Author- Dr. Mohammad Shamim, MD
Proteins are vital macromolecules with diverse roles essential for the structure, function, and regulation of the body’s tissues and organs. Let’s delve deeper into their functions under various headings, and also discuss the Recommended Dietary Allowance (RDA) for protein.
Structural Proteins
- Collagen: The most abundant protein in the body, collagen provides structural support to connective tissues, including skin, bones, tendons, and ligaments. It is crucial for skin elasticity and wound healing.
- Keratin: Found in hair, nails, and the outer layer of skin, keratin provides protective properties and strength.
- Elastin: Allows tissues to resume their shape after stretching or contracting. It is essential in arteries, lungs, and skin for maintaining elasticity.
Enzymatic Proteins
- Digestive Enzymes: These include:
- Pepsin: Breaks down proteins in the stomach.
- Amylase: Converts starches into sugars in the mouth and small intestine.
- Lipase: Breaks down fats into fatty acids and glycerol.
- Metabolic Enzymes: Catalyze biochemical reactions in cells:
- ATP Synthase: Produces ATP, the energy currency of the cell.
- Catalase: Breaks down hydrogen peroxide into water and oxygen, preventing oxidative damage.
Transport Proteins
- Hemoglobin: A red blood cell protein that binds oxygen in the lungs and releases it in tissues. It also transports carbon dioxide back to the lungs.
- Albumin: The most abundant protein in blood plasma, it maintains osmotic pressure and transports hormones, vitamins, and drugs.
- Transferrin: Binds and transports iron through the blood to various tissues.
Hormonal Proteins
- Insulin: Regulates blood glucose levels by promoting glucose uptake in cells.
- Growth Hormone: Stimulates growth, cell reproduction, and regeneration.
- Thyroxine (T4): Produced by the thyroid gland, it controls the rate of metabolism.
Immune Proteins
- Antibodies (Immunoglobulins): Identify and neutralize foreign objects like bacteria and viruses.
- Cytokines: Small proteins released by cells that have a specific effect on cell-to-cell communication and behavior.
- Complement Proteins: Part of the immune system that enhances the ability of antibodies to clear pathogens.
Contractile Proteins
- Actin and Myosin: Integral to muscle contraction, enabling movement and strength.
- Tropomyosin and Troponin: Regulate muscle contractions by controlling the interaction of actin and myosin.
Storage Proteins
- Ferritin: Stores iron and releases it in a controlled fashion.
- Casein: Found in milk, provides amino acids, carbohydrates, and calcium.
- Ovalbumin: The primary protein in egg whites, providing nourishment for embryo development.
Receptor Proteins
- G-Protein Coupled Receptors (GPCRs): Detect molecules outside the cell and activate internal signal pathways.
- Ion Channels: Facilitate the flow of ions across the cell membrane, essential for nerve impulse transmission.
- Insulin Receptor: Mediates the cellular effects of insulin.
Regulatory Proteins
- Transcription Factors: Bind to DNA and influence the transcription of specific genes.
Histones: Proteins that package DNA into nucleosomes, controlling gene expression
Signal Proteins
- Epidermal Growth Factor (EGF): Stimulates cell growth and differentiation.
- Nerve Growth Factor (NGF): Essential for the growth, maintenance, and survival of certain neurons.
- Adrenaline (Epinephrine): Mediates the fight-or-flight response by increasing blood flow to muscles, output of the heart, and blood sugar level.
Protective Proteins
- Heat Shock Proteins (HSPs): Help cells cope with stress by stabilizing new proteins and repairing damaged ones.
- Blood Clotting Proteins: Involved in coagulation to prevent blood loss, such as fibrinogen and thrombin.
Nutritional Proteins
- Casein and Whey: Milk proteins that provide essential amino acids and support muscle repair and growth.
- Albumin: Provides a rich source of essential amino acids.
Recommended Dietary Allowance (RDA) for Protein
The RDA for protein varies based on age, sex, and life stage. Here are general guidelines provided by the Food and Nutrition Board of the Institute of Medicine:
- Infants:
- 0-6 months: 9.1 grams/day
- 7-12 months: 11 grams/day
- Children:
- 1-3 years: 13 grams/day
- 4-8 years: 19 grams/day
- Males:
- 9-13 years: 34 grams/day
- 14-18 years: 52 grams/day
- 19+ years: 56 grams/day
- Females:
- 9-13 years: 34 grams/day
- 14-18 years: 46 grams/day
- 19+ years: 46 grams/day
- Pregnant Women: 71 grams/day
- Lactating Women: 71 grams/day
Conclusion
Proteins are indispensable for numerous bodily functions, from providing structural support to facilitating metabolic reactions, transporting molecules, and regulating immune responses. Ensuring adequate protein intake through diet is crucial for maintaining health and supporting the body’s dynamic processes.