DNA REPLICATIONDNA REPLICATION

Overview Information

Chromosome Structure

DNA Replication

The Beautiful ExperimentA. Two Theories

1. Conservative replicationa. one molecule made of “parent” DNA and the duplicate was all new DNA

2. Semi-conservative replication

a. each new strand made of parent and new DNA or old and new hybrid

B. Meselson and Stahl 1957

1. Determined that DNA replicated by means of semi-conservative mode

DNA Replication

The Beautiful ExperimentB. Meselson and Stahl 1957

1. Determined that DNA replicated by means of semi-conservative mode

2. Experimental design

DNA Replication

The Beautiful ExperimentB. Meselson and Stahl 1957

DNA REPLICATIONDNA REPLICATION

Overview Information• Each strand of the DNA double helix

has all the information needed to reconstruct the other half by the mechanism of base pairing.

• In most prokaryotes, DNA replication begins at a single point and continues in two directions.

Overview Information

DNA REPLICATIONDNA REPLICATION

• In eucaryotes chromosomes, DNA replication occurs at hundreds of places . Replication proceeds in both directions until each chromosome is completely copied.

• The sites where separation and replication occur are called the replication fork

• During DNA replication, the DNA molecule separates into two strands then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template for the new strand.

Overview Information

DNA REPLICATIONDNA REPLICATION

DNA REPLICATIONDNA REPLICATION

DNA REPLICATION DNA REPLICATION BLANKSHEETBLANKSHEET

A

A

C

T

C

G

A

G

G

T

T

T

G

A

G

C

T

C

C

A

STARTING DNA STRAND

TC

AA T

TG

A

G

C

T

G

C

A

C

G

A

G

G

T

DNA Helicase breaks hydrogen bonds

A

A

C

T

C

G

A

G

G

T

T

T

G

A

G

C

T

C

C

A

DNA LADDER OPEN

A

A

C

T

C

G

A

G

G

T

T

GT

G

A

T

T

T

G

A

G

C

T

C

C

AT

G

G

A

DNA Polymerase builds new strand a. Leading strand: built in continuous

5’– 3’ direction

b. Lagging Strand: built with Okazaki fragments in discontinuous 5’-3’ direction

A

A

C

T

C

G

A

G

G

T

T

T

G

A

G

C

T

C

C

A

A

A

C

T

C

G

A

G

G

T

T

T

G

A

G

C

T

C

C

A

Semi-conservative replication complete resulting in identical DNA copies consisting of old and new DNA

DNA REPLICATIONDNA REPLICATION

• Replication EnzymesReplication Enzymes

2. DNA polymerase: helps bonding of 2. DNA polymerase: helps bonding of new nucleotides to template strandnew nucleotides to template strand

1. DNA Helicase: unwinds helix at 1. DNA Helicase: unwinds helix at replication forkreplication fork

3. DNA Ligase: bonds Okazaki 3. DNA Ligase: bonds Okazaki fragments togetherfragments together