Question

Many pathological hyperlipoproteinemias result from abnormalitics in the rates of synthesis or clearance of lipoproteins in the blood. They are usually characterized by elevated levels of cholesterol and/or triacylglycerols in the blood. Type I has very high plasma triacylglycerol levels \((>1000 \mathrm{g} / \mathrm{dL})\) because of an accumulation of chylomicrons. Type II (familial hypercholesterolemia) has elevated cholesterol, specifically in the form of LDL. Another abnormality of lipoproteins is hypolipoproteinemia in which lipoproteins are not formed because of the inability to make a particular apoprotein. In abecalipoproteinemia chylomicrons, VLDL and LDL are absent from the blood. Which of the following is correct? A. In this discase, no apolipoproteins are synthesized. B. If the blood from these individuals were centrifuged, the lipid bands would be found primarily in the upper half of the tube. C. Failure to synthesize apolipoprotein ApoB-100 and ApoB-48 would account for the pattern shown in this disease. D. Apolipoproteins are composed mostly of \(\beta\) structure. E. All of the above.

Short answer

Answer: C. Failure to synthesize apolipoprotein ApoB-100 and ApoB-48 would account for the pattern shown in this disease.

Step-by-step solution

A. In this disease, no apolipoproteins are synthesized.

This statement is not correct. In abecalipoproteinemia, some apolipoproteins are still synthesized, just not the specific ones needed to form chylomicrons, VLDL, and LDL. Specifically, ApoB-48 and ApoB-100 are the ones not being synthesized in this disease. #Step 2: Analyzing Statement B#

B. If the blood from these individuals were centrifuged, the lipid bands would be found primarily in the upper half of the tube.

This statement is correct. When the blood is centrifuged, lipids, which are less dense than other blood components, will tend to rise and form a layer at the top of the tube. Because patients with abecalipoproteinemia lack chylomicrons, VLDL, and LDL, their lipid bands will primarily be found in the upper half of the tube. #Step 3: Analyzing Statement C#

C. Failure to synthesize apolipoprotein ApoB-100 and ApoB-48 would account for the pattern shown in this disease.

This statement is correct. ApoB-48 and ApoB-100 are essential for the formation of chylomicrons, VLDL, and LDL. Therefore, a failure to synthesize these two key apolipoproteins would result in abecalipoproteinemia, where chylomicrons, VLDL, and LDL are absent from the blood. #Step 4: Analyzing Statement D#

D. Apolipoproteins are composed mostly of \(\beta\) structure.

This statement is not correct. Apolipoproteins are proteins that bind lipids to form lipoproteins and are primarily composed of \(\alpha\)-helices, not \(\beta\) structures. #Step 5: Analyzing Statement E#

E. All of the above.

As we have seen, not all of the above statements are correct. Thus, this statement is also incorrect. #Conclusion# Based on our analysis of each statement, the correct answer is: C. Failure to synthesize apolipoprotein ApoB-100 and ApoB-48 would account for the pattern shown in this disease.