Biology Chapter on Macromolecules and Lipids

Chemical Composition of the Body

• Humans are complex systems composed of tissues and organ systems.
• Organ systems contain extracellular matrices and cells.
• Cells are composed of organelles and molecules.
• Molecules are collections of atoms held together by chemical bonds.
• Atoms are made up of subatomic particles: a nucleus with protons and neutrons, and surrounding electrons.

Ions

• An ion results when an atom gains or loses one or more electrons, leading to an electrical charge.
• The charge is indicated using plus and minus signs.
• The number of plus or minus signs indicates the number of electrons gained or lost.
• Examples: Cl⁻ represents a chlorine atom that gained an electron, Ca²⁺ represents a calcium atom that lost two electrons.

Molecular Structure

• Several ways exist to represent molecular structure which helps understand function.
• Two-dimensional representations show the connectivity of atoms.
• Three-dimensional models provide a better visualization of the molecule's shape.
• Space-filling models illustrate the relative sizes of atoms in a molecule.
• Examples given for two-dimensional and three-dimensional representations include methane (CH₄) and ammonia (NH₃).

Chemical Bonds and Interactions

• Strong Bonds:
  • Covalent bonds: atoms share electrons, seen in methane (CH₄)
  • Ionic bonds: opposite charges attract (e.g., sodium chloride, Na⁺Cl⁻).
• Weak Interactions:
  • Hydrogen bonds: attraction between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen). This is shown in water molecules.
  • Van der Waals forces: weak, short-range attractive forces between molecules.

Solvent + Solute(s) = A Chemical Solution

• A solution consists of a solvent and one or more solutes.
• Chemical concentration measures the amount of solute dissolved in the solvent.
• Molecular weight (MW) is the mass in grams of one mole of a solute.
• One molar (1M) solution contains one mole of solute per liter of solvent.
• Example: glucose (C₆H₁₂O₆) has a MW of 180 g/mol, so a 1 M solution requires 180 grams of glucose dissolved in 1 liter of water.

Polar and Non-polar Bonds

• Polar compounds have atoms with opposite charges at each end (e.g., water). They readily associate with each other.
• Nonpolar compounds have atoms with similar charges at each end (e.g., some hydrocarbons). They readily associate with each other.
• Hydrophilic molecules dissolve readily in water.
• Hydrophobic molecules do not dissolve readily in water but often dissolve in nonpolar solvents.

NaCl Dissolves in Water

• Sodium chloride (NaCl) consists of Na⁺ and Cl⁻ ions.
• Water, due to its polarity, dissolves Na⁺ and Cl⁻ ions, forming a solution.
• Water molecules surround and dissolve Na⁺ and Cl⁻.
• Na⁺ and Cl⁻ are solutes, and water is the solvent.

Non-polar and Polar regions

• Non-polar regions associate with each other.
• Polar regions form hydrogen bonds with polar water molecules.

Organic Molecules

• Organic molecules contain carbon (C) and hydrogen (H)
• Four main types: carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Structure: sugars and starches; contain C, H, O (often with hydroxyl OH groups linked to carbons.) They are characterized as covalent bonded chains.
• Function: energy storage and production.
• Examples: glucose, fructose, sucrose, glycogen.

Lipids

• Structure: based on fatty acid monomers; long hydrocarbon chains, can be saturated (single bonds) or unsaturated (double bonds).
• Function: energy storage, cell membranes, hormones, insulation.
• Examples: triglycerides, phospholipids, steroids, cholesterol.

Proteins

• Structure: based on amino acid monomers; diverse shapes with different levels of structures, contain C, H, O, N (often with sulfur), with covalent bonds between amino acids.
• Function: many roles, including enzymes, cell attachment, cytoskeleton, locomotion, and hormones.
• All amino acids share an amino group and a carboxyl group and vary with their differing "side chains." Side chains can be nonpolar, polar, or ionized.

Nucleic Acids (Nucleotides)

• Structure: sugar + bases + phosphate; repeating units (nucleotides) in a chain.
• Functions: information storage (DNA and RNA), energy storage and transfer (ATP), coenzymes.
• DNA: deoxyribose sugar, contains four bases (adenine, guanine, cytosine, and thymine); double helix.
• RNA: ribose sugar, contains four bases (adenine, guanine cytosine, and uracil); single strand.

DNA and RNA Comparison

• Structure and function differ in the sugars, bases and chain quantities, and overall structure.