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DNA REPLICATION
SERWELAS, CLAUDINE M.ESQUIVEL, CHERRY LYN
AAPD2-FGENETICSDR. LOS BANOS
What does DNA look like?• DNA has..• A sugar/phosphate
backbone • 4 Chemical bases
Sugar
The bases• It is composed of 4
chemical bases: Adenosine (A), Thymine (T), Cytosine (C) and Guanine (G).
• A always pairs with T• C always pairs with G• The pairs are held
together by hydrogen bonds (WNC’s).
What does DNA do?
• DNA is the genetic code.• It determines our physical characteristics:
from our hair color to what we are allergic to.• Our DNA codes for 20 amino acids which are
the building blocks of life.
What Is DNA Replication
• DNA Replication is the process in which the DNA within a cell makes an exact copy of itself.– Why does DNA replicate?
– During which phase of the cell cycle does DNA replicate?
DNA Replication models
The Three Possible DNA Replication Models
• Conservative- would leave the original strand intact and copy it.
• Dispersive-would produce two DNA molecule with sections of both old and new along each strand.
• Semiconservative –would produce DNA molecule with both one old strand and one new strand.
DNA Replication
Replicationbubble
Replicationfork
Replicationfork
Hydrogen bond
Replication occurs during Interphase
DNA replication is the process where an entire double-stranded DNA is copied to produce a second, identical DNA double helix.
DNA Replication
• Helicase unwinds the double helix starting at a replication bubble.
• The two strands separate as the hydrogen bonds between base pairs are broken.
• Two replication forks form and the DNA is unwound in opposite directions.
DNAhelicase
DNA Replication
•Helicase has completed unwinding the DNA strand.
•Single strand Binding Proteins (SSB) keep the two strands from re-annealing (coming back
together).
DNA Replication
Primase RNA Primer
•Primase is an RNA polymerase that makes the RNA primer.
•These primers “tell” the DNA polymerase where to start copying the DNA.
Leading Strand
Lagging Strand
DNA Replication
DNA Polymerase
• The DNA polymerase starts at the 3’ end of the RNA primer of the leading stand CONTINUOUSLY.• DNA is copied in 5’ to 3’ direction.• DNA polymerase copies the lagging strand DIS- continuously.
Leading Strand
Lagging Strand
3’ 5’
5’ 3’
Direction of Replication
Direction of Replication
DNA Replication
• The dis-continuous pieces of DNA copied on the lagging strand are known as Okazaki fragments.
DNA Replication
Another DNA Polymerase removes the RNA primers and replaces them with DNA.
DNA Replication
Finally the gaps in the sugar phosphate backbone are sealed by DNA ligase
There are now 2 identical double helices of DNA.
ligase
REACTION:
o The DNA occurs simultaneously forming sister chromatids.
o Nucleotides should always be in pair.o Nucleotides are held together with loose
hydrogen bonds.o Every cell in our body has the same copy of
DNA, and the DNA will copy itself trillion of times in our lifetime.
o Every copy of the DNA contains half of its original strand.
o DNA replication is semiconservative with each existing strand serving as template for synthesis of new strand.
o Replication begins at specific location called REPLICATION.
o On one strand (leading strand) synthesis is continuous
o On the other strand (lagging strand) synthesis is discontinuous.
o The 2 strands is producing a seriesOf okazaki fragments that must be Ligased together
DNA Replication ANIMATION
• http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html