Macromolecules in Food

Overview of Main Macromolecules

Food contains several essential macromolecules that are crucial for human physiology. Understanding their structure and function is foundational for anatomy and physiology students.

• Carbohydrates: Organic molecules composed of carbon, hydrogen, and oxygen. They serve as a primary energy source.

• Lipids: Hydrophobic molecules including fats, oils, and cholesterol. They are important for energy storage, cell membrane structure, and signaling.

• Proteins: Polymers of amino acids that perform a wide range of functions, including catalysis (enzymes), structural support, and transport.

• Additional info: Minerals (e.g., sodium, calcium) and vitamins are also present in food and are essential for various physiological processes.

Example: A hamburger contains carbohydrates (bun), lipids (cheese, meat), and proteins (meat, cheese).

Metabolism and Mass Balance

Mass Balance Model in Physiology

Metabolism refers to the sum of all chemical reactions in the body, including both anabolic (building up) and catabolic (breaking down) processes. The mass balance model helps explain how substances are processed and maintained in the body.

• Mass Balance Principle: Mass cannot be created or destroyed, only transformed. The food you eat is either used, stored, or excreted as waste.

• Anabolism: The process of building larger molecules from smaller ones (e.g., glycogenesis: formation of glycogen from glucose).

• Catabolism: The breakdown of larger molecules into smaller ones (e.g., glycogenolysis: breakdown of glycogen to release glucose).

Equation:

Example: Glucose absorbed from food can be stored in the liver as glycogen (anabolism) or released into the blood when needed (catabolism).

Carbohydrates: Structure and Function

Classification and Identification

Carbohydrates are classified based on their structure and complexity. Their digestion and absorption depend on their chemical properties.

• Monosaccharides: Simple sugars such as glucose and fructose.

• Disaccharides: Two monosaccharides joined together (e.g., maltose, lactose).

• Polysaccharides: Complex carbohydrates such as starch, glycogen, and cellulose.

Key Features:

• Carbohydrates contain carbon, hydrogen, and oxygen (CH2O units).

• Monosaccharides are polar and soluble in water.

• Complex carbohydrates differ in their branching and linkage types, affecting digestibility and function.

Example: Humans can digest starch and glycogen but not cellulose due to the absence of necessary enzymes.

3-Dimensional Structures and Storage Functions

The structure of polysaccharides determines their biological role and digestibility.

• Glycogen: Highly branched, stored in liver and muscle, easily mobilized for energy.

• Starch: Moderately branched, main storage carbohydrate in plants, digestible by humans.

• Cellulose: Linear, forms plant cell walls, not digestible by humans (fiber).

Table: Comparison of Polysaccharides

Lactose, Lactase, and Health Equity

Biochemistry and Physiology

Lactose is a disaccharide found in milk, composed of glucose and galactose. Lactase is the enzyme that breaks down lactose into absorbable monosaccharides.

• Lactose digestion: Requires lactase enzyme, produced in the small intestine.

• Lactase persistence: The continued production of lactase into adulthood; varies among populations due to genetic variation.

• Lactose intolerance: Occurs when lactase production decreases, leading to digestive symptoms upon consuming dairy.

Health Equity Issues:

• Lactase non-persistence is common globally; dairy consumption recommendations may not be appropriate for all populations.

• Bone health can be maintained with non-dairy sources of calcium and vitamin D.

• Research and dietary guidelines should consider cultural and genetic diversity.

Example: Many people of East Asian, African, and Indigenous descent have lactase non-persistence, yet Western dietary guidelines often emphasize dairy.

General Models in Physiology

Flux, Mass Balance, and Homeostatic Control

Physiology uses general models to explain and predict biological phenomena across scales.

• Flux: The rate of movement of substances (e.g., ions, molecules) across membranes or within compartments.

• Mass Balance: Used to predict changes in concentration or amount of substances in the body.

• Homeostatic Control Systems: Mechanisms that maintain internal stability (e.g., blood glucose regulation).

Equation (Flux):

Example: Blood glucose levels are regulated by insulin and glucagon through homeostatic control.

Strategies for Learning Physiology

Effective, Collaborative, and Scientific Approaches

Learning human physiology is enhanced by using evidence-based, collaborative strategies.

• Practice respectful communication and active listening.

• Share resources and build a supportive learning community.

• Take action when agreements are broken to maintain a positive environment.

Additional info: Intellectual humility and compassion are important for scientific collaboration and personal growth.