DNA STRUCTURE and
REPLICATION

Pranabjyoti Das
12/8/2013

Pranabjyoti Das

1
Deoxyribose Nucleic Acid
DNA usually exists as a double-stranded
structure, with both strands coiled together
to form the ...
Nucleoside & Nucleoside
A Nucleoside is a combination of Pentose sugar &
Nitrogen Base

A Nucleotide is a combination of n...
DNA BACKBONE

12/8/2013

Pranabjyoti Das

4
Nucleotides are matched between strands
through hydrogen bonds to form base pairs.
Adenine pairs with thymine and cytosine...
DNA strands have a directionality, and the
different ends of a single strand are called
the "3' (three-prime) end" and the...
These terms refer to the
carbon atom in deoxyribose to
which the next phosphate in
the chain attaches.
Directionality has
...
The pairing of bases in DNA through
hydrogen bonding means that the
information contained within each
strand is redundant....
DNA Replication

12/8/2013

Pranabjyoti Das

9
DNA replication is a biological process that occurs
in all living organisms and copies their exact DNA.
It is the basis fo...
The first major step for the DNA Replication to
take place is the breaking of hydrogen
bonds between bases of the two anti...
Helicase is the enzyme that
splits the two strands. The
structure that is created is
known as "Replication
Fork".

12/8/20...
12/8/2013

In order for DNA replication to begin, the
double stranded DNA helix must first be
opened. The sites where this...
The replication fork is a structure that forms
within the nucleus during DNA replication. It
is created by helicases, whic...
One of the most important steps of DNA
Replication is the binding of RNA Primase in the
initiation point of the 3'-5' pare...
RNA
Primase
lays down
the RNA
primers
so that
the
Polymeras
e III can
get to
work or
can
function.
12/8/2013

Pranabjyoti ...
The elongation process is different
for the 5'-3' and 3'-5' template. a)5'-3'
Template: The 3'-5' proceeding
daughter stra...
The
leading
strand
requires fewer steps
and
therefore
is
synthesized
the
quickest. Once a RNA
primer has been laid
down by...
3'-5'Template: The 3'-5' template cannot be
"read" by DNA Polymerase III. The replication
of this template is complicated ...
12/8/2013

In the synthesis of the lagging strand, the
helix uncoiling occurs in the opposite
direction to w/c Polymerase ...
In the lagging strand the DNA Pol IExonuclease- reads the fragments and
removes the RNA Primers. The gaps
are closed with ...
Each new double helix is consisted of one old and one new
chain. This is what we call semiconservative replication.

12/8/...
12/8/2013

The last step of DNA Replication is
the Termination. This process happens when
the DNA Polymerase reaches to an...
12/8/2013

The DNA Replication is not completed before
a mechanism of repair fixes possible errors
caused
during
the
repli...
END OF
PRESENTATION

Thanks
12/8/2013

Pranabjyoti Das

25
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Structure & Replication of DNA

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Structure & Replication of DNA

  1. 1. DNA STRUCTURE and REPLICATION Pranabjyoti Das 12/8/2013 Pranabjyoti Das 1
  2. 2. Deoxyribose Nucleic Acid DNA usually exists as a double-stranded structure, with both strands coiled together to form the characteristic double-helix. Each single strand of DNA is a chain of four types of nucleotides having the bases: Adenine Cytosine Guanine Thymine 12/8/2013 Pranabjyoti Das 2
  3. 3. Nucleoside & Nucleoside A Nucleoside is a combination of Pentose sugar & Nitrogen Base A Nucleotide is a combination of nucleoside & Phosphoric Acid 12/8/2013 Pranabjyoti Das 3
  4. 4. DNA BACKBONE 12/8/2013 Pranabjyoti Das 4
  5. 5. Nucleotides are matched between strands through hydrogen bonds to form base pairs. Adenine pairs with thymine and cytosine pairs with guanine 12/8/2013 Pranabjyoti Das 5
  6. 6. DNA strands have a directionality, and the different ends of a single strand are called the "3' (three-prime) end" and the "5' (fiveprime) end" with the direction of the naming going 5 prime to the 3 prime region. The strands of the helix are anti-parallel with one being 5 prime to 3 then the opposite strand 3 prime to 5. 12/8/2013 Pranabjyoti Das 6
  7. 7. These terms refer to the carbon atom in deoxyribose to which the next phosphate in the chain attaches. Directionality has consequences in DNA synthesis, because DNA polymerase can synthesize DNA in only one direction by adding nucleotides to the 3' end of a DNA strand. 12/8/2013 Pranabjyoti Das 7
  8. 8. The pairing of bases in DNA through hydrogen bonding means that the information contained within each strand is redundant. The nucleotides on a single strand can be used to reconstruct nucleotides on a newly synthesized partner strand. 12/8/2013 Pranabjyoti Das 8
  9. 9. DNA Replication 12/8/2013 Pranabjyoti Das 9
  10. 10. DNA replication is a biological process that occurs in all living organisms and copies their exact DNA. It is the basis for biological inheritance. 12/8/2013 Pranabjyoti Das 10
  11. 11. The first major step for the DNA Replication to take place is the breaking of hydrogen bonds between bases of the two antiparallel strands. The unwounding of the two strands is the starting point. The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine. There are three hydrogen bonds between Cytosine and Guanine. 12/8/2013 Pranabjyoti Das 11
  12. 12. Helicase is the enzyme that splits the two strands. The structure that is created is known as "Replication Fork". 12/8/2013 Pranabjyoti Das 12
  13. 13. 12/8/2013 In order for DNA replication to begin, the double stranded DNA helix must first be opened. The sites where this process first occurs are called replication origins. Helicase unwinds the two single strands Pranabjyoti Das 13
  14. 14. The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA. These two strands serve as the template for the leading and lagging strands, which will be created as DNA polymerase matches complementary nucleotides to the templates; The templates may be properly referred to as the leading strand template and the lagging strand template 12/8/2013 Pranabjyoti Das 14
  15. 15. One of the most important steps of DNA Replication is the binding of RNA Primase in the initiation point of the 3'-5' parent chain. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers (starters) for the binding of DNA nucleotides. 12/8/2013 Pranabjyoti Das 15
  16. 16. RNA Primase lays down the RNA primers so that the Polymeras e III can get to work or can function. 12/8/2013 Pranabjyoti Das 16
  17. 17. The elongation process is different for the 5'-3' and 3'-5' template. a)5'-3' Template: The 3'-5' proceeding daughter strand -that uses a 5'-3' template- is called leading strand because DNA Polymerase III can "read" the template and continuously adds nucleotides (complementary to the nucleotides of the template, for example Adenine opposite to Thymine etc). 12/8/2013 Pranabjyoti Das 17
  18. 18. The leading strand requires fewer steps and therefore is synthesized the quickest. Once a RNA primer has been laid down by Primase, the DNA Polymerase III can build the second strand continuously and in the same direction that the double helix is being opened. To complete the process, DNA Polymerase I replaces the RNA Primer with DNA. 12/8/2013 Pranabjyoti Das 18
  19. 19. 3'-5'Template: The 3'-5' template cannot be "read" by DNA Polymerase III. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase III reads the template and lengthens the bursts. The gap between two RNA primers is called "Okazaki Fragments". The RNA Primers are necessary for DNA Polymerase III to bind Nucleotides to the 3' end of them. The daughter strand is elongated with the binding of more DNA nucleotides. 12/8/2013 Pranabjyoti Das 19
  20. 20. 12/8/2013 In the synthesis of the lagging strand, the helix uncoiling occurs in the opposite direction to w/c Polymerase III works. The process therefore has to be done in pieces,PranabjyotiOkazaki Fragments. called Das 20
  21. 21. In the lagging strand the DNA Pol IExonuclease- reads the fragments and removes the RNA Primers. The gaps are closed with the action of DNA Polymerase which adds complementary nucleotides to the gaps and DNA Ligase which acts as a glue to attach the phosphate to the sugar by forming phosphodiester bond. 12/8/2013 Pranabjyoti Das 21
  22. 22. Each new double helix is consisted of one old and one new chain. This is what we call semiconservative replication. 12/8/2013 The total mechanism requires a cycle of repeating steps that include: 1) Creation of RNA Primers (Primase) 2) Synthesizing a short segment of DNA between the primers (Polymerase III) 3) Replacing the RNA primer with DNA (Polymerase I) and finally 4) The binding of these piecesDas Pranabjyoti (Ligase) 22
  23. 23. 12/8/2013 The last step of DNA Replication is the Termination. This process happens when the DNA Polymerase reaches to an end of the strands. We can easily understand that in the last section of the lagging strand, when the RNA primer is removed, it is not possible for the DNA Polymerase to seal the gap (because there is no primer). So, the end of the parental strand where the last primer binds isn't replicated. These ends of linear (chromosomal) DNA consists of noncoding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of DNA Replication. Pranabjyoti Das 23
  24. 24. 12/8/2013 The DNA Replication is not completed before a mechanism of repair fixes possible errors caused during the replication. Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps. Pranabjyoti Das 24
  25. 25. END OF PRESENTATION Thanks 12/8/2013 Pranabjyoti Das 25

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