Biomolecules - Chemical constituents of living cells

Chemical Analysis: Living tissues are analyzed by grinding in trichloroacetic acid ($Cl_3CCOOH$). This separates them into an acid-soluble pool (biomicromolecules with molecular weights $18$ to $800$ Daltons) and an acid-insoluble fraction (biomacromolecules with weights $> 10,000$ Daltons).

Amino Acids: These are substituted methanes containing an amino group ($-NH_2$), a carboxyl group ($-COOH$), and a variable side chain ($R$). At a specific $pH$, they exist as Zwitterions: $H_3N^+-CHR-COO^-$.

Proteins: Heteropolymers of amino acids linked by peptide bonds ($-CONH-$). They exhibit four levels of structure: Primary (sequence), Secondary ($\alpha$-helix, $\beta$-sheets), Tertiary (3D folding/functionality), and Quaternary (assembly of subunits).

Lipids: Water-insoluble molecules, not strictly polymers. They include fatty acids ($R-COOH$) and glycerol ($CH_2OH-CHOH-CH_2OH$). Phospholipids like Lecithin are vital components of the cell membrane.

Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds. Examples include Cellulose (linear glucose polymer), Starch (helical energy store in plants), and Glycogen (branched energy store in animals).

Nucleic Acids: Polymers of nucleotides. Each nucleotide consists of a nitrogenous base (Adenine, Guanine, Cytosine, Thymine/Uracil), a pentose sugar ($C_5H_{10}O_5$), and a phosphate group ($-PO_4^{3-}$).

Enzymes: Biological catalysts that lower the activation energy ($\Delta G^{\ddagger}$) of a reaction. They show specificity and are sensitive to temperature, $pH$, and substrate concentration $[S]$.