A DNA molecule is composed of two chains of nucleotides that wind about each other to resemble a twisted ladder. The sides of the ladder are made up of sugars and phosphates, and the rungs are formed by bonded pairs of nitrogenous bases. These bases are adenine (A), guanine (G), cytosine (C), and thymine (T).

1. TOPIC :
STRUCTURE AND
FUNCTION OF DNA
PRESENTED BY
GROUP 3
PRESENTED TO
MAM HIRA
LIAQUAT

2. • DNA is a fascinating molecule that carries
the genetic instructions for all living
organisms. It's often referred to as the
blueprint of life (because it contains the
instructions needed for an organism to
grow, develop, survive and reproduce).
• In this presentation, we'll explore the
structure and function of DNA and how it's
responsible for the diversity of
life on our planet.
Introduction to DNA

3. History of DNA
• It all began in the mid-1800s when
scientists first began to study the nucleus of
cells.
• Over time, researchers discovered that the
nucleus contained a substance called
chromatin, which was later found to be
composed of DNA and proteins.
• In the early 1900s, scientists began to
unravel the structure of DNA, our
understanding of DNA has continued to
grow, leading to a wide range of
applications in fields such as medicine,
agriculture, and forensics.

4. Discovery of DNA
• The discovery in 1953 of the
double helix, the twisted-ladder
structure of deoxyribonucleic
acid (DNA), by James Watson
and Francis Crick marked a
milestone in the history of
science and gave rise to modern
molecular biology, which is
largely concerned with
understanding how genes
control the chemical
processes within .

5. Location of DNA
 Within a cell, DNA is organized into
dense protein-DNA complexes called
chromosomes. DNA is found in
almost every cell in the human body.
 It is located in the nucleus of the
cell, which acts as the control center
for the cell.
 In addition to the nucleus, small
amounts of DNA can also be found
in the mitochondria, which are the
energy-producing
organelles within cells.

7. Location
• In eukaryotes, the
chromosomes are located in
the nucleus, although DNA
also is found in mitochondria
and chloroplasts. In
prokaryotes, which do not
have a membrane-bound
nucleus, the DNA is found as
a single circular chromosome
in the cytoplasm.

8. • DNA is made of two linked
strands that wind around
each other to resemble a
twisted ladder — a shape
known as a double helix.
Each strand has a backbone
made of alternating sugar
(deoxyribose) and phosphate
groups.
STRUCTURE OF
DNA

9. COMPONENTS OF DNA
STRUCTURE
DEOXYRIBOSE
(PENTOSE)
NITROGENOUS
BASE
PHOSPHATE
GROUP

10. PYRIMIDINES
• Thymine
• Cytosine
PURINES
• Adenine
• Guanine
NITROGENEOUS BASES
These are divided into two groups

12. • A nucleotide is the basic building block of nucleic acids
(RNA and DNA). A nucleotide consists of a sugar molecule
(either ribose in RNA or deoxyribose in DNA) attached to a
phosphate group and a nitrogen-containing base.
NUCLEOTIDE STRUCTURE

13. PHOSPHODIESTER BOND
A phosphodiester bond is a
chemical bond that forms when
exactly two hydroxyl groups in
phosphoric acid react with a
hydroxyl group on other
molecules forming ester bonds.
It is found in the DNA and RNA
backbone.

14. DNA DOUBLE HELIX

15. WATSON – CRICK MODEL OF DNA
• Deoxyribonucleic Acid (DNA) is a double-stranded, helical
molecule. It consists of two sugar-phosphate backbones on the
outside, held together by hydrogen bonds between pairs
of nitrogenous bases on the inside.
• The bases are of four types (A, C, G, & T): pairing always occurs
between A & T, and C & G.
• Watson and Crick shared the noble prize in 1962 for their discovery,
along with Maurice Wilkins (1916 - 2004), who had continued
research to provide a large body of crystallographic data supporting
the model

17. STRUCTURAL TYPES OF DNA
• A-Type DNA
• B-Type DNA
• C-Type DNA
• D-Type DNA
• E-Type DNA
• Z-Type DNA

18. A-TYPE DNA
A right handed, double helix with more compressed and wider form
than B-DNA.
Base pairs are tilted with respect to helix axis
Major groove is narrow and deep
Minor groove is wide and shallow
Dehydrated DNA takes an A-type during extreme situations such as
dessication
It has 11 base pairs,2.5nm
Less common type of DNA

19. B–TYPE DNA
• Right handed,helical structure with uniform diameter
• Base pairs are nearly perpendicular to the helix
• Major groove is wide and deep
• Minor groove is narrow and deep
• Most common form of DNA
• This is used for genetic information
• It has 10.5 base pairs and 20 angstrom in diameter

20. Z-TYPE DNA
 It is a left handed helical form of DNA
It is present in zigzag pattern
It is form in alternating purine-pyrimidine dinucleotide
repeat sequence
The deoxyribose-phosphate back bone follows zigzag
course
Major groove is narrow and deep
Minor groove is wide and shallow
Has 12 nucleotide base pairs
Thought to play role in gene expression

21. DNA REPLICATION
PROCESS
The process by which DNA forms the copy of itself is called DNA
replication process.
1.Replicating origin:
The DNA replication begins at one or more sites on DNA molecule,
where there is a specific sequence of nucleotides. These sites are called
replicating origin or replicating eye.
2.DNA Helicase:
This enzyme break the hydrogen bonds between two strands of DNA.

23. 3.DNA Polymerase:
There are three forms of DNA Polymerase,
 DNA Polymerase 1
 DNA Polymerase 2
DNA Polymerase 3
 It can add nucleotide that is already paired with the parent strands.
Hence DNA polymerase cannot initiate synthesis on its own.
It can add nucleotides only to the 3”end of a DNA strand. It means
that replication always 5-3 direction, on a growing DNA strand.

24. 4. RNA Primase:
• An enzyme, PRIMASE, constructs an RNA primer, a sequence
of about 10 RNA nucleotide, complementary to the parent
DNA template. DNA polymerase 3 recognizes the primer and
adds DNA nucleotides to it to construct the DNA strands. The
RNA nucleotides in the primers are the replaced by DNA
nucleotides.

25. .
5.Leading strand
• The strand which is build
continuously is called
leading strand.
• It grows towards
replicating fork.
6.Lagging strand
• The strand which is build
discontinuously is called
lagging strand.
• It grows away from
replicating fork.

26. 6.Okazaki fragments:
Lagging strand is synthesized discontinuously as a series of short
segments that are later connected. These are called okazaki
fragments.
7. DNA Ligase:
DNA ligase, attaches the okazaki fragments to the lagging strand.
8.DNA Polymerase 1:
DNA polymerase 1 functions to fill DNA gaps that arise during
DNA replication, repair and recombination.

27. MUTATIONS
• A mutation is a change in the DNA sequence of an organism.
Mutations can result from errors in DNA replication during cell
division, exposure to mutagens or a viral infection.
TYPES OF MUTATION
substitution
deletion
insertion
translocation

28. SICKLE CELLANEMIA
Sickle cell disease is a genetic disorder caused by mutation in the beta
globin gene that leads to faulty hemoglobin protein, called hemoglobin
S.
These sickle cells can block blood flow, and result in pain and organ
damage.