Which one of the following is a feature of Membrane ?
- A.Bilayer of phospholipid molecule in which proteins and cholesterol are embedded
- B.Bilayer of proteins molecule in which lipid and cholesterol are embedded
- C.Bilayer of neutral lipid in which proteins and cholesterol are embedded
- D.Bilayer of neutral lipid lacking cholesterol and proteins
Correct answer
Explanation
The correct answer is A, Bilayer of phospholipid molecule in which proteins and cholesterol are embedded. This is the fluid mosaic model of the cell membrane given by Singer and Nicolson in 1972.
Each phospholipid has a water-loving (hydrophilic) phosphate head and two water-fearing (hydrophobic) fatty acid tails. In water they line up in two layers, heads facing outwards and tails pointing inwards. Proteins float in this layer like tiles in a mosaic: some pass right through and act as channels and carriers, others sit on the surface as receptors. Cholesterol lies between the phospholipids of animal cell membranes and keeps the membrane flexible yet stable. The membrane is selectively permeable.
B is wrong because the bilayer is made of lipids, not proteins; proteins are embedded in it. C is wrong because the lipids are phospholipids, not neutral lipids such as fats. D is wrong because membranes do contain proteins and, in animals, cholesterol.
Exam tip: cell membrane = fluid mosaic model (Singer and Nicolson, 1972): phospholipid bilayer + proteins + cholesterol.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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