Which of the following describes a key difference among the 20 amino acids that are used to make proteins?

General
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which of the following describes a key difference among the 20 amino acids that are used to make proteins?

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Which of the following describes a key difference among the 20 amino acids that are used to make proteins?

Answer:
The primary difference among the 20 amino acids that are utilized to construct proteins is the nature of their side chains, commonly referred to as the “R groups.”

Solution By Steps:

  1. Basic Structure of Amino Acids:
    • All amino acids share a fundamental structure, which includes an amino group (\text{-NH}_2), a carboxyl group (\text{-COOH}), a hydrogen atom, and a distinctive side chain (the R group) all bonded to a central carbon atom, known as the α-carbon.
\begin{array}{cccc} & H & & \\ & | & & \\ H_{2}N- & C- & COOH & \\ & | & & \\ & R & & \end{array}

  1. The R Group:

    • The R group is what differentiates the 20 amino acids from one another. The R group can vary in size, shape, charge, hydrogen bonding capacity, and chemical reactivity.
    • Here are examples of different R groups:
      • Glycine has a single hydrogen atom as its side chain.
      • Alanine has a methyl group (\text{-CH}_3).
      • Phenylalanine has a phenyl group (\text{-CH}_2\text{-C}_6\text{H}_5).

  2. Classification Based on R Groups:

    • The R groups classify amino acids into categories such as nonpolar, polar, charged (acidic or basic), and aromatic. For example:
      • Nonpolar Amino Acids: Alanine, Valine
      • Polar Amino Acids: Serine, Threonine
      • Acidic Amino Acids: Aspartic acid, Glutamic acid
      • Basic Amino Acids: Lysine, Arginine
      • Aromatic Amino Acids: Phenylalanine, Tryptophan

  3. Functional Implications:

    • The differs in R groups contribute to the amino acids’ distinct physicochemical properties, which influence protein folding, stability, and function. For instance:
      • Hydrophilic amino acids tend to be located on the protein surface interacting with the aqueous environment.
      • Hydrophobic amino acids are usually found in the protein core, stabilizing the structure through hydrophobic interactions.
      • Charged amino acids play critical roles in the active sites of enzymes, binding of substrates, and stabilization of protein structures through ionic bonds.

Final Answer:
The key difference among the 20 amino acids that are used to make proteins is the structure and properties of their side chains (R groups).