Macromolecules in Biology

Introduction to Biological Macromolecules

All living organisms, from single-celled bacteria to complex animals, depend on four main classes of organic (carbon-based) compounds: carbohydrates, lipids, proteins, and nucleic acids. These are called macromolecules because they are large molecules essential for structure and function in cells. They play roles in energy storage, growth, repair, and communication.

• Carbohydrates: Provide energy and structural support.

• Lipids: Store energy and make up cell membranes.

• Proteins: Perform a wide range of functions, including catalyzing reactions and providing structure.

• Nucleic acids: Store and transmit genetic information (DNA and RNA).

Additional info: Nucleic acids are not included in the main tables but are essential for genetic information storage and transfer.

Dietary Sources and Animal Nutrition

Herbivores vs. Carnivores

Animals obtain macromolecules from their diets. Herbivores (e.g., elephants) eat plants, while carnivores (e.g., lions) eat other animals. The type of food consumed determines the macromolecules available for energy and growth.

• Herbivores: Diets high in carbohydrates (from plants), moderate in protein, low in fat.

• Carnivores: Diets high in protein and fat, low in carbohydrates.

Comparative Diet Table

The following tables compare the macromolecule content in the diets of elephants and lions.

Structure and Function of Macromolecules

Carbohydrates

Carbohydrates are made of carbon (C), hydrogen (H), and oxygen (O). They are the primary energy source for many organisms.

• Monosaccharide: Simple sugar (e.g., glucose).

• Disaccharide: Two monosaccharides joined (e.g., sucrose).

• Polysaccharide: Many monosaccharides joined (e.g., starch, cellulose).

General formula:

Lipids

Lipids are composed mainly of carbon, hydrogen, and a small amount of oxygen. They are used for long-term energy storage and make up cell membranes.

• Fatty acids: Long hydrocarbon chains.

• Triglycerides: Formed from glycerol and three fatty acids.

Proteins

Proteins are made of amino acids, which contain carbon, hydrogen, oxygen, and nitrogen (sometimes sulfur). They are essential for structure, function, and regulation of tissues and organs.

• Amino acid: Building block of proteins.

• Peptide bond: Covalent bond joining amino acids.

Comparing Macromolecules

Similarities

• All contain carbon, hydrogen, and oxygen.

• All are built from smaller subunits (monomers).

• All are essential for life processes.

Differences

• Different structures and functions.

• Proteins contain nitrogen (and sometimes sulfur), while carbohydrates and lipids do not.

• Carbohydrates have a 2:1 ratio of hydrogen to oxygen; lipids have much less oxygen.

Chemical Reactions and Energy

ATP and Energy Release

During metabolism, bonds in macromolecules are broken and reformed. Breaking bonds releases energy, often stored in ATP (adenosine triphosphate) molecules. The more carbon atoms in a molecule, the more energy it can provide when broken down.

Energy released per bond:

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Examples of Macromolecule Reactions

Carbohydrate Breakdown (Elephant Diet)

Example: Sucrose hydrolysis

• Reactants: Sucrose and water

• Products: Glucose and fructose

• Type of reaction: Hydrolysis

• Function: Provides energy for the organism

Protein Synthesis and Breakdown (Lion Diet)

Proteins are broken down into amino acids by hydrolysis and built by dehydration synthesis. Peptide bonds join amino acids, releasing water.

Example reaction:

• Reactants: Amino acids

• Products: Peptide (protein) and water

Lipid Synthesis (Lion Diet)

Triglycerides are formed from glycerol and three fatty acids via dehydration synthesis.

Energy Calculations in Digestion

Energy Released from Bond Breaking

When macromolecules are digested, bonds are broken, releasing energy. The number of bonds broken and formed can be used to calculate net energy gain.

Additional info: Each peptide bond broken releases 10 kcal of energy.

Protein Synthesis Energy Use

Cellulose Digestion in Herbivores

Cellulose Structure and Breakdown

Cellulose is a polysaccharide found in plant cell walls. Herbivores like elephants digest cellulose to obtain glucose for energy. The breakdown involves hydrolysis of glycosidic bonds.

• Step 1: Cellulose in plant cell walls

• Step 2-5: Sequential hydrolysis of cellulose to glucose monomers

Energy Released from Cellulose Breakdown

Comparative Energy Efficiency

Animals vs. Plants as Food Sources

Comparing the energy obtained from animal and plant sources helps determine which is more efficient for nutrient acquisition. Carnivores obtain more energy per gram from animal tissue (high in protein and fat), while herbivores rely on large quantities of plant material (high in carbohydrates).

• Claim: Animal tissue provides more energy per gram than plant tissue.

• Evidence: Higher fat and protein content in animal diets; more bonds to break for energy release.

Key Terms and Definitions

• Macromolecule: Large molecule made of smaller subunits (monomers).

• Monomer: Small molecule that joins with others to form a polymer.

• Polymer: Large molecule made of repeating monomers.

• Dehydration synthesis: Reaction joining monomers by removing water.

• Hydrolysis: Reaction breaking polymers into monomers by adding water.

• Peptide bond: Covalent bond joining amino acids in proteins.

• ATP: Adenosine triphosphate, the main energy carrier in cells.

Summary Table: Macromolecule Comparison