1. Show what you know in a creative manner.
1, 27 – What are enzymes? Why are they important?
2, 29, 30 – Explain Figure 8.13 in the handout. Define all the terms associated with the diagram.
4, 5, 28 – Explain Figure 8.14 in the handout and describe how enzymes affect the curve.
6, 7, 8, 25, 26 – Describe the terms in boldface, explain why enzymes are substrate-specific, and describe the difference between the lock-and-key and induced-fit models.
9, 10, 23, 24 – Describe how enzymes catalyse reactions in their active sites.
11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity.
13, 20 – Differentiate between cofactors and coenzymes.
14, 15, 19 – Differentiate between competitive inhibitors and noncompetitive inhibitors.
16, 17 - Describe allosteric regulation and the concept of cooperativity in haemoglobin.
3, 18 –Describe how allosteric regulation plays a role in feedback inhibition.

2. 1, 27 What are enzymes? Why are they important?

3. Enzymes

4. Enzymes are biological catalysts
Change the rates of a reaction (x ) without being consumed
Lower energy barriers  initial energy investment or activation energy(EA)
Cells can carry out necessary metabolic reactions even at moderate temperatures
Progress of the reaction
Products
Course of
reaction
without
enzyme
Reactants
with enzyme EA
EA with
is lower
∆G is unaffected
by enzyme
Free energy

5. 2, 29, 30 – Explain Figure 8. 13 in the handout
2, 29, 30 – Explain Figure 8.13 in the handout. Define all the terms associated with the diagram. 4, 5, 28 – Explain Figure 8.14 in the handout and describe how enzymes affect the curve.

6. 6, 7, 8, 25, 26 – Describe the terms in boldface, explain why enzymes are substrate-specific, and describe the difference between the lock-and-key and induced-fit models.

7. Enzymes are substrate specific
H2O H HO OH O
CH2OH
Sucrase
Sucrose
Glucose
Fructose
C12H22O11
C6H12O6 +
Substrate
Active site
Enzyme
Tertiary/Quaternary structure accounts for specificity
Active site – pocket or groove on surface of protein
Substrates have to be compatible with the active site  lock and key model
Substrates can cause the enzyme’s shape to change slightly to enhance activity “induced fit”
Can act on 1000 substrate molecules per second
Enzyme-substrate complex

8. 9, 10, 23, 24 – Describe how enzymes catalyse reactions in their active sites.

9. The catalytic cycle of an enzyme
Substrates
Products
Enzyme
Enzyme-substrate
complex
1 Substrates enter active site; enzyme
changes shape so its active site
embraces the substrates (induced fit).
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
3 Active site (and R groups of
its amino acids) can lower EA
and speed up a reaction by
• acting as a template for
substrate orientation,
• stressing the substrates
and stabilizing the
transition state,
• providing a favorable
microenvironment,
• participating directly in the
catalytic reaction.
4 Substrates are
Converted into
Products.
5 Products are
Released.
6 Active site
Is available for
two new substrate
Molecules.

10. 11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity.

11. Enzyme action is affected by conditions within the cell
temperature pH
concentration of substrate and product

12. Factors affecting enzyme action
Temperature
increase in effective collisions
optimum temperature – most rapid enzyme action
rapid fall – enzymes denatured above a given threshold temperature

13. Factors affecting enzyme action
2. pH
narrow range
activity falls of rapidly on both sides of optimum
structure is affected by degrees of acidity and alkanity

14. Factors affecting enzyme action
3. Substrate concentration [S]
E + S  ES  E + P
below saturation point –  [S]   E that can bind to S
point of saturation onwards -  [S]  no further increase in reaction rate

15. Factors affecting enzyme action
4. Enzyme concentration [E]
If excess substrate is available, rate  [E]
[P]  [E], c.p.

16. 11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity. 13, 20 – Differentiate between cofactors and coenzymes

18. Enzyme action is affected by conditions within the cell
presence of cofactors/coenzymes
presence of enzyme inhibitors
competitive inhibitors
noncompetitive inhibitors

21. 14, 15, 19 – Differentiate between competitive inhibitors and noncompetitive inhibitors.

22. Enzyme inhibitors (c) Noncompetitive inhibition
(b) Competitive inhibition
A competitive
inhibitor mimics the
substrate, competing
for the active site.
Competitive
inhibitor
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding
A noncompetitive
inhibitor binds to the
enzyme away from
the active site, altering
the conformation of
the enzyme so that its
active site no longer
functions.
Noncompetitive inhibitor
(c) Noncompetitive inhibition

23. 16, 17 - Describe allosteric regulation and the concept of cooperativity in haemoglobin.

24. Metabolic control depends on allosteric regulation
Regulatory molecules activate/inhibit enzyme shape and function by binding to allosteric sites
Protein action at active site is affected by binding at a different site

26. 3, 18 – Describe how allosteric regulation plays a role in feedback inhibition.

27. Feedback inhibition
Metabolic pathways make use of more than one enzyme
End product is an allosteric inhibitor that switches off enzyme action
e.g. synthesis of isoleucine from threonine