DNA structure & DNA Replication

DNA Structure

  • [A]=[T] and [G]=[C] are the 2 bases
  • The four DNA nitrogenous bases are:

- Adenine

- Guanine

- Cytosine

- Thymine

  • Pyrimidines: 1 ring
  • Purines: 2 rings

%%Trick: Adenine & Guanine have 2 n’s which makes them purines (2 rings) while Cytosine & Thymine don’t%%

  • Two types of bonds: Covalent & Hydrogen bonds
  • Hydrogen bonds are going to form between bases across from one another in the double helix
  • Covalent bonds are going to occur within each linear strand
  • 3’ to 5’ is the leading strand
  • 5’ to 3’ is the lagging stand

DNA Replication

  • The overall purpose of DNA replication is when a double-stranded DNA is replicated to produce 2 identical DNA molecules
  • Semi-conservative replication definition: When copying is finished, you have to separate helices, each consisting of one original strand plus one newly made strand.
  • It occurs in the nucleus

Enzymes involved/Importance:

  • Helicase (the unzipper; unzips the 2 DNA strands)
  • DNA Polymerase (the builder; replicates DNA molecules to build a new strand of DNA)
  • Primase (the initializer; Primase makes the primer this helps DNA polymerase know where to go to work)
  • Ligase (the gluer; Helps glue DNA fragments together)

Steps:

  1. Helicase unzips the 2 DNA strands which break up hydrogen bonds
  2. Single-stranded binding proteins (SSBP) are added to keep the strands open
  3. DNA primase lays down DNA primer
  4. DNA Polymerase binds to the separated chains of DNA
  5. Ligase “glues” together the fragmented pieces (Okazaki fragments) at the backbone