BIOC0001 - PRACTICAL A (MOLECULAR BIOLOGY) EXAM
QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS GRADED A++ LATEST UPDATE
What is supercoiling? What is its purpose?
The twisting of a DS DNA helix around itself allowing it to be packaged efficiently into a
cell.
Why might two sections of DNA which are the same length travel at different rates
during gel electrophoresis?
DNA can go from being supercoiled to relaxed during lab preparation.
Supercoiled DNA is more compact and travels further.
What are the 3 states DNA can be in?
1. Supercoiled.
2. Relaxed.
3. Linear.
What makes restriction endonucleases and why?
, Bacteria.
To defend against viral infection.
What is a feauture of all restriction sites?
They are palindromic.
Why are all restriction sites palindromic?
It allows the restriction endonuclease to cut both strands at the same point.
What is the gel used in gel electrophoresis? What type of molecule is it?
Agarose.
A polysaccharide.
Describe the movement of DNA fragments in agarose gel electrophoresis. What
determines the speed?
The negatively charged DNA (due to phosphates) moves towards the anode (positive
end) of the gel by moving through pores in the gel.
The larger the fragment, the more drag it will experience whilst moving through the gel
and so the slower it will move.
What chemical is used to visualise DNA and how does it work?
Ethidium bromide.
It intercalates (inserts) between bases and will fluoresce a pink-orange colour when
illuminated with UV light (300nm).
QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS GRADED A++ LATEST UPDATE
What is supercoiling? What is its purpose?
The twisting of a DS DNA helix around itself allowing it to be packaged efficiently into a
cell.
Why might two sections of DNA which are the same length travel at different rates
during gel electrophoresis?
DNA can go from being supercoiled to relaxed during lab preparation.
Supercoiled DNA is more compact and travels further.
What are the 3 states DNA can be in?
1. Supercoiled.
2. Relaxed.
3. Linear.
What makes restriction endonucleases and why?
, Bacteria.
To defend against viral infection.
What is a feauture of all restriction sites?
They are palindromic.
Why are all restriction sites palindromic?
It allows the restriction endonuclease to cut both strands at the same point.
What is the gel used in gel electrophoresis? What type of molecule is it?
Agarose.
A polysaccharide.
Describe the movement of DNA fragments in agarose gel electrophoresis. What
determines the speed?
The negatively charged DNA (due to phosphates) moves towards the anode (positive
end) of the gel by moving through pores in the gel.
The larger the fragment, the more drag it will experience whilst moving through the gel
and so the slower it will move.
What chemical is used to visualise DNA and how does it work?
Ethidium bromide.
It intercalates (inserts) between bases and will fluoresce a pink-orange colour when
illuminated with UV light (300nm).
