Which of the following is NOT a characteristic of the alpha-helix? (Choose all that apply) Group of answer choices One complete turn of the helix contains 6 amino acid residues. A right-handed helix that protects amino acid side chains down the centre. The C=O of residue i is hydrogen bonded to the N-H group of residue i + 4. Alpha-helices can be amphipathic in nature alternating one polar and non-polar amino acid in the sequence.
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Which is not a characteristic of an α-helix? a) The N–H and C=O bonds point along the axis of the helix in opposite directions. b) There are 3.6 amino acids in each turn of the helix. c) The C=O group of one amino acid is hydrogen-bonded to an N–H group of four amino acid residues farther along the chain. d) The R groups of the amino acids extend inward toward the core of the helix.
Sri K.
11. Which of the following residues would most likely be buried in the interior of a water soluble, globular protein? a. Asp b. Ser c. Lys d. Phe e. Gln 12. In the ̑-helix, the hydrogen bonds: a. are roughly parallel to the axis of the helix b. are roughly perpendicular to the axis of the helix c. occur mainly between electronegative atoms of the R groups d. occur mainly between some of the amino acid residues of the helix e. occur near the amino and carboxyl termini of the helix 13. Which of the following statements does not apply to collagen? a. It contains hydroxylated amino acids. b. The polypeptide forms a left-handed helix. c. Hydrogen bonds between the —OH groups of 4-hydroxyproline residues stabilize the helix. d. There is an absolute requirement for Gly every third position. e. The triple helical structure twists in the right-handed direction. 14. A D-amino acid residue would interrupt an ̑-helix made of L-amino acid residues. Another naturally occurring hindrance to the formation of an ̑-helix is the presence of: a. a negatively charged Arg residue. b. a nonpolar residue near the carboxyl terminus. c. a positively charged Lys residue. d. a Pro residue. e. two Ala residues next to each other.
The alpha helix is a particularly stable arrangement for a polypeptide chain. Alpha helices have 3.6 amino acids per turn of the helix and a diameter of ~12Å. Briefly explain why the alpha helix has these specific dimensions. In other words, what would happen if the helix was tighter—say only 3.0 amino acids per turn with a diameter of ~8Å—or looser, with 4.2 residues per turn and a diameter of 20Å?
Adi S.
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