1. Ch 04
Enzymes

2. Enzymes Old model: New model:___________
New model:___________

3. Enzymes Are biological ____________ Usually made up of ___________
__________reaction rate
_______the activation energy of the reaction
Are not changed by the reaction (so can be used again)
Do not change the nature of the reaction - the reaction could have occurred without the enzyme, just much slower

4. Enzymes lower activation energy:
All chemical reactions in body must be conducted at body temp.!!
How do enzymes lower activation energy ?
Enzymes bind to reactant molecules and bring them together in best position for rx.
Compare to Fig 4-1

5. Protein Binding is Selective
Ligands
Noncovalent bonds with other molecules
Molecules are complementary
Specificity
Affinity

6. Active Site:
Small region of the complex 3D structure is active (or binding) site.
Enzymes bind to substrate
Old vs. new model

7. Mechanisms of Enzyme Activity
The reactants are called substrates, and they fit into the active site

8. Lactose Glucose + Galactose
Naming Enzymes
The first enzymes discovered were given arbitrary names.
An international committee later decided to end all enzymes with the suffix – ____
Lactose Glucose + Galactose ?

9. Isoenzymes = different models of same enzyme (differ in 1 or few aa)
Catalize same reaction under different conditions and in different tissues/organs
Examples:
Amylase
LDH → importance in diagnostics

10. Creatine phosphate + ADP creatine + ATP
Clinical Application
Measuring enzymes in the blood
Example: CPK (= CK) is used by skeletal muscles, heart muscle and the brain to make ATP
Creatine phosphate + ADP creatine + ATP
CPK-1 - found in the brain and lungs.
CPK-2 - found in the heart.
CPK-3 - found in skeletal muscle.

11. Control of Enzyme Activity
measured by substrate conversion rate
Influenced by
_______
___________________________
Cofactors and coenzymes
Stimulatory or inhibitory effects of products

12. Effects of Temp. and pH Temperature pH Tyrosine Melanin
Tyrosinase is temperature sensitive  does not function at cat’s core body temperature (101.5° F)
tyrosinase

13. Cofactors & Coenzymes ___________ molecules (e.g. ?)
Lead to conformational change of active site
Organic molecules (vitamin
derivatives)
Function as carriers for hydrogen atoms and functional groups from one enzyme to the other.
E.g.: NADH and FADH2
Fig 2-12 c

14. Enzyme Activation and Inactivation
Enzymes often produced in an inactive form: zymogen
E.g.: pepsinogen  pepsin
Common mechanism of activation: Phosphorylation and dephosphorylation
Enzyme inactivation can also be controlled through turnover  degradation in ___________ and _____________.

15. Substrate Concentrations and Reversible Reactions
Saturation curve for fixed amount of __________
Fig 4.6

16. Law of mass action applies
Some reactions are reversible: Single enzyme drives reaction in both directions. Direction depends on the concentration of substrate/product.
Law of mass action applies
Example:
H2O + CO2 ↔ H2CO3
Many rxs are NOT reversible. Why not?

17. Metabolic Pathways
Metabolism definition: ___________ Most chemical reactions are linked together
Linear pathway
Intermediates
Circular pathway
Branched pathway

18. End Product Inhibition
Fig 4.9
Branch points often inhibited by negative feedback or end product inhibition Mechanism: Allosteric inhibition

19. Inborn Errors of Metabolism
Due to mutation in gene encoding an enzyme
Diseases occur due to
loss of end product
accumulation of intermediary products
Overproduction of alternate product
Compare to Fig 4.10

20. Inborn Errors of Metabolism cont.
Fig 4.10

21. Clinical Investigation:
Sheryl, an active 78-year-old.....
The end