Question

1- The cytoplasmic side of the plasma membrane’s lipid bilayer have high concentrations of (CHOOSE THREE):

a. Sphingomyelin

b. Phosphatidylethanolamine

c. Phosphatidylcholine

d. Phosphatidylinositol

e. Phosphatidylserine

f. Glycolipid

2- Which of the following characteristics DOES NOT keep proteins secured to the plasma membrane?

a. Transmembrane domains in the protein

b. Glycosylphosphatidylinositol (GPI) anchors

c. Fatty acid lipids covalently attached to the protein

d. Sugar molecules covalently attached to the protein

e. Associations with lipid rafts

3- Which of the following statements about the plasma membrane’s electrochemical gradient is TRUE?

a. Ion channels remain permanently open in order to maintain the gradient

b. The functions of nerve cells and muscle cells have nothing to do with the electrochemical gradient

c. At resting state, there is a higher concentration of sodium ions outside the cell than inside the cell

d. At resting state, there is a higher concentration of potassium ions outside the cell than inside the cell

e. The resting electric potential is positively charged inside the cell compared to the outside of the cell

Answer 1

1. The cytoplasmic side of the plasma membrane’s lipid bilayer have high concentrations of phospholipids: phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol. So the 3 options would be b,d and e.
2. Sugar molecules when covalently attached to the protein, this association leads to the process of Glycosylation, that makes the proteins unstable. So the answer should be d.
3. At resting stage, the ion channel remains closed. The Na+ ions concentration outside the cells remains high due to low permeability of cell membrane towards Na+ ions. So the answer should be c.