Chapter Nutrition What are Proteins
Definition of Proteins
Proteins are large biomolecules composed of one or more long chains of amino acids. They perform a vast array of functions within organisms, including catalyzing metabolic reactions and providing structural support.
Structure & Building Blocks
- Amino acids: 20 standard types, each with a central carbon, an amino group, a carboxyl group, and a unique side chain.
- Peptide bonds: Link amino acids into polypeptide chains.
- Levels of structure:
- Primary: amino acid sequence
- Secondary: α‑helix and β‑sheet folding
- Tertiary: three‑dimensional shape
- Quaternary: assembly of multiple polypeptides
Key Functions in the Body
- Enzymatic: Speed up biochemical reactions (e.g., amylase, lipase).
- Structural: Provide support (e.g., collagen in connective tissue).
- Transport: Carry molecules (e.g., hemoglobin transports oxygen).
- Regulatory: Hormones and receptors (e.g., insulin).
- Defensive: Immune proteins like antibodies.
Dietary Food Sources
| Source | Example Foods | Protein per 100 g |
|---|---|---|
| Animal | Chicken breast, eggs, yogurt | 20–31 g |
| Fish & Seafood | Salmon, tuna, shrimp | 20–25 g |
| Dairy | Milk, cheese, cottage cheese | 3–25 g |
| Plant | Tofu, lentils, chickpeas | 8–19 g |
| Nuts & Seeds | Almonds, peanuts, chia seeds | 15–25 g |
Daily Intake Recommendations
- Adults: 0.8 g per kg of body weight per day.
- Athletes & pregnant women: Up to 1.2–1.7 g/kg.
- Balance sources to include all essential amino acids.
Conclusion
Proteins are indispensable for growth, repair, and maintenance of body tissues. A varied diet combining animal and plant sources helps ensure adequate intake of essential amino acids and supports overall health.
