AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

Can someone be a dear and explain the difference between the first and second messenger model for me? And what the advantages are?

2nd Messenger Model
Hydrophillic hormones such as Insulin, Adrenaline and Glycagon cannot pass through the cell membrane. So they bind to cell membrane receptor which activates an enzyme within the cell which converts ATP into Cyclic AMP. This then activates other enzymes bringing about the desired response.

1st messenger model
Hydrophobic hormones such as Oestrogen can pass through the cell membrane. So it diffuses through the membrane and binds to a receptor, changing the receptors shape and so releasing a inhibtor. :smile:

Reply 1801

feelbetter

Original post by ?!master?!mini?!

stem cells constantly replicate themselves. So no treatment does not need to be repeated

thanks

Reply 1802

SashaLuLu

heyy can somebody....
'describe how an impulse is transmitted across an excitatory synapse' ??

Reply 1803

HarryHH

Original post by xelaman

2nd Messenger Model
Hydrophillic hormones such as Insulin, Adrenaline and Glycagon cannot pass through the cell membrane. So they bind to cell membrane receptor which activates an enzyme within the cell which converts ATP into Cyclic AMP. This then activates other enzymes bringing about the desired response.

1st messenger model
Hydrophobic hormones such as Oestrogen can pass through the cell membrane. So it diffuses through the membrane and binds to a receptor, changing the receptors shape and so releasing a inhibtor. :smile:

""Glycagon""???? I think you meant Glucagon?

Reply 1804

NRican

What big topic/section didn't come up in the June 10 paper?

Reply 1805

diskohuelga

10

Original post by xelaman

2nd Messenger Model
Hydrophillic hormones such as Insulin, Adrenaline and Glycagon cannot pass through the cell membrane. So they bind to cell membrane receptor which activates an enzyme within the cell which converts ATP into Cyclic AMP. This then activates other enzymes bringing about the desired response.

1st messenger model
Hydrophobic hormones such as Oestrogen can pass through the cell membrane. So it diffuses through the membrane and binds to a receptor, changing the receptors shape and so releasing a inhibtor. :smile:

thanks that's brilliant.
so the first messenger model has nothing at all to do with glucose concentration?

Reply 1806

NRican

Original post by strawberry_cake

For the essay, can we draw diagrams and annotate? Will we get extra marks for doing that?

You can, if it helps to make your point then you will get marked on it but not 'extra marks' :wink:

Reply 1807

xelaman

Original post by HarryHH

""Glycagon""???? I think you meant Glucagon?

Sure did

Reply 1808

Philip_H

Original post by diskohuelga

thanks that's brilliant.
so the first messenger model has nothing at all to do with glucose concentration?

Nope

Reply 1809

Abby :)

8

Original post by Phalange

Hey how was Psychology? :smile:

Hey!
It was very good... however i missed the big question that was on the back page. 0.o
Loads of people did too aparantly though. Eh, im such an idiot hahahaa.
Luckily its low grade boundaries!

Did you do it?

Reply 1810

Philip_H

Original post by NRican

What big topic/section didn't come up in the June 10 paper?

Erm... detecting external responses: Pacinian Corpuscle/Meissner's Corpuslce etc and Rods/Cones.

Reply 1811

cor_fortis

8

Original post by SashaLuLu

heyy can somebody....
'describe how an impulse is transmitted across an excitatory synapse' ??

impulse arrives at presynaptic membrane
causes influx of calcium ions
calcium ions bind to vesicles containing acetylcholine
vesicles undergo exocytosis
acetylcholine diffuses across synaptic cleft
binds to ligand-gated sodium ion channels on post-synaptic membrane
sodium ion influx
post synaptic membrane depolarises and impulse continues
(acetylcholine is broken down by enzymes in cleft and calcium ions are recycled)

slightly more detailed one below :smile:

courtesy of Stirlo

(edited 12 years ago)

Reply 1812

Stirlo

Original post by SashaLuLu

heyy can somebody....
'describe how an impulse is transmitted across an excitatory synapse' ??

An action potential arrives at the presynaptic knob.
The impulse causes voltage gated calcium channels to open and calcium ions flood into the presynaptic knob.
The influx of calcium ions causes the vesicles (containing acetlycholine) to fuse with the presynaptic membrane.
This releases the acetylcholine into the cleft
The neurotransmitter diffuses across the cleft to the post synaptic member where they bind to cholinergic receptors (or nicotinic cholinergic receptors in muscles).
This causes Sodium channels to open, causing sodium ions to enter the post synaptic membrane.
If this reaches the threshold value an action potential is produced.
Aceltycholinesterase hydrolyses the acetylcholine into it's substituents (which i forget, ethanoic acid + something). WHich are then actively transported back into the presynaptic knob to recombined using ATP into acetylcholine

Reply 1813

xelaman

Original post by diskohuelga

thanks that's brilliant.
so the first messenger model has nothing at all to do with glucose concentration?

No just its action is seen in the control of blood glucose-good essay subject :smile:

Reply 1814

cor_fortis

8

Original post by Stirlo

An action potential arrives at the presynaptic knob.
The impulse causes voltage gated calcium channels to open and calcium ions flood into the presynaptic knob.
The influx of calcium ions causes the vesicles (containing acetlycholine) to fuse with the presynaptic membrane.
This releases the acetylcholine into the cleft
The neurotransmitter diffuses across the cleft to the post synaptic member where they bind to cholinergic receptors (or nicotinic cholinergic receptors in muscles).
This causes Sodium channels to open, causing sodium ions to enter the post synaptic membrane.
If this reaches the threshold value an action potential is produced.
Aceltycholinesterase hydrolyses the acetylcholine into it's substituents (which i forget, ethanoic acid + something). WHich are then actively transported back into the presynaptic knob to recombined using ATP into acetylcholine

ethanoic acid and choline :smile:

Reply 1815

Phalange

Original post by Abby :)

Hey!
It was very good... however i missed the big question that was on the back page. 0.o
Loads of people did too aparantly though. Eh, im such an idiot hahahaa.
Luckily its low grade boundaries!

Did you do it?

LOL ow you missed it out. Seems like a lot of people did. Yep it was ok. Dodgy research methods as always. Left out 5 marks in Media but otherwise I think it was alright.

Reply 1816

93M

10

I've got a couple of hours to revise, what does everyone think the main things I should go over/learn are?

Reply 1817

flowerscat

10

Original post by Tericon

No, can you? That'd be great :smile:

Restriction mapping: using Fig 4 and 5 on page 269 of NT book.

Aim: Trying to find out how the DNA fragments are linked to each other, and what restriction sites separate them (imagine you are sequencing a chromosome and want to find out how the pieces of the DNA go back together once you have cut it with restriction enzymes for sequencing).

Method: Cut the DNA with each of the individual enzymes - run on a gel - this tells you how many restriction recognition sites there for each enzyme in the DNA.

Take 3 restriction enzymes. Start mixing them together in pairs, then using them for digest. Run on a gel.

Now using the first combination of enzymes, lay out the pieces that you get (90 kb + 10 kb). One cut must be due to BamH1 and the other due to HindIII. Since one of the fragments they generate is 10kb, then two sites must be quiet close to each other.

Look at the way the DNA has been cut by the set combination of enzymes - they will overlap with the first sample, but the "cuts" will be in different sections. (60 kb + 40 kb) As these fragments are smaller than 90 kb, Not I must be between BamH1 and HindIII

Do the same with the third. (70kb and 30 kb). Because of the 30 kb fragment, the only way the jigsaw will fit is if Not1 is closer to BamH1 than HindIII.

The easiest way to figure this out if you draw a circular loop of DNA and try and account for all the bands in the gel. You will see that there is no other way the jigsaw can fit together.