Question

Which of the following statements is most likely to be true of non polar R groups in aqueous solution? (A) They are hydrophilic and found buried within proteins. (B) They are hydrophilic and found on protein surfaces. (C) They are hydrophobic and found buried within proteins. (D) They are hydrophobic and found on protein surfaces.

Short answer

The most likely statement to be true is (C) They are hydrophobic and found buried within proteins.

Step-by-step solution

- Identify Key Characteristics of Non-Polar R Groups

Non-polar R groups are characterized by their inability to interact favorably with water. This means they are hydrophobic.

- Understand Hydrophobic vs Hydrophilic

Hydrophobic groups repel water and tend to avoid it. Conversely, hydrophilic groups interact well with water and are attracted to it.

- Determine Likely Location in Proteins

In aqueous solutions, hydrophobic (non-polar) groups tend to be found in the interior of proteins to avoid contact with water. This minimizes unfavorable interactions with the aqueous environment.

- Analyze Given Statements

Compare the given statements with the established characteristics: (A) They are hydrophilic and found buried within proteins. (B) They are hydrophilic and found on protein surfaces. (C) They are hydrophobic and found buried within proteins. (D) They are hydrophobic and found on protein surfaces.

- Select the Correct Statement

Given that non-polar R groups are hydrophobic and tend to avoid water, the most accurate statement is: (C) They are hydrophobic and found buried within proteins.

Key concepts

hydrophobic interactions

Hydrophobic interactions play a key role in the structure and stability of proteins. Hydrophobic interactions occur between non-polar molecules or parts of molecules. They tend to cluster together when in water, creating a stable structure by minimizing exposure to the aqueous environment.
In the context of proteins, non-polar R groups are hydrophobic. This means they avoid water and tend to be found in the interior of proteins. By doing so, they minimize exposure to water and reduce the free energy of the protein structure.
The clustering of hydrophobic groups in the protein's core pulls the protein into a more compact and stable shape, ultimately influencing the protein's overall conformation.

protein structure

Proteins are complex molecules with multiple levels of structure, all of which are essential for their function. The primary structure is the sequence of amino acids. This sequence determines the secondary, tertiary, and quaternary structures.
The secondary structure includes local conformations like alpha-helices and beta-sheets, stabilized by hydrogen bonds between the backbone atoms.
In the tertiary structure, the protein folds into a complex 3D shape. This folding is driven by interactions between the R groups, including hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges. Non-polar R groups tend to be buried in the protein core, away from water.
Finally, some proteins have a quaternary structure, where multiple polypeptide chains come together to form a single, functional protein. Each level of structure is influenced by the nature of the amino acids, including the hydrophobic non-polar R groups.

aqueous solution

An aqueous solution is a solution in which water is the solvent. In biological systems, most of the environment is aqueous, meaning that water-based interactions are crucial.
Water is a polar molecule and interacts favorably with other polar molecules and ions (hydrophilic interactions). However, it repels non-polar molecules, leading to hydrophobic interactions where non-polar molecules minimize contact with water.
In proteins, the aqueous environment influences the positioning of amino acid R groups. Hydrophilic (polar) R groups are more likely to be found on the protein surface, interacting with the water. Hydrophobic (non-polar) R groups, on the other hand, tend to be buried within the protein to escape the aqueous surroundings.
This arrangement helps the protein attain a stable structure, critical for proper function.