Topic 3.4: DNA replication

3.4.1 Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of new complementary strands by DNA polymerase.

Helicase

• Unwinds the DNA and separates the two polynucleotides strands by breaking the hydrogen bonds between complementary base pairs.
• The two separated polynucleotide strands act as templates for the synthesis of new polynucleotide strands  

DNA polymerase

• Synthesis the new strands from the two parental template strands
• Free deoxynucleoside triphosphate are aligned opposite their complementary base partner and are covalently bonded together by DNA polymerase to form a complementary nucleotide chain.
• The energy for this reaction comes from the cleavage of the two extra phosphate groups 

3.4.2 Explain the significance of complementary base pairing in the conservation of the base sequences of DNA

Each of the nitrogenous bases can only pair with its complementary pair.

• The significance of the mechanism outlined above is that the DNA molecule is copied precisely from one cell generation to the next
• The new strands formed will be identical to the original strands separated from the template
• The two DNA molecule formed will be identical to the original molecule

3.4.3 State that DNA replication is semi-conservative

DNA replication is a semi-conservative process because when a new strand of DNA is formed, one strand will be from the original DNA and one strand will be newly synthesized.