JJ

Biomolecules & Lab Tests - Quick Notes

  • Biomolecules in cells - Main types: proteins, carbohydrates, lipids, and nucleic acids; all are organic, carbon-based molecules essential for life.

    • Cells build larger polymers from smaller monomer units via dehydration synthesis (anabolic) and break down polymers into monomers via hydrolysis (catabolic).

    • Lab tests require carefully designed controls for accurate interpretation and validity.

  • Reactions involving biomolecules

    • Dehydration synthesis (dehydration reaction): chemical reaction joining two molecules by removing a water molecule, forming a larger macromolecule (polymer).

    • Hydrolysis: chemical breakdown of a compound due to reaction with water, breaking a macromolecule into smaller units (monomers).

    • General equations:

    • Dehydration: \text{Monomer}_1 + \text{Monomer}_2 \longrightarrow \text{Dimer} + \text{H}_2\text{O}

    • Polymer formation (general): n\, \text{monomers} \longrightarrow \text{polymer} + (n-1)\, \text{H}_2\text{O}

    • Hydrolysis: \text{Polymer} + \text{H}_2\text{O} \longrightarrow \text{Monomer}_1 + \text{Monomer}_2

  • Proteins

    • Built from 20 standard types of amino acids (monomers).

    • Basic amino acid structure: central (alpha) carbon bonded to an amino group (-\text{NH}_2), a carboxyl group (-\text{COOH}), a hydrogen atom, and a variable R group (side chain).

    • Proteins serve diverse functions (e.g., catalysis, structural support, transport).

    • Peptide bond: forms via dehydration synthesis between amino acids.

    • Proteins exhibit four levels of structure:

    • Primary structure: unique linear sequence of amino acids.

    • Secondary structure: local folds (alpha-helices, beta-pleated sheets) via hydrogen bonds.

    • Tertiary structure: overall three-dimensional shape from R-group interactions.

    • Quaternary structure: arrangement of multiple polypeptide chains in a complex.

    • Denaturation: loss of protein's specific shape and biological function due to extreme conditions.

  • Carbohydrates

    • Types: monosaccharides (simple sugars), disaccharides (two monosaccharides), and polysaccharides (complex carbohydrates).

    • Monosaccharides (single sugar units): General formula: (CH_2O)_n. Examples: glucose, fructose, galactose, ribose, deoxyribose.

    • Disaccharides: formed by joining two monosaccharides (e.g., lactose, sucrose, maltose).

    • Polysaccharides: long polymers of monosaccharides; serve as energy storage or structural components.

    • Starch (plants): energy storage, alpha-glycosidic linkages.

    • Glycogen (animals): highly branched energy storage in liver and muscles, alpha-glycosidic linkages.

    • Cellulose (plants): structural component of plant cell walls, beta-glycosidic linkages, largely indigestible by humans.

  • Lipids

    • Diverse group of hydrophobic (water-fearing) molecules, including fats, oils, steroids, and phospholipids.

    • Fatty acids: long hydrocarbon chains with a carboxyl group.

    • Saturated fatty acids: no carbon-carbon double bonds, straight chains, solid at room temperature.

    • Unsaturated fatty acids: one or more carbon-carbon double bonds, kinks in chain, liquid at room temperature (cis or trans).

    • Triglycerides: one glycerol molecule and three fatty acid chains; primary energy storage.

    • Phospholipids: glycerol backbone, two fatty acid tails, and a phosphate group. Amphipathic (polar/hydrophilic head, nonpolar/hydrophobic tails). Form phospholipid bilayer in cell membranes, dictating selective permeability.

    • Steroids: characterized by four fused rings (e.g., cholesterol, steroid hormones).

  • Lab tests and controls

    • Controls are essential experimental components that validate reliability and accuracy of results.

    • Positive control: contains the tested substance, gives a known positive result, confirms test functionality.

    • Negative control: lacks the tested substance, should give a negative result, confirms test specificity and rules out contamination or error.

    • Protein test (Biuret-type reagent): Blue to purple/pink in presence of peptide bonds.

    • Carbohydrates tests:

    • Iodine test for starch: Yellowish-brown to blue-black/purple.

    • Benedict's test for reducing sugars: Blue to green/yellow/orange/brick red with heat (indicating reducing sugars).

    • Lipids test: Emulsification test: Lipids dissolved in ethanol, then water added; forms cloudy white emulsion.

  • Enzymes and digestion (context for tests)

    • Enzymes are biological catalysts (typically proteins) that speed up biochemical reactions and are highly specific.

    • Proteases: break down proteins into amino acids.

    • Carbohydrate-digesting enzymes: break down carbohydrates into monosaccharides.

    • Lipases: break down lipids into fatty acids and glycerol.