DNA

• The two strands of DNA are antiparallel, meaning they run in opposite directions.
• Purines have double-ring structures, while pyrimidines have single-ring structures.
• DNA is made up of four different nucleotides, which can be represented by the letters A, C, G, and T.
• Each nucleotide has three parts - a sugar molecule (deoxyribose), a phosphate group, and one of four nitrogenous bases (adenine, thymine, cytosine, or guanine).
• The process of DNA replication proceeds in a semi-conservative manner, with each daughter cell inheriting one of the original strands and its complementary synthesized strand.

  
• In any given double stranded sample of DNA, A=T and C=G
• New nucleotides added to 3’ end or new strand which has free OH group.
• Replication complex binds specific DNA sequences in the DNA
• Helicase unwinds DNA to allow replication to proceed in two directions
• New dna synthesis occurs from 5’ to 3’
• Single stranded binding protein keeps DNA strands from annealing.
• As helicases unzips DNA it causes tension in the stranded portion. Topoisomerases relieve tension and reveal phosphodiester backbone.
• DNA replication starts off with a short RNA primer synthesized by primase.
• leading strand- elongates towards replication fork in continuous strands

  lagging- elongated away from replication fork in Okazaki fragments where each fragment has its own RNA primer.
• DNA ligase joins the Okazaki fragments together to form a continuous strand of DNA
• End replication error is when linear eukaryotic chromosomes have to cut off excess DNA after exonuclease removes the RNA primers which leaves out with single stranded bit of DNa at the ends, creating shorter chromosome.
• Instead there are telomeres on the ends of the chromosome where they are repetitive sequences and telomerase’s make telomere.
• DNA polymerase proofreads to avoid mutations and will cut ofd the incorrect base and replace it with the correct nucleotide base.
• Point mutation is a change in the nucleotide sequence of a gene.
• Chromosomal mutation is a change in the number or structure of chromosomes
• Spontaneous mutation is a random change in the DNA sequence of an organism.
• Induced mutation is a mutation that occurs when a cell is exposed to a mutagen
• Elongation occurs 5’ to 3’

  template is read from 3’ to 5’
• Okazaki fragment are joined together by ligase
• Silent mutation doesn’t affect protein function
• Somatic mutations are mutations that occur in somatic body cells and can be passed to daughter cells
• Germline mutations occur in gametes where gametes pass mutation at fertilization
• Telomeres are repetitive sequences of DNA and are lost overtime in most cells.
• Coding region is region translated to protein and non coding region is not translated into protein.
• Adenines form 2 hydrogen bonds with thymine and guanine forms 3 hydrogen bonds with cytosine.
• DNA polymerase adds nucleotides to the growing strand by forming phosphodiester bond between sugar-phosphate backbone of new nucleotide and existing nucleotide on template strand.
• DNA polymerase proofreads
• RNA primer has the three prime hydroxyl group which allows DNA polymerase to synthesize the corresponding bases
• Elongation occurs from 5 prime to 3 prime since the bond between nucleotides are formed by phosphodiester bonds which are covalent and these bonds are formed by dehydration synthesis so the phosphate would need the hydroxyl to release water.
• Leading strand is continuous because there is no problem with RNA primer being removed as it is made continuously towards the replication fork.