Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. How might a cell actively engineer this phospholipid redistribution?
A. by activating a scramblase and inactivating a flippase in the plasma membrane
B. by inverting the existing plasma membrane
C. by inactivating a scramblase in the plasma membrane
D. by inactivating both a flippase and a scramblase in the plasma membrane
E. by boosting the activity of a flippase in the plasma membrane
Answer: A. by activating a scramblase and inactivating a flippase in the plasma membrane
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A. protons. B. neutrons. C. electrons. D. protons and neutrons. E. protons and electrons.
The chemical interactions of large organic molecules are largely determined by:
a. their solubility in water. b. their functional groups. c. their polar nature. d. isomerization of these hydrocarbons into other forms. e. the hydrogens bonded to the carbon atom
Cyanide inhibits mitochondrial function; as a result, the rate of
A) ATP synthesis increases. B) ATP synthesis decreases. C) photosynthesis increases. D) protein synthesis increases.
The reference or primary line of longitude is:
a. the Tropic of Cancer. b. the Tropic of Capricorn. c. the Greenwich meridian. d. the equator. e. the International Date Line.