DNA Replication: A Process of Creating Identical Genetic Material for Cell Division, Lecture notes of Genetics

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DNA

Replication

Copy me! Copy me!

What is DNA REPLICATION?

-^ DNA Replication

:

process of copyingand synthesizing newDNA. • Occurs in

nucleus

before a cell divides

so that each new cell producedhas a complete setof chromosomes.

Mitosis -prophase -metaphase -anaphase -telophase G^1

G^2 S phase Interphase DNA replication takes place in the S phase.

Enzymes in DNA replication

HELICASE

unwinds

parental doublehelix

DNA POLYMERASE binds nucleotides to form new strands

LIGASE

joins Okazaki fragments

and seals other breaks in sugar-phosphate backbone

Replication Step 1: HELICASE

unzips DNA

down

the middle by breakingHydrogen bonds. 5’ 3’

Step 2:

DNA POLYMERASE

moves along

the 2 strands and base pairsnucleotides to each original parentstrand.

Overall direction^ of replication

3’^ 5’

5’^ 3’

7

Step 3:

Replication moves in only ONEdirection. So, small DNA segmentscalled OKAZAKI FRAGMENTS

are

made on the other strand.

5’^

5’^ 3’

Overall direction^ of replication

Okazaki fragment^ 3’

2 identical DNA molecules are

formed from the original.

Semi-conservative Model •^ Idea presented by Watson & Crick •^ The two strands of the parentalmolecule separate, and each acts as atemplate for a new complementarystrand •^ New DNA consists of 1 PARENTAL(original) and 1 NEW strand of DNA

Parental DNA

DNA Template New DNA

Any Questions?

-^ Finish your CornellNotes…