Q. 16.81 - An Introduction to General, Organic, and Biological Chemistry

Question

Consider the amino acids lysine, valine, and aspartate in an enzyme. State which of these amino acids have $R$ groups that would:

a. be found in hydrophobic regions.

b. be found in hydrophilic regions.

c. form hydrogen bonds.

d. form salt bridges.

Step-by-Step Solution

Answer

(Part a) Valine is a non-polar amino acid found in the hydrophobic region. 

(Part b) Lysine and aspartate have $R$ groups that are found in the hydrophilic region.

(Part c) Lysine and aspartate can form a hydrogen bond. 

(Part d) Lysine and aspartate are polar amino acids in which the positively charged ionized $R$ group of lysine forms a salt bridge with the $R$ group of aspartate. 

Step 1: Introduction (Part a) .

Hydrophobic amino acids are insoluble in water and have aliphatic side chains. 

These hydrophobic amino acids are found inside protein structures, whereas hydrophilic amino acids possess polar side chains and are found on the surface or outside of protein structures.

Step2: Given Information (part a).

Consider the enzyme amino acids lysine, valine, and aspartate.

To be found in hydrophobic environments.

Step3: Explanation (part a).

Lysine, valine, and aspartate are amino acids found in enzymes, with lysine and aspartate having polar $R$ groups in their side chains and valine having a non-polar $R$ group. As a result, valine is a non-polar amino acid found in the hydrophobic region.

Step4: Given Information (part b).

Consider the enzyme amino acids lysine, valine, and aspartate.

To be found in hydrophilic environments.

Step5: Explanation (part b).

Polar $R$ groups are found in the side chains of lysine and aspartate. As a result, lysine and aspartate have $R$ groups that are found in the hydrophilic region.

Step6: Given Information (part c).

Consider the enzyme amino acids lysine, valine, and aspartate.

To build Hydrogen bonds.

Step7: Explanation (part c).

Lysine and aspartate have polar $R$ groups, which are found at the protein structure's surface and form hydrogen bonds with water molecules. As a result, lysine and aspartate can form a hydrogen bond.

Step8: Given Information (part d).

Consider the enzyme amino acids lysine, valine, and aspartate.

To build salt bridges.

Step9: Explanation (part d).

Salt bridges are ionic attractions between polar acidic and polar basic amino acid ionized $R$ groups. Lysine and aspartate are polar amino acids in which the positively charged ionized $R$ group of lysine forms a salt bridge with the $R$ group of aspartate.