biology

Hi again young man,
@chem222


As advised B4, THINK THINK THINK! (not your fault that you do not do this; it is the way the world has gone in the new millenium partly cos of computerization of life ("look who is talking", he says! [I have an MSc in CS, too]).

OK back to Q:

This should be your line of thought:
1. If avoiding gluten in diet can still lead to persistence of symptoms, what does it mean? (Ok you probs know, that it is NOT just wheat that contains gluten (the substance that has a part called gliadin [plus another called reticulin]), but also so do barley, oats and rye) BUT THAT CANNOT EXPLAIN the symptoms WITHOUT GLUTEN [because gluten-free diet means avoiding wheat AND barley/oats/rye, too, yeah? - still with me?. Therefore, the antibody that is leading to the symptoms (by causing inflammation in the intestines) might also be produced in response to some other antigen (apart from gluten). Ok, we are coming closer to the answer, agreed?

Let us take it step by step: if an antibody is reacting against more than one antigen (perhaps an antigen "class", so to speak), what does that tell us? ..................................................................THINK!.............................................................YES, well done!........................................................................................................................................ getting there, slowly but surely!....................................

a) antibody is less specific
b) Ab might have more than one binding site for Ag (ANSWERS)

(NOT NEEDED FOR A Level just for extra knowledge:- (I am cheating cos I know this from medicine!) - there are five main classes of antibodies (no need to learn at A level but they are : IgA, IgD, IgG, IgE and IgM [Ig stands for immunoglobulin [also called gamma-globulin] and globulins are a part of blood proteins] and the main one in coeliac disease is IgM [large Ab] which has up to 10 binding sites for antigen [Ag], each with a slightly different amino acid sequence.)

2. (What Ab binds to)

Thought process: it/they must bind to some part of the digestive tract [you may not know, but one of the main symptoms is diarrhoea due to malabsorption [failure to absorb essential nutrients from food], so what can we say for the answer? Ok this is an unfair Q actually, BUT AS ALWAYS, KEEP IT SIMPLE!

a) binding to gliadin might lead to some side-effect in the gut
b) it might bind to a part of the intestine (endothelium, muscle layer, villi - cannot tell from info given)
(ANSWERS)

DETAILED INFO (outside A level syllabus - (just to understand - don't worry if you cannot remember!):
i) there are so-called anti-endomysial [endo] antibodies that are measured to diagnose coeliac disease
ii) the major symptoms of coeliac disease are mediated by antigen-presenting cells and might be cell-mediated (involving macrophages [one type of white cell (leucocyte Greek leuco = white; cytos = cell) that can act as a phagocyte [Greek phagis = to engulf; cytos = cell as b4)

ITEMS IN ITALICS are advanced though might help those aiming for A*

M (specialist biology tutor)