This document discusses enzymes and metabolic reactions. It explains that enzymes are protein catalysts that speed up chemical reactions in cells without increasing temperature. Enzymes work by reducing the activation energy of reactions and are substrate-specific. The active site of an enzyme binds to a specific substrate. Reaction rates are affected by factors like temperature, pH, substrate and inhibitor concentrations. Enzymes are regulated through feedback inhibition when products inhibit enzymes, and precursor activation when substrates activate enzymes.

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