1. Chapter 3 Proteins and Enzymes (Chapter 7)

2. Protein Structure – determined by folding Can be globular (spherical) or fibrous (long fibers) Proteins fold because of interactions between R groups o The structure directly determines its function

3. Four levels of protein structure Primary – sequence of amino acids Secondary – coils or folds in backbone Tertiary – interactions between R groups Quaternary – more than 1 polypeptide subunit

4. Fig. 5-21a Amino acid subunits + H 3 N Amino end 25 20 15 10 5 1 Primary Structure

5. Secondary – coils or folds in backbone H bonds between the backbone (not the R groups)  helix – a coil  pleated sheet – folded structure

6. Tertiary - interactions between R groups Hydrophobic interactions – nonpolar amino acids end up clustered in center o Van der Waals Hydrogen Bonds – polar amino acids H bond Polypeptide backbone Hydrophobic interactions and van der Waals interactions Hydrogen bond

7. Tertiary - interactions between R groups Ionic Bonds – positively and negatively charged aas bond Disulfide bridges – covalent bonds of two cysteines (–SH) Polypeptide backbone Disulfide bridge Ionic bond

8. Quaternary – more than 1 polypeptide subunit Polypeptides with tertiary structure are aggregated o Example - hemoglobin β Chains Heme Iron α Chains Hemoglobin

9. Denaturation - unraveling Caused by: o High or low pH o Increased salt concentration o High temps

10. Enzymes catalytic proteins speed up metabolic reactions by lowering energy barriers not consumed or changed

11. Enzymes substrate – the reactant that an enzyme acts on enzyme-substrate complex: the enzyme bound to its substrate active site – the region on the enzyme where the substrate binds induced fit – the way the substrate fits into the active site (the enzyme changes shape slightly)

12. Activation Energy (E A ) needed to start a chemical reaction o heat from the surroundings

13. Enzymes Lower the E A Barrier

14. Enzyme Activity Lower an E A barrier by: o Orienting substrates correctly o Straining substrate bonds o Providing a favorable microenvironment o Covalently bonding to the substrate

15. Affected by: o temperature o pH o chemicals that specifically influence the enzyme Enzyme Activity

17. Enzymes and Biotechnology Human babies are born with lactase, an enzyme that breaks down lactose found in milk Naturally, as humans age they become increasingly lactose intolerant as they stop producing lactase Some cultures have higher percentages of people who are lactose intolerant (Asia), some lower percentages (Europe) Lactase is produced on large scales to create lactose- free products

18. Enzymes and Biotechnology

19. Enzyme Inhibitors Competitive inhibitors Bind to the active site Compete with the substrate

21. Competitive Example: Ethylene glycol: antifreeze o Ethanol is used to treat ethylene glycol poisoning o Reversible inhibition Ethylene glycol Products formed ethanol (inhibitor) Cause irreversible damage to the kidneys

22. Competitive Example: Sulfanilamide: antibiotic o similar structure to para- aminobenzoic acid (PABA), (pathway for folic acid) o IRREVERSIBLE COMPETITIVE INHIBITION PABA Folic acid Sulphanilamide (inhibitor) NO Folic acid formation after inhibition

23. Enzyme Inhibitors Noncompetitive inhibitors Bind to another part of an enzyme Cause the enzyme (active site) to change shape

24. Noncompetitive Example: Morphine Binds to a site other than the active site of the enzyme Nitric oxide synthase The enzyme stays inhibited Arginine Nitric oxide Citrulline Nitric oxide synthase Opioids ( morphine) inhibit NOS

25. Noncompetitive Example: Cyanide (CN - ) Attaches to the –SH group of an enzyme CYTOCHROME C OXIDASE results in the inhibition of cellular respiration!!! OXYGEN WATER Cytochrome c oxidase CN - Cyanide

26. Feedback Inhibition The end product of a metabolic pathway shuts down the pathway Prevents wasting resources