What is semi-conservative replication?

Semi-conservative replication refers to the fact that each of the newly synthesised DNA molecules is made up of one original DNA strand and one new DNA strand.

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What is the role of DNA helicase in DNA replication?

DNA helicase breaks hydrogen bonds between complementary bases to unwind the double helix and separate the strands.

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What is the role of DNA polymerase in DNA replication?

DNA polymerase joins nucleotides together via phosphodiester bonds.


This forms the sugar-phosphate backbone of the new DNA strand.

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What is the role of DNA ligase in DNA replication?

DNA ligase joins Okazaki fragments together.

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In which direction does DNA polymerase build new strands?

DNA polymerase builds new DNA strands in the 5' to 3' direction.

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What are Okazaki fragments?

Okazaki fragments are short copied DNA fragments synthesised on the lagging strand of DNA.

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Why can DNA polymerase only synthesise short DNA fragments on the lagging strand?

DNA polymerase can only synthesise short DNA fragments on the lagging strand because the lagging strand is being synthesised in the opposite direction to the unwinding of the double helix.

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What are the steps involved in DNA replication?

  1. DNA helicase breaks hydrogen bonds between complementary bases to unwind the double helix and separate the strands.
  2. Free nucleotides move to and form hydrogen bonds with their complementary bases on each DNA strand.
  3. DNA polymerase joins the free nucleotides together via phosphodiester bonds to form the sugar-phosphate backbone of the new DNA strand.
  4. Two identical copies of DNA are made by semi-conservative replication.

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What reaction takes place to join nucleotides together during semi-conservative DNA replication?

A condensation reaction joins nucleotides together.

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