Proteins

1. Proteins Structure and Function

2. PROTEINS Proteins are essential to the structures and activities of life • . • . • .

3. Protein Functions The seven major functions of protein are • Structural: • Contractile: • Storage: • Defense: • Transport: • Signaling: • Enzymes:

4. Monomeric subunit of polypeptides (proteins) . Protein diversity is based on different arrangements of a common set of 20 amino acid monomers Amino acids

5. 20 natural amino acids • . • . • The structure of the R group determines the specific properties of each amino acid Properties defined by R-group include: • . • . • .

6. Essential Amino Acids • .

8. proteins = • Cells link amino acids together by dehydration synthesis • . • Dipeptides are two amino acids long; polypeptides are from several to more than a thousand amino acids long Peptide bond Carboxyl group Amino group Dehydration reaction Amino acid Amino acid Dipeptide

9. Synthesis of Polypeptides • . • Chain grows from amino terminus to carboxy terminus • . • R groups frequently interact with others

10. A protein's specific shape determines its function • . • This unique folding gives each protein their specific function. • A protein consists of one or more polypeptide chains spontaneously folded into a unique shape • .

11. LE 3-13 Groove Groove

12. A protein's shape depends on four levels of structure • Primary structure • Secondary structure • Tertiary structure • Quaternary structure

13. Primary Structure • . • amino acids linked by the peptide bond • . • Are often similar among proteins of similar function • Usually written from amino terminus to carboxy terminus

14. Secondary Structure • . • . • a helix-stabilized by frequent polar groups • b-pleated sheets are formed by consecutive polar groups on two regions of polypeptide repetitive or regular folding patterns

15. Tertiary Structure • . • 3 Dimension shape emerges Due to R group Interactions • Hydrophobic interactions • Nonpolar regions generally internalize in structure • Disulfide bridge • Very stable bond formed between two distant cysteine residues • Ionic interactions • Strong bond between oppositely charged side groups -Hydrogen bonds form between polar groups

17. Quaternary Structure • . • Interactions are maintained between polypeptide chains by bonds similar to tertiary structure • H-bonds, ionic interactions, hydrophobic interactions and disulphide bridges

18. Protein Structure Revisited

19. How many levels of protein folding are present in this image? Source: http://commons.wikimedia.org/wiki/Image:Hydrophobin.png

20. Collagen is an example of a protein with a quaternary structure • Three subunits wound into a helix • Structure provides great strength to long fibers

22. Factors Affecting Folding • Folding is influenced by environmental conditions • . • . • . • Some proteins have more than one folding pattern (conformation) depending on the environment • Many proteins undergo a conformational change when a substrate binds. • Conformational changes are usually reversible.

23. Denaturation • . • . • Denatured proteins may refold if the conditions are appropriate • . • Chapperones promote or stabilise a protein’s folding

24. Proteins when heated can unfold or "Denature". This loss of three dimensional shape will usually be accompanied by a loss of the proteins function. If the denatured protein is allowed to cool it will usually refold back into it’s original conformation.