Ch 9 covers the four major classes of biomolecules — carbohydrates, proteins, lipids, and nucleic acids — their structure, classification, and functions, along with enzymes.
Carbohydrates: monosaccharides (glucose, fructose), disaccharides (sucrose, lactose), polysaccharides (starch, cellulose, glycogen). Proteins: polymers of amino acids (20 types) joined by peptide bonds. Structure levels: primary → secondary (α-helix, β-sheet) → tertiary → quaternary. Lipids: fats (glycerol + fatty acids), phospholipids (cell membrane), steroids (cholesterol). Nucleic acids: DNA (double helix, ATGC) and RNA (single-stranded, AUGC).
Enzymes: biological catalysts (mostly proteins). Lower activation energy without being consumed. Lock and key model: enzyme active site fits substrate exactly. Induced fit: active site moulds to substrate. Factors: temperature, pH, substrate concentration. Inhibition: competitive (blocks active site), non-competitive (changes shape). Cofactors: metal ions; coenzymes: organic (NAD, FAD).
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Enzymes are biological catalysts — protein molecules that speed up chemical reactions in cells by lowering activation energy. Without enzymes, most biochemical reactions would be too slow to sustain life. They are highly specific (each enzyme catalyses one type of reaction), reusable, and regulated by the cell. Examples: amylase digests starch, DNA polymerase copies DNA.
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