3.9 - DNA Replication and the genetic Code

Question 1

Why is DNA replication described as semiconservative?

Answer 1

• strands from original DNA molecule act as templates
• new DNA molecule contains 1 old strand & 1 new strand

Question 2

What is semi-conservative replication?

Answer 2

1. for DNA to replicate the double helix structure has to unwind and then depreciate into two two strands
2. Hydrogen bonds holding the complimentary bases together must be broken
3. Free DNA nucleotides will then pair with their complimentary bases which have been exposed as the strands separate
   - hydrogen bonds are formed between them
   - new nucleotides join to their adjacent nucleotides with the phosphodiester bonds
   - 2 new molecules of DNA are produced
   - each one consists if one old strand of DNA and one new strand

Question 3

Explain the role OF DNA helicase in semi- conservative replication

Answer 3

Breaks H- bonds between base pairs to form 2 single strands
Each of which act as a template

Question 4

Identify features of the genetic code

Answer 4

1.Non- overlapping - each triplet is only read once
2. Degenerate - more than one triplet gifts for the same amino acids ( 64!possible triplets for 20 amino acids )
3. Universal - same bases and sequences used by all species

Question 5

Describe how DNA can be purified by precipitation

Answer 5

1. Add ethanol and a salt to aqueous solution
2. Nucleic acids precipitate out of solution
3. Centrifuge to obtain pellet of nucleic acid
4. Was pellet with ethanol and centrifuge again