Chapter 3: Macromolecules – General Biology Study Notes

Chapter 3: Macromolecules

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids. They are built from smaller units called monomers, which join to form polymers through covalent bonds.

• Key Macromolecules: Carbohydrates, Lipids, Proteins, Nucleic Acids

• Monomers: Simple building blocks (e.g., amino acids, monosaccharides, nucleotides)

• Polymers: Chains of monomers (e.g., polypeptides, polysaccharides, DNA/RNA)

Carbon: The Basis of Macromolecules

Carbon's unique properties allow it to form the backbone of macromolecules due to its four valence electrons, enabling the formation of four covalent bonds with various atoms.

• Carbon Skeletons:

  • Carbon atoms bond to other carbon atoms, forming chains and rings

  • Chains form the skeletons of most organic molecules, varying in length and shape

• Isomers:

  • Structural isomers: Same chemical formula, different arrangement of atoms

  • Optical isomers: Mirror images of each other (e.g., L-DOPA vs. D-DOPA)

Functional Groups

Functional groups are specific groups of atoms within molecules that determine their chemical properties and reactions.

• Hydroxyl group

• Carbonyl group

• Carboxyl group

• Amino group

• Sulfhydryl group

• Phosphate group

• Methyl group

Functional groups influence molecular shape and interactions.

Monomers and Polymers

Monomers are linked by covalent bonds to form polymers. The process involves condensation (dehydration) reactions, which remove water to form bonds, and hydrolysis reactions, which add water to break bonds.

• Condensation (Dehydration) Reaction: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis Reaction: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Table: Building Blocks of Organisms

Monomer	Complex Polymer (Macromolecule)	Covalent Bond Type
Amino acids	Proteins (polypeptides)	Peptide linkage
Monosaccharides	Carbohydrates (polysaccharides)	Glycosidic linkage
Nucleotides	Nucleic acids (DNA & RNA)	Phosphodiester linkage

Carbohydrates

Carbohydrates are energy-rich organic compounds made of carbon, hydrogen, and oxygen. They exist as monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides: Simple sugars (3-7 carbons), e.g., glucose ($C_6H_{12}O_6$)

• Disaccharides: Two monosaccharides joined by glycosidic linkage (e.g., maltose = glucose + glucose)

• Polysaccharides: Long chains of monosaccharides (e.g., cellulose, starch, glycogen, chitin)

Polysaccharides serve structural (cellulose, chitin) and storage (starch, glycogen) functions.

Lipids

Lipids are hydrophobic molecules, including fats, oils, phospholipids, steroids, vitamins, and waxes. They are not true polymers.

• Fats & Oils (Triglycerides): Glycerol + 3 fatty acids; long-term energy storage

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes

• Steroids: Four fused carbon rings; includes cholesterol, hormones

• Vitamins (A, D, E, K): Must be acquired through diet

• Waxes: Saturated fatty acid + saturated alcohol (e.g., beeswax)

Saturated fatty acids: No double bonds; solid at room temperature. Unsaturated fatty acids: One or more double bonds; liquid at room temperature.

Amphipathic molecules: Have both polar and nonpolar regions (e.g., phospholipids).

Proteins

Proteins are polymers of amino acids joined by peptide bonds. They perform diverse functions, including catalysis, defense, transport, signaling, movement, and structural support.

• Enzymatic proteins: Accelerate chemical reactions (e.g., pepsin, catalase, amylase)

• Defensive proteins: Protect against disease (e.g., antibodies)

• Storage proteins: Store amino acids (e.g., casein)

• Transport proteins: Move substances (e.g., hemoglobin)

• Signal proteins (hormones): Coordinate activities (e.g., insulin)

• Receptor proteins: Respond to chemical stimuli

• Contractile proteins: Movement (e.g., actin, myosin)

• Structural proteins: Support (e.g., collagen, keratin)

Levels of Protein Structure

1. Primary: Sequence of amino acids

2. Secondary: Local folding (alpha helix, beta sheet) stabilized by hydrogen bonds

3. Tertiary: Overall 3D shape, interactions among R-groups

4. Quaternary: Multiple polypeptide chains

Nucleic Acids

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides.

• Nucleotide: Pentose sugar, phosphate group, nitrogenous base

• Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)

• Purines: Adenine (A), Guanine (G)

• Phosphodiester linkage: Bonds nucleotides in a chain

DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Strands	Double	Single

• Chargaff's Rules: In DNA, A pairs with T, G pairs with C

• Central Dogma: DNA → RNA → Protein

• Gene: Sequence of DNA that codes for a polypeptide

Types of RNA

• mRNA (messenger RNA): Carries genetic code from DNA to ribosome

• rRNA (ribosomal RNA): Component of ribosomes

• tRNA (transfer RNA): Delivers amino acids during protein synthesis

Summary Table: Macromolecules

Macromolecule	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Energy storage, structure
Lipids	Fatty acid, glycerol	Triglyceride, phospholipid	Energy storage, membranes
Proteins	Amino acid	Polypeptide	Catalysis, structure, transport
Nucleic Acids	Nucleotide	DNA, RNA	Genetic information

Example: Cellulose is a polysaccharide composed of glucose monomers joined by beta glycosidic linkages, providing structural support in plant cell walls.

Additional info: These notes expand on the original lecture content by providing definitions, examples, and tables for clarity and completeness.