Amino Acids Basics

Amino Acids

• Amino acids are the fundamental building blocks of proteins.
• A free amino acid comprises an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (-H), and a variable side chain ("R").
• These components are attached to a central carbon atom, the α-carbon.

Chemistry of Amino Acids

• Amino acids are classified by their structure, properties, and reactions.
• The key elements found in the chemical structure are carbon, hydrogen, oxygen, and nitrogen.
• 300 amino acids exist naturally but 20 participate in protein biosynthesis, these are known as standard amino acids.

Classification of Amino Acids

• Amino acids can be classified based on their structure, polarity, nutritional requirements, and metabolic fates.

• Four common methods used to classify amino acids provide different ways of grouping, for example, the grouping between 20 acids and a basic outline for grouping.

  • Structure of amino acid
  • Nature of polarity
  • Nutritional requirement
  • Metabolic fate

• Based on R-group: Simple, Hydroxy, Sulfur-containing, Aromatic, Heterocyclic, Amine group, Branched chain, Acidic, Basic, Imino.

• Classification by nutritional requirement: Essential, semi-essential, and non-essential. These are based on a body's ability to synthesize the amino acids.

  • Essential amino acids: Cannot be produced by the body and must be obtained from the diet. Examples include leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, and tryptophan.
  • Semi-essential amino acids: The body can produce them, but not in sufficient quantities for growth, which entails supplementing the diet. Examples include arginine and histidine.
  • Non-essential amino acids: The body can produce them, so dietary intake is not always necessary, Examples include glycine, alanine, serine, asparagine, glutamine, tyrosine, proline.

• Based on metabolic fate: Glucogenic, ketogenic, and both glucogenic & ketogenic. These are based on metabolic pathways of the amino acids.

  • Glucogenic amino acids: Amino acids whose breakdown produces molecules that can be used to generate glucose by the body.
  • Ketogenic amino acids: Amino acids whose breakdown generates molecules that contribute to ketone body formation.
  • Glucogenic and ketogenic amino acids: Amino acids that can contribute to both glucose and ketone body production in the body.

Properties of Amino Acids

• Physical properties: Colorless, crystalline, often sweet or bitter-tasting. Can be soluble in water, acids, and alkalis, but are insoluble in organic solvents. Generally, have high melting points (greater than 200 degrees Celsius).

• Isoelectric point: The pH where the amino acid exists primarily as a zwitterion (with no net charge). Amino acids can exist as cations or anions depending on pH.

• Optical properties: The alpha carbon of amino acids is chiral (optically active). Most naturally occurring amino acids are L-isomers.

Reactions of Amino Acids

• Reactions due to amino group, carboxyl group, side chains, or combinations of these groups. Reactions often include:

  • Oxidative deamination
  • Transamination
  • Decarboxylation
  • Formation of amide linkages (such as peptide bonds)
  • Disulfide bond formation

Special Functions of Amino Acids

• Components of proteins and enzymes
• Precursors for various molecules in the body (ex: Niacin, serotonin, melatonin from tryptophan; melanin, thyroid hormone, catecholamines from tyrosine; GABA neurotransmitter from glutamic acid; Nitric oxide from arginine)

This quiz covers the fundamental aspects of amino acids, including their structure and classification. Learn about the key components that make up amino acids and their role in protein biosynthesis. Test your knowledge on the different types of amino acids and their classifications.