correctly complete the following statement: The side chains ('-R groups') of amino acids in a beta-sheet: A. alternate pointing "up" and "down" for each successive amino acid in the primary sequence. B. point in one direction in a parallel beta sheet and the opposite direction in an antiparallel beta-sheet. C. always point toward the direction of water. D. point in random directions. E. all point in opposite directions

A.  

Explanation:

The β-sheet is a twisted pattern in which the protein strands are laterally linked through hydrogen bonds. These β-sheet motifs are segments of 3 to 10 amino acids that are specially configured to form beta antiparallel strands. In β-sheet regions, the hydrogen bonds are localized among carbonyl and amino groups of the polypeptide backbone, and side chains (i.e., the R groups) are extended up and down in the plane of the β-sheet.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.