1. Enzymes B11 Reference: chapter 5 of your text Quiz Wed March 31
Test Thurs April 1st
Very short unit, builds on what you already know
Pay close attention to the study guide you were given (with answer key)

2. Metabolic Reactions and Energy Transformations
Metabolism is the sum of all the chemical reactions that occur in a cell.
A + B C + D
(reactants) (products)

3. 6.2 Metabolic Reactions and Energy Transformations
ATP: Energy for Cells
ATP stands for adenosine triphosphate, the common energy currency for cells.
ATP is generated from ADP (adenosine diphosphate) + an inorganic phosphate molecule ( P )

4. The ATP Cycle

5. Metabolic Reactions and Energy Transformations
Structure of ATP
ATP is a nucleotide that is composed of:
Adenine (a nitrogen-containing base)
Ribose (a 5-carbon sugar)
Three phosphate groups

6. Metabolic Reactions and Energy Transformations
Structure of ATP
ATP is a “high energy” compound because a phosphate group can easily be removed.

7. Metabolic Reactions and Energy Transformations
Coupled Reactions
The energy released by an exergonic reaction is used to drive an endergonic reaction.
Exergonic releases energy, endergonic needs energy “put in”

8. Coupled Reactions

9. Metabolic Pathways and Enzymes
Metabolic pathways are a series of linked reactions.
These begin with a specific reactant and produce an end product

10. Metabolic Pathways and Enzymes
Enzymes are usually proteins that function to speed a chemical reaction.
Enzymes serve as catalysts

11. A Metabolic Pathway

12. Metabolic Pathways and Enzymes
The Energy of Activation (Ea) is the energy that must be added to cause molecules to react with one another.

13. Energy of Activation

14. Metabolic Pathways and Enzymes
How Enzymes Function
Enzyme binds substrate to form a complex
E + S  ES  E + P

15. Enzymatic Action

16. Metabolic Pathways and Enzymes
How Enzymes Function
Enzyme binds substrate to form a complex
E + S  ES  E + P
Induced fit model
Substrate and active site shapes don’t match exactly
Active site is induced to undergo a slight change in shape to accommodate substrate binding

17. Induced Fit Model

18. Metabolic Pathways and Enzymes
Factors Affecting Enzymatic Speed
Substrate Concentration
Temperature and pH
Enzyme Activation
Enzyme Inhibition
Enzyme Cofactors

19. Metabolic Pathways and Enzymes
Substrate Concentration
Enzyme activity increases as substrate concentration increases because there are more collisions between substrate and enzyme
Maximum rate is achieved when all active sites of an enzyme are filled continuously with substrate

20. Metabolic Pathways and Enzymes
Temperature
Enzyme activity increase as temperature rises
Higher temperatures cause more effective collisions between enzymes and substrates
High temperatures may denature an enzyme, inhibiting its ability to bind to substrates

21. The Effect of Temperature on the Rate of Reaction

22. Metabolic Pathways and EnzymespH
Each enzyme has an optimal pH
Enzyme structure is pH dependent
Extremes of pH can denature an enzyme by altering its structure

23. Effect of pH on the Rate of Reaction

24. Metabolic Pathways and Enzymes
Enzyme Activation
Cell regulates metabolism by regulating which enzymes are active
Genes producing enzymes can be turned on or off to regulate enzyme concentration
In some cases a signaling molecule is used to activate an enzyme

25. Metabolic Pathways and Enzymes
Enzyme Inhibition
Occurs when enzyme cannot bind its substrate
Activity of cell enzymes is regulated by feedback inhibition
Ex: when product is abundant it binds to the enzyme’s active site and blocks further production
When product is used up, it is removed from the active site
In a more complex type of inhibition, product binds to a site other than the active site, which changes the shape of the active site
Poisons are often enzyme inhibitors

26. Feedback Inhibition

27. Metabolic Pathways and Enzymes
Enzyme Cofactors
Molecules which help enzyme function
Copper and zinc are examples of inorganic cofactors
Organic non-protein cofactors are called coenzymes
Vitamins are often components of coenzymes