Unit 2 – Chemistry of Life

  Contain:  Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur  Form the basic structure of many animal parts, such as muscle, skin, hair, and bone.  Enzymes are also proteins.

 Are formed from amino acids:  On the left: amine group  On the right: carboxyl group  “R” represents an atom or group of atoms which varies with each different amino acid.

 20 different amino acids form proteins  They join by dehydration synthesis:

 Two or more amino acids bonded together are called a peptide.  A chain of many amino acids is referred to as a polypeptide. The complete product, either one or more chains of amino acids, is called a protein.  There is unequal sharing of electrons in a peptide bond. The O and the N are negative and the H is positive.

 Protein structure is described in 4 levels:  1. Primary structure  2. Secondary structure  3. Tertiary structure  4. Quaternary structure

 Is a chain of amino acids joined by dehydration synthesis and held together by peptide bonds (strong covalent bonds: C-N)  Organized in linear arrangements  E.g. Cow insulin

 Proteins differ in 3 ways:  1. number of amino acids in the chain  2. types of amino acids  3. sequence of amino acids  Each different sequence is a different protein  Primary chains are 51 to thousands of amino acids long  There is an infinite number of different proteins

 The straight primary chain of amino acids spontaneously coils, forming hydrogen bonds between amino acids.  Eg. Alpha-helix (hair) hydrogen bonds  Secondary proteins are structural proteins (e.g. hair, cartilage) and are insoluble in water

 “Globs”  Interactions (hydrogen bonds) between R- groups of the amino acids hold these proteins in a 3-dimensional globular shape.  The specific globular shape is essential for the proteins of biological function.

 Primary chain of amino acids held together by peptide bond  Hydrogen bonds between some R-groups (weak bonds)

 Large globular proteins formed when 2 or more tertiary (globular) proteins join  E.g. hemoglobin – 4 globular proteins

 Globular proteins can easily be denatured.  For example, the hydrogen bonds holding the protein in its 3D shape are broken by acid, base, change in pH, or heat and the protein reverts back to its primary structure (chain of amino acids).

3D primary chain  The protein loses its biological function since its 3D shape is essential for it to function.  Once the heat, acid or base is removed, the protein may go back to its tertiary shape and resume its biological function.

 A permanent change in protein shape caused by too much heat, acid, or base.   “Permanent denaturation”  E.g. boiling an egg: no matter how long the egg cools, the proteins of the egg will never assume their original shape

 Hydrolysis is the reverse reaction to dehydration synthesis  Proteins you eat are hydrolyzed during digestion  Hydrolysis breaks the peptide bonds  i.e. destroys the primary structure  Protein + many water molecules  amino acids

 Video Intro for Protein Lab:   Video closure for Protein Lab  online.com/Objects/ViewObject.aspx?ID=BIC007 online.com/Objects/ViewObject.aspx?ID=BIC007