ENZYMES DEFINITION, FACTORS AFFECTING ENZYMES AND NAMING

1. ENZYMES and METABOLIC
REACTIONS

2. ENZYMES and METABOLIC REACTIONS
• How do reactions occur in cells?
– Molecules are in constant motion
– Collisions between molecules allow
reactions to occur

3. ENZYMES and METABOLIC REACTIONS
• How do reactions occur in cells?
– Molecules are in constant motion
– Collisions between molecules allow
reactions to occur
• How do we speed up reactions in cells?

4. ENZYMES and METABOLIC REACTIONS
• Enzymes
– Are protein catalysts that allow chemical
reactions to take place in our body without
increasing the temperature
– End with the suffix ‘-ase’

5. ENZYMES and METABOLIC REACTIONS
• Enzymes
– Are protein catalysts that allow chemical
reactions to take place in our body without
increasing the temperature
– End with the suffix ‘-ase’
– Examples: urease, amylase, sucrase

6. Catalysts
• Control the speed of reactions without
changing the products formed
– By reducing the activation energy

8. Catalysts
• Control the speed of reactions without
changing the products formed
– By reducing the activation energy
– Tunnel vs. Climbing a mountain
• Remain unchanged and can be used
over and over
• Often only needed in small amounts

11. Enzymes…
• Work on molecules called the substrate
– Can be anything

12. Enzymes…
• Work on molecules called the substrate
– Can be anything
• Are substrate-specific

13. Enzymes…
• Work on molecules called the substrate
– Can be anything
• Are substrate-specific
• Alter the substrate in some way
• Examples:

14. Substrate
approaches an
enzyme
The enzyme-
substrate
complex is
formed
Reaction is complete.
Enzyme remains
unchanged.
Products are formed.

15. Enzymes Models
• Where the substrate
joins the enzyme is
called the active site
• ‘Lock and Key
Model’
– The active site of an
enzyme is a perfect
match to a specific
substrate

16. Enzymes Models
• ‘Induced-Fit
Model’
– The active site
changes shape
slightly when the
E-S complex join
together
– Makes a tighter
fit

17. Factors that Affect Enzymes
• What happens at cooler
temperatures?
1. Temperature
– Reaction rates
increase as
temperature increases
– Peaks at ~ 37 - 40°C
then drops rapidly
– Why?
• E.g. egg frying

18. Factors that Affect Enzymes
2. pH
– Enzymes function within an optimal pH range
• Stomach pH
• Small intestine pH

19. Factors that Affect Enzymes
3. Concentration of Substrate Molecules
– Reaction rate increases as the substrate
concentration increases up to a point
– Animation link
– The limiting factor in the reaction may be
the amount of substrate or the amount of
enzyme available

20. Factors that Affect Enzymes
4. Inhibitor molecules
– Molecules that attach to the enzyme and
reduce its ability to bind substrate
– There are two types of inhibitors:
a. Competitive inhibitors
b. Non-competitive inhibitors

21. 4. Inhibitor molecules
a. Competitive inhibitors
• Attach to enzyme’s active site
• Shape is similar to substrate
• Compete with the substrate
• Often the end product of the reaction
E.g. drugs and
poisons
- CO
- Cyanide

22. 4. Inhibitor molecules
a. Non-competitive inhibitors
• Attach elsewhere on the enzyme (not the active site)
• Attachment changes the 3D shape of enzyme
• Reaction still occurs, but is inhibited

23. Regulation of Enzyme Activity
• Feedback Inhibition
– Animation
– Turns the path ‘off’
– Prevents accumulation of products
– Final product of pathway interferes with an
enzyme by binding with allosteric
(regulatory) site and altering the active site

24. Regulation of Enzyme Activity
• Precursor Activity
– Animation
– Turns the path ‘on’
– A substrate binds with the last enzyme in a
path improving the fit of the E-S complex
– Binds to the allosteric site
– Speeds up the final product formation

25. Regulation of Enzyme Activity
• Both feedback inhibition and precursor
activity are called allosteric activity
• Handout