chapter 7

• Proteins


  One of the most abundant organic molecules in living systems with the most diverse range of functions of all macromolecules
• Functions of proteins

  • Structural
  • Regulatory
  • Contractile
  • Protective
  • Transport
  • Storage
  • Membrane
  • Toxins
  • Enzymes
• Each cell in a living system may contain thousands of different proteins, each with a unique function
• Amino acids


  The monomers that make up proteins
• There are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order
• Enzymes

  Catalysts in biochemical reactions (like digestion) that are usually proteins, each specific for the substrate upon which it acts
• Hormones

  Chemical signaling molecules, usually proteins or steroids, secreted by an endocrine gland or group of endocrine cells that act to control or regulate specific physiological processes
• Protein shape


  • Critical to its function
  • Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation
• All proteins are made up of different arrangements of the same 20 kinds of amino acids
• Amino acid


  The monomers that make up proteins, each with a central carbon atom bonded to an amino group, a carboxyl group, and a variable R group
• Peptide bond


  The covalent bond formed between the carboxyl group of one amino acid and the amino group of a second amino acid, releasing a water molecule
• Polypeptide


  A polymer of amino acids
• Protein


  A polypeptide or polypeptides that have combined together, have a distinct shape, and have a unique function
• The sequence and number of amino acids ultimately determine a protein's shape, size, and function
• Cytochrome c is an important component of the molecular machinery that harvests energy from glucose, and has changed very little over millions of years
• Protein sequencing has shown that there is a considerable amount of sequence similarity among cytochrome c molecules of different species, allowing evolutionary relationships to be assessed
• In sickle cell anemia, the hemoglobin β chain has a single amino acid substitution, causing a change in both the structure and function of the protein
• Primary structure


  The unique sequence and number of amino acids in a polypeptide chain
• Secondary structure

  Folding patterns resulting from interactions between the non-R group portions of amino acids, including alpha-helix and beta-pleated sheet structures
• Tertiary structure


  The unique three-dimensional structure of a polypeptide, caused by chemical interactions between various amino acids and regions of the polypeptide
• Quaternary structure


  The interaction of multiple polypeptide subunits to form a complete protein
• Denaturation is the loss of a protein's shape, often reversible if the denaturing agent is removed, but sometimes irreversible
• Nucleic acids are key macromolecules in the continuity of life, carrying the genetic blueprint and instructions for cell functioning
• DNA


  The genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals
• RNA


  Mostly involved in protein synthesis, communicating genetic information from the nucleus to the rest of the cell
• Nucleotide


  The monomers that make up DNA and RNA, consisting of a nitrogenous base, a pentose sugar, and a phosphate group
• DNA has a double-helical structure composed of two strands of nucleotides bonded at the bases with hydrogen bonds