AMINO ACIDS

INTRODUCTION: Proteins occur in every living organism, are of many different types, and have many different biological functions. The keratin of skin and fingernails, the spider webs, and the estimated 50,000 or so enzymes that catalyze the biological reactions in our bodies are all proteins. Regardless of their function, all proteins have a fundamentally similar structure and are made up of many amino acids linked together in a long chain.

AMINO ACIDS AS BUILDING BLOCKS OF PROTEINS: Amino acids, as their name implies, are difunctional. They contain both a basic amino group and an acidic carboxyl group. Their value as building blocks to make proteins stems from the fact that amino acids can join together into long chains by forming amide bonds between the NH2 of one amino acid and the CO2H of another. For classification purposes, chains with fewer than 50 amino acids are often called peptides, while the term protein is generally used for larger chains.

AMINO ACIDS AND ACID-BASE BALANCE: Because amino acids contain both basic amino and acidic carboxyl groups, they undergo an intramolecular acid–base reaction and exist in aqueous solution primarily in the form of dipolar ions, called zwitterions. Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They are relatively soluble in water but insoluble in hydrocarbons and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic, meaning that they can react either as acids or as bases, depending on the circumstances. 

EXCHANGE OF IONS BETWEEN AMINO ACIDS: In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton onto its CO2 group to yield a cation; in aqueous base solution, the zwitterion is an acid that loses a proton from its NH3 group to form an anion.

RELATED

1.  PROTEINS

2.  DIVERSITY OF BIOMOLECULES

3.  NUCLEIC ACIDS

4.  FATTY ACIDS

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