Post on 03-Jan-2016
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What stage of mitosis/meiosis does DNA replicate ?
Agenda for Monday Nov. 1st 1.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
1. Unwinding
2. Base pairing
3. Joining
Unwinding1. DNA Helicase unwinds/unzips DNA strand
A. Hydrogen bonds are broken
2. Proteins adhere to DNA to keep strands separate
3. RNA Primase adds a short segment to each strand
Base Pairing
Steps1.DNA Polymerase catalyzes the addition of
nucleotides to the new DNA strandA. Always starts at 5’ and goes to 3’B. Strands are identical (A=T, C=G)
2.Two strands are created in different waysA. One is leading strand B. 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 DNAPut on a separate sheet of paper.
Discussion Questions1. 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