Topic 9: DNA Structure And Replication

Question 1

What are the structural components of nucleic acids?

Answer 1

Nucleic acids are polynucleotides which are linear polymers of nucleotides which are made up of base+sugar+phosphate

Question 2

What is the primary structure of DNA molecules?

Answer 2

Each single strand held together as nucleotide monomers joined via a covalent phosphodiester bond

Question 3

What is the secondary structure of DNA molecules?

Answer 3

Each single DNA strands held together by hydrogen bonds formed by complementary base pairs (purine and pyrimidine)

DNA strands complimentary and anti-parallel

Question 4

What is the tertiary structure of DNA molecules?

Answer 4

Right handed double helix with anti-parallel strands

Question 5

What is the quaternary structure of eukaryotic DNA?

Answer 5

Binding of DNA to histones to form nucleosomes, and then their organization into higher-order chromatin Fibres

Question 6

What are the 2 differences between DNA and RNA?

Answer 6

1. RNA has sugar ribose, DNA has sugar deoxyribose

2. RNA has nucleobase uracil, DNA has nucleobase thymine

Question 7

What is the relationship between DNA sequences, DNA molecules, chromatin and chromosomes?

Answer 7

DNA sequence is the order of nucleotides in DNA molecules, which coil to form chromatin, which form chromosomes

Question 8

What is the general outline of the mechanism of DNA replication in prokaryotes?

Answer 8

They have a circular naked chromosome

Initiation
Elongation
Termination

Question 9

What is the general outline of the mechanism of DNA replication in eukaryotes?

Answer 9

1. Initiation
2. Elongation
3. Termination

Question 10

What is semi-conservative replication?

Answer 10

2 copies of original DNA molecule are produced as each old DNA strand acts as a template for a new DNA strand

Question 11

What are the processes occurring at a DNA replication fork?

Answer 11

1. Initiation
   - DNA primase kick starts process by making a short RNA primer
   - DNA polymerase start making DNA from 3’ end
2. Elongation
   - Helicase unwinds double helix
   - DNA polymerase extends 3’ ends only, leading to a leading continuous strand and a lagging discontinuous strand
   - Okazaki fragments joined by DNA ligase
3. Termination
   - 2 facing replication forks meet
   - DNA ligase joins final fragments
   - 2 identical DNA molecules formed

Question 12

What are the 4 enzymes involved in the process of DNA replication and their functions?

Answer 12

DNA primase - creates RNA primer to kickstart process
DNA polymerase - replicate DNA from 3’ end
DNA ligase - joins Okazaki fragments
Helicase - unwinds double helix of DNA

Question 13

What is the relationship between DNA replication, DNA molecules and chromosomes?

Answer 13

Before DNA replication,

One chromosome only has one chromatid so only has one DNA molecule

After DNA replication,

One chromosome has 2 chromatids so has 2 DNA molecules