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Edexcel 6BIO2 ~ 3rd June 2013 ~ AS Biology

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Reply 580

jooh_23

could someone explain polygenic/monohybrid inheritance/ locus things/ continuous variation pleeeaaase :smile:

?

all a blur to me :?

Reply 581

Rubyturner94

Original post by jooh_23

could someone explain polygenic/monohybrid inheritance/ locus things/ continuous variation pleeeaaase :smile:

?

all a blur to me :?

polygenic inheritance- some characteristics show continuous variation such as height, this is because they are controlled by genes at many loci.
locus/loci- is the possition of a gene on a chromosome.
such characterisitics are also effected by environmental factors.
And some characteristics show discontinouos variation, they are controlled by genes at a single loci and the environment has little or know effect on it. such as blood group.
hope i helped, i dont like this topic much.
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Reply 582

Baa

Hi, I just wanted to ask do we need to know any specific examples of endemic species?? Thanks :smile:

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Reply 583

jooh_23

Original post by Rubyturner94

thank you!!! x :smile:

in the snab book its in a huge block of text, makes no sense at all

Reply 584

Rubyturner94

can someone give me all the points on zoos please? like a model answer?

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Reply 585

newyork newyork

Original post by StephenNaulls

- A polypeptide chain is synthesised in a ribosome when peptide bonds are formed between many amino acid monomers; the ribosome is attached to the cisternae of the rER.
- The polypeptide chain moves into the cisternal space of the rER, where it undergoes further processing in order to achiever a tertiary structure.
-The rER packages the protein into a vesicle.
- The vesicle fuses with the cis-face of the Golgi apparatus, thus causing the protein to enter the cisternal space.
- In the cisernal space, carbohydrate chains are added/trimmed in order to create a glycoprotein, for example, which creates a quaternary structure (not all proteins do this).
- The Golgi apparatus packages the glycoprotein into a vesicle at the trans-face.
- The vesicle fuses with the phospholipid bilayer; secreting the protein via exocytosis.

So they are involved in the processing and packaging of proteins- complex proteins could not be created without them.

Hope that helped :smile:

thank you

Reply 586

anonymouspie227

Original post by The Assassin

, my notes are awesome.

I know they are! (you didn't write that in the quote :tongue:

)
I spotted something in the notes...
In the table of starch and cellulose it said starch had h bonds with h20 hence soluble... :tongue:

(you've probably corrected since then but I downloaded the first version)
Anyway, how's revision going?

Reply 587

fadyfox95

gguys what is a totipotent and pluri potent cell.please provide the most info u can give.

Reply 588

username1054067

Original post by fadyfox95

gguys what is a totipotent and pluri potent cell.please provide the most info u can give.

Totipotent - can basically give rise to all cell types

Pluripotent - Can give rise to most except embryonic cells.

Reply 589

username1054067

Can someone he;p with this please?

Graph with Q:

Question:

Answer:

- why is it that though? I thought it was 5. is it a specific thing we need to know? then why does it say using the graph? :s-smilie:

Reply 590

fadyfox95

Original post by yarshad

Totipotent - can basically give rise to all cell types

Pluripotent - Can give rise to most except embryonic cells.

thanks, but I know that what I wanted to know which one has switched off and on genes, this stuff dude.

Reply 591

billyfisher100

Original post by yarshad

Can someone he;p with this please?

Graph with Q:

Question:

Answer:

- why is it that though? I thought it was 5. is it a specific thing we need to know? then why does it say using the graph? :s-smilie:

It's just graph skills and knowledge of interphase. Basically, it's the point from when the DNA begins to increase to where it finishes increasing which is about 3.75.

Reply 592

Rubyturner94

Original post by yarshad

Can someone he;p with this please?

Graph with Q:

Question:

Answer:

- why is it that though? I thought it was 5. is it a specific thing we need to know? then why does it say using the graph? :s-smilie:

the S phase is when the DNA content has DOUBLED, the x axis states the amount of DNA. at 7.5 it is constant, from 7.5 to 10 it is rising and at 10 it has doubled. therefore the time taken is 3.5.

Reply 593

Rubyturner94

Original post by fadyfox95

thanks, but I know that what I wanted to know which one has switched off and on genes, this stuff dude.

they both have genes switched on, but totipotent has all genes switched on, and pluripotet has some but not all.
correct me if i am wrong.

Reply 594

Phteven

Original post by fadyfox95

thanks, but I know that what I wanted to know which one has switched off and on genes, this stuff dude.

If a totipotent stem cell can become any kind of cell, surely you can safely assume for yourself that it has no genes switched off?

Conversely, pluripotent stem cells has some inactive genes. The presence of a chemical may cause some to become active/inactive also; this means that a different mRNA strand is transcribed, as the base sequence that determines the mRNA strand has changed. As a result, a different protein is synthesised. Since proteins determine the structure of the cell and control it's actions, the cell begins to change in order to carry out a specific function. The presence of the proteins causes more proteins to be made which furthers this effect; the cell has differentiated, or became specialised and this process is difficult to reverse.

Was that the sort of thing you were looking for? :smile:

(edited 10 years ago)

Reply 595

anonymouspie227

Original post by fadyfox95

gguys what is a totipotent and pluri potent cell.please provide the most info u can give.

1)Stem cells are unspecialised cells that can differentiate into any cell type.
In stem cells (totipotent) they have all the same genes but not all are expressed because not all are on/ active, hence ability to differentiate.
2)Under the correct conditions certain genes are activated others are inactivated (implying all are on in totipotent, my bad) and thus the whole protein synthesis process happens.
3) MRNA is transcribed from the active gene at DNA, then transported out nuclear membrane to ribosome for translation of protein.(from active gene)
4)The protein made determines cel structure and cell processes, including, which genes are switched on or off. And it's these changes that cause the cell to specialise and differentiate.

A totipotent stem cell has the ability to differentiate into any cell type including extra embryonic cells e.g placenta and umbillical cord cells, whilst pluripotent can differentiate into any cell but the extra embryonic. Adult bone marrow stem cells are limited in their
differentiation capabilities, whilst early foetus stem cells are totipotent...
There's ethical issues surrounding the use of embryo stem cells, the embryo was viable, and also the idea it's a genetically unique individual thus has a right to life from fertilisation( depends on where life starts to some)

Ermm, then theres some that feel that unfertilised embryos can be used as they're not viable (can't make a fetus) and only survive a few days, but they can't develop into all sorts
of specialised cells.

Erm, use the assassins notes, they're pretty good and the CGP revision guide for more!
Hope that helps! Sorry if any mistakes or typos *tell me where if I have, gotta fix it :tongue:

*

Right finally dig it,
Toti - all on

(edited 10 years ago)

Reply 596

username1054067

Original post by billyfisher100

It's just graph skills and knowledge of interphase. Basically, it's the point from when the DNA begins to increase to where it finishes increasing which is about 3.75.

So confused. DNA begins to increase? that's after 5 hours isn't it? :L it finishes increasing at 10 hours

Original post by Rubyturner94

the S phase is when the DNA content has DOUBLED, the x axis states the amount of DNA. at 7.5 it is constant, from 7.5 to 10 it is rising and at 10 it has doubled. therefore the time taken is 3.5.

?????? the X axis states the time in hours? :L

What???
7.5??

Reply 597

username1054067

Original post by fadyfox95

thanks, but I know that what I wanted to know which one has switched off and on genes, this stuff dude.

Totipotent, all genes switched on...

Pluripotent - less are switched on..

I'm guessing lol

Reply 598

Phteven

Original post by anonymouspie227

Stem cells become specialised because different genes are switched on.
If this is the case, then wouldnt all the genes be off in totipotent as it can specialise into any cell type? Whilst pluripotent a few?

Edit: I think I'm wrong lol, ignore me.

Scroll up to my explanation. It's because genes are transcribed to create proteins, which alter the shape, and, as a result, function of the cell. If no genes were turned on no proteins would be made- therefore the cell couldn't differentiate as proteins are what causes this to occur!

Do you get why now?