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AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

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Does the secondary messenger apply to insulin as well?

It does but I don't think we need to know the specifics (it has a different mechanism to glycogen/adrenaline). Here they are anyway:

1. Insulin binds to glycoprotein receptors embedded in the plasma membrane.
2. The hormone-receptor complex activates an Insulin-Receptor Substrate (IRS) inside the cell which acts as the second messenger molecule.
3. The IRS complex stimulates the Golgi apparatus to bud off vesicles containing glucose carrier proteins.
4. The vesicles fuse with the plasma membrane, increasing the number of glucose carriers on the membrane (and increasing the permeability of the membrane to glucose molecules).
5. The IRS complex also activates the glycogen synthase enzymes which stimulate glycogenesis. The IRS complex stimulates one enzyme, which in turn stimulates another. One IRS complex can stimulate many enzymes, due to the cascade effect.

But I reiterate, I'm fairly certain (95% confident) we don't need to know this.

Reply 461

Minnie me

does anyone know where i can find some good bio 4 youtube videos beth has a really good unit 5 one but i cannot find any decent u4 ones
thanks

Reply 462

biology911

Original post by Minnie me

can you please explain protein synthesis with tRNA, any help is much appreciated

tRNA action is dynamic, so static representations can limit your understanding. After doing your best with the book, try looking at a couple of simple animations on YouTube. Here’s a good start: http://www.youtube.com/watch?v=B6O6uRb1D38
You can ‘graduate’ to more complex videos, but make your own value judgement. All singing and dancing 3D ones are often very poor regarding explaining things!

Good luck

(edited 11 years ago)

Reply 463

emah123

Original post by Weirdo225

Noooo I only decided to resit because I hate unit 4 and find unit 2 more interesting, but because most of the unit 4 knowledge is still fresh in my head I decided to take that one too - I enjoy complicating things a lot haha :L

Unit 1 I got 82 UMS not great but still an A :smile:

I have 8 exams - regretting adding unit 2 into the mix but I'm sure ill get there xD

Im really worried that I wont get an A in biology though?!! Atleast you have better chances than me now as your retaking unit 2!!

what other exams do you have? have you revised for them?

Reply 464

master y

Original post by HELPIMSTUCK

Oh ok thanks! where did you get this info from? Also by the cascade effect, is that another word for positive feedback? :smile:

Reply 465

Weirdo225

Original post by emah123

Im really worried that I wont get an A in biology though?!! Atleast you have better chances than me now as your retaking unit 2!!

what other exams do you have? have you revised for them?

I've worried you now - sorry! I really don't think you need to worry about it at all :smile:

I'm just overly cautious and complicated xD just work your socks off for this and unit 4 and you'll be fine :smile:

I've got maths core 1, M1, core 4 aswell as M2, and then chemistry f325
The maths core 1 and m1 are just for higher UMS
So I'm only focusing on c4 and M2 at the moment, and chemistry is my only relief haha - one exam with not much stress at all hahaha

How about you?

Reply 466

Minnie me

Original post by biology911

Thanks very much I have learnt that once the mRNA is formed it binds to a ribosome and then a tRNA molecule with a complimentary anticodon to the mRNA codon comes to bind to the mRNA, this binding between tRNA and mRNA repeatedly occurs as the ribosome moves along the mRNA and reaches a stop codon. Each tRNA molecule that has bonded also has a amino acid attached, and when the tRNA do bind the different amino acids form peptide bonds with each other, this requires ATP and an enzyme. Once three codons are bonded the first tRNA is released from its amino acid, the process continues until a polypeptide is formed.
Do we need to know `in summary…` on page 227 in nelson thornes textbook

Reply 467

anisah150

Original post by Minnie me

does anyone know where i can find some good bio 4 youtube videos beth has a really good unit 5 one but i cannot find any decent u4 ones
thanks

I think theres one im not sure but i thinks its called khans academy try typing it in google ive seen the respiration videos on that site there really good :top:

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Reply 468

MLogan

Original post by Minnie me

does anyone know where i can find some good bio 4 youtube videos beth has a really good unit 5 one but i cannot find any decent u4 ones
thanks

where can i get the BIOL5 ones from? Mind posting the link please! :smile:

Reply 469

MLogan

Can someone please explain whether in genetically modified tomatoes the complementary mRNA acts as an inhibitor when it binds on to the mRNA and how does this prevent translation?

Thank you!

Reply 470

DoeADeer

Original post by Maid Marian

Same. I. Hate. This. Unit. I feel like crying when I flick through the CGP book. So much to learn. :frown:

My teachers haven't even started the homeostasis bits yet, nor have we finished the DNA technology. I don't know whether to try and learn it myself...

This really scares me :frown:

Three past papers isn't enough!!

I keep having panic attacks about these frigging exams D: I have ten exams, I am going crazy. Waaa. UGHHHH why am I still living aha??!?!? I need motivation.
Yeah, I think you should start self teaching tbh. Homeostasis isn't really a huge topic though, so your teacher will probably cover that quickly. My teacher is useeeeelesssssssssss! :frown:

Reply 471

DoeADeer

Original post by HELPIMSTUCK

WHAAAAAAAAAAAAAAT?! I can't remember learning this D:

Reply 472

MLogan

Original post by DoeADeer

WHAAAAAAAAAAAAAAT?! I can't remember learning this D:

I thought the exact same thing when i read over that post :|

Reply 473

igloo1

Original post by Zazuwaved

haven't properly revised that bit yet, but as far as I remember it's synthesised in the nucleolus (transcription) then it travels to the cytoplasm where splicing occurs (to remove the introns (bits which don't code for proteins)) then taken up by the ribosome, tRNA brings the anti-codon (complementary to the codon strand of mRNA) and amino acid. As the tRNA anti-codon pairs with the mRNA codon (through specific base pairing), the second tRNA joins the mRNA and the amino acid joins to the first (peptide bonds-condensation reaction).

Hope that's sufficient, basically mRNA is sort of a template for the amino acids to join up.

so basically, mRNA protein synthesis is just getting a complementary template of a strand of DNA to a ribosome, then tRNA happens?

Reply 474

igloo1

Original post by Minnie me

can you please explain protein synthesis with tRNA, any help is much appreciated

From what i understand, mRNA polymerase synthesises the DNA strand ( unzips it) and a mRNA complimentary template of the DNA is formed. This attaches to the ribosomes as " unpaired ends" . several codons are usually made from the mRNA genetic code. a tRNA molecule, an anticodon with complimentary sites to the codon ( say ACU with anticodon UGA) will pair, and an amino acid will be made from the mRNA code (ACU). You can work out the amino acid with a table if needed ( there's one in the NT book, chp 14). So, once all of these AA are made from the mRNA chain, the anticodons go elsewhere to find something else to pair with and repeat the process. The used mRNA chain disintegrates and that process repeats again to make more amino acids. The AA made from the codons join by polypeptide bonds to make a protein. This can travel anywhere to be used efficiently.
Hope this made some sort of sense!
Can you explain mRNA synthesis please? thanks!

Reply 475

Weirdo225

Original post by igloo1

May be wrong but here goes

At the gene that needs to be expressed, DMA helicase causes the DNA molecule to unwind. Forms to strands of DNA - sense and antisense. Sense strand is then transcribed using RNA polymerase to form an mRNA strand that is complementary to the DNA sense strand
As the RNA polymerase passes along the sense strand a molecule of DNA polymerase passes along behind it to join the DNA up back into its double helix shape

mRNA contains introns and exons. Only the exons are useful so the introns are edited/spliced out by splicosomes
You now have a molecule of mature mRNA

Then all the tRNA stuff happens using the mRNA

Reply 476

biology911

Original post by Minnie me

Do we need to know `in summary…` on page 227 in nelson thornes textbook

Yes, but by the looks of your own summary, you've already nailed it!

Reply 477

HELPIMSTUCK

Sorry for causing panic :redface:

Original post by DoeADeer

WHAAAAAAAAAAAAAAT?! I can't remember learning this D:

As I said, this isn't on the specification (only "second messenger model of adrenaline and glucagon action" is, not for insulin). He asked about it though, and my teacher only suggested it for essays.

Reply 478

erniiee

DNA technology is a bitch :rant:

Reply 479

Maid Marian

Original post by erniiee

DNA technology is a bitch :rant:

Tell me about it. I was practically crying over my notes before. It makes NO sense. I don't get it at all (although to be fair, we haven't covered half of it in class yet :colondollar: