1. SBI4U0
ENZYMES

2. ENZYMES An enzyme is a biological catalyst
Biological = protein
Catalyst = speeds up a reaction without being consumed or permanently altered in the process
All enzymes are proteins, but not all proteins are enzymes
All enzymes are catalysts, but not all catalysts are proteins
Examples?

3. ACTIVATION ENERGY
Every chemical reaction involves both breaking and forming chemical bonds
Breaking bonds requires energy
Forming new bonds releases energy
(Sometimes net release, sometimes net requirement)
Even though a particular reaction may be spontaneous, a small amount of energy must be initially invested
“Activation energy”
How do you earn interest at your bank?

4. Free energy is required to break bonds
Activation energy
Free energy is released when new bonds are formed

5. ENZYMES
Enzymes speed up chemical reactions by lowering their activation energy
The net change in free energy remains unchanged

6. SUBSTRATE
The reactants in an enzyme-catalyzed reaction are termed “substrates”
Substrate  product
Sucrose  glucose & fructose
Starch  glucose
Deoxynucleotide triphosphates  DNA
Etc.

7. ENZYME SPECIFICITY
No single type of enzyme can catalyze all chemical reactions
Enzymes display specificity as to what chemical reaction they catalyze
“Substrate specificity”
Specific enzymes catalyze each of the following reactions
Sucrose  glucose & fructose
Starch  sugars
Deoxynucleotide triphosphates  DNA

8. ENZYME STRUCTURE
Enzymes are proteins with specific three-dimensional shapes
Defined by chemical bonds
1o, 2o, 3o, & 4o structures
The portion of an enzyme that binds to the substrate is the “active site”
Complementarity of fit
Lock-and-key fit
Induced fit (shaking hands)

10. REACTION RATE
The rate of an enzyme-catalyzed reaction is dependent upon several factors
[Substrate]
[Enzyme]
Temperature pH
Cofactors
Inhibitors

11. [SUBSTRATE]
The rate at which an enzyme converts substrate into product can be increased by increasing substrate concentration
There is a limit
At some substrate concentration all of the enzymes’ active sites are bound to substrate
The enzyme is “saturated”
Adding more substrate will not increase the rate
Adding more enzyme will increase the rate

12. TEMPERATURE & pH
An enzyme’s three-dimensional shape is defined by various chemical bonds
Altering the temperature or pH can interfere with these bonds
Altered enzyme shape compromises activity
“Denaturation”

13. COFACTORS
Many enzymes require non-protein helpers for catalytic activity
“Cofactors”
Cofactors may be organic or inorganic
Inorganic cofactors are typically metal ions
Organic cofactors (“coenzymes”) are typically vitamins or are derived from vitamins
e.g., DNAse requires Mg2+ as a cofactor
Removal of Mg2+ inactivates the enzyme

14. INHIBITORS
Certain chemicals can selectively inhibit the activity of specific enzymes
May be reversible or irreversible
Generally weak vs. covalent bonds
Competitive inhibitors
Compete for binding to active site
Increased [substrate] can overcome
Noncompetitive inhibitors
Binding elsewhere alters shape, alters active site

15. Inhibitors:
A substrate competitive Noncompetitive normally to inhibitor inhibitor an active site

16. REGULATORS Allosteric enzymes: 2 different binding sites
One for substrate (active site) and one for allosteric regulator (allosteric site)
Regulator binding changes substrate active site shape. Allosteric regulation can activate or inhibit.

18. INHIBITORS Many poisons act by inhibiting enzymes
e.g., DDT inhibits key enzymes in the nervous system
e.g., many antibiotics inhibit (penicillin, etc.) key bacterial enzymes
Selective inhibition of key enzymes is an essential mechanism of metabolic control

19. FEEDBACK INHIBITION
Anabolic biosynthetic pathways produce an end-product such as an amino acid
This end-product should be produced only when needed
In many cases, this end-product acts as an inhibitor of an enzyme functioning early in the biosynthetic pathway
“Feedback inhibition”

20. Complete review questions (section 1.4) #1-8 page 77
Question #31 page 87
31.
(b) Capsaicin’s intense flavour results from the molecule’s long hydrocarbon tail. The chain allows it to bind very strongly
with its lipoprotein receptor, which has some hydrocarbon side chains of its own (like dissolves like!). The fatty tail
also allows the molecule to slip through lipid-rich cell membranes, making the burn more persistent.
(c) The perception that peppers are “hot” is not an accident. Capsaicin allows calcium ions to move through the cell
membrane from the extracellular fluid into the cell. That ultimately triggers a pain signal that is transmitted to the next
cell. When the cells are exposed to heat, the same events occur. Chili burns and heat burns are similar at the molecular,
cellular, and sensory levels.
(d) Capsaicin is found primarily in the pepper’s placenta—the white ribs that run down the middle and along the sides of a
pepper. Since the seeds are in such close contact with the ribs, they are also often hot.
(e) Capsaicin content is measured in parts per million and are converted into Scoville heat units, the industry standard for
measuring a pepper’s intensity. One part per million is equivalent to 15 Scoville units. Bell peppers have a value of
zero Scoville units; habaneras—the hottest peppers—register to Scoville units. Pure capsaicin has a
Scoville heat unit score of about 16 million.
(f) Capsaicin, which is a largely nonpolar molecule, does not mix with water. Drinking water will have little effect on the
burning sensation. The most useful liquid is milk (rinsing the mouth with it as you sip) or eating rice or bread, which
absorb the capsaicin.
(g) As a medicine, capsaicin is used to help relieve the pain associated with neuralgia. Capsaicin is also used to
temporarily help relieve pain from arthritis. It is also used as a repellent against dogs, birds, bears, and squirrels, and as
an insect repellent. It is the active ingredient in commercially available “pepper sprays.”
Complete review questions (section 1.4) #1-8 page 77

22. (b) Capsaicin’s intense flavour results from the molecule’s long hydrocarbon tail. The chain allows it to bind very strongly with its lipoprotein receptor, which has some hydrocarbon side chains of its own (like dissolves like!). The fatty tail also allows the molecule to slip through lipid-rich cell membranes, making the burn more persistent.

23. c) The perception that peppers are “hot” is not an accident
c) The perception that peppers are “hot” is not an accident. Capsaicin allows calcium ions to move through the cell membrane from the extracellular fluid into the cell. That ultimately triggers a pain signal that is transmitted to the next cell. When the cells are exposed to heat, the same events occur. Chili burns and heat burns are similar at the molecular, cellular, and sensory levels.

24. (d) Capsaicin is found primarily in the pepper’s placenta—the white ribs that run down the middle and along the sides of a pepper. Since the seeds are in such close contact with the ribs, they are also often hot.

25. (e) Capsaicin content is measured in parts per million and are converted into Scoville heat units, the industry standard for measuring a pepper’s intensity. One part per million is equivalent to 15 Scoville units. Bell peppers have a value of zero Scoville units; habaneras—the hottest peppers—register to Scoville units. Pure capsaicin has a Scoville heat unit score of about 16 million.

26. (f) Capsaicin, which is a largely nonpolar molecule, does not mix with water. Drinking water will have little effect on the burning sensation. The most useful liquid is milk (rinsing the mouth with it as you sip) or eating rice or bread, which absorb the capsaicin.

27. (g) As a medicine, capsaicin is used to help relieve the pain associated with neuralgia. Capsaicin is also used to temporarily help relieve pain from arthritis. It is also used as a repellent against dogs, birds, bears, and squirrels, and as an insect repellent. It is the active ingredient in commercially available “pepper sprays.”