Proteins are highly flexible macromolecules that play structural, functional, and regulatory roles in cells and tissues. Their functions can be organized as follows:
1. Catalytic Function.
- Enzymes are proteins that can catalyze reactions.
- They speed up biological reactions required for metabolism.
- All chemical reactions in living beings rely on enzymes.
2. Motor Function.
- Proteins facilitate movement, ranging from bacterial flagella to muscular contraction in higher animals.
- Muscle contraction and relaxation occur via the sliding of filaments:
- Myosin has dense filaments.
- Actin: thin filaments.
3. Transportation Function.
- Proteins move chemicals and ions throughout organisms.
- Plasma albumin transports tiny molecules in the blood.
- Hemoglobin carries oxygen and CO2 in red blood cells.
4. Mechanical Support and Protection Function
- Proteins offer structural integrity and protection.
- Collagen - bones and connective tissue.
- Keratin: hair, nails, skin
- Elastin offers elasticity to tissues.
5. Immune and defensive functions.
- Immune defence relies heavily on proteins.
- Antibodies (immunoglobulins) identify and kill foreign substances like viruses, bacteria, and allogeneic proteins.
These proteins defend organisms against hazardous external substances.
6. Regulatory Function.
- Proteins and peptides control metabolism, growth, development, and reproduction.
- Hormones - protein or peptide hormones regulate numerous physiological activities.
- Receptors are proteins that receive and deliver regulatory signals from hormones and other stimuli.
Summary
Proteins are essential for life, serving as catalysts, motors, transporters, structural components, immune defences, and regulators. Their adaptability underpins almost all biological activities required for survival, growth, and reproduction.
