7.2 dna replication

7.2 DNA Replication

Topic 7 Nucleic Acids & Proteins

DNA Replication 7.2.1 State that DNA replication occurs in a 5’→ 3’

direction. (The 5’ end of the free DNA nucleotide is added to the 3’ end of the chain of nucleotides that is already synthesized).

DNA Replication 7.2.2 Explain the process of DNA replication in

prokaryotes, including the role of enzymes (helicase, DNA polymerase, RNA primase and DNA ligase), Okazaki fragments and deoxynucleoside triphosphates.

The explanation of Okazaki fragments in relation to the direction of DNA polymerase III action is required. DNA polymerase III adds nucleotides in the 5’ → 3’ direction. DNA polymerase I excises the RNA primers and replaces them with DNA.

7.2.3 State that DNA replication is initiated at many points in eukaryotic chromosomes.

DNA Replication When cells divide, DNA replications needs to occur to

ensure each cell has a full set of chromosomes. DNA replication occurs along each chromosome in a

5’3’ direction. DNA replication in eukaryotic chromosomes is initiated

at many points. In eukaryotes, DNA replication involves many enzymes:

Helicase DNA polymerase III RNA primase DNA polymerase I DNA Ligase

DNA Replication Since DNA replication occurs only in a 5’ 3’ direction,

a problem arise due to the fact that the two DNA strands run in opposite directions.

The two strands are referred to as the leading strand and the lagging strand.

Replication on the leading strand is straight forward, with DNA polymerase III adding nucleotides in the 5’ 3’ direction.

On the lagging strand replication also occurs in the 5’3’direction. This results in the formation of fragments, between 1000 and 2000 nucleotide long. These fragments are called Okazaki Fragments and are later joined together by DNA Ligase.

Ref: Biology for the IB Diploma, Allott

Ref: IB Biology, Oxford Study Courses

Role of the Enzymes Helicase

Unwinds the DNA at the replications fork Breaks the hydrogen bonds between the bases

DNA Polymerase III Adds deoxynucleoside triphosphates to the 3’ end

RNA Primase Adds nucleoside triphosphates on the lagging strand to for an

RNA primer DNA Polymerase I

Removes the RNA primer Replaces it using deoxynucleoside triphosphates

DNA Ligase Joins the Okazaki Fragments together.

Deoxynucleoside Triphosphates

Ref: IB Biology, Oxford Study Courses

Deoxynucleoside Triphosphates

IBO guide: 7.2.1 State that DNA replication occurs in a 5’→ 3’

direction. (The 5’ end of the free DNA nucleotide is added to the 3’ end of the chain of nucleotides that is already synthesized).

IBO guide: 7.2.2 Explain the process of DNA replication in

prokaryotes, including the role of enzymes (helicase, DNA polymerase, RNA primase and DNA ligase), Okazaki fragments and deoxynucleoside triphosphates.

The explanation of Okazaki fragments in relation to the direction of DNA polymerase III action is required. DNA polymerase III adds nucleotides in the 5’ → 3’ direction. DNA polymerase I excises the RNA primers and replaces them with DNA.

7.2.3 State that DNA replication is initiated at many points in eukaryotic chromosomes.