Enzymes Notes #2- Enzyme Substrate Complexes and Factors Affecting Enzymes

1. EnzymesNotes #2- Enzyme Substrate Complexes and Factors Affecting Enzymes

2. Agenda • Sign up for rewrite if you want to take it (today is last day) • Video • Notes • Short Video • Group Activity • Planning and presentation • Practice

3. Video • https://www.youtube.com/watch?v=XTUm-75-PL4

4. Enzymes • Catalysts are substances that speed up chemical reactions.  Organic catalysts (contain carbon) are called enzymes. • Enzymes are specific for one particular reaction or group of related reactions. • Many reactions cannot occur without the correct enzyme present. • They are often named by adding “ASE" to the name of the substrate. Example: Dehydrogenases are enzymes that remove hydrogen.

5. Enzyme-Substrate Complexes • When a substrate binds to the active site of an enzyme it is said form a complex. • The original theory on how this worked was called the LOCK and KEY model • This was because the substrate shape fits into a specific enzyme because of it’s shape like a specific key fits only a specific lock

6. Lock and Key Model • As the substrates bind to the enzyme active site they are brought closer together allowing the reaction to occur • Sometimes the active site changes shape to bring the substrates even closer together • The reaction occurs and the product(s) are released. The enzyme returns to it’s normal tertiary configuration

7. Induced Fit Theory – Most current • “Induced-Fit model” is very similar but it claims that the enzyme has the ability to slightly alter its shape. The two models basically work the same way. • The substrate molecule does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit. • After the reaction, the products are released and the enzyme returns to its normal shape. • Only a small amount of enzyme is needed because they can be used repeatedly.

9. Video • https://www.youtube.com/watch?v=V4OPO6JQLOE

10. Roles of Enzymes • Some enzymes simply complex with substrates bringing them close together to react • Other enzymes participate in the reaction occuring: • Example: Trypsin • Trypsin digests protein by breaking peptide bonds • Active site contains 3 amino acids with R groups that interact with the peptide bonds • Breaks the bond and brings in water

11. Rate of Reaction • Reactions with enzymes are up to 10 billion times faster than those without enzymes. • Enzymes typically react with between 1 and 10,000 molecules per second. Fast enzymes catalyze up to 500,000 molecules per second. • Substrate concentration, enzyme concentration, Temperature, and pH  affect the rate of enzyme reactions.

12. Group Activity • 6 groups: • Substrate concentration • Temperature • pH • Enzyme concentration • Competitive inhibitor • -non-competitive inhibitor (and heavy metals) • Use page 108/109 and handout to prepare presentation • What is it? • Why/How does it impact speed of reaction • Key characteristics • Use a diagram…

13. Substrate Concentration • At lower concentrations, the active sites on most of the enzyme molecules are not filled because there is not much substrate.  Higher concentrations cause more collisions between the molecules.  With more molecules and collisions, enzymes are more likely to encounter molecules of reactant. • The maximum velocity of a reaction is reached when the active sites are almost continuously filled. Increased substrate concentration after this point will not increase the rate.  Reaction rate therefore increases as substrate concentration is increased but it levels off. Enzyme Active Site is Saturated Rate of Reaction Substrate Concentration

14. Enzyme Concentration • If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because there is not enough enzyme for all of the reactant molecules. • As the amount of enzyme is increased, the rate of reaction increases. If there are more enzyme molecules than are needed, adding additional enzyme will not increase the rate. Reaction rate therefore increases as enzyme concentration increases but then it levels off. Even when adding more enzymes, there isn’t any more available substrate to create product at a faster rate Rate of Reaction Enzyme Concentration

15. Effect of Temperature on Enzyme Activity Rate of Reaction 30 40 50 Temperature

16. Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases. Effect of Temperature on Enzyme Activity Rate of Reaction 30 40 50 Temperature

17. Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional. Effect of Temperature on Enzyme Activity Rate of Reaction 30 40 50 Temperature

18. Temperature • Higher temperature causes more collisions between the atoms, ions, molecules, etc. It therefore increases the rate of a reaction – “Turnover Rate”. More collisions increase the likelihood that substrate will collide with the active site of the enzyme. • Above a certain temperature, activity begins to decline because the enzyme begins to denature (unfold). • The rate of chemical reactions therefore increases with temperature but then decreases. Rate of Reaction 30 40 50 Temperature

19. Denaturation • If the hydrogen bonds within an enzyme are broken, the enzyme may unfold or take on a different shape. The enzyme is denatured. • A denatured enzyme will not function properly because the shape of the active site has changed. • If the denaturation is not severe, the enzyme may regain its original shape and become functional. • The following will cause denaturation: • Heat • Changes in pH • Heavy-metal ions (lead, arsenic, mercury) • Alcohol • UV radiation

20. Effect of pH on Enzyme Activity Each enzyme has its own optimum pH. Pepsin Trypsin Rate of Reaction 2 3 4 5 6 7 8 9 pH

21. pH • Each enzyme has an optimal pH. Pepsin, an enzyme found in the stomach, functions best at a low pH. Trypsin, found in the intestine, functions best at a neutral pH. • A change in pH can alter the ionization of the R groups of the amino acids. When the charges on the amino acids change, hydrogen bonding within the protein molecule change and the molecule changes shape. The new shape may not be effective. • The diagram shows that pepsin functions best in an acid environment. This makes sense because pepsin is an enzyme that is normally found in the stomach where the pH is low due to the presence of hydrochloric acid. Trypsin is found in the duodenum (small intestine), and therefore, its optimum pH is in the neutral range to match the pH of the duodenum. Pepsin Trypsin Rate of Reaction 2 3 4 5 6 7 8 9 pH

22. Regulation of Enzymes • The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

23. Regulation of Enzymes Cell can turn on DNA genes to build more enzymes when needed genetic regulation regulation of enzymes already produced Cells can use certain chemicals to slow down existing enzymes competitive inhibition noncompetitive Inhibition (next slide)

24. In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites. Competitive Inhibition

25. Competitive Inhibition This substrate cannot get into active site at this time Active site is being occupied by competitive inhibitor

26. Noncompetitive Inhibition Active site Inhibitor Altered active site • Another form of inhibition involves an inhibitor that binds to an allosteric siteof an enzyme.  An allosteric site is a different location than the active site. • The binding of an inhibitor to the allosteric site alters the shape of the enzyme, resulting in a distorted active site that does not function properly. Enzyme

27. Noncompetitive Inhibition • The binding of an inhibitor to an allosteric site is usually temporary.   Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

28. Agenda • Homework Check • Assignment Answer Review • Quiz • Video • Notes • Demo Activity • Review Worksheet

29. Video

30. The goal of this hypothetical metabolic pathway is to produce chemical D from A. B and C are intermediates. The next several slides will show how feedback inhibition regulates the amount of D produced. Feedback Inhibition A B C D enzyme 1 enzyme 2 enzyme 3 Enzyme regulation by negative feedback inhibition is similar to the thermostat example. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat.

31. C and D will decrease because B is needed to produce C and C is needed to produce D. The amount of B in the cell will decrease if enzyme 1 is inhibited. X X X Feedback Inhibition A B C D X enzyme 1 enzyme 2 enzyme 3 Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning.

32. B, C, and D can now be synthesized. B When the amount of D drops, enzyme 1 will no longer be inhibited by it. Feedback Inhibition A B C D X X X C D enzyme 1 enzyme 2 enzyme 3

33. Feedback Inhibition A B C D X enzyme 1 enzyme 2 enzyme 3 As D begins to increase, it inhibits enzyme 1 again and the cycle repeats itself.

34. Thyroxin and It’s Role in Metabolic Rate • Thyroxin: (AKA “Thyroid Hormone” “Thyroxine”) • - Thyroxin is a protein hormone that is secreted into the blood stream by cells of the thyroid gland • - The thyroid gland, which is located in the neck, accumulates iodine in order to produce the thyroxin hormone. • Thyroid Hormone Structure

35. Thyroxin acts by attaching to receptor sites on the surfaces of our body’s cells. When receptor sites are triggered they stimulate other chemicals in the cell to govern the rate at which the cells will consume oxygen. Thyroxin ultimately controls the body’s metabolism.

36. - Thyroxin does not have a target organ; but instead, stimulates most of the cells of the body to metabolize at a faster rate. It does this by increasing the production of respiratory enzymes, as well as stimulating the increase of oxygen uptake.

37. - Thyroxin not only governs metabolic rate but it also helps regulate the growth and development of an individual. - Thyroglobulin is the storage (precursor) form of Thyroxin. Iodine is required for thyroglobulin to be made. Without the presence of iodine the thyroid gland will increase in size in an effort to produce more Thyroxin. - Unfortunately, a lack of Iodine in the diet, results in a lack of thyroxin in the body (HYPOTHYROIDISM). This often leads to a condition known as simple goiter.

38. Simple Gloiter - A simple goiter occurs when the thyroid gland is unable to produce a sufficient amount of Thyroxin, the thyroid cannot meet the metabolic demands of the body. -The thyroid gland compensates by enlarging, this mechanism will often overcome a mild deficiency of the thyroid hormone.

39. Exophthalmic Goiter (Graves’ disease) This type of Goiter is not caused by a lack of thyroxin but rather by the excessive production of the thyroid hormone (HYPERTHYROIDISM). – - This condition is characterized by an enlarged thyroid gland, protrusion of the eyeballs, tachycardia (super fast heart rate) and nervous excitability.

40. Hypothyroidism vs. Hyperthyroidism Symptoms of Hypothyroidism: Low thyroxin in the blood