DNA Replication

What does DNA look like?DNA has..A

sugar/phosphate backbone

4 Chemical bases

Sugar

The bases It is composed of 4

chemical bases: Adenine (A), Thymine (T), Cytosine (C) and Guanine (G).

A always pairs with T

The Bases C always pairs with G

The pairs are held together by hydrogen bonds.

What does DNA do? DNA: deoxy ribose nucleic acid

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.

DNA Replication - the very basicsThe basics of DNA REPLICATION Unwind – Unzip – Add nucleotides – wind it all back

up.

If only it could be that simple Two things make it a little more complicated

DNA is a VERY LONG double helix chemical molecule It has a anti-parallel structure

Anti-parallel structure of DNA

It’s a long Double Helix

-

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 stranded Binding Proteins 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 pairs.

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/0471

393878/student/animations/dna_replication/index.html

http://www.youtube.com/watch?v=teV62zrm2P0

Done by:

Lume Landman 201218257

References

Mohapatra , L http://www.slideshare.net/lopamohapatra39/dna-replication-29922117?qid=f160c09e-4986-412e-b81e-ccf2da2dcab5&v=default&b=&from_search=1 (Accessed on 7 March)

Serwelas, CM and Esquivel, CL http://www.slideshare.net/claudeaa/dna-replication-11970385 (Accessed on 7 March)

http://www.slideshare.net/ihmcbiology1213/dna-replication-15152639(Accessed on 7 March)