Chitin, a modified form of cellulose, is not only cross-linked with proteins but its glucose units are modified with atoms of:
A. nitrogen.
B. hydrogen.
C. oxygen.
D. sulfur.
E. phosphorous.
A
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Cells sometimes use methylation: (Select all correct choices)
A. to prevent the expression of genes in transposable elements. B. to prevent the expression of genes from viruses that have been integrated into the genome. C. to prevent the expression of harmful (mutant) genes such as those responsible for cystic fibrosis.
Which of the following statements is true?
A. Integrins and cadherins facilitate cell adhesion to extracellular substrates. B. Cadherins on the surface of animal cells permit the adhesion of cells to other cells. C. Cadherins are used by plant cells to attach the plasma membrane to the cell wall. D. Integrins on one cell attach to cadherins on another cell to promote cell adhesion.
All of the following are examples of signal termination EXCEPT:a
one cAMP molecule activating many protein kinases. b. phosphodiesterase converting cGMP to GTP. c. GTPase converting GTP to GDP. d. the inactivation of G protein by the cholera toxin. e. phosphatase removing the phosphate group from a protein.
What are the two proteases in the small intestine that complete protein digestion?
a. aminopeptidase and dipeptidase b. aminopeptidase and disaccharidase c. nucleotidase and nucleosidase d. dipeptidase and phosphatase