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AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

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I'm going to look at the essay titles, cry, then answer the rest of the paper to warm my brain up for the essay. I might leave the Mega HSW question until after the essay, since its where I'll lose the most marks.
can anyone add anything to this?? resting potential....



1. Sodium Pottasium pump move 3 sodium ions out of the neurone and 2 pottasium ions into the neurone - establishing a concentration gradient

2. Sodium ion channels are closed and some pottasium ion channels are open

3. Pottasium ions diffuse out of the neurone via the open pottasium ion channels down their concentration gradient into the tissue fluid until an equilibrium is reached

4. Due to the loss of positive sodium ions, postive pottasium ions and negatively charged phosphate groups the neurone is negative relative to the outside

5. A membrane/resting potential has hence been established - with a stable difference of -70mv (approx.) between the neurone/axon and the tissue fluid
Original post by tehsponge
I'm going to look at the essay titles, cry, then answer the rest of the paper to warm my brain up for the essay. I might leave the Mega HSW question until after the essay, since its where I'll lose the most marks.


That sounds good. I should so that too. WHich one is the HSW question?
Original post by Destroyviruses
That sounds good. I should so that too. WHich one is the HSW question?


Its just before the essay.
Original post by paintedsmile
http://www.livingscience.co.uk/Year13.html

^ i found this address on another thread off last year if anyone needs essay examples and mark schemes just look at the back of the Module 678 Synoptic Past Papers at the bottom of the page.


Thank you! This is great.
Original post by Pixiefairy
.



Can you email them to me aswell please?
If you can then I will pm you my email.
Thanks:smile:
Reply 926
Original post by Cyanohydrin
can anyone add anything to this?? resting potential....



1. Sodium Pottasium pump move 3 sodium ions out of the neurone and 2 pottasium ions into the neurone - establishing a concentration gradient

2. Sodium ion channels are closed and some pottasium ion channels are open

3. Pottasium ions diffuse out of the neurone via the open pottasium ion channels down their concentration gradient into the tissue fluid until an equilibrium is reached

4. Due to the loss of positive sodium ions, postive pottasium ions and negatively charged phosphate groups the neurone is negative relative to the outside

5. A membrane/resting potential has hence been established - with a stable difference of -70mv (approx.) between the neurone/axon and the tissue fluid


Looks good to me. Only thing I would add is that it is active transport that is used in the Sodium Potassium Pump, using ATP. :smile:
does siRNA prevent translation or transcription? i swear it prevents translation of mRNA by causing an enzyme to break it up, but in the NT answers it says it prevents transcription..
Original post by vickidougal
does siRNA prevent translation or transcription? i swear it prevents translation of mRNA by causing an enzyme to break it up, but in the NT answers it says it prevents transcription..


I don't have NT with me, but I agree with you, it breaks up already made mRNA and so prevents translation.
Original post by FristyKino
Can you email them to me aswell please?
If you can then I will pm you my email.
Thanks:smile:


ofcourse, pm me your email :smile:
Reply 930
Original post by vickidougal
does siRNA prevent translation or transcription? i swear it prevents translation of mRNA by causing an enzyme to break it up, but in the NT answers it says it prevents transcription..


it binds with an enzyme and then guides the enzyme to mRNA where the enzyme eats it.... so i think its translation?!
i thought it was inhibitor molecules that bind to transcriptional factors that prevent transcription..?
Original post by aj2010
Would you be able to send it to me pleaseee? :smile::smile:


yess! pm me your email address
Original post by Pixiefairy
ofcourse, pm me your email :smile:


Could you send it to me as well if I PM you my email?
Could somebody please explain siRNA to me?
Original post by Destroyviruses
Oh me too si vous plais!!!

Email

Spoiler



done :smile:
Original post by Jing_jing
Could you send it to me as well if I PM you my email?


ofcourse!
Original post by Pixiefairy
done :smile:


Thankksssssssssssssssssssssssss:biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin::biggrin:
aw you're welcome :biggrin:
Original post by Ratiocinator
Could somebody please explain siRNA to me?


Hi

siRNA is a method which cells use to control gene expression (the other being the second messenger model)

Double-stranded RNA is cut into short fragments by an enzyme (name not required for the exam)

The short strands of RNA are called siRNA.

The double-stranded siRNA unwinds (as it is quiet short the H-bonds break easily)

One of the strands degrades. The other forms a RNA-induced silencing complex -RISC (name not required for the exam). RISC is a collection of one of the strands of siRNA with a complex of protein

This siRNA strand now binds with its complementary mRNA molecule in the cell. The proteins in the RISC complex break down the mRNA. Translation of gene is prevented = no gene expression.

Very useful in research if you wanted to prove that a gene was responsible for a particular phenotype. Design siRNA complementary to the gene, this "knocks out" gene function = change in phenotype indicates that gene was responsible for phenotype.:biggrin:
(edited 12 years ago)
Original post by empop92
it binds with an enzyme and then guides the enzyme to mRNA where the enzyme eats it.... so i think its translation?!
i thought it was inhibitor molecules that bind to transcriptional factors that prevent transcription..?


haha eats it!?! :biggrin:

Original post by Ratiocinator
Could somebody please explain siRNA to me?


1.Double stranded siRNA is broken up into smaller double stranded siRNA by an enzyme

2. The siRNA binds to the RISC protein forming a RISC-siRNA complex - this breaks the two strands - with one strand being the RISC-siRNA complex (with the siRNA being single stranded) and the other strand of siRNA being rapidly degraded

3. The RISC-siRNA complex binds to the mRNA molecules in the cytoplasm by comp base pairing

4. This binding causes the mRNA molcule to break into two strands - hence the cleaved mRNA can no-longer be translated

This occurs after transcription, but before translation.

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