This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cytoplasmic Membrane Systems – Vesicle Transport”.
1. A protein coat of diameter ________ is present on the transport vesicles.
a) 0.5-1 mm
b) 0.5-1 nm
c) 0.5-1 pm
d) 0.5-1 μm
Explanation: The Golgi complex was discovered by Camillo Golgi for which he was awarded Nobel Prize in 1908. It consists of flattened, disk-like membranous cisternae of diameter 0.5 to 1 μm.
2. Which molecule activates the formation of a transport vesicle?
c) DNA helicase
Explanation: A protein coat made of soluble proteins is assembled on the cytosolic surface of the donor membrane at the site where budding takes place; this assembly is triggered by the activation of G-protein.
3. COPII-coated vesicles move the materials from ____________ to ____________
a) ERGIC, Golgi complex
b) Golgi complex, ERGIC
c) ER, Golgi complex
d) Golgi complex, ER
Explanation: COPII-coated vesicles (COP is an acronym for coated proteins) transport the materials from endoplasmic reticulum (ER) to ERGIC and Golgi complex.
4. COPI-coated vesicles move the materials in __________________ direction.
Explanation: The COPI-coated vesicles transport the materials in retrograde direction; from endoplasmic reticulum (ER) to Golgi stack and from trans Golgi cisternae backward to cis Golgi cisternae.
5. Glycosyltransferases are selected by CopII-coat proteins.
Explanation: The COPII-coat selects and concentrates various proteins for transport sing vesicles. Proteins selected by COPII-coated vesicles include glycosyltransferases which function at later stages in a biosynthetic pathway.
6. Sar1 is a _______
Explanation: Among COPII proteins, Sar1 is a G-protein which initiates vesicle formation and regulates the assembly of the vesicle coat. G-proteins function as molecular switches inside the cells.
7. The protein coated vesicle must release its components into the Cytosol before fusing with the target site.
Explanation: Before fusing with the target site the protein coat is disassembled and contents released in the cytosol. This is triggered by the hydrolysis of GTP bound to Sar1.
8. ARF1 is a _______ binding protein.
Explanation: Similar to Sar1 protein found in COPII-coat proteins, ARF1 is a GTP-binding protein found in COPI-coat proteins. The GTP is hydrolyzed prior to disassembly of the coat.
9. Retrieval signals, present on the C-terminus of ER resident proteins are captured by the receptors present on __________________
a) Clathrin-coated vesicles
b) Golgi complex
c) COPI-coated vesicles
d) COPII-coated vesicles
Explanation: The COPI-coated transport vesicles operate in the retrograde direction and are responsible for retention of proteins that reside in the ER membrane or lumen and are accidentally carried away by the Golgi complex. Such proteins possess retrieval signals at their C-terminus which is captured by receptors on the COPI-coated vesicles, which transport them back to the endoplasmic reticulum.
10. Clathrin present on the clathrin-coated vesicles is a ______________
Explanation: Clathrin is a protein present on the outer surface of clathrin-coated vesicles forming a honeycomb-like lattice. The main function of these vesicles is to transport lysosomal enzymes.
11. GTP-bound ‘Rabs’ (G-proteins) associated with membranes by a __________ anchor.
d) ribonucleic acid
Explanation: Rabs are G-proteins that recruit specific cytosolic tethering proteins to specific membrane surfaces. These are associated with membranes by a lipid anchor.
12. Which state of the ‘Rabs’ is the active state?
Explanation: The ‘Rabs’ are encoded by over 60 diverse genes in humans and they cycle between two states; GTP-bound active state and GDP-bound inactive state.
13. t-SNAREs are present on the _____________________
a) budding vesicle
b) transportation material
c) target compartment
d) tethering proteins
Explanation: SNAREs are proteins that function in docking vesicles to the target compartment. There are two types of these proteins; v-SNAREs and t-SNAREs. The latter are present on the target compartments.
14. Synaptobrevin is a ______________
a) membrane vesicle
b) lipid anchor
Explanation: During the regulated release of neurotransmitters, synaptic vesicles are docked to the presynaptic membrane of the nerve cell. Synaptobrevin is a v-SNARE present on the membrane of a synaptic vesicle.
15. Which of the following are the targets of bacterial toxins botulism and tetanus?
Explanation: SNAREs present on the membranes of synaptic vesicles and presynaptic membranes are the only targets of potent bacterial toxins; botulism and tetanus. Cleavage of SNAREs by these toxins blocks the release of neurotransmitters and lead to paralysis.
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