G BHAGYARAJ ANCHAL Zoology Tutor 8281093200,8281094200

2. WELCOME

3. SUBMITTED BY,
G.BHAGYARAJ
65018140004
1st MSC ZOOLOGY
ST:STEPHEN’S COLLEGE PATHANAPURAM

4. MOLECULAR BIOLOGY ?
❖ The branch of biology that deals with the
structure and function of the macromolecules
essential to life is called molecular biology.

6. NUCLEIC ACIDS
 Nucleic acids are the macromolecules, essential
to all known forms of life. The term nucleic
acid is the overall name for DNA and RNA. They
are composed of nucleotides, which are
the monomers made of three components: pentose
sugar, phosphate group and nitrogenous base. If
the sugar is a compound ribose,
the polymer is RNA (ribonucleic acid); if the
sugar is derived from ribose as deoxyribose, the
polymer is DNA(deoxyribonucleic acid).

7. WHAT IS DNA ?

9. IMPORTANCE OF DNA
 DNA is vital for all living beings – even plants. It
is important for inheritance, coding for proteins
and the genetic instruction guide for life and its
processes. Chromosomes in the nucleus of a cell,
contain information for inheritance of features
from parents to next generation in the form of
DNA during reproduction

10. FACTS ABOUT DNA

12. CENTRAL DOGMA OF MOLECULAR
BIOLOGY

15. REPLICATION OF DNA
(INTRODUCTION)
 The word ‘REPLICA’ means the exact copy of something.
 Replication of DNA is the process in which DNA makes exact
copies of itself.
 Replication is the basis for inheritance.
 Fundamental process occurring in all cells for transfer of genetic
information to daughter cells
 Each cell must replicate its DNA before division.
 DNA is copied during the S or synthesis phase of interphase.
 New cells will need identical DNA strands.
 Approximately 20 or more enzymes and proteins are needed
during replication process.

17. In the late 1950s, three different
mechanisms were proposed for
the replication of DNA
– Conservative model
• Both parental strands stay
together after DNA replication
– Semi-conservative model
• The double-stranded DNA
contains one parental and one
daughter strand following
replication
– Dispersive model
• Parental and daughter DNA
are interspersed in both
strands following replication
POSSIBLE MODELS OF
DNA REPLICATION

18. REPLICATION OF DNA IS
SEMICONSERVATIVE

19. DIRECTIONALITY OF DNA
 Nucleotides in DNA backbone
are bonded together with
phosphodiester linkage
between 3’ & 5’ carbons.
 DNA molecule has direction.
 Complimentary strands run in
opposite direction.

20. BASIC RULES FOR DNA
REPLICATION
 The replication occurs in semi-conservative manner.
 Replication of DNA involves polymerisation of nucleotides
by enzyme DNA polymerase.
 DNA polymerisation always proceeds in 5’– 3’ direction.
 The nucleotide sequence that is formed in the daughter
DNA is complimentary to the to the base sequence in the
template strand.
 The new two strands of the parental DNA duplex are anti-
parallel to each other.

21. COMPONENTS INVOLVED IN
DNA REPLICATION
 DNA polymerases- Deoxynucleotide polymerization
 Helicase -Processive unwinding of DNA
 RNA primase- Initiates synthesis of RNA primers
 Single-strand binding proteins-Prevent premature
reannealing of dsDNA
 DNA ligase-Seals the single strand nick between the nascent
chain and Okazaki fragments on lagging strand

24. MECHANISM IN DNA
REPLICATION
DNA must always be protected inside
the nucleus except during cell division
(mitosis); it will get destroyed by
enzymes in the cytoplasm.
enzymes and free-nucleotides are
available for replication in the nucleus.

25. 1.INITIATION
An enzyme called helicase attaches to DNA and
breaks the Hydrogen bonds to unwind and
separate the complementary strands.
This creates a replication fork.

26. 2.ELONGATION
Another enzyme called DNA polymerase attaches to one
strand.
It reads the DNA code, and attaches complementary
nucleotides to the original exposed strand.
After it attaches each complementary nucleotide, it
proofreads for mistakes
Replication is Quick:
More Helicase and DNA Polymerase enzymes can attach at other
sites on the strands to speed up the process.
This creates the appearance of bubbles along the strand called
replication bubbles.

28. 3.TERMINATION
When complete, the result should be two perfect copies of the
original.
Though 3.3 billion base pairs of the human genome can be
copied in a matter of hours, few mistakes (mutations) occur.
This process is semi-conservative:
Each new molecule has one original strand and one new strand.

29. Prokaryotic DNA Replication Eukaryotic DNA Replication
Origin
Prokaryotic DNA replication has a
single origin.
Eukaryotic DNA replication has
multiple origins.
Time
Taken
Prokaryotic DNA replication takes
40 minutes.
Eukaryotic DNA replication may take
up to 400 hours or more.
Takes
Place At
Prokaryotic DNA replication occurs
in the cytoplasm.
Eukaryotic DNA replication occurs in
the nucleus.
Rate of
Base Pairs
Prokaryotic DNA replication has a
rate of 2000 base pairs per second
addition.
Eukaryotic DNA replication has a rate
of 100 base pairs per second.
Nucleotide
Prokaryotic DNA replication has
1000-2000 nucleotides long
Okazaki fragments.
Eukaryotic DNA replication has 100-
200 nucleotides long Okazaki
fragments.