Apolar

Some amino acids are nonpolar, meaning that the overall electronic charge of the molecule is essentially distributed among its atoms. Most nonpolar amino acids have side groups composed of carbon and hydrogen atoms, which share their electrons equally when bonded to one another. Proline is an unusual amino acid in that its side group is linked to its amino group such that a five-membered nonpolar ring structure is formed. Tryptophan contains two ring structures composed mainly of nonpolar carbon–hydrogen bonds. One ring possesses a nitrogen atom, but because the atoms to which it is bonded share their electrons equally, the charge is evenly distributed and the molecule is nonpolar. The side chain of phenylalanine is characterized by a nonpolar benzene ring composed entirely of carbon-hydrogen bonds, while methionine has a nonpolar sulfur-containing side chain. Although sulfur usually tends to accumulate electrons, the charge on methionine is evenly distributed because the sulfur atom shares its electrons equally with the two carbon atoms to which it is bound. The amino acids alanine, valine, leucine, and isoleucine all possess side groups containing combinations of nonpolar carbon-hydrogen bonds, resulting in an even charge dispersal throughout each molecule. Molecules which are nonpolar tend to be hydrophobic, meaning that they avoid interactions with polar molecules such as water. This is biologically significant because proteins tend to adopt structures that position nonpolar amino acids away from the aqueous external cellular environment.

Question 1: What makes non-polar amino acids apolar?
  1. Amino acids that have rounded ends.
  2. Equal distribution of electronic charges among the atoms or molecules.
  3. No charged molecules.
  4. Charges only at ends of molecules.


Answer 1 Answer - (b) Equal distribution of electronic charges among the atoms or molecules

Question 2: What do the side groups of Proline, Tryptophan, and Phenylalanine have in common that makes them non-polar?
  1. The presence of polar ring structures with equal distribution of charge among atoms.
  2. The presence of non-polar ring structures with equal distribution of charge among atoms.
  3. The presence of polar side-chains with equal distribution of charge among atoms.
  4. The presence of non-polar ring structures with at the ends of the amino acids.


Answer 2 Answer - (b) The presence of non-polar ring structures with equal distribution of charge among atoms.

Question 3: In Methionine, sulfur atom shares its electrons equally with the two --------- atoms to make the amino acid non-polar?
  1. oxygen
  2. hydrogen
  3. nitrogen
  4. carbon


Answer 3 Answer - (d) Carbon

Question 4: Non-polar molecules tend to be _____________, avoiding interactions with polar molecules such as water.
  1. hydrophobic
  2. hydrophilic
  3. neutral
  4. reactive


Answer 4 Answer - (a) Hydrophobic

Question 5: Most proteins tend to position ____________ amino acids inside to avoid with the _______________, external cellular environment.
  1. polar, watery
  2. apolar, salty
  3. non-polar, aqueous
  4. non-polar, hot


Answer 5 Answer - (c) Non-polar, aqueous