TBR lipid question

[ilovemedi]

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Am I wrong to think that there can be two correct answers in the TBR lipid chapter?

Modified Question: Elevated levels of cholesterol in the blood serum can lead to plaque deposits causing atherosclerosis. This disease reduces the diameter of the blood vessels and leads to adverse clinical conditions. Atherosclerosis results from:

A)removal of excess cholesterol form cellular lipid bilayers
B) Insolubuliity of cholesterol in water.

answer: B

I picked "A" because it seemed that it would explain the increased cholesterol in the blood, causing Atherosclerosis. B seemed true too, but not the real reason for me, as it's more of a characteristic of cholesterol. The answer states that there is no known mechanism where A could occur, even though theoretically, if it does, it's true. How do you approach these questions? It's like a grey area..

 

[image187]

Atherosclerosis is basically a whole inflammatory process starting with cholesterol in the blood getting stuck in the walls of arteries. It involves a bunch of immune and other cells, and ends with remodeled small muscle cells, artery cells, and other cells jammed up in the artery wall constricting its lumen. The blood cholesterol that is responsible for this is found in something called LDL (or low-density lipoprotein) which is basically a package of proteins and other molecules formed around the cholesterol with hydrophobic end in and hydrophilic ends out in order to transport the hydrophobic fat in the hydrophilic blood. The cholesterol needs to be transported in a lipoprotein in order to be moved around the body, and if it were soluble in the blood none of this atherosclerosis stuff would ever happen.

The books is right about removal of excess cholesterol from cell membranes. The membrane can basically maintained by being sucked back into the cell in vacuoles, remodeled, and then put back on a continuous basis.

 

[ilovemedi]

Okay, so I should just go with the answer that is always true? A, I guess, isn't always (or in this case) never happens in "real life"

 

[image187]

Okay, so I should just go with the answer that is always true? A, I guess, isn't always (or in this case) never happens in "real life"

yeah, these things are tricky sometimes. Definitely always go with whatever is always true, or go with the "best" answer even if some others are theoretically possible in your mind. You just have to learn how to do these certain types of questions, just takes practice. It's all a game

 

[Balantidiumcoli]

Okay, so I should just go with the answer that is always true?

Yep

Also, think of the fluid mosaic model. Cholesterol is a lipid and when lipids get stuck in the hydrophobic region of the membrane it is energetically unfavorable for them to escape. Also, if you think about how extracellular proteins are constructed of hydrophobic and hydrophobic ends with trans membrane proteins requiring a hydrophobic center to interact with the cytosol and not the intermembrane space you realize there aren't many realistic mechanisms designed to transport lipids *out* of the membrane space (in fact, when these lipids are modified within host cells they're still stuck in the membrane and simply form a vacuole).

 

[ilovemedi]

Thanks for the responses, everyone! Got it!