Biology 102 Lecture 5: Biological Molecules (cont.)

Lecture outline 1. Proteins Functions Functions Structure Structure 2. Nucleic acids Functions Functions Structure Structure

Proteins Proteins Key functions: 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 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 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 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 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. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.21

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 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 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 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) 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 Denaturation: IF secondary and higher level structure destroyed, protein can no longer function

Nucleic acids Functions of 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 As with all other polymers, the reaction is a dehydration synthesis  Phosphate group of one nucleotide bonds with the sugar of the adjacent nucleotide