Endocrinology+Immunity questions.....

[sps27]

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I will tell the ans later. This is TBR btw, passage 13 page 315 book 1 on physiology. Let everybody have a crack at it first. Some may already know this.

Question 1)

In cell # 1, the addition of bivalent anti-insulin receptor antibodies induces a response without the addition of insulin. In cell #2, addition of a fragment anti-receptor antibody (monovalent) induces no response without insulin. To cell # 2, antibodies against the monovalent anti-receptor antibodies are added. This will result in.....

a) no response
b) decreased glucose uptake
c) increased CO2 production
d) Increased insulin binding

Have way too many questions on this one. Anti-insulin receptor? Is it the same as glucagon receptor? Antibody to an anti-receptor? Is the receptor an antibody shaped entity? Why would Insulin matter if it is anti-insulin receptor? Also wondering about the terms 'monovalent', 'bivalent', 'cross linking' for antibodies? The typical diagram for antibody is a familiar Y structure. We know of 5 or 6 common antibodies like IgG, IgA, IgE, IgM, IgD. So which of these is bivalent, multivalent, monovalent? Also it seems an antigen can have multiple binding sites for antibodies and vice versa as well. Does anybody have a good link on all of this?


Question 2)

Through genetic manipulations, the insulin binding region of the Insulin receptor(IR) was fused with the kinase region of the epidermal growth factor (EGF) receptor (also a ligand activated kinase). The resulting hybrid receptor was transfected into a cell and the addition of insulin resulted in a functional EGF kinase. From this experiment, it can be concluded that IR and EGF have similar

a) ligand binding regions
b) signal transduction mechanisms
c) secondary messenger cascades
d) effects on carbohydrate, fat and protein metabolism.


So I thought they both have similar secondary messenger cascades but that can't be true since the effect of Insulin is not the same as EGF. The metabolism is a distraction here. I have not heard of growth factors being used in metabolism. Also Insulin is for glucose uptake, not fat or protein. These receptors are both tyrosine kinase activity driven. Are most peptide receptors tyrosine kinase driven? Not sure about signal transduction. I thought signaling is for translation of proteins, for attachment of ribosome+mRNA complex to ER. So I guess I need to read more on this. Does anybody have a good link on this stuff? (I have read TBR).


I wanted to know your thinking on these two questions. Like how you address questions like this. It seems more knowledge based so if you have links, resources with more info on this, please pass it on. Thanks!

 

[Jkh389]

Hi,

I didn't quite use TBR for biology because I had heard it wasn't as great as EK. With that said, I think TBR tries to "trick" or stump you by making a simple problem overly complicated.

#1 In this question, it basically tells you several things. Cell #1 produces an insulin response in the absence of insulin.. Cell #2 produces no insulin response in the absence of insulin. The difference between the two cells is that the first cell is bivalent, meaning it can "bind" with itself and cell 2 is monovalent, which will not in essence. So, when you add an anti antibody that binds with the monovalent, you are in turn making the cell look like Cell #1, which induces an insulin like response. That response is to take up glucose and the product of glucose metabolism is CO2 and H2O.

#2 in this question you should simplify it and read it as a hybrid receptor produces EGF response with the ligand. So, you can infer that this has to do with the messaging system which makes you zero in on A, B, or C. You can cross out A because they it is a hybridized receptor that was fused into the kinase region of EGF. So between B and C, we know that C is part of the signal transduction pathway. What the question doesn't mention though much effect about the insulin response, therefore, we do not know the specifics enough to choose C, which tends to be more downstream in the signal transduction mechanism for us to choose it.

 

[sps27]

Hi,

I didn't quite use TBR for biology because I had heard it wasn't as great as EK. With that said, I think TBR tries to "trick" or stump you by making a simple problem overly complicated.

#1 In this question, it basically tells you several things. Cell #1 produces an insulin response in the absence of insulin.. Cell #2 produces no insulin response in the absence of insulin. The difference between the two cells is that the first cell is bivalent, meaning it can "bind" with itself and cell 2 is monovalent, which will not in essence. So, when you add an anti antibody that binds with the monovalent, you are in turn making the cell look like Cell #1, which induces an insulin like response. That response is to take up glucose and the product of glucose metabolism is CO2 and H2O.

#2 in this question you should simplify it and read it as a hybrid receptor produces EGF response with the ligand. So, you can infer that this has to do with the messaging system which makes you zero in on A, B, or C. You can cross out A because they it is a hybridized receptor that was fused into the kinase region of EGF. So between B and C, we know that C is part of the signal transduction pathway. What the question doesn't mention though much effect about the insulin response, therefore, we do not know the specifics enough to choose C, which tends to be more downstream in the signal transduction mechanism for us to choose it.

Awesome! you are right on both counts. Question 1 is c) and question 2 is b). As you suggested, I will read the relevant chapters from EK bio. Hopefully it will make more sense then. You have used the term 'bivalent' cell i.e., a cell binding on to itself. I did not get that. Did you mean two copies of a cell with antibody of one copy binding a receptor on another? But how would an antibody, binding to a anti-insulin receptor, trigger an insulin response. Would you not need insulin, or something like insulin sitting on an insulin receptor to trigger an insulin response?

 

[Jkh389]

What I did for biology was I used examkrackers to study the material and their supplemental test questions. Once I was done with EK, I spent maybe two days reading the TBR sections for a little more thorough comprehension. I was basically supplementing the TBR as a reinforcer for the things I learned in EK. The extra knowledge material provided by the TBR I opted to not learn, such as all the little minute details involved in carbohydrates and glucose metabolism.

For bivalent & multivalent, what I mean is that it has the ability to bind two antigens. This will allow it to cross-link or a cluster into a mass. With a monovalent molecule, you cannot cross-link because there is only one binding location. However, when you add an antibody it will bind with one monovalent, but also have another site with which it can bind another monovalent receptor so that it can cross-link. It's basically making it look bivalent as cell #1 is.

 

[sps27]

What I did for biology was I used examkrackers to study the material and their supplemental test questions. Once I was done with EK, I spent maybe two days reading the TBR sections for a little more thorough comprehension. I was basically supplementing the TBR as a reinforcer for the things I learned in EK. The extra knowledge material provided by the TBR I opted to not learn, such as all the little minute details involved in carbohydrates and glucose metabolism.

For bivalent & multivalent, what I mean is that it has the ability to bind two antigens. This will allow it to cross-link or a cluster into a mass. With a monovalent molecule, you cannot cross-link because there is only one binding location. However, when you add an antibody it will bind with one monovalent, but also have another site with which it can bind another monovalent receptor so that it can cross-link. It's basically making it look bivalent as cell #1 is.

Gotcha. That makes a lot more sense. I was missing the cross linking piece of information and the monovalent / bivalent distinction. Thank you.

 

[Jkh389]

No problem. Feel free to PM me any more questions you have. I'm a bit better with physical sciences and organic than biology, but will try to help anyway I can!

 

[sps27]

No problem. Feel free to PM me any more questions you have. I'm a bit better with physical sciences and organic than biology, but will try to help anyway I can!

Thanks Jkh389. I am glad there is one person in the forum still available to answer questions....ha ha....most I think are busy enjoying their time off from mcat, and why not. I would do the same, if I was done with mcat........

 

[mcloaf]

Hi,

I didn't quite use TBR for biology because I had heard it wasn't as great as EK. With that said, I think TBR tries to "trick" or stump you by making a simple problem overly complicated.

#1 In this question, it basically tells you several things. Cell #1 produces an insulin response in the absence of insulin.. Cell #2 produces no insulin response in the absence of insulin. The difference between the two cells is that the first cell is bivalent, meaning it can "bind" with itself and cell 2 is monovalent, which will not in essence. So, when you add an anti antibody that binds with the monovalent, you are in turn making the cell look like Cell #1, which induces an insulin like response. That response is to take up glucose and the product of glucose metabolism is CO2 and H2O.

#2 in this question you should simplify it and read it as a hybrid receptor produces EGF response with the ligand. So, you can infer that this has to do with the messaging system which makes you zero in on A, B, or C. You can cross out A because they it is a hybridized receptor that was fused into the kinase region of EGF. So between B and C, we know that C is part of the signal transduction pathway. What the question doesn't mention though much effect about the insulin response, therefore, we do not know the specifics enough to choose C, which tends to be more downstream in the signal transduction mechanism for us to choose it.

What I did for biology was I used examkrackers to study the material and their supplemental test questions. Once I was done with EK, I spent maybe two days reading the TBR sections for a little more thorough comprehension. I was basically supplementing the TBR as a reinforcer for the things I learned in EK. The extra knowledge material provided by the TBR I opted to not learn, such as all the little minute details involved in carbohydrates and glucose metabolism.

For bivalent & multivalent, what I mean is that it has the ability to bind two antigens. This will allow it to cross-link or a cluster into a mass. With a monovalent molecule, you cannot cross-link because there is only one binding location. However, when you add an antibody it will bind with one monovalent, but also have another site with which it can bind another monovalent receptor so that it can cross-link. It's basically making it look bivalent as cell #1 is.

Just wanted to chime in and clear something up here.

As far as we know, the cells in experiment 1 and experiment 2 are the same. It is the antibodies being added that are bivalent and monovalent, respectively.

What experiments 1 and 2 show us is that dimerization of the insulin receptor will activate the insulin signaling cascade even in the absence of insulin. In the presence of a monovalent antibody, which cannot bind two receptors at once and bring them into contact with one another, we don't get a response. However, adding the other bivalent antibody which can bind to two tails of monovalent antibody to bring them together (and thus bring together the receptors to which the movovalent antibodies are bound) will again activate the signaling cascade.

Biologically this question is a little off since the insulin receptor actually exists as a dimer already via disulfide linkages, but that's sort of beyond the scope of this question.

 

[drechie]

can someone clarify why in the #2, the reasoning process used to cross out A? (Ligand binding regions answer)

 

[shefv]

Hi,

I didn't quite use TBR for biology because I had heard it wasn't as great as EK. With that said, I think TBR tries to "trick" or stump you by making a simple problem overly complicated.

#1 In this question, it basically tells you several things. Cell #1 produces an insulin response in the absence of insulin.. Cell #2 produces no insulin response in the absence of insulin. The difference between the two cells is that the first cell is bivalent, meaning it can "bind" with itself and cell 2 is monovalent, which will not in essence. So, when you add an anti antibody that binds with the monovalent, you are in turn making the cell look like Cell #1, which induces an insulin like response. That response is to take up glucose and the product of glucose metabolism is CO2 and H2O.

#2 in this question you should simplify it and read it as a hybrid receptor produces EGF response with the ligand. So, you can infer that this has to do with the messaging system which makes you zero in on A, B, or C. You can cross out A because they it is a hybridized receptor that was fused into the kinase region of EGF. So between B and C, we know that C is part of the signal transduction pathway. What the question doesn't mention though much effect about the insulin response, therefore, we do not know the specifics enough to choose C, which tends to be more downstream in the signal transduction mechanism for us to choose it.

I am confused about Q1 - how does adding the antibody to cell 2 make it more like cell 1?