Biology - Atoms and Molecules

Biology: Macromolecules (Chapter 3)

I. Introduction to Biology

  • Definition: Biology is the study of life, focusing on the structure, function, growth, evolution, and distribution of living organisms.

II. Macromolecules

  • Macromolecules are large molecules synthesized from smaller subunits (monomers).

    • Carbohydrates: Molecules composed of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1.

    • Chitin: A structural polysaccharide found in the exoskeletons of arthropods.

    • Cellulose: A structural polysaccharide that forms the cell wall in plants.

    • Glycogen: A storage polysaccharide in animals, which should be discussed later.

    • Starch: A storage polysaccharide in plants, consisting of glucose monomers. Formula: CnH{2n}O_n.

    • Glucose: A simple sugar (monosaccharide) with the molecular formula C6H{12}O_6.

  • Proteins: Large biomolecules consisting of one or more long chains of amino acid residues.

    • Monomer: Amino acids (there are 20 different types).

    • Polymer: Polypeptides are formed by linking amino acids through peptide bonds.

    • Amino acid structure includes:

    • Amino Group: NH_2

    • Carboxyl Group: COOH

    • R Group: Determines the properties of the amino acid.

  • Levels of Protein Structure:

    • Primary: Sequence of amino acids.

    • Secondary: Local folding into structures such as alpha-helixes and beta-sheets.

    • Tertiary: Overall 3D shape of a polypeptide, stabilized by interactions between R groups.

    • Quaternary: Arrangement of multiple polypeptide chains.

  • Chemical Reactions:

    • Dehydration Synthesis: A reaction that joins monomers to form polymers by removing a water molecule.

    • Example: ext{Monomer}1 + ext{Monomer}2
      ightarrow ext{Polymer} + H_2O.

    • Hydrolysis: A reaction that breaks polymers into monomers by adding water.

    • Example: ext{Polymer} + H2O ightarrow ext{Monomer}1 + ext{Monomer}_2.

  • Nucleic Acids: Macromolecules that store and transmit genetic information.

    • Monomer: Nucleotides, consisting of a sugar, phosphate group, and nitrogenous base.

    • Polymer: DNA and RNA.

    • DNA Structure: Double-stranded helices containing adenine (A), thymine (T), cytosine (C), and guanine (G). Base pairing follows Chargaff's rules: A = T and C = G.

    • RNA Structure: Single-stranded molecule with uracil (U) replacing thymine (T).

III. Lipids

  • Definition: Lipids are hydrophobic molecules that do not dissolve in water due to their nonpolar C-H bonds.

    • Types of Lipids:

    • Fats: Composed of one glycerol and three fatty acids (can be saturated or unsaturated).

    • Phospholipids: Composed of one glycerol, two fatty acids, and a phosphate group, essential in forming cellular membranes.

    • Steroids: Composed of fused ring structures and are important signaling molecules.

    • Vitamins: Essential nutrients that are not synthesized in sufficient quantities in the body.

  • Fatty Acid Types:

    • Saturated: Contain single bonds between carbon atoms; solid at room temperature.

    • Unsaturated: Contain one or more double bonds; usually liquid at room temperature.

    • Trans Fats: Artificially created fats through hydrogenation, known to be detrimental to health.

IV. Conclusion

  • Understanding macromolecules (carbohydrates, proteins, nucleic acids, and lipids) is fundamental in biology, as they are involved in the structure and function of cells and organisms.