Session 4 Flashcards
What are the 2 types of Nitrogenous bases?
Purines (2 ring structure, G & A)
Pyrimidines (1 ring structure, C & T & U)
What forms a base pair?
One Purine and one Pyrimidine eg C & G. A & T
In which direction is DNA/RNA labelled?
5’ to 3’ (Free Phosphate is the 5’. Free -OH is at the 3’ end)
Explain RNA stem-loop structure
Single strand loops back on itself, thus one side will run antiparallel and hydrogen bonds will form between complimentary bases
How many hydrogen bonds are between C&G bases?
3 H bonds
How many hydrogen bonds are between A&T bases?
2 H bonds
What are the key features of a DNA double helix?
Entirely complimentary and antiparallel to each other
One complete turn is 10 base pairs
0.34nm between base pairs
Purines and pyrimidines are planar and unsaturated
What are Nucleosomes?
DNA is wound around histone core, which is charged
Each nucleosome is coiled to form solenoid structures
What happens during Initiation of DNA replication?
Helicase unravels the DNA double helix. Requires specific proteins to interact with DNA and recruit DNA polymerase. Primase is needed to initiate each strand
What happens during Elongation of DNA replication?
Leading strand is replicated 5’ –> 3’ as normal.
Lagging strand is replicated discontinuously in Okazaki fragments. These fragments are then joined by DNA ligase
What happens during Termination of DNA replication?
Lead strands move towards lagging strands and vice versa. The terms ‘leading’ and ‘lagging’ have no bearing once ligase has joined up all the fragments
Define Semi-Conservative
One of the strands in the daughter cell is the original parent strand of DNA
How are Helicase enzymes involved in DNA replication?
Uses ATP to unwind the DNA helix and allow DNA replication
Around the replication fork helicases reform the DNA helix.
In what direction does a DNA chain grow?
5’ –> 3’
