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 INTRODUCTION
Saturday, May 9, 2020

9:56 PM

• Sugar
- In DNA=

- In RNA= lack 1 atom of o at 2' position

 Nucleosides
N2 base + P + pentose sugar (ribose)
Sugar-n-glycosidic bond-base

• N base

 Nucleotides
nucleosides + P
Purine
- Adenine (6-aminopurine)

- Guanine ( 6-oxy-2-aminopurine)

Pyrimidine
- Cytosine (2-oxy-4-aminopyrimidine)

- Uracil (2,4- dioxypyrimidine)

Nucleotide structure

- Thymine (6-methyl-2,4-dioxypyrimidine)
•
-

ATP
ATP - chemical link b/w catabolism and anabolism
Energy currency
phosphodiester bond and phosphoanhydride bond ( high energy bond)

• Polynucleotides
- Polymer of nucleotides

• Chargaff's rules

- 1st= A=T , G=C
- 2nd = composition of DNA vary from 1 species to another
Hence,
A:T=1 and G:C=1
A+G=T+C
%G+C ≠ %A+T (≠ means not necessarily)

(A+G) + (T+C)= 100%

○ Modes of replication

introduction Page 1

○

○

- Semi conservative mode of replication was CORRECT
...
)
- 1958
- Model org- E
...
coli in
of 14N
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- Allow to reproduce
...

- After 1 cycles,
DNA has INTERMEDIATE density (15N-14N)

- 2 cycles,
half intermediate n half DNA of (14N-14N)
- And hence proved that semiconservative mode of
replication is correct !

introduction Page 2

 DNA POLYMERASE AND REPLICATION
Saturday, May 9, 2020

11:39 PM

•
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DNA polymerase
DNA replicating enzyme
Arthur kornberg -1955 in E
...

Got Noble prize

•




-

What he used?
4 dNTPs
E
...
)
Mg2+

DNA pol function
Catalyze formation of phosphodiester bond b/w 3' OH and 5'P grp
...

Nucleotides added rapidly= in E
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Direction of synthesis= 5' to 3'
•
1
...

3
...


 PROKARYOTES


INITIATION



- PRIMOSOME
Complex of E
...

1
...
coli replicator- Ori C- 3 copies of 13 bp
4 copies of 9 bp
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Dna A (ini
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Leading to denaturation of 13bp region
4
...

5
...
By breaking H-bond………
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Helicase recruits DNA primase forming PRIMOSOME
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Formation of primer
9
...
SSB (single strand binding )protein binds to each strand =
stabilize and prevents reforming ds DNA
...
Leading strandDNA pol III binds at site of primer…
...
Lagging strandmultiple primer here… DNA pol III add
piece of DNA=okazaki fragments
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DNA pol I replaces primer with DNA
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DNA gyrase relaxes - tension
6
...


• REPLICONS or REPLICATION UNIT
- Strech of DNA from origin of replication to 2
terminal of replication on each side of origin
...
cycle=
20 mins

3 mins

Fork movement=
22mb/hr

18kb/hr

• HOLIDAY MODEL OF RECOMBINATION

DNA Pol and replication in pro and eu_ Page 3

• HOLIDAY MODEL OF RECOMBINATION

• ROLLING CIRCLE MECHANISM OF REPLICATION

- Robert holliday
- Holliday junction is a branched nucleic acid structure
that contain ds arms which are joined together
...


-

- Helps in synthesizing plasmids,
genome of bacteriophage etc
- Topoisomerase relieves the
supercoils
...
cerevisiae- ~100bp seq= ARS (autonomously replicating sequences)
...

Orc binds to the 2 regions of replicons and recruits other replication protein
...

The cell cycle consists of four stages- G1- cell prepares for DNA replication;
S- DNA replication occur
G2- cell prepares for cell division;
M- the division of the cell by mitosis
...

The first step = replicator selection, in which ORC binds to each replicator in the stage and recruits
other proteins to form prereplicative complexes (pre -RCs)
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- Replication of nuclear DNA required 3 of these
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Pol α (primase) -initiates new strands in replication
- add 10nts of RNA
...

- Synthesize DNA on lagging strand
2
...
Pol
- Nuclease- remove these flaps
- Ligase - joined 2 okazaki fragments
...
DNA pol are involved in specific DNA repair proceess and other
replicate mitochondrial and chloroplast DNA
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- DNA gyrase - type II topoisomerase
- relieves the mechanical strain
- remove +ve supercoils
...

- Leading strand= 3'-5'
= add nts in 5'-3'
- Vice versa for lagging strand……

DNA Pol and replication in pro and eu_ Page 5



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