Biochemistry Fundamentals: Amino Acids, Proteins, and Sugars

Amino Acids and Amphoteric Properties

Amino acids are amphoteric, resulting in three forms: cationic (positive), anionic (negative), and the dipolar ion or zwitterion.

Amino acids behave differently depending on the pH of their environment. They all have a characteristic pH value, known as the isoelectric point (pI), at which the amino acid exists 100% as a dipolar ion.

• Acidic pH: At a pH lower than the pI, the amino acid exists in a high percentage (though not 100%) in the cationic form.
• Basic pH: At a pH higher than the pI, the anionic form predominates.

Peptide Bonds

A peptide bond is formed through the loss of a water molecule (H₂O) from the carboxyl group (-OH) of one amino acid and the amino group (-NH₂) of another.

Protein Denaturation

Denaturation is the disruption of all levels of protein structure (secondary, tertiary, and quaternary) without breaking the peptide bond. When a protein is denatured, it ceases to perform its function because it loses its specific shape and often becomes insoluble.

Hydrolysis

Hydrolysis is the breaking of peptide bonds. It occurs in the presence of specific enzymes, water, and certain conditions of pH and temperature. This is an energy-intensive process.

Isomerism

Isomerism is categorized into two types:

• Structural (flat): Includes position, chain, and functional group isomers.
• Stereoisomerism (space): Includes geometric (cis-trans) or optical isomers.

Cis-Trans Isomerism

Cis-trans (geometric) isomerism occurs in compounds with a rigid structure, such as carbon-carbon double bonds in alkenes.

• The cis isomer has the two heavier groups on the same side of the plane containing the double bond.
• The trans isomer has these groups on opposite sides of the plane containing the double bond.

Mutarotation

Mutarotation is the property of certain carbohydrates to change their optical rotation over time until reaching a stable value. This occurs due to the equilibrium in aqueous solution between alpha, beta, and open-chain anomers.

Reducing Power of Carbohydrates

Carbohydrates are oxidized in the presence of reagents such as Fehling's and Tollens' (mild oxidants), resulting in the formation of acids. All monosaccharides are reducing sugars, whereas some disaccharides, such as sucrose, are not. Reducing carbohydrates possess a free anomeric carbon.