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