Question

What is the subunit of a protein, and how do two subunits join to form a peptide bond? (pages $34-35$ )

Short answer

The subunit of a protein is an amino acid, which consists of a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R group). Peptide bond formation occurs between the amino group of one amino acid and the carboxyl group of another through a condensation reaction, which involves the loss of a water molecule. The resulting covalent bond is called a peptide bond (-C(=O)NH-), and it links amino acids together to form a polypeptide chain, the primary structure of a protein.

Step-by-step solution

Define the subunit of a protein.

The subunit of a protein is an amino acid. Amino acids are the building blocks of proteins, which are joined together through peptide bonds to form polypeptide chains.

Understand the structure of an amino acid.

An amino acid consists of a central carbon atom (called the alpha carbon) covalently bonded to four different groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a side chain (R group), which is unique to each amino acid. The amino and carboxyl groups of amino acids are responsible for forming peptide bonds.

Describe the process of peptide bond formation.

The peptide bond formation occurs between the amino group of one amino acid and the carboxyl group of another amino acid. The process, known as a condensation reaction, involves the loss of a water molecule (H2O). The nitrogen atom of the amino group (-NH2) forms a covalent bond with the carbon atom of the carboxyl group (-COOH) of the adjacent amino acid, resulting in the peptide bond (-C(=O)NH-).

Summarize the peptide bond formation between two amino acid subunits.

In summary, the subunit of a protein is an amino acid. Two amino acids can join together through a peptide bond, which is formed by the condensation reaction between the amino group of one amino acid and the carboxyl group of another amino acid. This peptide bond formation leads to the creation of a polypeptide chain, which is the primary structure of a protein.

Key concepts

amino acid structure

Amino acids are the fundamental building blocks of proteins. Each amino acid has a basic structure that includes:

• A central carbon atom, called the alpha carbon.
• An amino group (-NH${}_2$).
• A carboxyl group (-COOH).
• A hydrogen atom.
• A unique side chain, often referred to as the R group.

The R group is what distinguishes the 20 different standard amino acids from one another. Each R group has specific properties that influence the overall behavior and function of the amino acid in a protein. Understanding the structure of amino acids is crucial for grasping how they connect to form proteins.

protein subunits

The subunits of proteins are amino acids. When these subunits link together, they form the backbone of a protein. A simple protein consists of many amino acids joined by peptide bonds.
Each protein is made up of sequences of amino acids, which can be thought of as beads on a string. Each amino acid in the chain acts as a subunit or building block.
Proteins can contain hundreds or even thousands of amino acids, allowing for an enormous diversity of protein structures and functions.

condensation reaction

A condensation reaction is a chemical process that joins two molecules together, resulting in the formation of a peptide bond. In the context of proteins, this reaction involves the amino group of one amino acid and the carboxyl group of another.

How Does It Occur?

• The amino group (-NH${}_2$) of one amino acid reacts with the carboxyl group (-COOH) of another.
• A molecule of water (H${}_2$O) is removed.
• The nitrogen from the amino group and the carbon from the carboxyl group form a covalent bond, known as a peptide bond (-C(=O)NH-).

This reaction is essential for the formation of all proteins and allows for the creation of long chains, known as polypeptides.

polypeptide chain

A polypeptide chain is a sequence of amino acids linked together by peptide bonds. These chains fold into specific three-dimensional shapes to form proteins. The sequence of amino acids in a polypeptide chain is crucial, as it determines the protein's structure and function.
Polypeptide chains can be quite long, containing from several to thousands of amino acid residues. Multiple polypeptide chains may come together to form more complex protein structures, but each chain begins as a linear entity before folding.

primary protein structure

The primary protein structure refers to the unique sequence of amino acids in a polypeptide chain. This sequence is determined by the genetic code and dictates everything about the protein's final shape and function.
Just like letters in a sentence, the order of amino acids in the sequence is critical. Any change in the sequence can result in an entirely different protein with a different function.
Studying the primary structure of a protein helps scientists understand how genetic instructions are translated into functional molecules.