96%(23)22 out of 23 people found this document helpful
This preview shows page 10 - 11 out of 11 pages.
Ans:The amino acids are Asp, Glu, His, Cys, Tyr, Lys, and Arg. Section: 2.140)How does the protein backbone add to structural stability? Ans:The protein backbone contains the peptide bond, which is an amide containing an NH group and a C=O (carbonyl) group. Peptide bonds are kinetically stable once formed, having very low rates of hydrolysis. Hydrogen-bond formation between the hydrogen on the nitrogen and the oxygen from other carbonyls in either alpha helices or in beta sheets support the protein conformation. Section: 2.241)Why are all the theoretical combinations of phi and psi not possible? Ans:Steric hindrances of the side chains make certain combinations and angles impossible. Section: 2.242)Describe some of the features of an α helix. Ans:The α helix is a coil stabilized by intrachain hydrogen bonds between the carbonyl oxygen of a residue and the amide hydrogen of the fourth residue away. There are 3.6 amino acids per turn. The hydrogen bonds are between amino acid residues that have three intervening residues. Thus, these amino acid residues are found on the same side of the coil. The helix is almost always right-handed, although left-handed helices are, in theory, possible. Section: 2.343)What is the “hydrophobic effect” as it relates to protein structure? Ans:The three-dimensional structure of a water-soluble protein is stabilized by the tendency ofhydrophobic groups to assemble in the interior of the molecule. Section: 2.144)-Keratin is referred to as a coiled-coil protein. Describe the protein structure of -keratin. Ans:Two α helices entwined to form a very stable double helix of approximately 100 nm in length. Section: 2.3
45)What are prions? Ans:Prions are proteins that can assume (after infection or by other causes) a new protein structure, which is self-propagating. Mammalian prion diseases are fatal. Section: 2.646)What does the modification involving the attachment of acetyl groups to the amino termini of proteins do? Ans:The acetylation of the amino termini of proteins makes these proteins more resistant to degradation. Section: 2.647)In the ribonuclease experiments performed by Anfinsen, what was the significance of the presence of the reducing agent β-mercaptoethanol? Ans:The reducing agent reduced incorrectly paired disulfide bonds, allowing them to reform with the correct pairing until the most stable conformation of the protein had been obtained. Section: 2.648)What is the advantage of having certain areas of partially correct folded regions? Ans:If some regions interact preferentially, lending stability to certain conformations as the protein folds, they can impact the overall structure of the protein. Section: 2.6