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