1. IB Biology HL 1 Mrs. Peters Fall 2013
Enzymes
IB Biology HL 1
Mrs. Peters
Fall 2013

2. 3.6.1 Enzymes
All enzymes are proteins with characteristic three dimensional shape
Shape determines the function of the enzyme
Work until shape is changed and can’t function any longer

3. 3.6.1 Enzymes
Biological catalysts that lower the activation energy of a reaction which speeds up the rate of a reaction such as digestion or respiration.
Enzymes reduce the amount of energy required to make the reaction take place; lower the activation energy
DRAW THIS DIAGRAM!

4. 7.6.3 Activation Energy
For any reaction to start it usually requires the input of energy (Activation Energy)
Enzymes function to lower the activation energy of a specific reaction
The amount of energy required to start the reaction is reduced because the enzyme is doing the reaction.

5. 3.6.1 Enzymes The Parts of the Enzyme-Substrate Complex
Enzyme: protein that conducts specific reactions
Substrate: what it reacts with to produce a product
Active site: where the substrate binds to the enzyme
DRAW THE YELLOW MODEL, LABEL PARTS

6. 3.6.2 Enzymes Enzyme Specificity: each enzyme fits only 1 substrate.
Lock and Key Model
Enzyme is like the lock, substrate is like the key…only one key fits the lock
Induced Fit
A substrate enters the active site, inducing the enzyme to change its shape slightly, so the active site fits the substrate more snuggly
Ex: like a clasping handshake

7. 7.6.1 Enzymes
Enzyme Cycle
Substrate attaches to enzyme active site by weak bonds (hydrogen and ionic)
Enzyme completes the reaction, converting substrate to product
Product leaves the active site
Enzyme takes up the next substrate in the active site, repeating cycle.

8. 7.6.1 Enzymes & Metabolic Pathways
Several enzymes are used to complete a reaction
The product of each enzyme is the substrate for the next enzyme until the final product is produced.
Draw this diagram!

9. 3.6.3 Enzyme Activity and Substrate Concentration
Enzyme activity is directly affected by substrate concentration
Amount of substrate present at the time of the reaction
Enzymes can only make as much product as there is substrate available
Enzymes will continue to work until all substrate is used up
Adding additional substrate will produce more product

10. 3.6.3 Enzyme Activity and Substrate Concentration
Reaction Rate:
As active sites fill with substrate, the rate of reaction increases, increasing the amount of product produced
When all active sites are full and there are no more available sites, the reaction will continue at a stable rate producing products
DRAW THIS DIAGRAM!

11. 3.6.3 Enzyme Activity and pH Enzyme activity affected by pH
All enzymes have an optimum pH at which most active (work the most efficiently)
pH range for enzyme activity is relatively small, won’t work outside that range
reaction will increase to a point before being disrupted
changes in environmental pH will cause denaturation
Draw this diagram!

12. 3.6.3 Enzyme Activity and Temp.
Enzyme activity affected by temperature
All enzymes have an optimum temperature at which most active
If temperature increases, reaction will increase to a point before being disrupted
Significant increased temperature causes denaturation
Enzyme won’t function after denaturation
Draw this diagram!

13. 3.6.4 Denaturation
Denaturation is a structural change in a protein that results in the loss (usually permanently) of its biological properties.
Enzymes can be denatured by changes in temperature and pH.
Original environment is changed in some way
Placed in environments that are outside their optimum range
Temperature usually has to be hotter than it’s optimum range, if it is colder, the enzyme will work slowly or not at all, but won’t be effected permanently

14. Enzyme Activity
Cofactors: small molecules that bind with enzymes, necessary for function
Inhibitors: molecules which selectively disrupt the action of enzymes

15. 7.6.4 Enzyme Inhibitors Inhibitor Types
Competitive: a molecule similar in shape to the substrate that competes with substrate for active site, blocks substrate from attaching to the active site, temporarily shutting down the enzyme

16. 7.6.4 Enzyme Inhibitors Inhibitor Types
Non-competitive: a molecule that binds to a location separate from active site, changing shape of enzyme, blocking the substrate from attaching to the active site, temporarily shutting down the enzyme

17. 7.6.4 Enzyme Inhibitors Comparison
Competitive
Structurally similar to the substrate molecule
Occupies and blocks the active site, lowering the rate of the reaction
If inhibitor concentration is low, increasing the substrate concentration will reduce the inhibition
Noncompetitive
Structurally unlike the substrate molecule
Binds to a site away from the active site, changing the shape of the active site, lowering the rate of the reaction
If inhibitor concentration is low, increasing the amount of substrate has no effect, enzyme stays inhibited

18. 7.6.4 Enzyme Inhibitors Comparison
Competitive Exs:
Penicillin blocks the active site of bacteria enzyme
Oxygen: competes with CO2 for the active site of ribulose bisphoste carboxylase (RuBP) in photosynthesis
Disulfiram: competes with acetaldehyde in the liver
Noncompetitive Exs:
Cyanide and carbon monoxide will block cytochrome oxidase in respiration, leading to death
Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions (a cofactor for enzymes)

19. 7.6.5 Enzyme Inhibition
End-Product Inhibition: the end product of a metabolic pathway reaction acts as an inhibitor of an enzyme earlier in the pathway (usually the first enzyme) causing the pathway to stop producing product

20. 7.6.5 Enzymes and Allostery
Allosteric Enzymes: a series of the same enzyme bonded together
Allosteric Regulation: molecules bind to an allosteric site (non-active site) to either inhibit or activate enzyme activity
Activators: molecules that activate, or turn on the allosteric enzyme by attaching to the allosteric site
Inhibitors: molecules that will shut off, or inhibit the allosteric enzyme by attaching to the allosteric site, changing the shape of the active site

21. 3.6.5 Enzyme Uses Example #1 (KNOW THIS EXAMPLE) Other Examples
Lactase in the production of lactose-free milk
Lactase breaks down lactose into glucose and galactose, uses the hydrolysis reaction
Lactose-free milk is made so people who are lactose intolerant can still receive the nutrition of milk without indigestion.
Other Examples
Enzymes are used in digestion
Amylase, pepsin, trypsin
Many enzymes are used in Biotechnology to cut DNA or add nucleotides together to create new DNA copies (***we will cover this later during the DNA and Biotech units)

22. Enzyme Practice Questions
With a partner, write the answer first without notes!
Explain how competitive and non-competitive inhibition can include allostery.
Explain how the concentration of substrate and competitive inhibitors can effect enzyme reactions.
Describe how lock and key and induced fit explain enzyme specificity.
Now, go back and use your notes, a new color writing utensil, and Mrs. Peters to fill in more information for each answer.

23. Enzymes Cooperactivity: resembles allosteric activation
One substrate binding to an active site opens all other active sites of the enzyme, if multiple subunits together form the enzyme