1. ENZYMES

2. Define the following terms:
Anabolic reactions:
Catabolic reactions:
Metabolism:
Catalyst:
Metabolic pathway:
Specificity:
Substrate:
Product:
Reactions that build up molecules
Reactions that break down molecules
Combination of anabolic and catabolic reactions
A substance that speeds up reactions without changing the produced substances
Sequence of enzyme controlled reactions
Only able to catalyse specific reactions
The molecule(s) the enzyme works on
Molecule(s) produced by enzymes

3. Naming enzymes: Intracellular enzymes Extracellular enzymes
Recommended names
Systematic name
Classification number
Work inside cells eg.DNA polymerase
Secreted by cells and work outside cells eg. pepsin, amylase
Short name, often ending in ‘ase’ eg. creatine kinase
Describes the type of reaction being catalysed eg.
ATP:creatine phosphotransferase Eg

4. Timeline of enzyme discovery
1835:
Breakdown of starch to sugar by malt
1877:
Name enzyme coined to describe chemicals in yeast that ferment sugars
1897:
Eduard Buchner extracted enzyme from yeast and showed it could work outside cells
1905:
Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning
1926:
James B Sumner produced first pure crystalline enzyme (urease)
and showed enzymes were proteins :
Protein nature of enzymes finally established when digestive enzymes
crystallised by John H Northrop
1946: Sumner finally awarded Nobel prize

5. Enzymes lower the activation energy of a reaction
of uncatalysed reactions
Initial energy state
of substrates
Activation energy
of enzyme catalysed
reaction
Energy levels of molecules
Final energy state of products
Progress of reaction (time)

6. Enzymes lower activation energy by forming an enzyme/substrate complex
Substrate + Enzyme
Enzyme/substrate complex
Enzyme/product complex
Product + Enzyme

7. In anabolic reactions enzymes bring the substrate molecules together.
In catabolic reactions the enzyme active site affects the bonds in substrates so they are easier to break

8. Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its shape
How ever crystallographic studies indicate proteins are flexible.

9. The Induced-fit hypothesis suggests the active site is flexible and only assumes its catalytic conformation after the substrate molecules bind to the site.
When the product leaves the enzyme the active site reverts to its inactive state.

10. Enzymes are globular proteins
Active site has a specific shape due to tertiary structure of protein.
A change in shape of the protein affects shape of active site and the function of the enzyme.
Click to link to jmol interactive representation courtesy of University of Arizona

11. Characteristics of enzymes
Only change the rate of reaction. They do not change the equilibrium or end products.
Specific to one particular reaction
Present in very small amounts due to high molecular activity: Turnover number = number of substrate molecules transformed per minute by one enzyme molecule
Catalase turnover number = 6 x106/min

12. How would you measure the effect of an enzyme?
Compare uncatalysed rate with catalysed.
Enzymes can increase rate by a factor of between 108 to 1026

13. Characteristics of enzymes
Rate of enzyme action is dependent on number of substrate molecules present
Vmax = maximum rate of reaction
Vmax approached as all active sites become filled
Rate of Reaction (M)
Some active sites free at lower substrate concentrations
Substrate concentration

14. Why do scientists measure the initial rate of reaction of enzyme-catalysed reactions?
They measure rate at start of reaction before any factors, eg. substrate concentration, have had time to change.
Rate of Reaction (M)
Independent variable

15. Rate of enzyme –catalysed reactions are affected by temperature.
Temperature coefficient Q10:
rate of reaction at (x + 10) oC
Q10 =
rate of reaction at x oC
Q10 for between oC is 2

16. Enzymes denature at 60oC
Optimum temperature
Enzyme denaturing and losing catalytic abilities
Rate doubles every 10oC
Rate of reaction
Temperature
Some thermophilic bacteria have enzymes with optimum
temperatures of 85oC

17. pH affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape.
trypsin
cholinesterase
pepsin
Rate of Reaction (M) 2 4 6 8 10 pH

18. Enzymes in medicine
Glucose oxidase + peroxidase + blue dye on dipsticks to detect glucose in urine:
Glucose oxidase
Glucose
Hydrogen peroxide
peroxidase
Dye: Blue---Green---Brown
Dye changes according to amount of glucose
Enzyme-linked immunosorbent assays (ELISAs) detect antibodies to infections.