Biological Macromolecules

Biological Macromolecules

  • Four Major Classes of Macromolecules

    1. Carbohydrates

    2. Lipids

    3. Proteins

    4. Nucleic Acids

  • Definition of Organic Molecules:

    • All organic molecules contain carbon.

    • They may also contain hydrogen, oxygen, nitrogen, and some other minor elements.

Background: Macromolecules

  • What are Macromolecules?

    • Large organic molecules found in cells that are made by combining smaller ones, known as monomers.

  • Definitions:

    • Monomers: Small organic molecules used to build macromolecules.

    • Polymers: Many monomers bound together to form larger molecules.

Polymerization

  • Monomers and Polymers:

    • When monomers undergo polymerization, they create a polymer through chemical reactions.

Mechanisms of Macromolecule Formation

  • Condensation/Dehydration Reactions:

    • These reactions are responsible for the synthesis of macromolecules.

    • Process: Each monomer typically has a hydroxide (OH) on one end and a hydrogen (H) on the other.

  • Formation of a Macromolecule:

    • When two monomers come together, a water molecule (H2O) is formed and lost, which results in a covalent bond between the two monomers, leading to macromolecule synthesis.

  • Hydrolysis Reactions:

    • This refers to breaking apart a bond between monomers by adding water (H2O), leading to macromolecule breakdown.

Carbohydrates

  • Composition of Carbohydrates:

    • Made up of carbons, hydrogens, and oxygens.

    • Monomer: Monosaccharide with the general formula CnH2nOn.

    • Example: Glucose has 6 carbons (C6H12O6), while ribose has 5 carbons.

  • Types of Carbohydrates:

    • Disaccharides: Composed of 2 carbohydrate monomers (e.g., sucrose, lactose).

    • Polysaccharides: Composed of more than 2 carbohydrate monomers (e.g., starch, cellulose).

  • Stereoisomers:

    • Same molecule with slightly different configurations.

    • They have the same formula and bonding relationships but differ spatially.

  • Polymers Formation:

    • Polymers of carbohydrates are formed through condensation reactions, where hydroxyl (–OH) groups are involved.

  • Covalent Bond:

    • α-1,4-glycosidic bond: A special name for the covalent bond formed between monosaccharides.

Types of Polysaccharides

  • Storage Polysaccharides:

    • Glycogen: Animal storage form for glucose.

    • Starch: Plant storage form for glucose.

  • Structural Polysaccharides:

    • Cellulose: Forms the cell wall of plants and is difficult to break down.

    • Chitin: Forms the cell wall of fungi and the external skeleton of bugs.

Proteins

  • Functions of Proteins:

    1. Gene regulation

    2. Motor proteins

    3. Defense proteins

    4. Metabolic enzymes

    5. Cell signaling

    6. Structural proteins

    7. Transporters

  • Structure of Proteins:

    • Proteins are polymers made from amino acids (20 types), which differ slightly in their chemical structure.

    • Monomer: Amino acids; Polymer: Polypeptides.

  • Components of an Amino Acid:

    • Amino Group (NH2)

    • Carboxyl Group (COOH)

    • R Group: The side chain that gives each amino acid its unique properties.

  • Polypeptide Formation:

    • Formed through condensation reactions leading to peptide bonds, linking amino acids together.

  • Protein Configuration (Conformation):

    • Primary Structure: Sequence of amino acids.

    • Secondary Structure: Folding or coiling due to hydrogen bonds (e.g., alpha-helix and beta-sheets).

    • Tertiary Structure: Overall 3D shape resulting from various chemical interactions.

    • Quaternary Structure: Formed when multiple polypeptide chains function together.

  • Denaturing of Proteins:

    • Denaturation dramatically alters a protein's shape and disrupts its function, which can be irreversible or reversible depending on the circumstances.

    • Factors that can denature proteins include:

    • Temperature

    • Salinity

    • Organic solvents

    • pH

Nucleic Acids

  • Flow of Information in the Cell:

    • DNA is responsible for storing genetic information, which is then translated into proteins that perform various cellular functions.

  • Major Polymer Types:

    1. DNA (Deoxyribonucleic acid)

    2. RNA (Ribonucleic acid)

  • Monomer: Nucleotides

    • Polymer: Nucleic acids.

  • Nucleotide Structure:

    • Composed of a phosphate group, a pentose sugar, and a nitrogenous base.

  • Differences in Nucleotide Structure:

    • DNA contains deoxyribose sugar; RNA contains ribose sugar.

  • Nitrogenous Bases:

    • Purines: Two rings (Adenine - A and Guanine - G)

    • Pyrimidines: One ring (Cytosine - C, Thymine - T, and Uracil - U).

  • Base Pairing:

    • In DNA, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C) through hydrogen bonds, resulting in a double-stranded structure.

  • Directionality in DNA Polymer:

    • Nucleotides are joined by condensation reactions which create phosphodiester bonds, establishing a 5' end and a 3' end for DNA strands.

Lipids

  • Characteristics of Lipids:

    • Not a “true” macromolecule; do not have a set monomer.

    • They are diverse in types and primarily composed of carbon and hydrogen, which gives them their hydrophobic properties.

  • Types of Lipids:

    • Triglycerides:

    • Comprised of glycerol and fatty acids.

    • Functions in energy storage and are major dietary fats.

    • Phospholipids:

    • Made up of a diglyceride and are important in membrane formation due to their amphipathic nature (having both polar and non-polar regions).

    • Steroids:

    • Characterized by a ring structure and non-water soluble properties.

    • Example: Cholesterol, which serves as a signaling molecule.