DNA replication modelling

DNA Replication

DNA Replication

Hayoon Cheong

DNA Polymerase

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DNA polymerase I, II and III

DNA Polymerase I

DNA Polymerase II

DNA Polymerase III

DNA polymerase II assists the repair work that couldn't handle efficiently. It gives support of fixing error that might have been missed during the initial replication process. Also, it helps to deal with exposure of harmful substances. (No exonuclease action)

DNA polymerase I edits or repairs mistakes or damaged parts in DNA sequence by removing the damaged part and replacing it with correct sequnce. After the replication process in mostly done, it comes to tide up by removing RNA primers and replace with the correct DNA sequence. (Exonuclease action)

DNA polymerase III reads the existing DNA and creates new DNA nucleotides by adding the correct base opposite to the existing ones as it moves along the DNA strands. It travels from 5' end to 3' end which means that new nucleotides are added to the 3' end of the DNA strand.

DNA Strands

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Leading strand and Lagging strand

Leading strand

Leading strand is the strand in DNA in which replication is continuous, and on which nucleotides are added in a long chain, growing in a direction as the replication fork opens up (5' to 3' end)

Leading strand

Lagging strand is the strand in DNA on which nucleotides are added in chucks, called Okazaki fragments. As it is formed backwards of replication fork, the replication is discontinuous (3' end to 5' end)

Nucleotide paring and bonding

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How does nucleotides pair and bond?

Nitrogenous bases pairing and bonding

Nucleotide paring and bonding involve the complementary base paring of adenine (A) with thymine (T) and guanine (G) with cytosine (C), forming stable hydrogen bonding. Adenine always forms two hydrogen bonding with thymine and cytosine always forms three hydrogen bonding with guanine.

Sugar-phosphate backbone

Suagar-phosphate backbone is the structural component that runs along the outside of the DNA double helix. It's formed by the alternating arrangement of sugar and phosphate molecules. Sugar includes five carbon numbered from 1' to 5'. A phoshpate is attached to the 5' carbon, the nitrogenous base is attached to the 1' carbon and the other four is attached to nitrogen-containing bases.