Macromolecules: Structure, Function, and Properties

Macromolecules in Biology

Definitions: Monomer and Polymer

Macromolecules are large, complex molecules essential for life. They are typically formed by the joining of smaller units called monomers.

• Monomer: A small, repeating molecular unit that can join with other similar units to form a larger molecule. Example: Glucose is a monomer of starch.

• Polymer: A large molecule composed of many repeated subunits (monomers) bonded together. Example: Cellulose is a polymer made of glucose monomers.

Analogy: A polymer is like a train, and each monomer is a train car. Linking many cars together forms the whole train, just as linking monomers forms a polymer.

Major Biological Macromolecules

There are four main classes of biological macromolecules: lipids, carbohydrates, proteins, and nucleic acids. Each has unique monomers, polymers, and functions.

Macromolecule	Elements Found	Monomer Example	Polymer Example
Lipids	Carbon (C), Hydrogen (H), Oxygen (O)	Glycerol & Fatty Acids	Triglyceride
Carbohydrates	Carbon (C), Hydrogen (H), Oxygen (O)	Monosaccharide (e.g., Glucose)	Polysaccharide (e.g., Starch, Cellulose)
Proteins	Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), (sometimes Sulfur (S))	Amino Acid	Polypeptide/Protein
Nucleic Acids	Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P)	Nucleotide	DNA, RNA

Saturated vs. Unsaturated Fats

The structure of fatty acids determines whether a fat is saturated or unsaturated, which in turn affects its physical properties.

• Saturated Fats: Have no double bonds between carbon atoms; all carbons are saturated with hydrogen. They are typically solid at room temperature (e.g., butter).

• Unsaturated Fats: Contain one or more double bonds, causing kinks in the chain. These are usually liquid at room temperature (e.g., olive oil).

• Physical State: The kinks in unsaturated fats prevent tight packing, making them liquid, while saturated fats pack closely and are solid.

Polarity and Solubility of Lipids

• Polarity: Lipids are generally non-polar due to long hydrocarbon chains.

• Solubility: They are insoluble in water because water is polar and "like dissolves like." Lipids dissolve in non-polar solvents.

Formation of Polymers: Example of Triglyceride Synthesis

Polymers such as triglycerides form through dehydration synthesis (condensation reaction), where water is removed as monomers join.

• Triglyceride Formation: Three fatty acids bond to one glycerol molecule, releasing three water molecules.

Equation:

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

Structure of Amino Acids

Amino acids are the building blocks of proteins. Each has a central carbon atom bonded to four groups:

• Amino group ($-\text{NH}_2$)

• Carboxyl group ($-\text{COOH}$)

• Hydrogen atom

• R group (side chain, varies for each amino acid)

Generic Structure:

$\text{H}_2\text{N}-\text{CH}(\text{R})-\text{COOH}$

Similarity and Difference in Amino Acids

• Same Parts: All amino acids have the amino group, carboxyl group, and hydrogen attached to the central carbon.

• Difference: The R group (side chain) is unique for each amino acid and determines its properties.

Structure of Nucleotides

Nucleotides are the monomers of nucleic acids. Each nucleotide consists of three parts:

• Phosphate group

• Pentose sugar (either ribose or deoxyribose)

• Nitrogenous base (A, T, C, G, or U)

Example: ATP (adenosine triphosphate) is a nucleotide with three phosphate groups, ribose sugar, and adenine base.

Sugars in Nucleic Acids and Their Polymers

• Deoxyribose: Found in DNA (deoxyribonucleic acid)

• Ribose: Found in RNA (ribonucleic acid)

• Polymers: DNA and RNA are polymers of nucleotides containing these sugars.

Bases in DNA and RNA

• DNA Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

• RNA Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

• Unique Base: Uracil is unique to RNA and replaces thymine.