This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cytoplasmic Membrane Systems – Endocytosis”.
1. Endocytosis and phagocytosis refer to the same process.
Explanation: Endocytosis is the process where the cell engulfs cell surface receptors bound with ligands; whereas phagocytosis is the process where the cell uptakes particulate matter.
2. Which of the following is a type of endocytosis?
Explanation: Pinocytosis, also called bulk–phase endocytosis is the non–specific uptake of extracellular material. This process also removes portions of the plasma membrane and function in membrane recycling.
3. The process in which cell uptakes extracellular material bound to cell surface receptors is known as __________________
c) receptor–mediated endocytosis
d) bulk–phase endocytosis
Explanation: The specific uptake of extracellular materials in which they are bound to external surface of the plasma membrane, is known as receptor–mediated endocytosis.
4. Receptor–mediated endocytosis (RME) leads to the formation of ___________ coated pits.
Explanation: Substances bound to receptors enter a cell by receptor–mediated endocytosis and collect in specialized domains of the plasma membrane called the ‘coated pits’. Clathrin is present on the electron–dense coat of these pits.
5. A molecule of clathrin has a ______________ structure.
Explanation: A molecule of clathrin has three heavy and three light chains joined at the center, forming a three–legged structure called triskelion.
6. Which adaptor molecule operate in clathrin–mediated endocytosis?
Explanation: AP2 adaptor molecules are associated with clathrin coated pits formed in the plasma membranes as a result of receptor–mediated endocytosis.
7. Dynamin is a _____________________
a) adaptor molecule
b) accessory protein
c) integral membrane protein
Explanation: Dynamin is a large GTP–binding accessory protein that aids in the release of clathrin–coated vesicle from the membrane on which it is formed.
8. Receptor down regulation leads to a decrease in the sensitivity of the cell towards further stimulation.
Explanation: There are two different types of receptors involved in the endocytosis. The endocytosis mediated by the second group of receptors leads to their destruction, called the receptor down regulation. This decreases the sensitivity of the cell towards further stimulation.
9. Following internalization, vesicle–bound materials are transported to _________________
Explanation: Following the internalization of materials from the extracellular environment to the intracellular environment, the vesicle bound materials are transported to endosomes.
10. Late endosomes are located near the _____________
Explanation: The complex network of tubules and vesicles is collectively known as endosomes. There are two classes of endosomes: early endosomes, located near the cell periphery, and late endosomes, located near the nucleus.
11. Transformation from an early to a late endosome is characterized by a decrease in ______________
b) lipid content
d) protein content
Explanation: Transformation from an early endosome to a late endosome is characterized by a decrease in the pH and a major change in the internal morphology of the structure.
12. Receptors dissociate from their bound ligands as a result of ________________
a) high H+ concentration
b) low H+ concentration
c) high Cl– concentration
d) low Cl– concentration
Explanation: The receptors dissociate from their bound ligands as a result of high H+ concentration in the early endosomes. Following which they are concentrated into specialized tubular compartments representing the recycling centers of endosomes.
13. Where do the materials ingested by endocytosis, reach after travelling through the late endosome?
d) early endosome
Explanation: After endocytosis materials reach the late endosome, where the bound ligands are concentrated. After late endosome the materials reach lysosome for further processing.
14. ‘Niemann–Pick type C disease’ is caused due to deficiency of a specific ________________
Explanation: ‘Niemann–Pick type C disease’ is an inherited disorder in which a protein required to transfer cholesterol out of the lysosomes is lacking. Consequently, cholesterol is accumulated in these organelles leading to nerve degeneration.
15. Mycobacterium tuberculosis inhibits the fusion of its phagosome with _________________ following phagocytosis.
Explanation: Mycobacterium tuberculosis is the agent responsible for tuberculosis. Following its phagocytosis, the bacterium inhibits the fusion of phagosome with the lysosome, preventing its deactivation in the cell.
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