Biology Unit 3 Questions Megathread

[Keo]

Quaternary structures = two or more polypeptide chains

What are the lymphocytes that undergo clonal expansion/selection theory?
is it B cells and helper T cells
or
B cells, helper T cells and cytotoxic T cells?

B-cells undergo clonal expansion; this then produces plasma cells and b-memory cells. These plasma cells produce antibodies specifically for the presented antigen

[amun]

 OKay guys how much of  parasympathetic and sympathetic do we need to know

[Lesliel1]

the electrons are from the Hydrogen ions. Ions have protons and then electrons orbiting around nucleus.

what whoaaa? LOL which molecules are carrying the electrons? and the hydrogen ions cant have a electron orbiting around them because the hydrogen ions being carried are positive so the carry molecules are only carrying protons... D=?

[liuetenant]

the electrons are from the Hydrogen ions. Ions have protons and then electrons orbiting around nucleus.

what whoaaa? LOL which molecules are carrying the electrons? and the hydrogen ions cant have a electron orbiting around them because the hydrogen ions being carried are positive so the carry molecules are only carrying protons... D=?

i think the electrons are released when the hydrogen ions are split from the electron carriers, since now there is no pairing ofthe ions with the carriers to hold onto the electrons...as a result, those electrons will kind of be free to roam....but yes, hydrogen ions are not electrons coz they dnt have that electron!

also, is tissue rejection done by t cells only? no humoral response?

[lexitu]

On tissue rejection (from something I've posted elsewhere)

Transplants are pretty interesting. Even though it is not the person's self-MHC I proteins that exist on the transplanted tissue cell surfaces, sometimes cytotoxic T cells are able to bind to the MHC I proteins and the foreign antigens that they are displaying and "kill" the cell in the same way that they would if it was the person's own body cell that was infected. Here's a chunk from my uni textbook:

Before the onslaught can begin, the cytotoxic T cell must "dock" on the target cell by binding to a self-nonself complex. Remember, all body cells dis- play class I MHC antigens, so all infected or abnormal body cells can be destroyed by these T cells. The attack on foreign human cells, such as those of a graft, is more difficult to explain because here all of the antigens are nonself. However, apparently the Tc cells sometimes "see" the foreign class I MHC antigens as a combination of self class I MHC protein bound to foreign antigen. Once· cytotoxic T cells recognize their targets, there are two major mechanisms by which they can deliver a lethal hit.

So as you can see, T cells are pretty important - both cytoxic, and T helper (which are needed for activation). Also important are NK cells, phagocytes, and antibodies (so B cells). Both humoral and cell-mediated responses are important.

----

And guys, let's not let Chemistry override Biology

[lexitu]

OKay guys how much of  parasympathetic and sympathetic do we need to know

Basic level stuff, unlikely it would come up, but definitely possible.

[Kaille]

dumb question but can bacteria like yersinia pestis (black death) be tramsmitted by sharing needles with contaminated blood?

[lexitu]

Don't know about that particular bacterium but yes of course, generally. If it inhabits the blood then don't see why not.

[liuetenant]

uh oh, what's the effector part of a stimulus-response model again? just clarifiying, it's the target organ, not the hormone or signal because they're just the signalling molecules? therefore, in the case of say glucose regulation, the effector is the pancreas?  which then effects liver cells to do its stuff?

[HERculina]

On tissue rejection (from something I've posted elsewhere)

Transplants are pretty interesting. Even though it is not the person's self-MHC I proteins that exist on the transplanted tissue cell surfaces, sometimes cytotoxic T cells are able to bind to the MHC I proteins and the foreign antigens that they are displaying and "kill" the cell in the same way that they would if it was the person's own body cell that was infected. Here's a chunk from my uni textbook:

Before the onslaught can begin, the cytotoxic T cell must "dock" on the target cell by binding to a self-nonself complex. Remember, all body cells dis- play class I MHC antigens, so all infected or abnormal body cells can be destroyed by these T cells. The attack on foreign human cells, such as those of a graft, is more difficult to explain because here all of the antigens are nonself. However, apparently the Tc cells sometimes "see" the foreign class I MHC antigens as a combination of self class I MHC protein bound to foreign antigen. Once· cytotoxic T cells recognize their targets, there are two major mechanisms by which they can deliver a lethal hit.

So as you can see, T cells are pretty important - both cytoxic, and T helper (which are needed for activation). Also important are NK cells, phagocytes, and antibodies (so B cells). Both humoral and cell-mediated responses are important.

----

And guys, let's not let Chemistry override Biology

Do 2nd line of defence always fail in organ tranplants? 

[lexitu]

What do you mean by fail? :S Both the second and third line work together to remove the transplant. It's a long process...

[HERculina]

hm well

However, apparently the Tc cells sometimes "see" the foreign class I MHC antigens as a combination of self class I MHC protein bound to foreign antigen. Once· cytotoxic T cells recognize their targets, there are two major mechanisms by which they can deliver a lethal hit.

as well as doing the above, do the cytotoxic T cells bind to antigen fragments presented on a phagocyte in second line of defence like normal immune responses?

[lexitu]

Ah okay, I see what you mean Cytotoxic T cells (in all immune responses) bind to MHC I proteins and the antigens they present so this usually means normal body cells not part of the immune system.

Helper T cells bind to class II MHC proteins that display foreign antigens - these antigens have been engulfed and then presented on the MHC II markers

Cytotoxic T cells bind to class I MHC proteins that display foreign antigens - these antigens are being produced inside the cell


Does that help?

[Russ]

The only time a cytotoxic T cell will bind a macrophage is to destroy it, if it's infected.

[WhoTookMyUsername]

does the blood regulatory pathway have a 'control center' per se?