A plant produces flowers that are open through the day and the night. An experimenter places pollen on the stigmas of freshly opened flowers and covers them after pollination to prevent natural pollinators from having access to the flowers. When experimental pollination was carried out during the day, 40% of the flowers yielded fruit. When experimental pollination was carried out during the night, 80% of the flowers yielded fruit. However, when flowers were  kept  open  to  natural  pollination  during  the  day  (covered  at  night),  35%  of  flowers  produced  fruit.  20%  of flowers exposed to natural pollination during the night (covered during the day) produced fruit. Which of the following statements is NOT a plausible explanation of these results ?

#Question id: 737

#Unit 1. Molecules and their Interaction Relevant to Biology

Which structure below indicates the proper hydrogen-bonding pattern between amino acids in an α-helix? (Dashed lines represent the hydrogen bonds.)

#Question id: 736

#Unit 1. Molecules and their Interaction Relevant to Biology

The most important contribution to the stability of a protein’s conformation appears to be the:

#Question id: 735

#Unit 1. Molecules and their Interaction Relevant to Biology

The a-keratin chains indicated by the diagram below have undergone one chemical step. To alter the shape of the a-keratin chains—as in hair waving—what subsequent steps are required?

#Question id: 734

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following statements is true for two different tripeptides consisting of either glycine or proline?

#Question id: 733

#Unit 1. Molecules and their Interaction Relevant to Biology

Which one of the statements on protein conformation, detailed below is INCORRECT?

#Question id: 732

#Unit 1. Molecules and their Interaction Relevant to Biology

Ramachandran plots can help increase the accuracy of models derived from x-ray crystallography data. The plot below was created by measuring phi, and psi for each amino acid residue in a 2.2 A resolution crystal structure. In the plot, which excludes Gly and Pro residues, selected residues (dots) are numbered 1 through 5.

Which of the following statements can be correctly stated for this plot in reference to selected residues?

A. Residues 1 and 3 are in either B sheets

B. residue 2 is in a right-handed a helix, and residue 4 is in a left-handed a helix.

C. If residue 5 were Gly, it might be in an acceptable position in the plot