When a sarcomere is at rest, the myosin binding sites on actin are blocked by _____.
A. phosphorous
B. sodium
C. tropomyosin
D. the myosin heads
E. AMP
Answer: C
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In what way is artificial selection different from natural selection?
A) There's no difference; both have caused evolution throughout the history of life on Earth. B) Artificial selection applies to changes in domestic animals only, while natural selection applies to all other species. C) In artificial selection, human preference is the selecting force; in natural selection, environmental conditions are the selecting force. D) Artificial selection causes one species to change to another, while natural selection only modifies existing species.
Translational controls regulate the:a
activity of a protein product. b. rate at which an mRNA molecule is translated. c. rate at which an mRNA molecule is synthesized. d. uptake of nucleic acids into the cell. e. attachment of phosphate groups to polypeptides.
Which is antibody is secreted as a dimer for stability and is found in mucus and other exo¬crine gland secretions?
A. IgA B. IgE C. IgM D. IgG E. IgD
Which of the following statements about membrane-enclosed organelles is true?
(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane. (b) The nucleus is the only organelle that is surrounded by a double membrane. (c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell's volume is occupied by membrane-enclosed organelles; the other 90% of the cell volume is the cytosol. (d) The nucleus is the only organelle that contains DNA.