2.3.5 DNA Replication

Question 1

How does semi conservative replication of DNA work?

Answer 1

• Prior to mitosis
• DNA is doubled
• Occurs during S phase of cell cycle
• DNA Helicase unwinds DNA double helix
• Hydrogen bonds between nitrogenous bases on antiparallel strands break
• 2 single DNA stands form
• Each strand acts as template strand
• Free activated nucleotides (nucleoside triphosphates) align with their exposed complementary bases from the template strand
• Activated nucleotides joined together by DNA polymerase, breaking off 2 phosphate groups which release energy to create phosphodiester bonds between the deoxyribose sugar and phosphate groups of adjacent nucleotides
• Sugar-phosphate backbone created
• Hydrogen bonds form between the complementary base pairs
• Thus a new strand of DNA is created
• Half the original molecule is conserved, hence SEMI Conservative

Question 2

Why is it important to retain 1 DNA strand?

Answer 2

• Ensures there is genetic continuity (genetic information is inherited down generations from parent cells)
• Cells in body are replaced regularly, so we need new cells to be able to do the same as the old ones

Question 3

How can mutations occur?

Answer 3

• Bases may be inserted into the complementary strand in the wrong order
• Extra base may be inserted by accident
• Base may be left out by accident
• These errors in semi-conservative replication can cause random, spontaneous mutations