Key Properties and Functions of Proteins, Enzymes, Immunoglobulins, and Nucleic Acids

Key Properties of Proteins

• Their molecular weight ranges from 1,000 to several hundred thousand.
• Generally water-soluble, with the exception of hydrophilic membrane proteins.
• Absorb light in the UV range, with maximum absorption at 280nm due to the presence of aromatic amino acids.
• Have a specific isoelectric pH (pI). Positively charged below pI, negatively charged above pI.
• Proteins are charged, which depends on the buffer.
• Move under the electric charge and can be separated by electrophoresis.
• Give a color reaction with reagents, such as a blue color with ninhydrin.

Classification of Proteins

Basis of Structure

1. Globular: All enzymes and intracellular proteins are globular, such as myoglobin and hemoglobin.
2. Fibrous: Mostly extracellular, such as collagen.

Basis of Composition

1. Simple Protein: e.g., albumin, lysozyme.
2. Conjugated Protein: e.g., myoglobin, cytochrome, immunoglobulin.

Enzymes

Enzymes are biological catalysts—i.e., substances of biological origin that accelerate chemical reactions. The orderly course of metabolic processes is only possible because each cell is equipped with its own genetically determined set of enzymes. Enzymes are also involved in many regulatory mechanisms that allow the metabolism to adapt to changing conditions. Almost all enzymes are proteins.

Immunoglobulins

Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells (white blood cells). They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. Soluble antigen receptors, which are formed by activated B cells and released into the blood, are known as antibodies. They are also members of the immunoglobulin family. Antibodies specifically bind to antigens in both the recognition phase (cellular receptors) and during the effector phase (synthesis and secretion) of humoral immunity.

Nucleic Acids

Nucleic acids function primarily as informational molecules for the storage and retrieval of information regarding the primary sequence of polypeptides. There are two types of nucleic acids: DNA and RNA. DNA serves as a cellular database by storing an immense amount of information. RNA is needed to convert DNA information into polypeptide sequences.

Performance Factors of Biosensors

Ideal Biosensor Characteristics

1. Sensitivity: High ΔS/ΔC_analyte (S = signal).
2. Simple calibration (with standards).
3. Linear Response: ΔS/ΔC_analyte constant over a large concentration range.
4. Background Signal: Low noise, with the ability for correction (e.g., a second fiber sensor head lacking biological species to measure background O₂ changes).
5. No hysteresis—signal independent of the prior history of measurements.
6. Selectivity: Response only to changes in target analyte concentration.
7. Long-term Stability: Not subject to fouling, poisoning, or oxide formation that interferes with the signal; prolonged stability of the biological molecule.
8. Dynamic Response: Rapid response to variation in analyte concentration.
9. Biocompatibility: Minimize clotting, platelet interactions, and activation of complement when in direct contact with the bloodstream.