Macromolecules: Structure, Function, and Digestion in General Biology

Macromolecules: Big Molecules Acquired from Diet

Overview of Macromolecules

Cells require large molecules, known as macromolecules, for structure, energy, and function. These macromolecules must be broken down into smaller components to be utilized by the cell.

• Fats/Lipids

• Carbohydrates (complex carbs)

• Proteins

• Nucleic acids

Key Features:

• Macromolecules are too large to be transported directly into cells.

• They must be digested into simpler building blocks.

Structure: Macromolecules have complex structures with many bonds between molecules.

• Hydro = Water

• Lysis = Break

Hydrolysis is the process of breaking bonds using water. Simple dissolution in water does not break these bonds; specific mechanisms are required.

Three Ways to Break Bonds in Macromolecules

• Heat

• Acid

• Enzymes (primary method; enzymes are a type of protein)

Enzymatic Hydrolysis and Digestion

Enzymatic hydrolysis is essential for digestion, breaking down macromolecules into absorbable units.

• Starch (complex carbohydrate) → Glucose: Main energy source for cells

• Lipids (fats) → Fatty acids

• Proteins → Amino acids (enzymatic hydrolysis involves 20 amino acids)

Carbohydrates

Glucose

Glucose is a simple sugar and a primary energy source for cells.

• Provides short-term energy

• Cannot be stored as glucose for long periods

• Glucose is water-soluble

• When glucose enters a cell, water follows it due to osmosis

Glycogen

Glycogen is a medium/long-term energy storage molecule in animals.

• Converts excess, unused glucose into glycogen, stored in muscle and liver

• Glycogen is not water-soluble

• When glycogen stores are full, excess glucose is converted to fat

Starch

Starch is the primary energy storage molecule in plants.

• Humans have enzymes to digest starch

Cellulose

Cellulose is a major component of plant cell walls, providing rigidity.

• Dietary fiber: Nutrition label includes cellulose

• Promotes regularity in digestion

• Gut bacteria can digest cellulose, producing short-chain fatty acids beneficial for health

Fats/Lipids

General Properties

• Most energy-dense macromolecule: ~2x calories per gram compared to carbohydrates/proteins

• Long-term energy storage

• Fat molecule: Triglyceride = 3 fatty acids

Unsaturated Fats

Unsaturated fats have a kink in one tail, are liquid at room temperature, and are more likely to be used as energy.

• Promote liver's production of HDL cholesterol, which removes LDL cholesterol from blood

• Reduce risk of heart disease

Saturated Fats

Saturated fats have straight tails, are more likely to be stored as fat, and promote production of LDL cholesterol, which can build up in arteries.

• Common sources: steak, butter

HDL cholesterol = good LDL cholesterol = bad

Proteins

Functions of Proteins

Proteins are essential macromolecules with diverse functions in the cell.

• Enzymes: Catalyze biochemical reactions

• Transport of nutrients

• Signaling (cell communication)

• Antibodies (immune defense)

• Structure (e.g., cytoskeleton)

• Storage (e.g., storage proteins in seeds)

Genetic Basis and Diversity

• Each of the 20,000–25,000 genes in human DNA codes for a unique protein

• Proteins can be modified to have new functions

• Humans can produce over 100,000 different proteins

• "Ingredients" for proteins are the 20 amino acids

Summary Table: Macromolecules and Their Properties

Macromolecule	Monomer/Building Block	Main Function	Storage Form	Examples
Carbohydrates	Monosaccharides (e.g., glucose)	Energy (short-term)	Glycogen (animals), Starch (plants)	Glucose, Starch, Cellulose
Fats/Lipids	Fatty acids, Glycerol	Energy (long-term), Structure	Triglycerides	Butter, Oils
Proteins	Amino acids	Enzymes, Structure, Transport, Signaling	Various (no universal storage form)	Hemoglobin, Enzymes
Nucleic acids	Nucleotides	Genetic information	DNA, RNA	DNA, RNA

Key Equations

• Hydrolysis Reaction:

$\text{Macromolecule} + \text{H}_2\text{O} \rightarrow \text{Monomers}$

• Triglyceride Formation:

$\text{Glycerol} + 3\ \text{Fatty Acids} \rightarrow \text{Triglyceride} + 3\ \text{H}_2\text{O}$

• Protein Synthesis:

$\text{Amino Acids} \xrightarrow{\text{Ribosome}} \text{Protein}$

Additional info: Academic context and definitions have been expanded for clarity and completeness. The summary table is inferred from standard biology curriculum.