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(a) c tip (c) (d) denaturation of proteins containing β sheets extension of β sheets into much longer β strands formation of biofilms by infectious bacteria β-sheet stabilization of abnormally folded proteins 44 Collagen is a protein that participates in both the cytoskeleton and the extracellular matrix. A. True B. False 45 The assembly of both collagen and elastin fibers requires the formation of disulfide bonds. A. True B. False 46 Globular proteins fold up into compact,spherical structures that have uneven surfaces. They tend to form multisubunit complexes, which also have a rounded shape. Fibrous proteins, in contrast, span relatively large distances within the cell and in the extracellular space. Which of the proteins below is not classified as a fibrous protein? ta elastase (b) collagen (c) keratin (d) elastin 47 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 f) a change that decreases the rate of hydrolysis of GTP by Ras You have two purified samples of protein Y: the wild-type (nonmutated) protein a mutant version with a single amino acid substitution. When washed th filtration column, mutant protein Y runs through the column more slowly than th protein. Which of the following changes in the mutant protein is most likely to explain this result? Hint:important to know how the Gel Filtration Columns work ie.on what basis does it separates proteins. 48 ough the same gel- e normal the loss of a binding site on the mutant-protein surface through which protein Y normally forms dimers a change that results in the mutant protein acquiring an overall positive instead of a negative charge (b) (e) a change that results in the mutant protein being larger than the wild-type protein (d) a change that results in the mutant protein having a slightly different shape from the wild-type protein