The Structure and Function of Macromolecules

  • Macromolecules
    • Are large molecules composed of smaller molecules
    • Are complex in their structure
    • Most macromolecules are polymers, built from monomers
    • Four classes of life’s organic molecules are polymers
    • Carbohydrates
    • Proteins
    • Nucleic acids
    • Lipids
    • A polymer
    • A long molecule consisting of many similar building blocks called monomers
    • Specific monomers make up each macromolecule
      • E.g. amino acids are the monomers for proteins
  • The Synthesis and Breakdown of Polymers
    • Monomers form larger molecules by condensation reaction called dehydration synthesis
    • Polymers and disassemble by hydrolysis
    • Addition of water molecules
    • Although organisms share the same limited number of monomer types, each organism is unique based on the arrangement of monomers into polymers
    • An immense variety of polymers can be built from a small set of monomers
  • Carbohydrates
    • Serve as fuel and building material
    • Include both sugars and polymers
    • Starch, cellulose, etc.
  • Sugars
    • Monosaccharides
    • Are the simplest sugars
    • Can be used for fuel
    • Can be converted into other organic molecules
    • Can be combined into polymers
    • Can be linear
    • Can form rings
    • Disaccharides
    • Consist of two monosaccharides
    • Are joined by a glycosidic linkage
    • Polysaccharides
    • Are polymers of sugars
    • Serve many roles in organism
    • Storage Polysaccharides
    • Starch
      • Is a polymer consisting entirely of glucose monomers
      • Is the major storage form of glucose in plants
    • Glycogen
      • Consists of glucose monomers
      • Is the major storage form of glucose in animals
    • Cellulose
      • Is a polymer of glucose
      • Has different glycosidic linkages than starch
      • Difficult to digest
      • Cows have microbes in their stomach to facilitate this process
    • Chitin
      • Is found in the exoskeleton of arthropods
      • Can be used as surgical thread
  • Lipids
    • Are the one class of large biological monomers that do not consist of polymers
    • Share the common trait of being hydrophobic
  • Fats
    • Constructed from two types of smaller molecules
    • A single glycerol and usually three fatty acids
    • Vary in length and number and location of double bonds they contain
    • Saturated fatty acids
    • Have the maximum number of hydrogen atoms possible
    • Have no double bonds
    • Unsaturated fatty acids
    • Have one or more double bonds
    • Phospholipids
    • Have only two fatty acids
    • Have a phosphate group instead of third fatty acid
    • Structure
      • Consists of a hydrophobic “head” and hydrophobic “tails”
      • Results in a bilayer arrangement founds in cell membranes

         

  • Steroids
    • Lipids characterized by a carbon skeleton consisting of four fused rings
    • Cholesterol
    • Found in cell membranes
    • Is a precursor for some hormones
  • Proteins
    • Proteins have many structures, resulting in a wide range of functions
    • Proteins do most of the work in cells and acts as enzymes
    • Proteins are made of monomers called amino acids
    • Enzyme
    • Type of protein that acts as a catalyst, speeding up chemical reactions
    • Polypeptides
    • Polymers of amino acids
    • A protein consists of one or more polypeptides
    • Amino acids
    • Are organic molecules possessing both carboxyl and amino groups
    • Differ in their properties due to differing side chains, called R groups
    • Linked by peptide bonds
  • Protein Conformation and Function
    • A protein’s specific conformation (shape) determines how it functions
  • Four Levels of Protein Structure
    • Primary structure
    • Unique sequence of amino acids in a polypeptide
    • Secondary structure
    • Folding or coiling of the polypeptide into a repeating configuration
    • Includes the a helix and β pleated sheet
    • Tertiary Structure
    • Overall three-dimensional shape of a polypeptide
    • Results from interactions between amino acids and R groups
    • Quaternary structure
    • The overall protein structure that results from the aggregation of two or more polypeptide subunits
  • Sickle Cell Disease
    • Results from a single amino acid substitution in the protein hemoglobin
  • What determines Protein Conformation
    • Protein conformation depends on the physical and chemical conditions of the protein’s environment
    • Temperature, pH, etc.
    • Denaturation is when a protein unravels and loses its native conformation
  • The Protein Folding Problem
    • Most proteins
    • Probably go through several intermediate states on their way to a stable conformation
    • Denaturated proteins no longer work in their unfolded conditions
    • Proteins may be denaturated by extreme changes in pH or temperature
    • Chaperonins
    • Protein molecules that assist in the proper folding of other proteins
    • X-ray crystallography
    • Used to determine a protein’s three-dimensional structure
  • Nucleic Acids
    • Store and transmit hereditary information
    • Genes
    • Are the units of inheritance
    • Program the amino acid sequence of polypeptides
    • Are made of nucleotide sequences of DNA
    • DNA
    • Deoxyribonucleic acid
    • Stores information for the synthesis of specific proteins
    • Found in the nucleus of the cell
    • Functions
      • Directs RNA synthesis
      • Transcription
      • Directs protein synthesis through RNA
      • Translation
    • Structure
    • Nucleic acids exist as polymers called polynucleotides
    • Each polynucleotide
      • Consists of monomers called nucleotides
      • Sugar + phosphate + nitrogen base
    • Nucleotide monomers
      • Made up of nucleosides (sugar + base) and a phosphate group
    • Nucleotide polymers
      • Are made up of nucleotides linked by the -OH on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon of the next
    • Gene
      • The sequence of bases along a nucleotide polymer
    • DNA double helix
      • Have two polynucleotides that spiral around an imaginary axis
      • Form a double helix
      • Consists of two antiparallel nucleotide strands
    • A, T, C, G
      • The nitrogenous bases in DNA
      • Form hydrogen bonds in a complementary fashion
      • A with T only
      • C with G only
  • DNA and Proteins as Tape Measures of Evolution
    • Molecular comparisons
    • Help biologists sort out the evolutionary connections among species