Stretches of a gene that code for protein products are known as what?
a. mRNA
b. intron
c. exon
d. codon
e. None of the above
C
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A(n) ________ is composed of tetrameric protofilaments.
A) extracellular matrix B) microtubule C) bacteriophage D) microfilament E) intermediate filament
The molecule that rapidly replenishes ATP at the beginning of muscle activity is
A. actin. B. creatine phosphate. C. dystrophin. D. acetylcholine. E. myosin.
Blood vessels show which sign of aging?
a. elastin fibers in their walls are replaced by collagen or calcium deposits b. they become softer and expand more easily c. the smooth muscle layer constricts more readily d. elastin fibers double in quantity e. veins develop more valves
Repolarization of a postsynaptic cell can occur when:a
there is a high enough concentration of neurotransmitters in the synaptic cleft. b. neurotransmitters undergo exocytosis from the presynaptic cell. c. enzymes degrade neurotransmitters in the synaptic cleft. d. neurotransmitters are not removed from their receptors. e. neurotransmitters undergo reuptake at the postsynaptic cell