Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules?
(a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends.
(b) Depolymerization initiates at the plus ends of filaments.
(c) Nucleotide hydrolysis promotes depolymerization of filaments.
(d) Free subunits (actin and tubulin) carry nucleoside triphosphates.
(b) The shrinkage of microtubules that occurs involves a switch from growth to shrinkage only at the plus end of microtubules. However, actin loses subunits from its minus end during actin treadmilling.
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Short repeated sequences of DNA that vary in number from one chromosome to the next are called:
A. variable number tandem repeats. B. restriction fragment length polymorphisms. C. single nucleotide polymorphisms. D. copy number variants.
Nitrogenous waste is excreted from Malpighian tubules mainly in the form of
a. nitrate. b. ammonia. c. uric acid. d. amino acids. e. urea.
________ produces the second messengers IP3 and diacylglycerol (DAG)
Fill in the blank with correct word.
Allergic reactions are triggered by the release of ________ from certain cells.
A. serotonin B. epinephrine C. acetylcholine D. histamine