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AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

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Could somebody please explain siRNA to me?

siRNA (small interfering RNA) is a double stranded RNA molecule which interferes with gene expression. DNA goes through the process of translation and produces a single strand of mRNA. The siRNA molecule will have one strand which is complimentary. It releases the other strand, binds to the mRNA and proteins/enzymes digest the mRNA, meaning it does not get to translation.

That is what I remember. I think the siRNA molecule is attatched to the protein/enzyme which may digest at the end.

Hope that helps :smile:

Reply 941

flowerscat

Original post by FristyKino

Can someone please differentiate between 'sticky ends' and 'blunt ends' in 2-4 lines please.
Thankyou

Blunt ends = restriction enzyme cuts right through the middle (usually) of the restriction site, leaving two fragments with flush ends (like cutting a strip of paper straight across with sharp scissors)

Sticky ends = restriction enzyme does not cut at the same base on both strands of DNA, thus the cut is "staggered" leaving "sticky" bases on both sides - these bases are called "sticky" because they are not H-bonded, and so will readily H-bond with incoming DNA.

Efficiency of ligation with sticky ends is much higher than with blunt ends.

Advantage of blunt ended ligation is that both the vector and the gene can be cut with a different set of enzymes, yet will still be able to bond to each other. With sticky ends, both vector and gene must be cut with the same restriction enzyme. Though it is possible to control what restriction sites you have on vectors, find the same restriction site on an unknown gene is quiet hard.

Reply 942

diskohuelga

I'm only starting revision for bio5 properly now...am I completely ****ed?

Reply 943

indifferencepersonified

Original post by Pixiefairy

yess! pm me your email address

There are a long line of us who said yes but couldn't find the original post to quote you :tongue:

Send to me too please :smile:

Reply 944

student777

Can anyone please explain muscle contraction really simply? I was just looking over it today, and the NT book, my notes and factsheets say different things :/

Reply 945

mlbyrne30

Original post by Pixiefairy

i have over 20 essays and analysis on them if anyone wants i can email it to them :biggrin:

Could you send these to me too :biggrin:

?? Do I need to pm you my email address??
Thank you so much :smile:

Reply 946

Cyanohydrin

Original post by diskohuelga

I'm only starting revision for bio5 properly now...am I completely ****ed?

think positive.

Reply 947

Pixiefairy

Original post by indifferencepersonified

There are a long line of us who said yes but couldn't find the original post to quote you :tongue:

Send to me too please :smile:

lol, what's your email address?

Reply 948

Pixiefairy

Original post by mlbyrne30

Could you send these to me too :biggrin:

?? Do I need to pm you my email address??
Thank you so much :smile:

hello!, yes please, pm me your email address and i can email you it straight away

Reply 949

SkyHunter

Thought this might be helpful...some essay questions with anaylsis :biggrin:

biologysynopticstudentcreche.pdf714.0KB

Reply 950

Nutterfly

Original post by Pixiefairy

i have over 20 essays and analysis on them if anyone wants i can email it to them :biggrin:

Any chance I can have them? Will pm my email =)

Reply 951

Pixiefairy

Original post by Nutterfly

Any chance I can have them? Will pm my email =)

ofcourse

Reply 952

OriginOfShowbiz

Original post by diskohuelga

I'm only starting revision for bio5 properly now...am I completely ****ed?

You're not alone. I haven't even touched chapter 16 because I was busy revising for other subjects, and we didn't go over it in class at all since my teacher never shows up.
Ah crap.

Reply 953

laura123

Does anyone know "how the structure of cells is related to their function". Nightmare essay title!

Reply 954

Master.K

Could somebody please break down 'In Vivo' and 'In Vitro' to main points......I'm really struggling with it. :frown:

Reply 955

Master.K

Original post by OriginOfShowbiz

You're not alone. I haven't even touched chapter 16 because I was busy revising for other subjects, and we didn't go over it in class at all since my teacher never shows up.
Ah crap.

Original post by diskohuelga

I'm only starting revision for bio5 properly now...am I completely ****ed?

Ditto!.....Last still got two whole days....use them wisely!
Short term memory FTW! :biggrin:

Reply 956

flowerscat

Original post by student777

Can anyone please explain muscle contraction really simply? I was just looking over it today, and the NT book, my notes and factsheets say different things :/

Muscle contraction: Sliding filament theory:

An impulse arriving at the neuromuscular junction causes the release of achetylcholine into the space between the neurone and the muscle cells.

This causes depolarisation at the muscle cells, resulting in release of calcium ions (*from the sarcoplasum reticulum, which is a special type of endoplasmic reticulum found in muscle cells). This calcium travels rapidly down the muscle cells (*via transverse tubules)

Calcium binds to troponin. Troponin causes tropomyosin to change shape, revealing the myosin-binding sites on actin.

Mysoin binds to actin, forming a "cross-bridge".

ADP (which is attached to the myosin head) now detaches, providing the energy for the myosin head to "nod" forwards.

This causes the actin filament to slide over myosin. The muscles shorten (contract). * this is called the power stroke.

ATP now binds to the myosin head, causing it to detach from actin.

ATP is hydrolysed, providing the energy for the myosin head to return to its upright position.

Myosin head now binds further along the actin filament and the whole process is repeated.

When an impulse is no longer received, calcium ions are mopped up (into the sarcoplasmic reticulum) and the tropomyosin once again blocks the myosin-binding sites on actin.

* a single power stroke only contracts muscles by 1%, whereas 35% contraction is need to actually perform work - therefore a powerstroke must be repeated several times in one muscle contraction.

Information marked with an * does not form part of the AQA syllabus, have included it here to make the explanation clearer.

(edited 12 years ago)

Reply 957

Cyanohydrin

Original post by laura123

Does anyone know "how the structure of cells is related to their function". Nightmare essay title!

- Bilayer allows water and simple non polar molecules to move through

- Facilitated diffusion via channel proteins

- Active Transport

- Mitochondria provides ATP and mitochondria % varies dependent on cells

- Cell specialisation (talk a bit out transcription)

- Nucleus - how DNA is protected from the cytoplasm by another bilayer

- Plant cells

- Lysosomes get rid of waste

- Prokaryotes features (i.e. flagella for movement) - sharing of DNA etc

- Able to replicate; hence can repair damaged tissue, grow an egg to a baby and so on (talk a bit about cell division)

Reply 958

OriginOfShowbiz

Original post by Master.K

Ditto!.....Last still got two whole days....use them wisely!
Short term memory FTW! :biggrin:

WE CAN DO THIS!
:tongue:

Reply 959

Carpet21

Ok I need major reassurance. I've been so caught up with chemistry as I was convinced that was going to be my downfall, that I've done no and I mean NO biology. We haven't had a proper teacher all year so everything on the course is completely new to me and I have Monday and Tuesday to learn it all. How likely is it that I can scrape a D with two days revision??