1.5.2 DNA replication ❤️

Why is semi-conservative replication important

Ensures genetic continuity between generations of cells

Describe the process of semi conservative replication

1. DNA helicase breaks hydrogen bonds between complementary base pairs, unwinding the double helix

2. Both strands act as templates

3. Free DNA nucleotides are attracted to exposed bases and join by specific complementary base pairing

4. Hydrogen bonds form between pairs

5. DNA polymerase joins adjacent nucleotides on the new strand by condensation reactions

6. Forming phosphodiester bonds

Define semi-conservative

Each new DNA molecule consists of one original template strand and one new strand

Why does DNA polymerase move in opposite directions along DNA strands (enzyme action)

• DNA has antiparallel strands

• So shapes/ arrangements of nucleotide on two ends are different

• Since DNA polymerase is an enzyme with a specific active site, it can only bind to substrate with complementary shape

• Which is the phosphate end of developing strand

Name 2 scientists who proposed models of the chemical structure of DNA and DNA replication

Watson and Crick

Describe the work of Meselson and Stahl (invalidated Watson and cricks model)

1. Grew bacteria in medium containing heavy nitrogen, so heavy nitrogen is incorporated into DNA bases. DNA extracted and centrifuged, settles near bottom as there’s 2 heavy strands

2. Bacteria transferred to medium containing light nitrogen, allowed to divide one. DNA extracted and centrifuged, settles near middle as contains 1 heavy and 1 light

3. Bacteria in light nitrogen is allowed to divide again. DNA extracted and centrifuged. Half settles in middle (1 heavy, 1 light). Half settles near top (2 light)

Draw the results of Meselson and Stahl

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