The Ras protein is a GTPase that functions in many growth-factor signaling pathways
In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells?
(a) a change that prevents Ras from being made
(b) a change that increases the affinity of Ras for GDP
(c) a change that decreases the affinity of Ras for GTP
(d) a change that decreases the rate of hydrolysis of GTP by Ras
(d) Ras is a proto-oncogene. When it is active, it promotes cell growth. Choice (d) is the only option that would lead to an increase in Ras activity. Choices (a), (b), and (c) would decrease its activity.
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A linear stretch of DNA that specifies the
sequence of amino acids in a polypeptide is called a(n) a. codon. b. intron. c. messenger. d. gene. e. enzyme
The matrix is to the mitochondrion as the ________ is to the chloroplast
Fill in the blank with correct word.
The functional link between cardiac muscle cells is called ____
a. intrinsic pacemakers b. nodes c. intercalated discs d. bundle branches e. extrinsic pacemakers
Cells with no nucleus
a. prokaryotic b. eukaryotic