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DNA replication ,repair and recombination ومن أحياهاPage 0 ق الطبي الفريميكادي اDNA replication ,repair and recombination DONE BY : Shatha Khtoum and Heba abu hazeem GENETICS

DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

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Page 1: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 0

GENETICS

الفريق الطبي

االكاديمي

DNA replication ,repair and recombination

DONE BY :

Shatha Khtoum and

Heba abu hazeem

.

GENETICS

Page 2: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 1

In last lecture we talked about DNA polymerases activity, and

most important one DNA polymerase III which has the activity

of 5' 3' polymerase activity and the 3' 5' exonuclease activity

but doesn't have the 5' 3' exonuclease activity. However, there

is some exceptions; some DNA polymerases do not have this

3’5’ exonuclease activity, ex: HIV.

In HIV; because of do not have this 3’5’ exonuclease activity,

the HIV will transcribe RNA to DNA (polymerase and RNase H,

cooperate to convert the RNA into a double-stranded linear

DNA). Because it doesn’t have the 3’5’ exonuclease activity, so

it’ll make a lot of steps to convert RNA to DNA by reverse

transcriptase. As a result, it will evolve … *didn’t hear it clearly*

(2:00) so you can’t treat HIV by drugs because it evades drugs,

why? Because it’s not have good reading during replication. It

takes a lot of steps and each time it replicates a new genome

will produce. Very fast it’s evolve, very fast it’s change its

genome and by doing this it escapes drugs.

-DNA replication in prokaryotic or eukaryotic, it’s directed to

specific sequences in the genome not in any place but in a

specific sequences, that called “origin of replication”.

In prokaryotes, because the genome is small in relative to

eukaryotes, it’s about 5-6 million pair of base in comparative to

eukaryotes which is 3 billion pair of base prokaryotes have

origin of replication because the genome is small, but only one

t’s big of replication because i many originsthe eukaryotes have

and linear which requires a lot of origin of replication.

will recognize those specific sequences replication proteinsThe

and bind to them and start replication.

Shatha Khtoum
Cross-Out
Shatha Khtoum
Typewritten Text
mistakes
Shatha Khtoum
Typewritten Text
it will evolve very fast and its genome will change each time it replicates
Shatha Khtoum
Cross-Out
Page 3: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 2

As we know DNA replication needs template and reader (in

NA polymerase; there’s polymerase the reader is D prokaryotes

I, II, III / the principle one is DNA polymerase III, polymerase I, II

are important for editing). As you know polymerase is

important for remove the primers and fill the gaps between

okazaki fragments.

Also, there must be a catalytic action in the DNA replication to

make the phosphodiester bonds.

-What makes the phosphodiester bonds during DNA

replication? DNA polymerase.

DNA polymerase reads and do the catalysis the So,

ynthesis . And remember it reads and sphosphodiester bonds

the DNA in 5’ to 3’ direction, there is no catalytic reaction the 3’

to 5’ direction.

In prokaryotes, the number of DNA polymerase I or II is several

hundreds, while there are only 3 to 4 copies of DNA polymerase

III.

enzyme in processiveDNA polymerase III is the principal and

, it doesn’t leave the DNA strand during DNA DNA replication

, while DNA polymerase I is not processive and can replication

leave the DNA strand (it leaves once it leaves the primer).

-Why DNA polymerase I does not stay, while DNApolymerase III

stay?

DNA polymerase I has 5’3’ exonuclease while DNA polymerase

III doesn’t have 5’3’ exonuclease. So, DNA polymerase I fills

between the Okazaki fragments and jump to the other

fragments, once it finishes the RNA primer removal it leaves. If

the okazaki frgaments by 5’3’ degradeit stays, it will

exonuclease activity.

Page 4: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 3

DNA polymerase III stays on the replication fork doing the

, this clamp protein called “clamp”replication because of a

protein will grap the DNA stands and DNA polymerase to the

replication fork and prevent DNA polymerase III from leaving.

-DNA clamp in eukaryotic and prokyotic is very important. If

the cell. And this killyou inhibit the DNA clamp protein, you will

used as a strategy to kill bacteria.

-The primase: it’s a RNA polymerase. It synthesizes short RNA sequences that are complementary to a single-stranded piece of DNA (15-20 pair of base). Since the DNA polymerase can't initiate the process of polymerization, we need a primer or the DNA replication will not occur. -What is the primer? It is a small stretch of RNA (small stretch of ribonucleotide) which is complimentary to the template at specific regions.

-In addition to the fact that DNA polymerase can't initiate polymerizing the new strand, it is also need (OH) at 3' end of the primer in order to synthesis the (3'- 5' phosphodiester bond) to incorporate the new deoxy nucleotides with primer. Side Note: - Usually the primer is RNA but in some cases it could be DNA or proteins.

SSB proteins: special kind of proteins found in the fork called

.tranded binding proteinsingle s What is the importance of those proteins?

to the single strand after unwinding of the 2 bindThey will -strands.

Page 5: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

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the single stand from degradation by nucleases. protectThey - er the repairing of the 2 strands aft preventThey will -

unwinding.

DNA replication fork:

Page 6: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 5

Page 7: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

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Helicase are very important to open the double stranded DNA. plays a major role in preventing the two strands from winding, it requires ATP in order to open the 2 strands for the DNA polymerase.

DNA polymerase III has the ability to add 6000 pair of base per min, if it less than that the replication will stop. And this is a strategy to make antibiotics in the prokaryotes to stop the replication and thus will kill the cell

-Topoisomerase: are enzymes that convert DNA molecules to different isomers.

topoisomers1.the super coiled form of while the unwinding of the two During DNA replication and

by helicase, the fixed end of the DNA molecule will strandsstop the movement of l condense forming “knots”, which wil

disadvantage. thus the DNA replication will stop helicase On the other hand, the condensed form of the DNA will be

easily packaged smaller than the relaxed form so it will be advantage. inside the nucleus

Page 8: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 7

This is also a place to find antibiotics to inhibit topoisomerases in prokaryotes.

topoisomers 2.the relaxed form of

The normal DNA molecule does not contain knots (no supercoils). although the condensed form is smaller in size than the relaxed form, both of them have the same number of nucleotides. *In the cell there are two enzymes that called topoisomerases (I and II) the function: converts the DNA molecule from one topoisomer to another topoisomer. The type II of topoisomerase is called gyrase. Topoisomerase I makes cut in one strand and the other one will evade and do the supercoiling. While the topoisomerase II does the cuts in the two strands of DNA and each of them relieve the supercoiling and return back to the relaxed form.

The relaxed B form of DNA, each pair it has 10.5 bp per turn. If this number has change whether it is less or more, well it is creating tension and supercoiling. So, this is a problem in DNA replication -the supercoiling and tension- and this problem solved by topoisomerase.

-What is the importance of DNA ligase? It joins the okazaki fragments by filling the gaps between them by making phosphodiester bonds.

Page 9: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

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Page 10: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

Page 9

Now we will talk about application of the DNA replication

polymerase chain reaction.

Remember when you take your DNA and extend it, it’s about 3

meters in length. So, if you are looking for a single gene in this

big molecule, you will be unable to find that gene because

there is a million. So, the scientists find a method to find those

gene, it called polymerase chain reaction. In which you could

choose any piece of DNA and amplify this piece to one billion

cuts.

To identify a genetic disease, you should characterize the

specific gene that is responsible for that genetic disease. How

to amplify these genes? By polymerase chain reaction.

Page 11: DNA replication ,repair and recombination€¦ · اهايحأ نمو DNA replication ,repair and recombination. Page 9 . Now we will talk about application of the DNA replication

DNA replication ,repair and recombination ومن أحياها

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In this reaction, first step you should denature the DNA, you

separate the two-double strand. Then, you use primer in order

to do the replication. Then add DNA polymerase to this

reaction. You will start with one molecule and now you have

two molecules.