Elements of Life and Macromolecules

1.2 Elements of Life

  • Organisms are composed of matter, which occupies space and possesses mass.
  • Matter consists of atoms, which are made up of protons, neutrons, and electrons.
  • Atoms combine to form matter in various states (solids, liquids, gases) and elements.
  • Elements are substances that cannot be broken down further by chemical reactions.
  • Key elements for AP Biology include:
    • Oxygen (O)
    • Carbon (C)
    • Hydrogen (H)
    • Nitrogen (N)
    • Calcium (Ca)
    • Phosphorus (P)
    • Potassium (K)
    • Sulfur (S)
    • Sodium (Na)
    • Chlorine (Cl)
    • Magnesium (Mg)
  • Compounds are substances made of two or more elements in a fixed ratio, such as water (H_2O).
  • Living systems require constant exchange of energy and macromolecules for growth and reproduction.

Atoms

  • Atoms are the smallest unit of mass that retain an element's properties.
  • Subatomic particles:
    • Protons: positive charge
    • Neutrons: neutral charge
    • Electrons: negative charge
  • Atomic number: number of protons in the nucleus. For example, Carbon has an atomic number of 6.
  • Atomic mass number: sum of protons and neutrons in the nucleus. For example, Carbon-12 has an atomic mass of approximately 12.

Isotopes

  • Isotopes are atoms of the same element with different numbers of neutrons.
  • Radioactive isotopes decay spontaneously and release energy; used for fossil dating and medical imaging.
  • Carbon-14 (radiocarbon): Radioactive isotope with 6 protons and 8 neutrons; used for dating sites, fossils, and artifacts.

Electron Shells

  • Electron's potential energy is called an energy level or electron shell.
  • Electrons absorb energy and move to higher energy levels farther from the nucleus.
  • Electrons release energy and move closer to the nucleus.

Elemental Building Blocks

Carbon

  • Carbon is the primary building block of macromolecules (carbohydrates, lipids, proteins, and nucleic acids).
  • It's a major component of organic compounds and cells.
  • Carbon can form four covalent bonds (tetra-valence).
  • Atoms need to be stable, and Carbon is relatively stable when bonded with other molecules.
  • Carbon needs four more electrons to fill its outer shell to satisfy the octet rule.
  • Octet rule: atoms gain, lose, or share electrons to achieve an electron configuration of eight valence electrons; for example, methane (CH_4).

Nitrogen

  • Nitrogen is a building block in proteins, nucleic acids, amino acids, and enzymes.
  • Plays crucial roles in metabolism, cell division, and DNA replication.
  • Component of many hormones, like adrenaline and insulin.
  • Nitrogen is important in the nitrogen cycle, which balances nutrients in ecosystems.
  • Nitrogen fixation: conversion of atmospheric nitrogen into usable forms by plants and microorganisms.

Phosphorus

  • Phosphorus is a key component of nucleic acids, certain proteins, and lipids.
  • Involved in DNA and RNA (genetic material).
  • Involved in biological processes like energy production and maintaining nutrient balance in ecosystems.

Macromolecules

  • Macromolecules are large molecules formed by polymerization.

  • Monomers form covalent bonds to create polymers.

  • Four major classes of macromolecules:

    • Carbohydrates: composed of monosaccharides
    • Lipids: composed of fatty acids and glycerol
    • Proteins: composed of amino acids
    • Nucleic Acids: composed of nucleotides (sugar residues and nucleobases)