Question

What two functional groups are bound to the central carbon of every free amino acid monomer? a. an R-group and a hydroxyl group b. an N-H group and a carbonyl group c. an amino group and a hydroxyl group d. an amino group and a carboxyl group

Short answer

The correct answer is option d: an amino group and a carboxyl group are bound to the central carbon of every free amino acid monomer.

Step-by-step solution

Understanding amino acid structure

Amino acids are organic molecules, comprising a central carbon atom (also known as the alpha-carbon), an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R-group).

Analyzing the given options

Now let's analyze each option given: a. An R-group and a hydroxyl group: While amino acids do have an R-group attached to the central carbon, a hydroxyl group is not universally present in all amino acids. b. An N-H group and a carbonyl group: An N-H group is part of the amino group, and a carbonyl group is part of the carboxyl group. However, this option only mentions part of these functional groups, which is misleading. c. An amino group and a hydroxyl group: Similar to option a, a hydroxyl group is not universally present in all amino acids. d. An amino group and a carboxyl group: This option mentions both functional groups that are universally bound to the central carbon of every amino acid monomer.

Choose the correct answer

Based on our analysis, the correct answer is option d: an amino group and a carboxyl group are bound to the central carbon of every free amino acid monomer.

Key concepts

Functional Groups

Functional groups are specific groups of atoms within molecules that have distinct chemical properties. These groups play a crucial role in the behavior and reactions of molecules, including amino acids. In the context of amino acids, two key functional groups are the amino group

• positively charged at physiological pH
• comprises an nitrogen atom (N) bonded to hydrogen atoms

and the carboxyl group

• negatively charged at physiological pH
• contains a carbon atom double-bonded to an oxygen atom, and bonded to a hydroxyl group

These groups are essential for the structure and function of proteins as they enable the formation of peptide bonds, linking amino acids into long chains. This ability to form peptide bonds is critical for protein synthesis, leading to complex structures that perform various functions in the body.

Alpha-Carbon

In the structure of an amino acid, the central atom is known as the alpha-carbon. The alpha-carbon is pivotal as it acts as a meeting point for several important components:

• A hydrogen atom
• An amino group (NH₂)
• A carboxyl group (COOH)
• A unique side chain (R-group)

The alpha-carbon gives amino acids their unique properties and their ability to form diverse proteins. The R-group, or side chain, varies among different amino acids and is responsible for their unique characteristics, influencing how they interact and bond with each other.

Amino Group

The amino group is one of the defining features of amino acids. It consists of a nitrogen atom bonded to two hydrogen atoms (\[\text{NH}_2\]). This group plays a pivotal role in the properties of amino acids due to its ability to participate in bonding:

• Forms hydrogen bonds
• Can act as a base, accepting protons

The presence of an amino group in amino acids is important as it facilitates the formation of peptide bonds with the carboxyl group of adjacent amino acids. This bond formation is essential for building proteins, which are polymers of amino acids.

Carboxyl Group

The carboxyl group is a fundamental component of amino acid structure, characterized by the formula \[\text{COOH}\]. It consists of a carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group (OH):

• Plays a role in the acidity of amino acids
• Can lose a proton, generating a negative charge

The carboxyl group is critical for the reactivity of amino acids as it participates in peptide bond formation. This bonding, attaching amino acids through their carboxyl and amino groups, is essential for creating protein chains necessary for life processes.