DNA replication

Question 1

Process of DNA replication

Answer 1

1. Dna helicase breaks the H bonds between bases and unwinds double helix.
2. two strands which both acts as templates
3. Free floating DNA nucleotide attracted to exposed bases via complementary base pairing and hydrogen bonds form between them.
4. DNA polymerase joins adjacent nucleotides ton new strands by condensation forming a phosphodiester bond.

Question 2

Why is DNA semi conservative and why is it important

Answer 2

Replication is semi-conservative as each new strand formed contains one original and one new strand. This ensures genetic continuity between generations of cells.

Question 3

Describe the experiment conducted by Meselson and Stahl

Answer 3

• Bacteria grown in a nutrient containing heavy nitrogen for several generations
• Nitrogen was incorporated into the DNA bases of a bacteria
• Bacteria then transferred into a nutrient solution containing light nitrogen and allowed to grow and divide twice.
• During this process DNA from different samples of bacteria was extracted, suspended in a solution in separate tubes and spun in centrifuge.

Question 4

How did Meselson and Stahl’s research provide evidence for semi-conservative replication

Answer 4

Sample 1= DNA from bacteria grown for several generations in a nutrient solution containing 15Nitrogen . DNA molecules contain two heavy strands.
Sample 2 = DNA from bacteria grown originally in a nutrient solution containing 15nitrogen then transferred for one division to a solution containing 14nitrogen . DNA molecules contain 1 original and 1 new light strand
Sample 3=DNA from bacteria grown originally in a nutrient solution 15nitrogen then transferred for two divisions to a solution containing 14nitrogen. As a result 50% DNA molecules contain 1 original heavy stand and 1 new light strand and 50% contain both light strands