1. Do-Now
1.) Name three chemical reactions taking place in your body right now.

2. Chapter 3: Enzymes
INB Pg 20

3. Enzymes Enzymes are protein molecules that act as biological catalysts
Catalyst: molecule that speeds up a chemical reaction and remains unchanged after rxn
Enzymes usually end in –ase
Virtually every metabolic rxn is catalyzed by an enzyme

4. Enzymes Globular proteins
Precise 3D shape
Multiple chains
Hydrophilic R groups on outside = water soluble
Active site: region on an enzyme to which another molecule/molecules- called a substrate- can bind

5. Lock and Key Hypothesis
Idea that enzyme has a particular shape to which the substrate fits exactly
Substrate=key. Held in place by temporary bonds
Enzyme=lock

6. Lock and Key Hypothesis
Each type of enzyme will act on only one type of substrate molecule
Shape of active site will only allow one shape to fit
Enzyme is said to be specific for substrate

7. Induced Fit Hypothesis
Modified the lock and key hypothesis in 1959
New evidence suggested that enzymes are more flexible than is suggested by a rigid lock and key
Basically same as lock and key, but adds the idea that the enzyme, and sometimes substrate, changes shape slightly as substrate enters enzyme

8. Induced Fit Hypothesis
Ensures a more perfect fit
Makes catalysis more efficient

9. Do Now 11/20
Compare and contrast the lock and key hypothesis with the induced fit hypothesis.

10. Catalysis and synthesis
An enzyme may catalyze a reaction in which it joins together two peptides (synthesis)
An enzyme may catalyze a reaction in which the substrate molecule is split into two or more molecules (catalysis/decomposition)

11. Catalysis
Enzyme-product complex is briefly formed before the release of products
Interaction between the R groups of the enzyme and the atoms of the substrate can break, or encourage formation of, bonds in the substrate molecule, forming products
When the rxn is complete, the products leave the active site
Enzyme is unchanged and ready to accept another substrate
Rate of rxn is extremely rapid

12. Lysozyme
Found in tears, saliva, and other secretions. Breaks the polysaccharide chains in the cell walls of bacteria

13. Enzymes
As catalysts, enzymes increase the rate at which chemical reactions occur
Most of the rxns in living things would be too slow w/o an enzyme to sustain life

14. Chemical Reactions Energy needed to start reaction = activation energy
Enzymes work by lowering activation energy

15. Other ways to increase rxn rate
Increase concentration of substrate
Increase energy of reactants (heating)
Ex: Benedict’s test
Most rxns occur at temps higher than our body temp, which is why enzymes are necessary

16. The course of a reaction
When enzyme and substrate are first mixed, there are a large number of substrate molecules
At any moment, virtually every enzyme molecule has a substrate in its active site

17. The course of a reaction
Initially, the rate at which a reaction occurs will depend only on how many enzyme molecules there are and the speed at which the enzyme can convert substrate into product
However, as more substrate is converted to product, there are fewer and fewer substrate molecules, which slows down the rate of reaction

18. Do Now 11/24
Which statement describes the currently accepted theory of how an enzyme and its substrate fit together?
As the product is released, the enzyme breaks down.
The enzyme is like a key that fits into the substrate, which is like a lock.
The active site is permanently changed by its interaction with the substrate.
As the substrate binds to the enzyme, the shape of the active site changes to accommodate the reaction.
What is this hypothesis called?

19. The effect of enzyme concentration
Directly proportional to reaction rate
As we increase the concentration of an enzyme, we have more active sites available for the substrate.
As long as there is plenty of substrate available, the initial rate of reaction increases linearly with enzyme concentration

20. The effect of substrate concentration
As concentration of substrate increases, the initial rate also increases
If we continue increasing substrate concentration, it will eventually max out because there are no more available active sites
If more substrate is added, the enzyme simply cannot work faster. The enzyme is working at its maximum possible rate, known as Vmax (V=velocity)

21. Temperature and enzyme activity
Low temp=low particle movement. Substrate move very slowly and will not often collide with the active site
As temp increases, substrates move faster and collide with active site more. Reaction rate increases
At a certain temperature (specific for diff. enzymes), hydrogen bonds begin to break in the enzyme (remember, it is a protein) and the enzyme will denature (loose its structure and function)

22. Temperature and enzyme activity
Denaturing of an enzyme is often irreversible
Substrate cannot fit into denatured active sites, so no activity takes place
The temperature at which an enzyme catalyzes a reaction at the maximum rate is called the optimum temperature

23. pH and enzyme activity
pH is a measure of hydrogen ions in solution. The lower the pH, the higher the hydrogen ion solution.
Hydrogen can interact with R groups of amino acids which affects bonding in amino acids, which can change the structure (and function) of an enzyme
Enzymes work best under specific pH ranges.

24. Check your understanding
Proteases (enzymes that break down proteins) are used in biological washing powders.
How would a protease remove a blood stain on clothes?
Most biological washing powders are recommended for use at low washing temperature. Why is this?

25. Check your understanding
Hemoglobin is the colored pigment that causes blood stains. Protein-digesting enzymes hydrolyze hemoglobin to amino acids, which are colorless. They are also soluble, so will wash away in water.
Many protein-digesting enzymes have an optimum temperature of around 40 °C. If the temperature of a reaction is too high, the enzyme will denature.

26. homework
Page 64 #2, #6, #7, #9
Quiz on enzymes on 12/3