1. Chapter 20 Enzymes and Vitamins
Lecture Presentation
Chapter 20 Enzymes and Vitamins
Karen C. Timberlake

2. Chapter 20 Enzymes and Vitamins
A physician assistant (PA) helps a doctor by examining and treating patients as well as prescribing medications. His or her duties may include obtaining patient medical records and histories, diagnosing illnesses, educating and counseling patients, and referring the patient, when needed, to a specialist.

3. Chapter 20 Readiness Core Chemistry Skills Interpreting Graphs (1.4E)
Identifying the Primary, Secondary, Tertiary, and Quaternary Structures of Proteins (19.4, 19.5)

4. 20.1 Enzymes and Enzyme Action
Enzymes are biological catalysts that
increase the rate of a reaction by changing the way a reaction takes place.
are not changed in the process of the reaction.
lower the activation energy of the reaction.
Learning Goal Describe enzymes and their role in enzyme-catalyzed reactions.
The enzyme carbonic anhydrase lowers the activation energy for the reversible reaction that converts CO2 and H2O to bicarbonate and H+.

5. Enzymes Lower Activation Energy
Enzymes increase the rate of a chemical reaction by reducing the energy required to convert reactant molecules to products.
An enzyme in the blood called carbonic anhydrase catalyzes
the rapid interconversion of carbon dioxide and water to bicarbonate and H+.
the reverse reaction, converting bicarbonate and H+ to carbon dioxide and water.

6. Enzymes and Active Sites
Nearly all enzymes
are globular proteins with a unique three-dimensional shape that recognizes and binds a small group of reacting molecules, called substrates.
have a tertiary structure that includes a region called the active site where one or more small groups of substrates bind to create a chemical reaction.
have specific amino acid residues within the active site that interact with functional groups of the substrate to form hydrogen bonds, salt bridges, and hydrophobic interactions.

7. Enzymes and Active Sites
Enzymes like lactase have an active site where the substrate fits for catalysis to occur. The quaternary structure of lactase consists of four subunits. The substrate, lactose (gray), is held in place in the active site by hydrogen bonds with amino acid side chains.

8. Specificity of Enzymes
Some enzymes show absolute specificity by catalyzing only one reaction for one specific substrate.
Other enzymes catalyze a reaction of two or more substrates.
Some enzymes catalyze a reaction for a specific type of bond.

9. Enzyme-Catalyzed Reaction
The combination of an enzyme and a substrate forms an enzyme–substrate (ES) complex.
The ES provides an alternative pathway for the reaction with lower activation energy.
Within the active site, amino acid R groups catalyze the reaction to form an enzyme-product (EP) complex.
Core Chemistry Skill Describing Enzyme Action

10. Enzyme–Substrate Complex
A flexible active site in lactase and the flexible substrate lactose adjust to provide the best fit for the hydrolysis reaction. Once the disaccharide is hydrolyzed, the monosaccharide products are released from the enzyme, which is ready to bind another lactose.

11. Models of Enzyme Action
A lock-and-key model has a rigid substrate binding to a rigid enzyme, much like a key fitting into a lock.
The induced-fit model, a more dynamic model of enzyme action, states that the active site is flexible enough to adapt to the shape of the substrate.
The induced-fit model has the substrate and enzyme working together to acquire a geometrical arrangement that lowers the activation energy.

12. Study Check 1. Which is the active site? A. the entire enzyme
B. a section of the enzyme
C. the substrate
2. In the induced-fit model, what happens to the shape of the enzyme when the substrate binds?
A. stays the same
B. adapts to the shape of the substrate

13. Solution 1. Which is the active site? B. a section of the enzyme
2. In the induced-fit model, what happens to the shape of the enzyme when the substrate binds?
B. adapts to the shape of the substrate