<p> Proteins Functions: 1. Build and repair cell structure 2. Speed up chemical reactions (enzymes) 3. As a last resort, to be used as energy.</p><p>Subunits:  amino acids</p><p>R</p><p>There are 20 types of amino acids. </p><p>Amino acids are bonded together through dehydration synthesis: The function of the protein depends on its structure. When a protein loses its structure, it has been denatured.</p><p>Protein Structure (p. 559-561) http://www.youtube.com/watch?v=iaHHgEoa2c8&feature=related (better anim at end) . Primary structure (basic structure): o Polypeptide chain (PpC). o Sequence of amino acids (AA) determines rest of structure and function. o Change of 1 AA can inactivate protein . Thus, changes to DNA can be disastrous . Secondary structure: (H-bonds between carbonyl and amino groups of AA) o Certain AA are polar, while others are non- polar (see p. 18). Non-polar AA R-groups tend to end up on the inside of the protein in an aqueous environment. o Sections of the PpC may have repeating polar/non-polar AA, causing the section to </p><p> zigzag: Polar R- Polar R- group group</p><p>C</p><p>Non-Polar Non-Polar R-group R-group o As the PpC grows and loops back around,</p><p> the zigzags can line up beside each other:</p><p>H-bonds This causes -pleated sheets to form. They are held in place by H-bonds ( ) between the C=O and H-N o Other sections contain fewer non-polar AA, and can twist forming an  helix (less common)</p><p> o Other sections have no distinct pattern. . Tertiary structure: (bonds between R-groups) o Additional folds caused by R group interactions with each other . H-bonds are formed between nearby R- groups . S-S from 2 cysteines – disulfide bridge. . Proline causes a kink . Ionic bonds form between charged R groups . Quaternary structure: o Only occurs in proteins made up of more than 1 PpC, like Hemoglobin. o Describes how chains fit together. ** All these folds make protein VERY stable.</p><p> Better Animation: http://www.stolaf.edu/people/giannini/flashanimat/p roteins/protein%20structure.swf</p>