Edexcel A2 Biology Unit 4(6BIO4) 13/06/11 - OFFICIAL THREAD !

i dont understand what is meant by short tandem repeats in the introns? anyone help pleaaaaaaaaaaaaase :confused:

Reply 384

Original post by pearlover

i dont understand what is meant by short tandem repeats in the introns? anyone help pleaaaaaaaaaaaaase :confused:

Introns - regions of a gene that do not code for a protein

Within these introns there are sequences of bases that are repeated several times. These are STRs. The length of the sequences and the times they are repeated vary depending on the individual.

It is these sequences that are used in DNA profiling

(from my memory so if I am wrong, feel free to correct me anyone)

Reply 385

Schoolio93

9

I just don't understand the immune system part - it's so compliacted. Any adivce on what we exactly need to know?

Do we need to know the structures of B-cells and T-cells and where they are produced?

Reply 386

Original post by Schoolio93

I just don't understand the immune system part - it's so compliacted. Any adivce on what we exactly need to know?

Do we need to know the structures of B-cells and T-cells and where they are produced?

It is VERY VERY complex. Since you're a future medic, I've heard immune system is arguably the hardest thing you learn in med school.

We just need to non-specific responses (inflammation etc etc.) and specific responses (T-cells, B-cells) and role of antigens and antibodies.

Doubt you need to know structure.
B-cells basically have antibodies and receptors on their surfaces. T cell have receptors.

Doubt you need to know this but:
B-cell produced in bone marrow

T-cell - produced in bone marrow, but mature in thymus.

Reply 387

Original post by InItToWinItGetIt?

Introns - regions of a gene that do not code for a protein

Within these introns there are sequences of bases that are repeated several times. These are STRs. The length of the sequences and the times they are repeated vary depending on the individual.

It is these sequences that are used in DNA profiling

(from my memory so if I am wrong, feel free to correct me anyone)

thank you so much! :smile:

another question though, is it just the introns then that are used in DNA profiling? what about the exons?

Reply 388

mobius323

10

Original post by pearlover

thank you so much! :smile:

another question though, is it just the introns then that are used in DNA profiling? what about the exons?

Exons would be cut out by restriction enzymes. Only introns are used in DNA profiling as the amount of variation of STR's between people is phenomenal.

Reply 389

Original post by pearlover

thank you so much! :smile:

another question though, is it just the introns then that are used in DNA profiling? what about the exons?

I'd be inclined to say no but I'm not sure.

The reason I would side towards no, is that exons code for proteins and we as humans have largely similar (if not the same) proteins in our bodies, so there wouldn't be much point in looking for similarities as most (if not all) will be similar.

Reply 390

mooniibuggy

14

Original post by Schoolio93

I just don't understand the immune system part - it's so compliacted. Any adivce on what we exactly need to know?

Do we need to know the structures of B-cells and T-cells and where they are produced?

This might help:

http://www.deberker.com/deberker/Bio_Revision_Aids_files/Immune.pdf

Reply 391

Original post by mooniibuggy

This might help:

http://www.deberker.com/deberker/Bio_Revision_Aids_files/Immune.pdf

That is a VERY nice way of summarising things. Thanks :biggrin:

*goes to print it*

Reply 392

Original post by InItToWinItGetIt?

I'd be inclined to say no but I'm not sure.

The reason I would side towards no, is that exons code for proteins and we as humans have largely similar (if not the same) proteins in our bodies, so there wouldn't be much point in looking for similarities as most (if not all) will be similar.

okai i get it thank you sooo much! u've been helping like everyone on this thread... wish you best of luck and hope u do really well.. m sure u will :tongue:

Reply 393

Original post by mobius323

Exons would be cut out by restriction enzymes. Only introns are used in DNA profiling as the amount of variation of STR's between people is phenomenal.

thanks soo much! that makes so much sense now! :biggrin:

good luck for ur exam

Reply 394

doobucks

16

Original post by InItToWinItGetIt?

I'd be inclined to say no but I'm not sure.

The reason I would side towards no, is that exons code for proteins and we as humans have largely similar (if not the same) proteins in our bodies, so there wouldn't be much point in looking for similarities as most (if not all) will be similar.

They use the introns only, they analyse short tandem repeats which are in the Introns.

Reply 395

Telford

hey, i just did a past paper and it asked for two examples of plant fibres! and i could have sworn that was unit 2, does that mean we can get asked questions on any unit?

Reply 396

Schoolio93

9

Original post by Telford

hey, i just did a past paper and it asked for two examples of plant fibres! and i could have sworn that was unit 2, does that mean we can get asked questions on any unit?

xylem and schlerenchyma or cellulose - yes we do need to know some stuff from unit 2, but only like 5 marks. So it's all about luck whether you get a q. you know or not.

Reply 397

Schoolio93

9

Original post by mooniibuggy

This might help:

http://www.deberker.com/deberker/Bio_Revision_Aids_files/Immune.pdf

thank you so much!! But isn't the info too simple? What about MHC APC complexes, C4 receptors ???

Reply 398