What stage of mitosis/meiosis does DNA replicate ? Agenda for Monday Nov. 1st DNA replication

Central Dogma

3 theories of DNA replication How are two daughter strands are created? DNA needs to replicate – creates new cells These strands should be accurately copied and transmitted from the parental cell to the daughter ones Meiosis and Mitosis 3 possible models of creating new DNA

Conservative Replication Conservative replication – would leave intact the original DNA molecule and generate a completely new molecule

Dispersive Replication Dispersive Replication would produce two DNA molecules with sections of both old and new DNA interspersed along each strand

Semiconservative Replication Semiconservative replication would produce molecules with both old and new DNA, but each molecule is composed of one old strand and one new one This is how DNA replicates

Semiconservative Replication Watson and Crick suggested replication method Semiconservative replication DNA separates, serve as templates, and produce DNA molecules that have one strand of parental DNA and one new strand of DNA Occurs during interphase of mitosis and meiosis

3 steps of replication Unwinding Base pairing Joining

Unwinding DNA Helicase unwinds/unzips DNA strand Hydrogen bonds are broken Proteins adhere to DNA to keep strands separate RNA Primase adds a short segment to each strand

Base Pairing Steps DNA Polymerase catalyzes the addition of nucleotides to the new DNA strand Always starts at 5’ and goes to 3’ Strands are identical (A=T, C=G) Two strands are created in different ways One is leading strand One is the lagging strand

Leading Strand Elongated as the DNA unwinds New nucleotides are added continuously

Lagging Strand Elongates away from replication fork Created in segments Okazaki Fragment 100 – 200 nucleotides long Fragments are later connected

**New RNA Primer each time

Joining Many areas along DNA strand where DNA replication can being DNA polymerase comes to an RNA primer it removes primer and fills with DNA nucleotide DNA Ligase links two sections of DNA together

Prokaryote vs. Eukaryote Prokaryotes 1 origin Eukaryote Many origins

Replicate your DNA Put on a separate sheet of paper. Discussion Questions 1. Compare the two new strands of DNA. Are they the same or different? Why? 2. How does the structure of a DNA molecule help account for the great variety of life that exists on earth?

Questions Answer questions 1-5 on page 335 in your book