Dna.model.vanleer

DNA REPLICATION

(OCCURS IN THE NUCLEUS)

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’ 5’

Hydrogen bonds

Hydrogen bonds are used to hold together the bases.

• In DNA, adenine (A) goes with thymine (T) and guanine (G) goes with cytosine (C). A, T, C, and G are all nitrogen bases. If A and T or C and G are not paired up together it will create a mutation and the DNA will not replicate.

• Purines- Adenine, Guanine• Pyrimidines- Cytosine, Thymine

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’ 5’

DNA helicase

When the strand is 5’ to 3’ it splits from the bottom up.

Stra

nd o

ne

Strand two

• DNA is split by DNA helicase. As DNA splits, free nucleotides bind to the exposed bases of the non-coding strand. This process is helped by RNA polymerase.

• Strand one is the leading strand and strand two is the lagging strand.

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

RNA polymerase helps the direction of synthesis.

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’ 5’

DNA helicase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

DNA polymerase is the enzyme that rebuilds the two separated strands of DNA.

• The primary role of DNA polymerase is to accurately and efficiently replicate the genome in order to maintain the genetic information.

• DNA polymerase adds nucleotides continuously on Strand one.

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’

5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’5’

DNA helicase

DNA polymerase

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’5’

DNA helicase

DNA polymerase

When DNA polymerase is done, it replicates the one strand of DNA into two.

phosphate

Sugar

Thymine

Adenine

Guanine

Cytosine

5’ 3’

3’ 5’

DNA helicase

DNA polymerase

Oka

zaki

Fr

agm

ents

Oka

zaki

Fr

agm

ents

DNA ligase stitches together the Okazaki fragments together.

Telomerase is an enzyme that adds telomerase repeat sequences to the 3’ end of DNA strands.

• Okazaki fragments are formed because DNA polymerase which acts as the synthesizer of DNA can only work at one strand at a time. The fragments are short, newly synthesized DNA fragments that are formed by lagging template strand during DNA replication.

• The fragments are “stitched together by the enzyme ligase.

• DNA needs to replicate. When cells divide, the new cells produced must have a full set of genes in order to function correctly. Genes are made of DNA so it is necessary to replicate the DNA before the cells divide. Cells divide for reproduction, growth and repair. DNA needs a complete set of genes for it to function properly.