NAME:-MUSKAN SAIF SHAIKHCLASS:-SYBSC

ROLL NUMBER:-63TEACHER:-MADHURIMA MAM

MICROBIOLOGY

ROLLING CIRCLE MODEL OF DNA REPLICATION

INTRODUCTION :-

• Rolling circle replication produces multiple copies of a single circular template using To Plasmid.

• Rolling circle replication describes a process of unidirectional nucleic acid replication that can rapidly synthesize

multiple copies of circular molecules of DNA or RNA, such as plasmids, the genomes of bacteriophages, and

the circular RNA genome of viroids. Some eukaryotic viruses also replicate their DNA or RNA via the rolling circle

mechanism.

• The RCA mechanism is widely used in molecular biology & biomedical nanotechnology, especially in the field

of biosensing

• The derivative from of rolling circle replication has been successfully used for amplification of DNA from very small

amounts of starting material.[1] This amplification technique is named as Rolling circle amplification (RCA)

ROLLING CIRCLE MODEL OF DNA REPLICATION

STEPS INVOLVED IN ROLLING CIRCLE DNA

REPLICATION :-

• Circular dsDNA will be nicked

• The 3’ end is elongated: leading strand

• The 5’ end is displaced: lagging strand,made up of Okazaki fragments.

• Replication of both unnicked and displaced ssDNA.

• Displaced DNA circulates and synthesize it’s own complimentary strand.

NICK-INITIATION-ELONGATION-TERMINATION:FORMATION OF DNA STRAND

FOR THE PROCESS OF PRODUCING TWO IDENTICAL COPIES FROM ONE

ORIGINAL DNA MOLECULE

THREE BASIC STEPS ARE INVOLVED:-

1} INITIATION:-

• During initiation some enzymes like Helicase cut the hydrogen bond and produce the nick in the strand of DNA to make it available for the enzymes to carry out further process of replication.

• Single strand binding protein restrict the rebinding of hydrogen bonds.

• Enzymes and proteins reach to the nick, make the complex and replication starts.

2} ELONGATION :-

• Now the OH group of broken strand will use the unbroken strand as template.

• The polymeras will start to move in a circle for elongation,due to which it is named as Rolling circle model.

• End will be displaced and grow out like a waving thread.

3} TERMINATION:-

• At the point of termination the DNA is cleaved from the circle resulting ina double stranded circular DNA molecule and a single strand circular DNA molecule.

• The linear single stranded DNA molecule is circularizes by the action of ligase and hence forms a coil again.

*EXAMPLE:-

CONGUATION OF F+ AND F- BACTERIA USING

ROLLING CIRCLE MECHANISM

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