Final answer:
In folded proteins, nonpolar amino acids are located in the interior due to hydrophobic interactions, while polar and charged amino acids are on the surface due to their hydrophilic nature. Proteins embedded in a lipid bilayer have nonpolar amino acids in the membrane-embedded regions and polar residues exposed to water. Correct protein folding is essential for function, and misfolding can lead to diseases.
Step-by-step explanation:
In the structure of folded proteins, the location of amino acid residues depends on their polarity. Nonpolar amino acids tend to be found in the interior of globular proteins; they are hydrophobic, which means they avoid water and are driven to the center of the protein away from the aqueous environment. This phenomenon is called hydrophobic interaction. As a result, the protein folds in such a way that these nonpolar amino acids are sheltered inside.
On the other hand, polar and charged amino acids are typically found on the surface of soluble proteins. These amino acids can form hydrogen bonds and interact favorably with water, therefore they are hydrophilic. They seek interaction with the aqueous environment, leading to their exposure on the protein's exterior. When considering proteins embedded in a lipid bilayer such as the plasma cell membrane, the distribution of amino acids is different. The nonpolar amino acids tend to be found in the membrane-embedded parts of the proteins, aligning with the hydrophobic interior of the lipid bilayer; whereas polar and charged residues are more common on the surfaces that are exposed to the aqueous environment on either side of the membrane.
Protein Folding and Function
These sorting of amino acids during protein folding is crucial for the protein's functionality. Specific folding patterns, such as the alpha-helix and beta-pleated sheet, are formed by hydrogen bonds and are key components of the protein's secondary structure. Additionally, interactions between cysteine side chains form disulfide linkages, which further stabilize the protein's structure. If the protein fails to fold correctly, known as misfolding, this can lead to loss of function and result in diseases caused by improperly folded proteins.