Final answer:
In proteins, non-polar amino acids like alanine and phenylalanine are typically found in the interior due to their hydrophobic nature, while polar and charged amino acids are usually on the exterior. Methionine is also more likely to be in the interior compared to cysteine, which can form polar disulfide bonds.
Step-by-step explanation:
The localization of amino acids within a protein is determined by whether they are polar and charged or non-polar. Polar and charged amino acids tend to be found on the exterior of a soluble protein due to their affinity for water (hydrophilic), while non-polar amino acids are usually found in the interior as they tend to avoid water (hydrophobic).
- Between alanine and glycine, alanine is more likely to be found in the interior because it has a non-polar side chain.
- Between glutamate and aspartate, both of which are charged, neither is favored for the interior, but glutamate has a longer side chain, which might more often result in its exclusion.
- Tyrosine vs phenylalanine: Tyrosine has a polar side chain and is more likely found on the surface, while non-polar phenylalanine is more likely in the interior.
- Between methionine and cysteine, methionine's non-polar character makes it more likely to be found in the protein's interior versus the sometimes polar due to its potential to form disulfide bonds with cysteine.
These localizations contribute to the protein's structure, with inner non-polar amino acids creating a stable hydrophobic core, and outer polar amino acids interacting with the aqueous environment. Understanding these principles is also important when considering the protein's orientation in a lipid bilayer, where non-polar amino acids would likely interact with the hydrophobic tails of the lipids.