6. Duplicação do DNA

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DNA REPLICATION
SERWELAS, CLAUDINE M.
ESQUIVEL, CHERRY LYN
AAPD2-F
GENETICS
DR. LOS BANOS
What does DNA look like?
• DNA has..
• A sugar/phosphate 
backbone 
• 4 Chemical bases
Suga
r
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
Replication
bubble
Replication
fork
Replication
fork
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.
DNA
helicase
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 series
Of okazaki fragments that must be 
Ligased together
DNA Replication ANIMATION
• http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html
	DNA REPLICATION
	What does DNA look like?
	The bases
	What does DNA do?
	What Is DNA Replication
	DNA Replication models
	The Three Possible DNA Replication Models
	DNA Replication
	Slide 9
	Slide 10
	Slide 11
	Slide 12
	Slide 13
	DNA Replication
	Slide 15
	REACTION:
	PowerPoint Presentation
	Slide 18
	DNA Replication ANIMATION