[Campbell Biology P.987] According to the introductory text, which of the following statemen... | Practice Question

According to the introductory text, which of the following statements regarding the PCSK9 enzyme and its effect on LDL cholesterol is INCORRECT?

  • A: PCSK9 is a liver enzyme.
  • B: Mutations that increase the activity of PCSK9 are known to increase LDL cholesterol levels.
  • C: Inactivating mutations in PCSK9 are hypothesized to lower LDL cholesterol levels.
  • D: PCSK9 activity generally helps to reduce the level of LDL cholesterol in the blood.
  • E: The study involved individuals with one copy of the PCSK9 gene inactivated.

Explanation

The text states: 'Because mutations that increase the activity of PCSK9 are known to increase the level of LDL cholesterol in the blood, the researchers hypothesized that inactivating mutations in this gene would lower the LDL level.' This implies that PCSK9's normal activity or increased activity increases LDL, not lowers it. Therefore, the statement that PCSK9 activity generally helps to reduce LDL is incorrect.