DNA Function + Structure

Question 1

DNA in prokaryotes:

Answer 1

No nuclear membrane, DNA in single chromosome.

Question 2

DNA in eukaryotes:

Answer 2

DNA in nucleus, bound to histones. Looks large and dark in mitosis since chromatin condense into chromosomes.
DNA in mitochondria is maternal.

Question 3

Functions of DNA:

Answer 3

• DNA - template and regulator for transcription and protein synthesis.
• DNA is the genetic material causes hereditary and genetic diseases.

Question 4

What is the structure of nucleic acids?

Answer 4

Nucleic acid - Phosphate group, sugar, nitrogenous base
eg. DNA,RNA

Question 5

What is the enzymes involved in DNA replication and what do they do?

Answer 5

Topoisomerase - Unwinds the double helix by relieving the supercoils
DNA helicase: Separates the DNA apart, by breaking hydrogen bonds between bases
DNA polymerase: Reads 3’ to 5’ and synthesises DNA
creates DNA by working in pairs to make 2 new strands of
DNA..

Question 6

What proteins are involved in DNA replication and what do they do?

Answer 6

Primer - short strand of DNA, start point for DNA
synthesis, DNA polymerase can only add nucleotides to existing DNA
Single strand binding protein (SSB) - keeps two strands of
DNA apart whilst synthesis of new DNA occurs - prevents
annealing to form double stranded DNA

Question 7

Why is DNA synthesised from 5’ to 3’ ?

Answer 7

• DNA polymerase reads the template strand from 3’ to 5’
• DNA is synthesised on the daughter strand from 5’ to 3’
  since DNA runs antiparallel, the daughter strand is synthesised from 5’ to 3’
• Phosphate at the 5’ is used by enzyme as activation energy
  3’ has unreacted O2. 5’ has phosphate group, need a phosphate group for energy.

Question 8

What is semi conservative DNA?

Answer 8

DNA double helix retains one strand of the original DNA

Question 9

Briefly state the points of DNA replication?

Answer 9

1. Topoisomerase and DNA helicase unwinding
2. SSB attachment
3. Primate enzyme synthesis RNA primer
4. DNA polymerase synthesise DNA
5. RNAase H removes primers
6. DNA polymerase fill gap of primers
7. DNA ligase joins DNA pieces

Question 10

Explain the process of DNA replication in detail:

Answer 10

1. Topoisomerase unwinds DNA, DNA helicase separates DNA
   exposing two single DNA strands to create two replication forks. DNA replication takes place simultaneously at each fork.
2. SSB’s coat single DNA strands to prevent re annealing.
3. Primate enzyme uses the original DNA sequence on the parent strand to synthesise a short RNA primer. To extend a nucleotide chain.
4. DNA polymerase synthesises a new DNA strand by extending an RNA primer in the 5’ to 3’ direction.
5. As replication proceeds, RNAse H recognises RNA primers bound to the DNA template, removes primers by hydrolysing the RNA.
6. DNA polymerase then fills gap left by RNAase H
7. DNA ligase joints short DNA pieces into one strand.