16.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 protein is not classified as a fibrous protein?
(a)elastase (b)collagen (c)keratin (d)elastin
17.You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a
single amino acid substitution. When washed through the same gel-filtration column, mutant protein Y runs through
the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely
to explain this result?
(a)the loss of a binding site on the mutant protein surface through which protein Y normally forms dimers
(b)a change that results in the mutant protein’s acquiring an overall positive instead of a negative charge
(c)a change that results in the mutant protein’s being larger than the wild-type protein
(d)a change that results in the mutant protein’s having a slightly different shape from the wild-type protein
18.Which of the following statements is true?
(a)Disulfide bonds are formed by the cross-linking of methionine residues.
(b)Disulfide bonds are formed mainly in proteins that are retained within the cytosol.
(c)Disulfide bonds stabilize but do not change a protein’s final conformation.
(d)Agents such as mercaptoethanol can break disulfide bonds through oxidation.
19.Proteins bind selectively to small molecule targets called ligands. The selection of one ligand out of a mixture of
possible ligands depends on the number of weak, noncovalent interactions in the protein’s ligand-binding site. Where
is the binding site typically located in the protein structure?
(a)on the surface of the protein (b)inside a cavity on the protein surface
(c)buried in the interior of the protein (d)forms on the surface of the protein in the presence of ligand
thanks
