Cell Division andDNA Replication

Ref p13 HB, Textbook p164

TASK

NOW, USE P164 OF YOUR TEXTBOOK TO ANSWER THE TOP HALF OF YOUR HANDBOOK P13.

Cell division Nuclear division – process by which the

nucleus divides by mitosis or meiosis

Cell division – follows nuclear division. Process by which the whole cell divides.

The Requirements for Semi-Conservative Replication of DNA

(p13 HB)

• The 4 types of nucleotide, containing A,C,G,T must be present.

• Both strands of the DNA molecule must act as a template for the attachment of these nucleotides.

• The enzymes DNA helicase and DNA polymerase are needed to catalyse the reaction.

• A source of chemical energy (ATP) is needed to drive the process.

DNA can self replicate

• DNA Replication takes place during interphase before cell division

• The two polynucleotide chains ‘unzip’ and free nucleotides pair up with each chain to form two new complete molecules of DNA.

• In this way, an accurate identical copy of the genetic information can go into each of the 2 daughter cells formed during cell division.

Q Why is the process of DNA Replication said to be

semi-conservative?

One of the original ‘parent’ strands from a DNA molecule, is present in each of the two new ‘daughter’ DNA molecules.

DNAReplication

A

C

G

T

T

C

A

G

Firstly, the double helix of DNA untwists (unwinds).

DNAReplication

A

C

G

T

T

C

A

G

Then an enzyme called DNA helicase starts to uncouple the two DNA polynucleotide chains by breaking the Hydrogen bonds between the complementary organic base pairs.

DNAReplication

A

C

G

T

T

C

A

G

Then an enzyme called DNA helicase starts to uncouple the two DNA polynucleotide chains by breaking the Hydrogen bonds between the complementary organic base pairs.

DNAReplication

A

C

G

T

T

C

A

G

Then an enzyme called DNA helicase starts to uncouple the two DNA polynucleotide chains by breaking the Hydrogen bonds between the complementary organic base pairs.

DNAReplication

A

C

G

T

T

C

A

G

As this is happening, two more enzymes called DNA polymerase start to move down the opened strands of DNA

DNAReplicationThe role of the DNA polymerase is to add free nucleotides from within the nucleus of the cell, to both strands of the DNA molecule - lets make the diagram smaller so we can fit everything in...

DNAReplication

As the enzymes move along each DNA strand, two new identical DNA molecules are formed. Each new DNA molecule retains half (1 strand) of the original DNA molecule. This is called semi conservative DNA replication- lets make

DNAReplicationWhen the enzymes reach the end of the DNA molecule, they are released and are free to start on another strand.

The two new double helixes of DNA are ready to take part in cell divisionlets make

Why is it called semi-conservative DNA

Replication?

One of the original parent DNA molecule strands is present in each of the two new DNA molecules

DNA Replication animation

DNA replication animation –

Windows on life

TASK: Now do the DNA Replication cut, arrange,

stick and colour sheet.