Muscles that encircle tubes and act as circular valves are called
A. sphincters.
B. frenula.
C. cannula.
D. anastomoses.
E. buccinators.
Answer: A
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Not all proteins achieve quaternary structure. What determines quaternary structure in proteins?
a. Quaternary structure results from protein denaturation and renaturation with the unraveled protein returning to its original shape and function. b. Quaternary structure results from modification once the protein is released from the cell and enters the extracellular space. c. Quaternary structure results from several formed polypeptides that interact with one another to form a larger, functional unit. d. Quaternary structure results from protein synthesis in the ribosome dictated by the detailed instructions of the mRNA.
Which zone is also known as the spray zone?
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Electrical impulses that stimulate contraction of heart muscles are initiated in the
A) left ventricle. B) bundle of His. C) sinoatrial node. D) atrioventricular node. E) Purkinje fibers.