This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cell Signaling and Signal Transduction – Role of Calcium”.
1. The concentration of Calcium in a resting cell is ___________
a) 10 M
b) 10-2 M
c) 10-5 M
d) 10-7 M
Explanation: The concentration of Calcium ions in a resting cell is usually maintained at very low levels, approximately 10-7 M. However, outside the cells (extracellular space) in the ER lumen or a plant cell vacuole, the concentration is much higher.
2. Abnormal elevation of cytosolic Calcium can occur following a _____________
Explanation: The membranes of cell (plasma membrane) and endoplasmic reticulum are highly impermeable to calcium. Abnormal elevated levels of cytosolic calcium exist following a stroke, leading to massive cell death.
3. Calcium acts as an intracellular messenger.
Explanation: Calcium plays a vital role in a number cellular processes such as fertilization, muscle contraction, muscle movement. In each of these activities an extracellular message is received at the cell surface that leads to an increase in the calcium concentration in the cytosol.
4. Fura-2 is an example of __________________
a) fluorescent molecule
b) cell surface receptor
c) cell surface antigen
Explanation: Fura-2 is a highly sensitive, fluorescent molecule that binds to calcium ions by diffusing across the plasma membrane of a cell. This compound was developed in 1980s in the laboratory of Roger Tsien at the University of California, San Diego.
5. Upon fertilization, a wave of calcium release is observed throughout the cell.
Explanation: Upon fertilization of the egg by a sperm, a growing concentration of calcium ions can be seen that spreads from the point of entry of the sperm till the other end of the egg cell.
6. How many types of calcium ion channels are present on ER membrane?
Explanation: Two types of calcium channels are present on the membrane of endoplasmic reticulum – IP3 receptors and ryanodine receptors. The latter are present primary in excitable cells like cardiac cells.
7. Ryanodine is a _______________
Explanation: Ryanodine is a toxic plant alkaloid which binds to the ryanodine receptors (RyRs). These receptors mediate the rise in calcium levels following an action potential in cardiac and skeletal muscle cells.
8. Which receptors open up during the calcium-induced calcium release?
a) Ryanodine receptors
b) IP3 receptors
c) ligand-gated channels
d) C2H2 receptors
Explanation: When limited amount of calcium ions enter the cell through open channels in the endoplasmic reticulum (ER) membrane, there is a subsequent opening of the ryanodine receptors, causing the influx of Ca2+ ions in the cytosol – calcium-induced calcium release.
9. Which ions activate cyclin-dependent kinases, following fertilization?
Explanation: The rise in cytoplasmic calcium concentration following fertilization triggers a diverse array of events. Activation of cyclin-dependent kinases that drive the zygote towards first mitotic division is one such event.
10. Which of the following is a calcium-binding protein?
Explanation: Calcium brings about a vast variety of responses in the cell and these are done in conjunction with other proteins that bind to calcium, calmodulin is such a protein found universally in all plants, animals and other eukaryotes.
11. Calmodulin has low affinity for _____________
a) magnesium ions
c) non-stimulated cells
d) stimulated cells
Explanation: Calmodulin contains 4 binding sites for calcium. It does not have sufficient affinity for Ca2+ ions in non-stimulated cells. When the calcium ions concentration increases in response to a stimulus, the ions bind to calmodulin, changing its conformation.
Sanfoundry Global Education & Learning Series – Cell Biology.
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