1. By: Monique Hernandez
& Trevor Dunbar

2. 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

3. Stages of Mitosis:

4. First Step: Open Up the Double Helix
 Where: Origin of Replication on DNA strand

5. 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

6. 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

7. Second Step: Prime the DNA Strand
 Leading Strand: Strand on which there is continuous
synthesis of DNA
 http://www.youtube.com/watch?v=dsoOPDgV0wc

8. 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

9. 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

10. 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

12. Chromosomes
 DNA and associated proteins
are organized into
chromosomes
 DNA + histone proteins=
Chromatin

13. 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

14. Structure of a Chromosome
 Telomere: ends of
chromosomes, important for
stability
 Centromere: central region of
chromosome, kinetochores
form here and the spindle
microtubules attach