Question

(a) What is an \(\alpha\) -amino acid? (b) How do amino acids react to form proteins? (c) Draw the bond that links amino acids together in proteins. What is this called?

Short answer

An \(\alpha\)-amino acid is an organic molecule with an amino (-NH2) group and a carboxyl (-COOH) group bonded to the same \(\alpha\)-carbon atom, which also bonds to a hydrogen atom and a unique R-group. Amino acids react to form proteins through a condensation reaction between their amino and carboxyl groups, resulting in a covalent bond called a peptide bond and releasing a water molecule. The peptide bond, represented as \(R_1-C(O)-NH-R_2\), forms between the carbonyl carbon of one amino acid's carboxyl group and the nitrogen of another amino acid's amino group.

Step-by-step solution

Definition of an α-amino acid

An \(\alpha\)-amino acid is an organic molecule containing both an amino (-NH2) group and a carboxyl (-COOH) group bonded to the same carbon atom, known as the \(\alpha\)-carbon atom. In addition to these two functional groups, the \(\alpha\)-carbon atom is also bonded to a hydrogen atom and a unique side chain (R-group). The R-group determines the specific characteristics of each amino acid.

Amino acids reaction to form proteins

Amino acids react to form proteins through a condensation reaction (also called a dehydration reaction) between the amino group of one amino acid and the carboxyl group of another amino acid. This reaction results in the formation of a covalent bond called a peptide bond, while releasing a water molecule.

Drawing the bond linking amino acids in proteins

The bond that links amino acids together in proteins is called a peptide bond. The peptide bond is formed between the carbonyl carbon (C) of one amino acid's carboxyl group and the nitrogen (N) of the other amino acid's amino group, as illustrated below: $$ R_1 - C(O) - NH - R_2 $$ Here, R1 and R2 represent the side chains of the two amino acids involved in the bond formation.

Naming the bond in proteins

The bond that links amino acids together in proteins is called a peptide bond.

Key concepts

Protein Formation

Proteins are essential organic molecules that play a crucial role in almost every biological process. They are formed by linking amino acids together into a chain. This process occurs through a series of reactions, primarily condensation reactions.
During this process, amino acids connect through peptide bonds to create long chains called polypeptides. Once a polypeptide chain forms, it folds and twists into specific shapes, ultimately resulting into a functional protein.
Protein formation is not only about just connecting amino acids; the sequence and type of amino acids in the chain determine the protein's properties and function. There are four structural levels to a protein:

• Primary structure: The linear sequence of amino acids.
• Secondary structure: Localized conformations, like alpha-helices and beta-sheets.
• Tertiary structure: 3D shape formed by folding.
• Quaternary structure: Combination of multiple polypeptides.

Each level of protein structure is crucial for the final shape and function of the protein. The specific folding of the polypeptide determines how protein will interact with other molecules.

Peptide Bond

A peptide bond is the link formed between two amino acids. This bond is central to the formation of proteins. It is a covalent bond and forms through a condensation (or dehydration) reaction.
In this reaction, the carboxyl group of one amino acid interacts with the amino group of another amino acid, releasing a molecule of water in the process.
The reaction can be described as follows: the carbon atom in the carboxyl group (\( C(=O)OH \)) forms a bond with the nitrogen atom in the amino group (\( NH_2 \)). This linkage results in the characteristic peptide bond (\( C(O) - NH \)).
Peptide bonds have partial double bond character, due to resonance, which restricts rotation and gives the protein its structural integrity. The sequence in which amino acids are linked through peptide bonds in the polypeptide chain determines the eventual function and specificity of the resulting protein.

Organic Molecules

Organic molecules are compounds mainly composed of carbon atoms in combination with elements like hydrogen, oxygen, and nitrogen. Amino acids, the building blocks of proteins, are a type of organic molecule.
Each amino acid contains a central carbon known as the \( \alpha \)-carbon, which is bonded to four different groups: an amino group (\( NH_2 \)), a carboxyl group (\( COOH \)), a hydrogen atom, and a variable R-group.
The R-group (or side chain) is what makes each amino acid unique and is responsible for the amino acid's chemical properties and its role within a protein.
Understanding the nature of organic molecules like amino acids is essential because they form the basis of all forms of life. They are involved in countless biological processes and can vary greatly in their complexity and function. This diversity allows for the wide variety of proteins necessary for life's multitude of physiological functions.