How to answer questions on gene electrophoresis?
Hi 
i was doing this past paper question from aqa alevel biology paper 2 2024 and there is a question on to show the relative positions of the bands but idk how to actually figure that out. can some one explain please? thank you so much
i was doing this past paper question from aqa alevel biology paper 2 2024 and there is a question on to show the relative positions of the bands but idk how to actually figure that out. can some one explain please? thank you so much
(edited 1 month ago)
Reply 1
Hi! I’m in Yr13 doing AQA A level biology and I recognised this question so I hope I can help
So, for experiment 1 BamH1 cuts the DNA. If you look at the lines without arrows, you can see the DNA is cut in 2 places making 3 different sized fragments.
In experiment 2, both restriction endonucleases cut the DNA so there will be 5 fragments formed (as there are 4 lines/cuts).
To summarise, we know there are 3 DNA fragments in experiment 1 and 5 in experiment 2. To determine their positions on the gel, you compare the lengths of the DNA fragments (as this corresponds to mass - longer fragments have more nucleotides etc) The longer fragments will remain closer to the top of the gel plate (as they move slower). So, the shorter fragments will be closer to the bottom.
What I did was draw on the diagram the lengths of the different DNA fragments cut for each experiment, and number them according to length so I would be able to order them. So, the longest DNA fragment (which is from experiment 1) can be drawn at the top of the gel plate. Then the next longest is from experiment 2, so that can be drawn a bit further down. The next longest are the fragments between the two cuts by BamH1 (non-arrow lines). These are the same length for each experiment so they are drawn next to each other. Continue with this for the rest of the fragments.
I hope this helps!!
So, for experiment 1 BamH1 cuts the DNA. If you look at the lines without arrows, you can see the DNA is cut in 2 places making 3 different sized fragments.
In experiment 2, both restriction endonucleases cut the DNA so there will be 5 fragments formed (as there are 4 lines/cuts).
To summarise, we know there are 3 DNA fragments in experiment 1 and 5 in experiment 2. To determine their positions on the gel, you compare the lengths of the DNA fragments (as this corresponds to mass - longer fragments have more nucleotides etc) The longer fragments will remain closer to the top of the gel plate (as they move slower). So, the shorter fragments will be closer to the bottom.
What I did was draw on the diagram the lengths of the different DNA fragments cut for each experiment, and number them according to length so I would be able to order them. So, the longest DNA fragment (which is from experiment 1) can be drawn at the top of the gel plate. Then the next longest is from experiment 2, so that can be drawn a bit further down. The next longest are the fragments between the two cuts by BamH1 (non-arrow lines). These are the same length for each experiment so they are drawn next to each other. Continue with this for the rest of the fragments.
I hope this helps!!
Reply 2
azamy
OP
6
Thank youu
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