AQA A2 Biology BIOL5 - 17th June 2015

Can glucagon act as a second messenger? Or is it just Adrenaline?

It's split into 5 stages:

Firstly, Extraction so you would use PCR in order to amplify DNA and produce a large sample.
Secondly, Digestion so you would use restriction endonucleases in order to produce fragments of a gene. This would be based on complimentary base pairing and would produce a specific section of a gene.
Thirdly, Separation. In this you would use gel electrophoresis in order to separate your fragments. Long fragments move shorter distances whereas shorter fragments will move further. You would then southern blot. This is blotting on nylon which would use capillary action to remove liquid from your DNA sample.
Fourthly- hybridisation. You would separate into single strands and add an Xray or fluorescent probe. This would allow you to identify the base sequence in the fifty step where you would use a filament overlay or you would use autoradiography (depending if fluorescent or Xray) to compare the structures to known base sequences.

Thanks, and just to confirm, the aim of this is to map up dna sequence which can be used for a variety of reasons including forensics work?

Is it true for the essay, that you can write about anything you want, and only lose 3 marks for relevancy (providing the Biology is all correct)

I'm not sure but isn't it that neither are second messengers but they stimulate a second messenger to arise called cAMP (by ATP)

Maybe an essay about how different organisms are adapted and that could include how cells are adapted in leaves? Countercurrent flow in fish maybe?


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can someone explain transcriptional factors to me please?

Can anyone explain why myelin sheaths make transmission of an action potential faster in really basic terms? Still don't fully understand it.

can someone explain transcriptional factors to me please?

Can anyone explain why myelin sheaths make transmission of an action potential faster in really basic terms? Still don't fully understand it.

Both work in the second messenger model. Basically, both of them can be involved in the cAMP pathway, and then allow enzymes to work and make glucose from glycogen and glycerol by inhibition of enzymes and activation of others.

Myelin is an insulator
sodium ions can only enter at the Nodes of Ranvier
Saltatory conduction
^ FASTER.

Non-myelinated = no myelin = no insulator
Action potentials along the whole membrane as a wave

So it can form Glucagon-receptor complex?

Myelin sheaths will do two things:
Firstly, they will mean that the axon will be insulated which will mean that any impulses will be passed more rapidly.
Secondly, it will mean that saltatory conduction takes place. Rather than action potentials passing down the full length of the axon, where they would in a nonmyelinated sheath be passed down in a localised current down the full length of the axon and would be depolarised in one area and then depolarise the next area and so on, in saltatory conduction action potentials jump between adjacent nodes of Ranvier.

This means that then action potentials will move quickly down the axon as they don't need to depolarise along the full length of the axon, and only at certain intervals in the nodes.


We were taught it like a mexican wave- so where one person raises their hands then the next person does then the next person is like a nonmyelinated sheath,
but then if a whole group of people raised their hands at once, the wave would travel more quickly - so thats like if it was myelinated and only at the nodes of ranvier.

Can someone please explain how a generator potential is set up in a rod cell?


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