The Building Blocks: Amino Acids
All proteins are built from amino acids linked by peptide bonds. There are 20 standard amino acids used by the human body. These are classified based on whether the body can synthesize them:
- Essential Amino Acids: Nine amino acids the body cannot synthesize and must get from the diet, including histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
- Non-Essential Amino Acids: Eleven amino acids the body can synthesize.
- Conditionally-Essential Amino Acids: Amino acids that become essential during illness or stress, like arginine and glutamine.
Classification by Composition: Simple, Conjugated, and Derived
Proteins can be classified by their chemical composition. More details on simple, conjugated, and derived proteins are available from {Link: FAO https://www.fao.org/4/x5738e/x5738e04.htm}.
Simple Proteins
These yield only amino acids upon hydrolysis. Examples include albumins and globulins.
Conjugated Proteins
These contain a protein and a non-protein part, such as glycoproteins or lipoproteins.
Derived Proteins
Derived proteins result from the hydrolysis of simple or conjugated proteins. Examples include primary derived proteins like fibrin and secondary derived proteins like proteoses and peptones.
Classification by Nutritional Quality: Complete vs. Incomplete
Dietary proteins are categorized by their essential amino acid content.
Complete Proteins
Contain all nine essential amino acids. Animal foods and some plant foods like soy are complete.
Incomplete Proteins
Most plant foods lack one or more essential amino acids. Combining different plant proteins can provide a complete profile.
Classification by Shape and Function
Proteins vary in shape and roles.
Shape
- Globular Proteins: Compact, soluble, often functional.
- Fibrous Proteins: Long, insoluble, provide structural support.
Function
Proteins perform diverse roles like providing structure, catalyzing reactions, and transporting molecules.
Animal vs. Plant-Based Protein: A Nutritional Comparison
Understanding the nutritional differences between protein sources is important for a balanced diet. More information on protein requirements is available from the National Institutes of Health (NIH).
| Feature | Animal-Based Protein | Plant-Based Protein (Most) |
|---|---|---|
| Completeness | Complete | Incomplete |
| Amino Acid Profile | Provides all essential amino acids | Requires variety for a complete profile |
| Fat Content | Can be high in saturated fat | Generally lower in saturated fat, may contain healthy fats |
| Other Nutrients | Source of iron, zinc, B vitamins | Rich in fiber, phytonutrients |
| Dietary Strategy | Simple to ensure essential amino acids | Requires conscious combining |
Conclusion
What is classified as protein encompasses various categories based on composition, nutritional value, shape, and function. From simple and conjugated proteins to complete and incomplete dietary sources, each type is vital for life. Consuming a diverse range of protein sources ensures the body receives all necessary essential amino acids.
