The structure of alpha helix is stabilized by hydrogen bonds between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the amino-terminal side of that peptide bonds. Within the helix, every peptide bond (except those close to each end of the helix) participates in such hydrogen bonding. Each successive turn of the helix is held to adjacent turns by three to four hydrogen bonds, conferring significant stability on the overall structure. Which of the following are correct statements regarding these findings?

A. At the ends of a helical segment, there are always three or four amide carbonyl or amino groups that participate in this stabilised helical pattern of hydrogen bonding.

B. Helix ends are exposed to the surrounding solvent, where they hydrogen-bond with water, or other parts of the protein may cap the helix to provide the needed hydrogen-bonding partners.

C. Helix can form in polypeptides consisting of either L- or D-amino acids but a D-amino acid will disrupt a regular structure consisting of L-amino acids, and vice versa.

D. The most stable form of a helix consisting of L-amino acids is left-handed.

E. 310 helix occupies similar place as turns in Ramachandran plot due to its confirmation

#Question id: 9622

#Unit 9. Diversity of Life Forms

Which of the following numbers represents a polyphyletic taxon? 

#Question id: 9621

#Unit 9. Diversity of Life Forms

If this evolutionary tree is an accurate depiction of relatedness, then which of the following should be correct?

1. The entire tree is based on maximum parsimony.

2. If all species depicted here make up a taxon, this taxon is monophyletic.

3. The last common ancestor of species B and C occurred more recently than the last common ancestor of species D and E.

4. Species A is the direct ancestor of both species B and species C.

5. The species present at position 3 is ancestral to C, D, and E

#Question id: 9620

#Unit 9. Diversity of Life Forms

The two extant species that are most closely related to each other are

#Question id: 9619

#Unit 9. Diversity of Life Forms

A common ancestor for both species C and E could be at position number 

#Question id: 9617

#Unit 9. Diversity of Life Forms

The common ancestors of birds and mammals were very early (stem) reptiles, which almost certainly possessed 3-chambered hearts (2 atria, 1 ventricle). Birds and mammals, however, are alike in having 4-chambered hearts (2 atria, 2 ventricles). The 4-chambered hearts of birds and mammals are best described as

#Question id: 9615

#Unit 9. Diversity of Life Forms

In angiosperm plants, flower morphology can be very intricate. If a tree, such as a New Mexico locust, has flowers that share many morphological intricacies with flowers of the sweet pea vine, then the most likely explanation for these floral similarities is the same general explanation for the similarities between the