Q-1. Eukaryotic plasma membrane is made up of all except (AIIMS May 2009 and May 2010)
a) Carbohydrate
b) Triglycerides
c) Lecithin
d) Cholesterol
Answer: Triglycerides
Explanation:
Membranes are complex structures composed of lipids, proteins and carbohydrates-containing molecules.
The major lipids in membrane are:
Phospholipids:
Phospho-Glycerides-Phosphatidic acid
Sphingomyelin
Glycosphingolipids:
Cerebroside
Ganglioside
Cholesterol: Most common sterol
Important point:
Choline containing phospholipids (Phosphatidyl choline also called lecithin and sphingomyelin) are located mainly in outer layer and amino-phospholipids (Phosphatidyl-serine) are preferentially located in inner layer.
Q-2. Membrane fluidity is increased by
a) Stearic acid
b) Palmitic acid
c) Cholesterol
d) Linoleic acid
Answer: Linoleic acid
Explanation:
Saturated fatty acids have straight tails, whereas un-saturated fatty acids which generally exist in the cis form in membrane make kinked tails.
Important point:
As more kinks are inserted in the tails, the membrane becomes less tightly packed and therefore more fluid.
Q-3. Which of the following membranes would be having highest protein content per gram tissue? (AIIMS May 2002)
a) Inner mitochondrial membrane
b) Outer mitochondrial membrane
c) Plasma membrane
d) Myelin sheath
Answer: Inner mitochondrial membrane
Explanation:
Ratio of protein to lipid in different membranes:
Inner mitochondrial membrane: 3.2
Sarcoplasmic reticulum: 2.0
Outer mitochondrial membrane: 1.1
Myelin sheath: 0.23
Q-4. Marker of cell membrane is/are
a) 5-Nucleotidase
b) LDH
c) Galactosyl transferase
d) None
Answer: 5-Nucleotidase
Explanation:
Enzymatic Markers of Different Membranes:
Plasma membrane:
5-Nucleotidase
Adenyl cyclase
Na+ K+ ATPase
Endoplasmic Reticulum:
Glucose 6 Phosphatase
Inner Mitochondrial Membrane:
ATP Synthase
Golgi apparatus:
Cis- GlcNac transferase I
Trans- Galactosyl transferase
Medial- Golgi Mannosidase II
Trans Golgi network- Sialyl transferase
Q-5. Plasma-membrane marker (s) is /are
a) 5’- Nucleotidase
b) Galactosyl Transferase
c) ATP Synthetase
d) Adenyl cyclase
e) Na+ K+ ATPase
Answer: a, d and e
Explanation:
See above explanation.
Q-6. Which of the following is /are plasma membrane enzyme(s)
a) Glucose- 6- phosphatase
b) 5’-Nucleotidase
c) Adenyl cyclase
d) Na+ – K+ ATPase
e) Sialyl transferase
Answer: a, d and e
Explanation:
See above explanation.
Q-7. Neutral molecules are transported by
a) Porin channels
b) Ionophores
c) Simple diffusion
d) None of the above
Answer: Simple diffusion
Explanation:
Neural molecules are usually transported freely across plasma membrane by simple diffusion as a free diffusion or through channel proteins.
Important point:
Simple diffusion of a solute across membrane is limited by the thermal agitation of that specific molecule, by the concentration gradient across the membrane and by solubility in the hydrophobic core of the membrane bilayer.
Q-8. Which of the following statements about facilitated diffusion is true?
a) It is a form of active transport
b) It requires a carrier protein
c) Rate of transport is proportionate to the concentration gradient
d) Requires creatine phosphate
Answer: It requires a carrier protein
Explanation:
Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific trans-membrane integral proteins.
Important points:
Facilitated diffusion is a form of passive transport.
Rate of transport in facilitated diffusion is proportionate to concentration gradient only at low concentrations, before the carrier protein becomes saturated.
Q-9. Which of the following statements about facilitated diffusion is true?
a) It is a form of active transport
b) It requires a carrier protein
c) Rate of transport is proportionate to the concentration gradient
d) Requires creatine phosphate
Answer: It requires a carrier protein
Explanation:
See above explanation.
Q-10. Sweat chlorides are in increased in
a) Addition’s disease
b) Conn’s syndrome
c) Cystic fibrosis
d) Pheochromocytoma
Answer: Cystic fibrosis
Explanation:
Cystic fibrosis is a recessive genetic disorder due to mutation in the gene encoding CFTR (Cystic fibrosis trans-membrane regulator protein), a cyclic AMP-regulated chloride transporter.
Important point:
It is characterized by chronic bacterial infections of the airways and sinuses, fat mal-digestion due to pancreatic exocrine insufficiency, infertility in male due to abnormal development of vas deferens and elevated levels of chloride in sweat (> 60 mmol/L).