Macromolecules

3.1 Carbon & Organic Frameworks

Carbon Framework: Biological molecules consist primarily of carbon atoms bonded to one another and to hydrogen, oxygen, nitrogen, sulfur, or phosphorus.
Functional Groups: Acts like "attachments" to a core carbon "power unit," giving molecules distinct chemical properties.
- Hydroxyl ( $-\text{OH}$ ): Polar; found in carbohydrates, proteins, nucleic acids, lipids.
- Carbonyl ( $-\text{C=O}$ ): Polar; found in carbohydrates, nucleic acids.
- Carboxyl ( $-\text{COOH}$ ): Acidic; found in proteins, lipids.
- Amino ( $-\text{NH}_2$ ): Basic; found in proteins, nucleic acids.
- Sulfhydryl ( $-\text{S-H}$ ): Form disulfide links; found in proteins.
- Phosphate ( $-\text{PO}_4^{2-}$ ): Charged; found in nucleic acids.
- Methyl ( $-\text{CH}_3$ ): Nonpolar; found in proteins, nucleic acids.
Isomers: Same molecular formula, different structures.
- Structural Isomers: Identical groups bonded to different carbons (e.g., Glucose vs. Fructose).
- Stereoisomers: Same carbon backbone, differ in spatial group attachment (e.g., Glucose vs. Galactose).
- Enantiomers: Non-superimposable mirror-image chiral molecules.
Reactions:
- Dehydration Synthesis: Monomers assemble into polymers by removing $\text{H}_2\text{O}$ .
- Hydrolysis: Polymers break down into monomers by adding $\text{H}_2\text{O}$ .

3.2 Carbohydrates (1:2:1 C:H:O Ratio)

Carbohydrate Type	Subunits & Linkages	Functions & Examples
Monosaccharides	Single sugar units ( $3\text{C}$ Glyceraldehyde, $5\text{C}$ Ribose/Deoxyribose, $6\text{C}$ Glucose/Fructose/Galactose)	Energy source; structural components of nucleotides.
Disaccharides	Two monosaccharides joined via dehydration	Sucrose: Plant sugar transport; Lactose: Milk sugar; Maltose: Malt sugar.
Storage Polysaccharides	$\alpha\text{-glucose}$ , $\alpha$ -1,4 and $\alpha$ -1,6 linkages	Starch (Amylose/Amylopectin) in plants; Glycogen (highly branched) in animals.
Structural Polysaccharides	$\beta\text{-glucose}$ or N-acetylglucosamine, $\beta$ -1,4 linkages	Cellulose in plant cell walls; Chitin in fungal cell walls and arthropod exoskeletons.

3.3 Nucleic Acids

Monomer: Nucleotide = 5-carbon sugar + Phosphate group + Nitrogenous base.
Bases:
- Pyramidines (single ring): Cytosine, Thymine (DNA only), Uracil (RNA only).
- Purines (double ring): Adenine, Guanine.
Base Pairing:
- Adenine pairs with Thymine/Uracil ( $2\text{ H-bonds}$ ).
- Cytosine pairs with Guanine ( $3\text{ H-bonds}$ ).
DNA vs. RNA:
- DNA: Double-stranded helix, antiparallel strands ( $5' \to 3'$ and $3' \to 5'$ ), uses deoxyribose sugar.
- RNA: Single-stranded, uses ribose sugar. Types include mRNA (messenger), tRNA (transfer), rRNA (ribosomal).
Energy Currency: ATP (Adenosine Triphosphate) provides cellular energy when phosphate bonds break. Electron carriers include $\text{NAD}^+$ and FAD.

3.4 Proteins

Functions: Enzyme catalysis, defense, transport, support, motion, regulation, storage.
Monomer: Amino acids linked via peptide bonds. Classified into 5 groups based on R-group properties (Nonpolar, Polar uncharged, Acidic, Basic, Special).
Levels of Structure:
1. Primary: Linear amino acid sequence.
2. Secondary: Local folding ( $\alpha$ -helices, $\beta$ -pleated sheets) via backbone hydrogen bonds.
3. Tertiary: Overall 3D shape driven by hydrophobic interactions, ionic bonds, disulfide links, and Van der Waals forces.
4. Quaternary: Complex of multiple polypeptide chains.
Helper Structures:
- Motifs: Common folding patterns ("words").
- Domains: Functional units performing specific tasks ("paragraphs").
- Chaperone Proteins: Assist in proper protein folding and refolding.

3.5 Lipids

Property: Insoluble in water due to nonpolar $\text{C-H}$ bonds.
Triglycerides: $1\text{ glycerol} + 3\text{ fatty acid chains}$ .
- Saturated: No double bonds; straight chains.
- Unsaturated: Contains double bonds causing kinks.
Phospholipids: Glycerol backbone + $2\text{ fatty acids}$ (hydrophobic) + 1 phosphate group (hydrophilic). Forms cell membranes via lipid bilayers or micelles.
Other Lipids: Steroids, Terpenes, Prostaglandins, Waxes, Carotenoids.