(2.3) Nucleic Acids Flashcards
What is a nucleotide?
A monomer of DNA
What are the different parts of a nucleotide?
- Phosphate group
- Pentose sugar
- Nitrogenous base
What are the two types of pentose sugars?
- Deoxyribose
- Ribose
How is deoxyribose different from ribose?
Deoxyribose contains a H group rather than an OH group
What are purines?
Double ringed structures (contain a pentagon shape with a hexagon shape)
What are the purines called?
Adenine and Guanine
What are pyrimidines?
Single ringes structures (a hexagon shape)
What are the pyrimidines called?
Cytosine, Thymine and Uracil (in RNA)
Why do pyrimidines and purines always join together in the double helix structure?
So the rungs of DNA are always the same length
What do DNA rungs contain?
Base pairs
What does it mean by a 5” to 3” and a 3” to 5” direction?
It refers to where the nucleotides join to and which carbons in the pentose sugar
What is the reason for the phosphate backbone running in different directions?
The two different sides run in an anti-parallel fashion and it mens the double helix is twisted
What is the role of DNA gyrase?
It untwists the Double helix structure
What is the role of DNA helicase?
It unzips the helix by breaking the hydrogen bonds between the nitrogenous bases
What is the role of single stranded binding proteins?
Prevents the two strands from reannealing after DNA helicase has done its job
What does reannealing mean?
Binding back together
Which direction does DNA polymerase travel in?
5 prime to 3 prime direction
What is the role of DNA polymerase?
It binds to the leading strand and forms covalent bonds between nucleotides by joining the phosphate backbone by forming phosphodiester bond
How is the lagging strand synthesised in DNA replication?
Discontinuosly which creates okazhaki fragments
What is the role of DNA ligase?
Sticks together the okazhaki fragments
What experiment means semi-conservative replication is evidential?
Meselton Stahl experiment
What was the Meselton Stahl experiment?
- heavy nitrogen in 2 test tubes
- grew bacteria and isolated DNA
- found as generations went on the new DNA was less dense
How is DNA semi-conservative?
Because one new strand and one old strand in the new DNA helix
Describe DNA replication
- DNA gyrase untwists the helix
- DNA helicase unzips the helix by breaking hydrogen bonds
- Single stranded binding proteins attach to stop reannealing
- DNA polymerase binds to the leading strand forming covalent bonds between complementary nucleotides
- The lagging strand is synthesised discontinuosly
- DNA ligase sticks together the Okazhaki fragments
- Eventually replication forks join together and create new DNA helixes
