Year 12 Biology Macromolecules Unit Chapter 2: M7

M7: Specific Base-Pairing is the mechanism of DNA Replication Learnt so far: DNA is a double helix. Complimentary base pairs A-T & G-C. The bases are joined by weak hydrogen bonds. Each strand of a DNA molecule contains/stores the information necessary to reconstruct the other. It’s a copying mechanism.

Replication This copying (replicating) occurs just prior to cell division. DNA needs to be copied because, as you would remember, each cell must have the same information as its parent cell. Normally Chromosomes are single stranded –replication doubles the DNA. This produces 2 chromatids joined by a centromere.

DNA Replication Summary Possible because of the complimentary base pairing system. These complimentary strands separate as a result of a protein enzyme called Helicase which splits the double helix. Each strand is now a template to be copied in order to double the amount of DNA. These exposed strands or templates are in the nucleus. They’re exposed because the weak hydrogen bonds that join the bases have been broken.

Process Free Nucleotides in the nucleus are directed by enzymes to bond with their complimentary base and the two templates become two new strands of DNA, exact copies of one another. The process is semi conservative, because an original strand forms one side of each new strand. This “semi-conservative” nature has been verified with radioactive tracers. Nucleotides are added at a very fast rate: 50 per second in mammals.

Relevant Enzymes The process of replication occurs under the influence of more than a dozen enzymes including: DNA polymerase: This joins the free nucleotides to make the new strand. Ligase: This joins the strands back together fully ensuring the sugar phosphate backbone is sealed for the two new double helices of DNA.

M12: DNA allows genetic information to be inherited. Specific base pairing: A-T, C-G, allows DNA to make an exact copy of its self (replication). This is an essential part of reproduction and inheritance. As it allows an exact replica of the information or genetic instructions to be passed onto the next generation. And of course from that generation to the next…..