By: Monique Hernandez

& Trevor Dunbar

Why does DNA Replicate? To make an identical copy of DNA for cell division in Mitosis and

Meiosis

Meiosis is a specialized cell division process for sexual reproduction

Cell division for cells other than sex cells, is known as Mitosis

Stages of Mitosis:

First Step: Open Up the Double Helix

Where: Origin of Replication on DNA strand

Key Players: DNA helicase: A protein that works to “unzip” the DNA

and separate the antiparallel strands

Single stranded binding proteins: keep the newly single stranded DNA stable and work to prevent hairpin helices on lagging strand

How do chromosomes not get tightly tangled? Topoisomerase 1: works to relieve tension made in

DNA strand by making a break in the backbone of a single strand.

Topoisomerase 2: works to relieve tension during the “unzipping” of DNA by making a double stranded break.

http://www.youtube.com/watch?v=EYGrElVyHnU

Second Step: Prime the DNA Strand

Leading Strand: Strand on which there is continuous synthesis of DNA

http://www.youtube.com/watch?v=dsoOPDgV0wc

Leading Strand Key Players: Primase will add an RNA primer to the DNA strand.

DNA polymerase will bind to the RNA primer and begin synthesizing DNA in the 5’3’ direction

The clamp protein binds to DNA polymerase and prevents it from dissociating from the DNA template strand

Lagging Strand Discontinuous synthesis of DNA; backstitches in the

5’3’ direction

The segments synthesized by DNA polymerase are called “Okazaki fragments”

http://www.youtube.com/watch?v=H_l0rnvPcTA

Lagging Strand Key Players: Every ~100 nucleotides, RNA primers are added by a

DNA primase

DNA polymerase will let go of DNA once it meets the next RNA primer

Exonuclease will recognize RNA primer and cut it out.

DNA polymerase will fill in the missing gap with nucleotides

DNA ligase will seal the nicks in the strand

Chromosomes DNA and associated proteins

are organized into chromosomes

DNA + histone proteins= Chromatin

Chromosomes

Genome of eukaryotes is too large to put on a single piece of DNA.

It is broken up into separate chromosomes

Each chromosome carries 1000’s of genes

Humans have 46 chromosomes

Structure of a Chromosome

Telomere: ends of chromosomes, important for stability

Centromere: central region of chromosome, kinetochoresform here and the spindle microtubules attach