Cell Biology Multiple Choice Questions on “Cellular Membranes – Structure and Function of Membrane Proteins”.
1. Which of the following is covalently attached to a lipid molecule in cell membrane?
A. Integral protein
B. Transmembrane protein
C. Peripheral protein
D. Lipid-anchored protein
Answer: D
Clarification: Lipid-anchored proteins are located outside the lipid bilayer on either the extracellular or cytoplasmic surface. They are covalently linked to lipid molecules in the cell membrane. Peripheral proteins are associated to the cell membrane surface by non-covalent bonds.
2. Integral proteins are also known as ____________
A. Intrinsic proteins
B. Glycosylated proteins
C. Transmembrane proteins
D. Bilayer proteins
Answer: C
Clarification: Integral proteins are also known as transmembrane proteins as they pass entirely through the lipid bilayer. Transmembrane proteins have domains that protrude both from extracellular side and cytoplasmic side of the cell membrane.
3. The concept of transmembrane proteins was obtained from the results of which technique?
A. Freeze-fraction replication
B. Freeze-fracture replication
C. Fraction replication
D. None of the mentioned
Answer: B
Clarification: The concept that transmembrane proteins penetrate through the membrane was obtained from the results of freeze-fracture replication. In this procedure, a frozen solid tissue is fractured with a knife blade and metals are deposited on their exposed surfaces to form shadowed replica. This is viewed under electron microscope and it looks like a path strewn with pebbles, called as membrane-associated particles.
4. Transmembrane domain of a transmembrane protein is present as _______________
A. Alpha-helix
B. Beta-sheet
C. Triple beta-sheet
D. None of the mentioned
Answer: A
Clarification: The transmembrane domain of a cell membrane protein is the part that spans through the lipid bilayer of cell membrane. It mainly consists of a chain of about 20 non-polar amino acids arranged in an alpha- sheet structure.
5. Hydropathy plot helps to _______________
A. Identify hydrophobic amino acids
B. Determine arrangement of amino acids in a transmembrane protein
C. Provides an average hydrophobicity of short peptide segments
D. All of the mentioned
Answer: D
Clarification: A hydropathy plot is a method by which transmembrane segments of a protein can be identified if the amino acid sequence of the protein is known. Hydropathy plot assigns each site with a value to measure the hydrophobicity of an amino acid at a site and also at its neighbours. This helps to determine the arrangement of amino acid in the transmembrane domain, based on its hydrophobic character.
6. The channel in a membrane protein by which an ion or molecule can be transported in and out of the cell membrane is known as ___________
A. Permeation pathway
B. Permeate channel
C. Permeation channel
D. Channel pathway
Answer: A
Clarification: Transmembrane proteins act as channels from the intracellular and extracellular transport of ions and molecules. The channel through which the transport is done is called permeation pathway as it helps in the permeation of solutes and ions through the membrane.
7. Greater degree of unsaturation in fatty acids of cell membrane _________
A. Lowers the transition temperature
B. Raises the transition temperature
C. Has no effect on transition temperature
D. Doubles the transition temperature