Amino acids, the building blocks of proteins, exhibit a range of important physiological properties related to their structure and function.
General Physical Properties
- State: Amino acids are typically white, crystalline solids at room temperature.
- Melting and Boiling Points: They possess relatively high melting and boiling points compared to many other organic molecules of similar size. This is due to their zwitterionic nature, which leads to strong electrostatic interactions.
- Solubility: Most amino acids are soluble in polar solvents like water, owing to their charged groups. They are generally insoluble in nonpolar organic solvents.
- Taste: The taste of amino acids varies; some are sweet (e.g., glycine), some are tasteless (e.g., alanine), and some are bitter (e.g., leucine).
Zwitterionic Nature
Amino acids exist as zwitterions at physiological pH. This means they contain both a positively charged amino group (-NH3+) and a negatively charged carboxyl group (-COO-). This internal salt formation is crucial for their solubility and reactivity.
Amphoteric Properties
Amino acids are amphoteric, meaning they can act as both acids and bases. This is due to the presence of both acidic (carboxyl) and basic (amino) groups. This property allows amino acids to act as buffers, resisting changes in pH.
Optical Activity
With the exception of glycine, all amino acids are optically active. This means they can rotate plane-polarized light. This is because the α-carbon atom in most amino acids is chiral (asymmetric), bonded to four different groups.
Reactions of Amino Acids
Amino acids undergo various chemical reactions, including:
- Peptide Bond Formation: Amino acids link together through peptide bonds to form peptides and proteins. This reaction involves the carboxyl group of one amino acid reacting with the amino group of another, releasing a water molecule.
- Reactions with Ninhydrin: Amino acids react with ninhydrin to produce a purple-colored product (Ruhemann's purple). This reaction is used for the detection and quantification of amino acids.
- Deamination: The removal of the amino group from an amino acid.
- Transamination: The transfer of the amino group from one amino acid to a keto acid.
Physiological Roles
The physiological properties of amino acids are fundamental to their roles in:
- Protein Synthesis: Amino acids are the monomers that are polymerized to form proteins, which carry out a vast array of cellular functions.
- Metabolism: Amino acids participate in various metabolic pathways, serving as precursors for other biomolecules.
- Neurotransmission: Some amino acids act as neurotransmitters, transmitting signals between neurons in the brain (e.g., glutamate, GABA).
- Buffering: Their amphoteric nature allows amino acids and proteins to act as buffers, helping to maintain stable pH levels in bodily fluids.
In summary, the physiological properties of amino acids—including their zwitterionic form, amphoteric nature, optical activity, reactivity, and varying tastes—are vital for their diverse biological functions.
