Question

list and describe the four major macromolecules (biomolecules)

Answer 1

The four major biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Brief descriptions follow for each (monomer, structure, key functions, examples).

1. Carbohydrates
- Monomer: monosaccharides (glucose, fructose, galactose).
- Polymer: disaccharides (sucrose, lactose) and polysaccharides (starch, glycogen, cellulose, chitin).
- Bond type: glycosidic bonds formed by dehydration synthesis; broken by hydrolysis.
- Elements: C, H, O (general formula roughly (CH2O)n).
- Main functions: immediate and short-term energy source (glucose), energy storage (glycogen in animals, starch in plants), structural support (cellulose in plant cell walls, chitin in arthropod exoskeletons), cell recognition/signaling (glycoproteins/glycolipids).
- Examples: bread (starch), blood glucose, plant fiber (cellulose).

2. Lipids
- Monomers: not true repeating monomers for all lipids; common subunits are fatty acids and glycerol (for triglycerides) or fatty acids + other groups (phospholipids), or steroid ring structures.
- Types: triglycerides (fats and oils), phospholipids, steroids (cholesterol, steroid hormones), waxes.
- Bond type: ester bonds (in triglycerides) and hydrophobic interactions; nonpolar overall.
- Elements: C, H, O (often much more H relative to O); some contain P (phospholipids) or other atoms.
- Main functions: long-term energy storage (fats), insulation and cushioning, membrane structure (phospholipid bilayer), signaling and hormones (steroids), water-proofing (waxes).
- Examples: butter/olive oil (triglycerides), cell membranes (phospholipids), cholesterol (steroid).

3. Proteins
- Monomer: amino acids (20 common amino acids).
- Polymer: polypeptides/proteins joined by peptide (amide) bonds from dehydration synthesis.
- Structure levels: primary (sequence), secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multi-subunit complexes).
- Elements: C, H, O, N, often S (in cysteine) and sometimes other elements bound to cofactors.
- Main functions: enzymes (biological catalysts), structural support (collagen, keratin), transport (hemoglobin, membrane transporters), signaling (hormones, receptors), immune defense (antibodies), movement (actin/myosin).
- Examples: enzymes like amylase, muscle proteins, insulin.

4. Nucleic acids
- Monomer: nucleotides (sugar + phosphate + nitrogenous base).
- Polymer: DNA and RNA (polynucleotide chains) with phosphodiester bonds linking nucleotides.
- Elements: C, H, O, N, P.
- Main functions: storage and transmission of genetic information (DNA), directing protein synthesis and various catalytic/regulatory roles (RNA: mRNA, tRNA, rRNA, regulatory RNAs).
- Examples: genomic DNA, messenger RNA, ATP (a nucleotide that also functions as an energy currency).

Common chemistry note: Macromolecules are typically built by dehydration (condensation) reactions and broken down by hydrolysis. Their structure determines their biological function.