DNA Replication

Question 1

what 4 things are required for semi-conservative replication to take place?

Answer 1

• 4 types of nucleotides (adenine, guanine, cytosine or thymine must be present)
• both strands of the dna molecule
• the enzyme DNA polymerase
• a source of chemical energy is required to drive the process

Question 2

describe the process of semi conservative replication

Answer 2

1. DNA helicase breaks the H bonds linking base pairs of DNA
2. as a result the double helix seperates into its two strands and unwinds
3. each exposed polynucleotide strand then acts as a template to which complimentary free nucleotides bind by specific base pairing
4. nucleotides are joined together in a condensation reaction by the enzyme DNA polymerase to form the missing polynucleotide strand on each of the two original polynucleotide strands of dna
5. each of the new dna molecules contains one of the original dna strands, that is, half the original dna has been saved and built into each of the new dna molecules.

Question 3

if the bases on a portion of the original strand of dna are ATGCTACG, determine the equivalent sequence of bases on the newly formed strand.

Answer 3

TACGATGC

Question 4

explain why the process of dna replication is described as semi-conservative

Answer 4

because half of the original dna is built into the new dna strand

Question 5

if an inhibitor of dna polymerase were introduced into a cell, explain what the effect would be on a dna replication

Answer 5

the linking together of the new nucleotides could not take place. while the nucleotides would match up to their complimentary nucleotides on the original dna strand, they would not join together to form a new strand

Question 6

what evidence is there for semi conservative replication

Answer 6

1. get a sample of bacteria (ecoli) they grew it in both heavy nitrogen 15 and light nitrogen 14
2. they took a sample of 14 and 15 nitrogen to keep for later, they put the 15 into the 14 and let that replicate for one generation
3. they got all the samples together and spun them in a centrifuge, this allowed the nitrogen to settle
4. the light nitrogen settled at the top whereas the heavy nitrogen settled at the bottom. the sample with both nitrogens settled in the middle
5. this suggested that the replication was semi conservative and the sample contained both heavy and light nitrogen