REPLICATION OF DNA - C-alm, A-lert, R-esilient, N-ascent

38 Pages·2012·0.92 MB·English

REPLICATION OF DNA
1
Restriction enzyme
• Endonuclease – cleave
the nt in the middle of
DNA molecule
• Exonuclease - cleave
the nt from the end of
DNA molecule
2
The flow of genetic information
• Duplication of DNA to
produce a new DNA
molecule with the same
base sequence as original
• A necessary process
whenever a cell divides to
produce daughter cells
• Flow of genetic
information
DNA –RNA-Protein
3
Replication process
• A complex process
• Ensures fidelity
• 3 important challenge
1. Separating the two strands – the double
helix must be unwound if they are to be
separated. At the same time, the unwound
portions must be protected from the action
of nucleases that prefer to attack ss DNA.
2. Synthesizing DNA from 5’ end to the 3’end.
3. Guarding against error in replication –
ensuring the correct base is added

4
Types of replication
• Conservative
The parental strands never completely separate
After on round replication, one daughter duplex contains only
parental strands and the other only daughter strands

• Semi conservative
The process of unwinding, of the double helical daughter
molecules – that is composed of a parental strand and a newly
synthesized strand formed from the complementary strand

• Theta replication – replication in a circular form -prokaryote
5
Semiconservative replication
6
Steps involved in DNA replication
a) Identification of the origins of replication
b) Unwinding (denaturation) of dsDNA to provide ssDNA
template
c) Formation of the replication fork
d) Initiation of DNA synthesis and elongation
e) Formation of replication bubbles with ligation of the
newly synthesized DNA segments
f) Proof reading process

DNA replication in Prokaryote and eukaryote generally involve
the same steps, except in eukaryote the process is more
complex due to the presence of histone complex
7
DNA REPLICATION IN E.COLI-FAMOUS
MODEL
8
a) Origin of replication
• Origin of replication (oriC )- spesific sites where
replication starts
• Sequence specific DNA binding proteins (O Protein) will
bind to ori
• Adjacent to ori is A+T region
• Binding of O protein lead to local denaturation and
unwinding of A+T region
9
b)
Unwinding of DNA to form SS DNA which act as template
• Interaction of O protein provide a short region
of ssDNA essential for initiation of replication
• This region – a template for initiation
• DNA helicases helps in unwinding of DNA
• DNA helices produces nicks in one strand of
double helix
• Single stranded binding proteins (SSB
Proteins) – bind to SS each strand and
stabilize the complex and prevents re-
annealing
10