Question

Cholesterol present in LDL (low-density lipoproteins) A. binds to a cell receptor and diffuses across the cell membrane. B. when it enters a cell, suppresses activity of ACAT (acyl CoAcholesterol acyl transferase). C. once in the cell, is converted to cholesteryl esters by LCAT (lecithin- cholesterol acyl transferase). D. once it has accumulated in the cell, inhibits replenishment of LDL receptors. E. represents primarily cholesterol that is being removed from peripheral cells.

Short answer

C. Is cholesterol converted to cholesteryl esters by LCAT (lecithin-cholesterol acyl transferase) once in the cell? D. Does accumulated cholesterol in the cell inhibit the replenishment of LDL receptors? E. Does LDL cholesterol primarily represent cholesterol that is being removed from peripheral cells?

Step-by-step solution

A. binds to a cell receptor and diffuses across the cell membrane.

This statement is true. Cholesterol from LDL particles binds to the LDL receptor on the cell membrane, and then the LDL particle is internalized by the cell via a process called endocytosis, which results in the release of cholesterol into the cell. #Step 2: Read the second statement#

B. when it enters a cell, suppresses activity of ACAT (acyl CoAcholesterol acyl transferase).

This statement is true. When cholesterol enters a cell, it suppresses the activity of the enzyme ACAT, which is responsible for the formation of cholesteryl esters. This is because an increase in intracellular cholesterol levels leads to downregulation of ACAT activity, which serves to prevent excessive cholesterol accumulation within the cell. #Step 3: Read the third statement#

C. once in the cell, is converted to cholesteryl esters by LCAT (lecithin-cholesterol acyl transferase).

This statement is false. LCAT is an enzyme that is responsible for converting free cholesterol into cholesteryl esters in the blood, not inside the cell. ACAT is the enzyme that carries out this conversion within the cell. #Step 4: Read the fourth statement#

D. once it has accumulated in the cell, inhibits replenishment of LDL receptors.

This statement is true. After cholesterol accumulates in the cell, it regulates the expression of LDL receptors, leading to a decrease in the number of these receptors on the cell surface. This reduces the ability of the cell to take up additional LDL cholesterol from the bloodstream. #Step 5: Read the fifth statement#

E. represents primarily cholesterol that is being removed from peripheral cells.

This statement is false. LDL cholesterol is primarily responsible for delivering cholesterol to peripheral cells. It is HDL (high-density lipoprotein) cholesterol that is primarily responsible for removing cholesterol from peripheral cells and transporting it back to the liver for excretion or recycling.