially double stranded and partially single stranded).
• • DNA polymerase takes the complementary nucleotide and breaks the bond between the alpha phosphate attached to the sugar and the beta phosphate and attaches the alpha phosphate to the last 3’ OH group. 
• As the helicases unwind the DNA in each direction from the origin of replication, a bubble forms with so-called replication forks on either end where the old double stranded DNA is being split to act as the template for the formation of two new strands.
• DNA polymerase synthesizes new DNA strands, the primase adds primers every few hundred bases on the lagging strand creating lots of short stretches of DNA, called Okazaki fragments. DNA polymerase I removes RNA primers and fills gaps, and DNA ligase joins fragments.
• DNA polymerase I chews up the RNA primers and fills in the gaps with newly synthesized strands.
• DNA polymerase's proofreading function corrects errors during recombination by removing bases. Mismatch repair occurs during recombination and excision repair mechanisms during the rest of the time fix errors post-replication, ensuring DNA integrity.