DNA Replication Part 1 PDF

30/09/23 DNA: Learning objectives: de ne the chemical structure of DNA and it’s organisation into chromosomes. Learning objectives: describe how DNA replication occurs- what is meant by high delity copy and how DNA is divided bet ween daughter cells. DNA as the genetic material: Double stranded DNA...

30/09/23 DNA: Learning objectives: de ne the chemical structure of DNA and it’s organisation into chromosomes. Learning objectives: describe how DNA replication occurs- what is meant by high delity copy and how DNA is divided bet ween daughter cells. DNA as the genetic material: Double stranded DNA is less vulnerable to chemical damage. Helix enables translesion synthesis and proofreading during replication. The nitrogen’s in bold are where hydrogen bonding occurs. The purines are adenine and guanine and the pyrimidines are thymine and cytosine. DNA Replication: On the lagging strand DNA is replicated in chunks; the 3’ end is not yet available and DNA Polymerase is only complementary to the 3’ end. s 3 original d The other side of the template is unwound and becomes available An RNA primer is synthesised by DNA Polymerase alpha which initiates normal replication by DNA Polymerase. Series of new DNA fragments and gaps. These are called Okazaki fragments. Once the RNA primer has been removed there is a gap so the adjacent Okazaki fragment is extended down. These are joined by DNA Ligase. This continues up the strand. DNA Double Helix: A-DNA: occurs when DNA is bound to protein. It is right handed and there are 11 per turn. They aren’t stacked neatly and helix is more distorted which makes it more Protected from radicals for example. B-DNA: typical structure. Right handed. Bases stack and 10.5 bases per turn. Z-DNA: the helix is left handed. Found in gene regulation. Alternating purine and A B Z Pyrimidine. 12 bases per turn. Also nd H-DNA ( triplex DNA ) involved in gene regulation. Organising DNA into chromosomes: A telomere is a region of repetitive nucleotide sequence at the end of each chromosome. Each time the DNA is replicated, the telomere regions gets shorter. This leads to a theoretical limit to the amount of times a cell can divide until the telomere is so short that it inhibits division. This limit is known as the hay ick limit. Once the limit is reached it stops dividing.