A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases, altho
ugh they don't often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting? A. ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR.
B. ATPase activity must be transferring Pi to the SR to enable this to occur.
C. ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient.
D. ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient.
E. ATPase activity must be routing calcium ions from the SR to the cytosol, and then to the cell's environment.
The correct answer is C ATPase activity must be pumping calcium from Cytosol to the sarcoplasmic reticulam(SR) against their concentration gradient.
Explanation:
The concentration ofCa2+ ion in Sarcoplasmic reticulam of muscle is many times higher than that of Cytosol.
Sarcoplasmic reticulam of muscle is a reservior of calcium ion (Ca2+) ions and after the occurance of muscle contraction Ca2+ are transported from low calcium concentration region that is cytosol to high calcium concentration region that is Sarcoplasmic reticulam through active transport by the help of ATPase enzyme.
Polytene chromosomes may be defined as the giant chromosomes that contain alternate dark and light bands when view under the microscope. These chromosomes are found in the salivary gland of Drosophila.
These glands are functionally highly active and contain thousand of DNA strands. These chromosomes are aligned parallel with each other as the replication is normal but the cells are unable to separate and fails to undergo the process of cytokinesis.
