DNA is the molecule that stores genetic information. It is composed of nucleotides containing nitrogenous bases, sugars, and phosphates. The four bases in DNA are adenine, guanine, cytosine, and thymine. DNA exists as two strands coiled around each other in the shape of a double helix. Each strand acts as a template for the other. DNA is replicated through a semi-conservative process where each original strand acts as a template for a new partner strand. This ensures each new cell contains an exact copy of the original DNA.

1. DNA STRUCTURE

2. DNA STRUCTURE
In 1962, scientists Francis Crick and James Watson were awarded the
Nobel prize for their roles in discovering the structure of DNA, which is
an acronym for deoxyribonucleic acid Anything that is alive, from
bacteria to elephants, has DNA. DNA stores genetic material and
passes it on to the next generation. A copy of a living entity's DNA is
passed to developing offspring. Once the DNA is passed to the
developing offspring, it is used to make that offspring's body parts.

3. DNA STRUCTURE
DNA is a huge molecule called a
macromolecule. However, DNA fits into small cells
because it is packed in a process called
supercoiling, in which DNA is wrapped around
proteins called nucleosomes. Proteins called histones
hold the coils together.
Strands of DNA are divided into chromosomes, a
full set of which is stored in the nucleus of each
cell. These chromosomes, which basically instruct
how the entire body is built, are called genes. A
gene determines how a specific trait will be
expressed.

4. Parts of a Chromosome
A chromatid is one of the two
identical copies of DNA making up a
duplicated chromosome, which are
joined at their centromere, for the
process of cell division (mitosis or
meiosis). They are called sister
chromatids so long as they are
joined by the centromeres. When
they separate (during anaphase of
mitosis and anaphase 2 of
meiosis), the strands are called
daughter chromosomes.
In other words, a chromatid is "one-
half of a replicated chromosome". It
should not be confused with the
ploidy of an organism, which is the
number of homologous versions of
a chromosome.

5. Parts of a Chromosome
The centromere is the part of
a chromosome that links sister
chromatids
A telomere is a region of
repetitive nucleotide
sequences at the end of a
chromosome, which protects
the end of the chromosome
from deterioration or from
fusion with neighboring
chromosomes. Its name is
derived from the Greek
nouns telos 'end' and merοs
'part.' Telomere regions
deter the degradation of
genes near the ends of
chromosomes by allowing
chromosome ends to
shorten, which necessarily
occurs during chromosome
replication.

6. DNA STRUCTURE
Chemically, DNA is made of three
components: nitrogen-rich bases, deoxyribose
sugars, and phosphates. When combined, these
components form a nucleotide. Nucleotides come
together in pairs to form a single molecule of DNA.

7. DNA STRUCTURE
There are four nitrogen-rich bases. These are
adenine, guanine, thymine, and cytosine. Adenine and
guanine have purine bases, which means they are a
compound of two rings. Thymine and cytosine have
pyrimidine bases, which means they have a single six-
sided ring structure. These rings stack up in DNA to
make the molecule compact and strong.
In order to make a complete nucleotide, the bases are
attached to deoxyribose and a phosphate
molecule. Nucleotides are the building blocks of
DNA. To make a complete DNA molecule, these
nucleotides join together to make matched pairs and
form long double strands called double helixes.

8. Nitrogenous bases are typically classified
as the derivatives of two parent
compounds, pyrimidine and purine. They
are non-polar and due to their
aromaticity, planar. Both pyrimidines and
purines resemble pyridine and are thus
weak bases and relatively unreactive
towards electrophilic aromatic
substitution. Their flat shape is particularly
important when considering their roles in
nucleic acids as nucleobases (building
blocks of DNA and RNA):
adenine, guanine, thymine, cytosine, and
uracil. These nitrogenous bases hydrogen
bond between opposing DNA strands to
form the rungs of the "twisted ladder" or
double helix of DNA or a biological catalyst
that is found in the nucleotides. Adenine is
always paired with thymine, and guanine is
always paired with cytosine. Uracil is only
present in RNA: replacing thymine and
pairing with adenine.

9. A nitrogen-containing ring
structure called a base. The
base is attached to the 1'
carbon atom of the pentose.
In DNA, four different bases
are found:
two purines, called adenine
(A) and guanine (G)
two pyrimidines, called
thymine (T) and cytosine (C)
*A always pairs with T
*C always pairs with G

10. DNA STRUCTURE
A deoxyribonucleotide is the monomer, or single unit, of
DNA, or deoxyribonucleic acid. Each deoxyribonucleotide
comprises three parts: a nitrogenous base, a deoxyribose
sugar, and one phosphate group. The nitrogenous base is
always bonded to the 1' carbon of the deoxyribose, which
is distinguished from ribose by the presence of a proton
on the 2' carbon rather than an -OH group. The
phosphate groups bind to the 5' carbon of the sugar.
When deoxyribonucleotides polymerize to form DNA, the
phosphate group from one nucleotide will bond to the 3'
carbon on another nucleotide, forming a phosphodiester
bond via dehydration synthesis. New nucleotides are
always added to the 3' carbon of the last nucleotide, so
synthesis always proceeds from 5' to 3'.

11. DNA
replication

12. DNA replication is a biological
process that occurs in all living
organisms and copies their DNA; it is
the basis for biological inheritance.
The process starts when one double-
stranded DNA molecule produces
two identical copies of the molecule.

13. Each strand of the original double-stranded
DNA molecule serves as template for the
production of the complementary strand, a
process referred to as semiconservative
replication.
Cellularproofreading and error toe-checking
mechanisms ensure near perfect fidelity for
DNA replication.
DNA replication can also be performed in
vitro (artificially, outside a cell).

14. DNA polymerases, isolated from
cells, and artificial DNA primers are used
to initiate DNA synthesis at known
sequences in a template molecule.
Thepolymerase chain reaction (PCR), a
common laboratory technique, employs
such artificial synthesis in a cyclic
manner to amplify a specific target DNA
fragment from a pool of DNA.

15. Different Proteins
Needed in DNA Replication

16. Legend:
The major types of
proteins, which must work
together during the replication of
DNA, are illustrated,
showing their positions.

17. When DNA replicates, many different
proteins work together to accomplish the
following steps:
1. The two parent strands are unwound with
the help of DNA helicases.
2. Single stranded DNA binding
proteins attach to the unwound
strands, preventing them from winding back
together.

18. 3. The strands are held in position, binding
easily to DNA polymerase, which catalyzes the
elongation of the leading and lagging strands.
(DNA polymerase also checks the accuracy of
its own work!).

19. 4. While the DNA polymerase on the
leading strand can operate in a
continuous fashion, RNA primer is
needed repeatedly on the lagging strand
to facilitate synthesis of Okazaki
fragments.DNA primase, which is one of
several polypeptides bound together in a
group called primosomes, helps to build
the primer.

20. 5. Finally, each new Okazaki
fragment is attached to the
completed portion of the lagging
strand in a reaction catalyzed
by DNA ligase.

21. Amplification of DNA by
fragment PCR
• Introduction
• The polymerase chain reaction (PCR) is a
relatively simple technique that amplifies a
DNA template to produce specific DNA
fragments in vitro. Traditional methods of
cloning a DNA sequence into a vector and
replicating it in a living cell often require days
or weeks of work, but amplification of DNA
sequences by PCR requires only hours.

22. • While most biochemical analyses, including
nucleic acid detection with
radioisotopes, require the input of significant
amounts of biological material, the PCR
process requires very little. Thus, PCR can
achieve more sensitive detection and higher
levels of amplification of specific sequences in
less time than previously used methods.

23. Basic PCR
• The PCR process was originally developed to
amplify short segments of a longer DNA
molecule (Saiki et al. 1985). A typical
amplification reaction includes target DNA, a
thermostable DNA polymerase, two
oligonucleotide primers, deoxynucleotide
triphosphates (dNTPs), reaction buffer and
magnesium.

24. • Once assembled, the reaction is placed in a
thermal cycler, an instrument that subjects
the reaction to a series of different
temperatures for set amounts of time.
• This series of temperature and time
adjustments is referred to as one cycle of
amplification. Each PCR cycle theoretically
doubles the amount of targeted sequence
(amplicon) in the reaction. Ten cycles
theoretically multiply the amplicon by a factor
of about one thousand; 20 cycles, by a factor
of more than a million in a matter of hours.

25. • Each cycle of PCR includes steps for template
denaturation, primer annealing and primer
extension. The initial step denatures the
target DNA by heating it to 94°C or higher for
15 seconds to 2 minutes. In the denaturation
process, the two intertwined strands of DNA
separate from one another, producing the
necessary single-stranded DNA template for
replication by the thermostable DNA
polymerase. In the next step of a cycle, the
temperature is reduced to approximately 40–
60°C.

26. • At this temperature, the oligonucleotide primers
can form stable associations (anneal) with the
denatured target DNA and serve as primers for
the DNA polymerase. This step lasts
approximately 15–60 seconds. Finally, the
synthesis of new DNA begins as the reaction
temperature is raised to the optimum for the
DNA polymerase. For most thermostable DNA
polymerases, this temperature is in the range of
70–74°C. The extension step lasts approximately
1–2 minutes. The next cycle begins with a return
to 94°C for denaturation.

27. • Each step of the cycle should be optimized for
each template and primer pair combination. If
the temperature during the annealing and
extension steps are similar, these two steps
can be combined into a single step in which
both primer annealing and extension take
place. After 20–40 cycles, the amplified
product may be analyzed for
size, quantity, sequence, etc., or used in
further experimental procedures.

29. Marri Untivero
PRESENTED BY: Astrid Dominguez