This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Chemical Composition of Membranes”.
1. The lipids present in cell membrane are _____________
a) Polar
b) Non- polar
c) Charged
d) Ampipathic
View Answer
Explanation: The lipids that form the main constituent of cellular membrane has both hydrophobic and hydrophilic regions. They are made up of polar hydrophilic heads as well as non-polar hydrophobic tails made up of carbon chains.
2. The model of a lipid bilayer lined by a layer of protein molecules on both sides was put forward by _____
a) Davson and Danielli
b) Singer and Nicolson
c) Watson and Crick
d) None of the mentioned
View Answer
Explanation: The model of a lipid bilayer lined by a layer of protein molecules on both sides was the concept put forward by scientists Hugh Davson and James Danielli. However, the fluid mosaic model of cell membrane was put forward by S. Jonathan Singer and Garth Nicolson. Watson and Crick put forward the structure of DNA double helix.
3. The phosphoglycerides in cell membrane are of the _________ type.
a) Triglyceride
b) Diglyceride
c) Monoglyceride
d) Polyglyceride
View Answer
Explanation: Membrane glycerides, which contain a phosphate group has two fatty acids. Therefore, they are phosphor-diglycerides. Only two of the hydroxyl groups of the glycerol are esterified to a hydrophilic phosphate group.
4. Shingolipids is the derivative of ______________
a) Sphingosine
b) Shingomycin
c) Sphingoceramicin
d) Sphingolipid polymer
View Answer
Explanation: Shingolipids are the derivative of sphingosine, an amino alcohol that contains a long hydrocarbon chain. Sphingosine is a ceramide linked to fatty acid by its amino group.
5. Which of the following is not a component of cell membranes?
a) Phosphodiglycerides
b) Sphingolipids
c) Cholesterol
d) Phosphotriglycerides
View Answer
Explanation: Phospholipids present in cell membrane are diglycerides and not triglycerides. Triglycerides have three fatty acids and are not ampipathic in nature. It also consists of sphingolipid and cholesterol.
6. In animals, the amount of cholesterol present in cell membrane is ___________
a) 20%
b) 15%
c) 50%
d) 33.33%
View Answer
Explanation: Animal cell membrane is made up of 50% protein and 50% Lipids. 60% of all lipids in the membrane are cholesterol molecules. About one third of the cell membrane is made up of cholesterol(1/3rd of 100%= 33.33%).
7. Which part of cholesterol molecule is not embedded in the lipid bilayer?
a) Hydroxyl end of cholesterol
b) Entire molecule of cholesterol
c) Hydrophobic rings
d) Hydroxyl end and 1⁄4th of the hydrophobic rings
View Answer
Explanation: Cholesterol molecules are oriented with their small hydrophilic hydroxyl groups toward the membrane surface and the remainder of molecule embedded in lipid bilayer. The hydrophilic rings of a cholesterol molecule are flat and rigid and interfere with the fatty acid tails of phospholipids.
8. Which of the following is exoplasmic?
a) Phosphatidyl choline
b) Phosphatidyl serine
c) Phosphatidyl ethanolamine
d) Phosphatidyl inositol
View Answer
Explanation: The phospholipids of cell membrane are composed of phosphatidyl choline (PC), phosphatidyl serine (PS), phosphatidyl ethanolamine (PE) and phosphatidyl inositol (PI). PC is exoplasmic and present towards the extracellular fluid. PS, PE and Pi are cytosolic and located towards the cytoplasm.
9. Which of the following facilitates binding of positively charged amino acid residues?
a) Phosphatidyl choline (PC)
b) Phosphatidyl serine (PS)
c) Phosphatidyl ethanolamine (PE)
d) Phosphatidyl inositol(PI)
View Answer
Explanation: PS, concentrated in the inner leaflet of cell membrane, has a negative charge at physiologic pH and thus binds positively charged amino acid residues of lysine and arginine. The appearance of PS on the outer surface of aging lymphocytes marks the cells for destruction by macrophages. Appearance of PS on the outer surface of platelets can lead to blood coagulation.
10. Which of the following promote curvature of cell membrane?
a) Phosphatidyl choline (PC)
b) Phosphatidyl serine (PS)
c) Phosphatidyl ethanolamine (PE)
d) Phosphatidyl inositol(PI)
View Answer
Explanation: PE promotes the curvature of cell membrane. This is important in the budding and fusion of cell membranes during maturation.
11. Carbohydrates present in cell membrane are generally ___________
a) Monosaccharides
b) Disachharides
c) Oligosaccharides
d) Polysaccharides
View Answer
Explanation: The modification of membrane proteins by addition of carbohydrates occurs by a process called glycosylation. The carbohydrate of glycoproteins is present as short, branched hydrophilic oligosaccharides. In contrast to long-chained polysaccharides, they only have upto 15 sugars per chain.
12. Lipid rafts are ___________
a) Patches of glycoproteins in the lipid bilayer
b) Patches of cholesterol and sphingolipids in lipid bilayer
c) Patches of only cholesterol in lipid bilayers
d) Detached patches of proteins floating on the lipid bilayer
View Answer
Explanation: When membrane lipids are extracted from cell and used to produce artificial lipid bilayers, cholesterol and sphingolipids tend to self-assemble into microdomains highly ordered than surrounding lipid. Microdomains float within the fluid environment and are known as lipid rafts.
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