Question

Amino acids are joined into proteins by (a) \(3^{\prime}-5^{\prime}\) linkage; (b) a glycosidic bond; (c) \(\beta(1 \longrightarrow 4)\) linkage; (d) a condensation reaction; (e) none of these.

Short answer

The correct answer is (d) - a condensation reaction.

Step-by-step solution

Analyzing Option A

The terminology \(\(3^{\prime}-5^{\prime}\)\) linkage usually refers to the phosphodiester bonds that link nucleotides together in a chain to form nucleic acids like DNA and RNA. This type of bond is not involved in the formation of proteins from amino acids.

Analyzing Option B

A glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another molecule. It is most commonly found in glycoproteins, glycolipids and in the formation of polysaccharides like cellulose, not in the formation of proteins from amino acids.

Analyzing Option C

\(\beta(1 \longrightarrow 4)\) linkage is a type of glycosidic bond that links monosaccharide units to form polysaccharides like cellulose and chitin. It has no role in protein synthesis.

Analyzing Option D

In a condensation reaction, two molecules come together to form a larger molecule, with the elimination of a smaller molecule (usually water). When amino acids come together to form a protein, they do so through condensation reactions. Each amino acid has an amino group \((\(-NH2)\)\) and a carboxyl group \((\(-COOH)\)\). In the condensation reaction that forms the peptide bond, the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water.

Analyzing Option E

Option E would be correct if none of the previous options were involved in the formation of proteins from amino acids, but we have seen that option D, a condensation reaction, is the correct answer.

Key concepts

Amino Acids

Amino acids are the building blocks of proteins, which are essential biomolecules for many functions in living organisms. They have a basic structure comprising an alpha carbon atom, which is bonded to:

• An amino group (-NH2)
• A carboxyl group (-COOH)
• A side chain (R group) that varies among different amino acids
• A hydrogen atom

Each amino acid is distinguished by its unique side chain or R group, which gives it specific properties and determines its role in a protein. There are 20 different standard amino acids found in nature, and the sequence of amino acids in a protein determines its structure and function.

Different amino acids can be classified based on the properties of their side chains, such as being hydrophobic, hydrophilic, acidic, or basic. This diversity allows proteins to perform a wide array of functions within the cell, including acting as enzymes, signaling molecules, or structural components.

Peptide Bond

The peptide bond is a strong covalent bond that links amino acids together to form proteins. When two amino acids come together to form a peptide bond, the process involves the reaction of the amino group (-NH2) of one amino acid with the carboxyl group (-COOH) of the other. This reaction is part of a larger process called protein synthesis, where proteins are assembled from simpler subunits.

The formation of a peptide bond creates a new molecule, called a dipeptide, and releases a molecule of water. Each peptide bond has partial double bond character due to resonance, which provides stability and restricts rotation around the bond.

In proteins, hundreds or thousands of amino acids are connected by peptide bonds to form polypeptides, which then fold into specific three-dimensional shapes depending on the sequence of amino acids. This folding is crucial for the protein's function.

Condensation Reaction

A condensation reaction is a fundamental chemical process that occurs when two molecules combine to form a larger molecule, and a small molecule, such as water, is released. This reaction is key to forming peptide bonds in proteins.

In the context of protein synthesis, each time a peptide bond is formed between two amino acids, a water molecule is released through a process known as dehydration synthesis. This type of condensation reaction is essential for building up complex molecules from simpler units.

Condensation reactions are important in many biological and chemical processes, not just in forming proteins. They also play a crucial role in synthesizing other biomolecules, such as carbohydrates and lipids, by bonding smaller molecules into larger macromolecules needed for life.