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Biology LibreTexts

Unit 2: The Molecules of Life

  • 2.1: Organic Molecules
  • 2.2: Hydrocarbons
  • 2.3: Fats
    Fat molecules are made up of four parts: a molecule of glycerol (on the right) and three molecules of fatty acids.
  • 2.4: Phospholipids
    Phospholipids are fat derivatives in which one fatty acid has been replaced by a phosphate group and one of several nitrogen-containing molecules.
  • 2.5: Cholesterol
    The cholesterol molecule is a steroid that is essential to life. It has also been responsible for 17 Nobel Prizes, countless pages of reports in scientific journals and the popular press, and mounting anxiety on the part of health-conscious people. The human body contains about 100 g of cholesterol. Most of this is incorporated in the membranes from which cells are constructed and is an indispensable component of them. The insulating layers of myelin wound around neurons are rich in cholesterol.
  • 2.6: Carbohydrates
    Carbohydrates were once thought to represent "hydrated carbon". However, the arrangement of atoms in carbohydrates has little to do with water molecules. Starch and cellulose are two common carbohydrates. Both are macromolecules with molecular weights in the hundreds of thousands. Both are polymers built from repeating units, monomers, much as a chain is built from its links. The monomers of both starch and cellulose are the same: units of the sugar glucose.
  • 2.7: Amino Acids
    Amino acids are the building blocks (monomers) of proteins. 20 different amino acids are used to synthesize proteins. The shape and other properties of each protein is dictated by the precise sequence of amino acids in it.
  • 2.8: Enantiomers
    In three-dimensional (3D) space, the four covalent bonds of carbon atoms point toward the corners of a regular tetrahedron.
  • 2.9: Polypeptides
    Polypeptides are chains of amino acids. Proteins are made up of one or more polypeptide molecules. The amino acids are linked covalently by peptide bonds. The picture below shows how three amino acids are linked by peptide bonds into a tripeptide.
  • 2.10: Proteins
    Proteins are macromolecules. They are constructed from one or more unbranched chains of amino acids; that is, they are polymers. An average eukaryotic protein contains around 500 amino acids but some are much smaller (the smallest are often called peptides) and some much larger (the largest to date is titin a protein found in skeletal and cardiac muscle; one version contains 34,350 amino acids in a single chain!).
  • 2.11: Rules of Protein Structure
  • 2.12: Glycoproteins
  • 2.13: Nucleotides
  • 2.14: Proteomics
    While we humans probably have only some 21 thousand genes, we probably make at least 10 times that number of different proteins. The great majority of our genes produce pre-mRNAs that are alternatively-spliced. The study of proteomics is important because proteins are responsible for both the structure and the functions of all living things. Genes are simply the instructions for making proteins. It is proteins that make life.