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Learning Goal - DNA Replication

4 important questions on Learning Goal - DNA Replication

State that DNA polymerases can only add new nucelotides to an existing strand, and in one particular directionality.

DNA polymerase can only add the 5' end of new nucleotides to the 3' end of existing nucleotides due to it's specificity, creating a need for the antiparallelity of the growing strand that starts from the 5' end, unlike the existing one that starts from the 3' end, so that DNA polymerase can continue adding nucelotides to the exposed 3' end of the growing strand. In terms of the kind of covalent bonds between base pairs: there are 3 hydrogen bonds between guanine and cytosine and 2 between adenine and thymine.

Compare the pace and direction of replication on the leading and lagging strands of DNA.

The fact that DNA polymerase 3 moves the in same direction the replication fork is opening up increases the pace of the leading's strand's synthesis, where the fact that the enzyme moves against the direction in which the replication fork is opening for the lagging strand slows down the pace of its synthesis. Replication of the leading strand is from 5' to 3', while that of the lagging strand is from 3' to 5'

Outline the formation of Okazaki fragments on the lagging strand.

RNA primers are placed at the 5' end of the lagging strand on the replication bubble, away from the replication fork, which DNA polymerase 3 uses as a starting point to synthesise the new strand. At the next replication bubble, another primer is placed in the same manner again to signal to the DNA polymerase on the location to start. As such, the new strand is synthesised in Okazaki fragments that are eventually made into a whole strand by the action of DNA ligase, which glues the fragments together.

State the function of DNA proofreading.

DNA proofreading is typically done by DNA polymerase 3 in prokaryotes, and prevents any mutation from coming about due to an incorrect replication of DNA base sequences.

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Biology HL

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