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Biology 102 Lecture 5: Biological Molecules (cont.) Lecture outline 1. Proteins Functions Structure 2. Nucleic acids Functions Structure Proteins Key functions: Structure Skin (collagen); hair and nails (keratin) Movement Proteins in muscle (actin and myosin) Defense Antibodies Signals Several hormones (growth hormone, insulin) Receptors for neurotransmitters Channels in membranes Catalysis Enzymes Amino acids are the monomers of proteins Composition Amino group Carboxylic acid group “R”-group: variable Properties of particular amino acids are based on their R-groups There are 20 total amino acids • Here are a few examples Protein synthesis Proteins are formed when amino acids link together with a dehydration synthesis reaction Note where they link together Note the formation of water: dehydration synthesis Four levels of protein structure Primary structure of proteins The primary structure of proteins is its particular sequence of amino acids Secondary structure of proteins Secondary structure occurs due to regularly spaced hydrogen bonds The structural properties of silk are due to beta pleated sheets. The presence of so many hydrogen bonds makes each silk fiber stronger than steel. Fig. 5.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Tertiary structure of a protein Results from various interactions between R groups. hydrogen bonds among polar and/or charged areas ionic bonds between charged R groups, Hydrophobic interactions among hydrophobic R groups. Disulphide bridges that form strong, stable bonds between parts of the molecule Tertiary structure (cont.) Quaternary structure Results from interactions of two or more polypeptide chains Hemoglobin is the interactions of two different types of chains (alpha and beta), with two of each per molecule Importance of tertiary and quarternary structure Shape of the protein is tied to its function Example: Lock and key fit of an enzyme and the reactants (substrates) that it brings together Higher levels of protein structure are directly tied to the amino acid sequence (primary structure) Change in primary structure can drastically alter protein function Example: Hemoglobin/sickle cell anemia Denaturation: IF secondary and higher level structure destroyed, protein can no longer function Nucleic acids Functions of nucleic acids Molecules of heredity (DNA, RNA) Second messengers inside the cell (cAMP) Short-term energy carriers (ATP) Coenzymes Monomers of nucleic acids are nucleotides Nucleotides can bond together to form nucleic acids As with all other polymers, the reaction is a dehydration synthesis Phosphate group of one nucleotide bonds with the sugar of the adjacent nucleotide