DNA Replication

[Pages:14]DNA Replication

Copy me! Copy me!

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What is DNA REPLICATION?

? DNA Replication: process of copying

DNA replication takes place in the S phase.

and synthesizing new

S

DNA.

phase

? Occurs in nucleus before a cell divides so that each new cell produced has a complete set

G1 Interphase G2

Mitosis

-prophase -metaphase -anaphase -telophase

of chromosomes.

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How does DNA Replication begin?

? Begins at Origins of Replication ? Two strands open forming Replication

Forks (Y-shaped region) ? New strands grow at the forks

Parental DNA Molecule

5' 3'

3'

Replication Fork

5'

3

Enzymes in DNA replication

HELICASE unwinds DNA POLYMERASE

parental double binds nucleotides

helix

to form new strands

LIGASE joins Okazaki fragments and seals other breaks in sugarphosphate backbone

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Replication Step 1:

HELICASE unzips DNA down the middle by breaking Hydrogen bonds.

3' 3' 5' 5' 3'

5' 3' 5'

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Replication Step 2:

Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides

5'

Nucleotide

3'

RNA 5'

Primer

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Step 2:

DNA POLYMERASE moves along

the 2 strands and base pairs

nucleotides to each original parent

strand.

Overall direction

of replication

3'

3' 5'

5' 3'

5'

3'

57 '

Step 3:

Replication moves in only ONE direction. So, small DNA segments called OKAZAKI FRAGMENTS are made on the other strand.

Overall direction

of replication

3'

3' 5'

5' 3'

Okazaki fragment

5'

3'5'

3'

5'

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