1. Enzymes

2. 2.5.1 Enzymes have an active site to which specific sites bind
Enzymes are globular proteins that work as catalysts- speed up chemical reactions without being changed or used up: “biological catalysts”
Substrates- substances that enzymes convert into products

3. Enzymes Enzymes are found in all living cells
Secreted by some cells to work outside the cell
Living organisms produce thousands of enzymes because thousands of reactions take place and each enzyme is specific to a reaction
Enzyme-substrate specificity- enzymes only catalyze one biochemical reaction because the binding sites specifically match the substrate

4. 2.5.2 Enzymes catalysis involves molecular motion and the collision of substrates with the active site
Enzyme activity is the catalysis of a reaction by an enzyme. This occurs in 3 stages
Substrate binds to the active site of the enzyme. Some enzymes have 2 substrates that bind to different active sites.
While the substrates are bound to the active site, they change into different chemical substances, which are the products
The products separate from the active site, leaving it vacant for substances to bind again
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5. A substrate can only bind to the active site if it moves very closely to it. This coming together is a collision.
Since this takes place in or around the cell, substrates are dissolved in water around the enzyme (because water is liquid, its molecules and the particles inside it are in constant motion) The substrates and enzymes are constantly moving, eventually coming into contact
Successful collisions are ones in which the substrate and active site are correctly aligned to allow binding to take place.

6. 2.5.3 Temperature, pH, and substrate concentration affect the rate of activity of enzymes
Enzyme activity is affected by temperature in two ways
In liquids, the particles are in constant, random motion. Increasing temperature increases kinetic energy, and particles move faster, increasing the chance of a collision  increased enzymatic activity
When enzymes are heated, the intermolecular bonds move and the chance of the bonds breaking is increased. When bonds break, the structure changes, which results in the active site changing shape. This is denaturation, and the enzymes can no longer catalyze.

7. pH- enzymes are sensitive to pH
Most enzymes have an optimum pH at which activity is highest, if pH increases or decreases, enzyme activity decreases and eventually stops altogether. (Enzyme is denatured due to the presence of H ions)
Different enzymes function at different pH levels
Below is a graph at which the enzyme functions at optimal levels at a pH of 8

8. Enzyme activity is affected by substrate concentration
Enzymes can’t catalyze reactions until the substrate binds to the active site. If the concentration of substances increases, active site collisions will take place more frequently and the rate increases.
HOWEVER, once the substrate binds the active site, that enzyme is occupied. As more and more substances bind, fewer enzymes are available to bind. The increase in reaction rate gets smaller as concentration increases.

9. 2.5.4 Enzymes can be denatured
Enzymes are proteins, and like proteins, their structure can be irreversibly altered by certain conditions (pH, temperature).
When subjected to these conditions, the structure of the enzyme is altered, thus the active site is altered and the substrate can no longer bind to it. Or, if it can bind to it, the reaction that normally takes place does not occur.
In many cases denaturation causes enzymes that were dissolved in water to become insoluble and form a precipitate.

10. 2.5.5 Immobilized enzymes are widely used in industry.
1887- Hans and Edward Buchner demonstrated that extract of yeast, containing no yeast cells could convert sugar to alcohol.
This was important for many reasons:
The door was opened to use enzymes to catalyze chemical processes outside living cells
This provided evidence that falsified Theory of vitalism (substances in animals and plants can only be made under a vital spirit or vital force). Remember, the artificial synthesis of urea provided evidence against this theory and this provides further evidence against it.

11. Enzymes in industry are usually immobilized- attached to other materials or into aggregates so that movement of the enzyme is restricted. Methods of immobilization attached to glass surfaces entrapped in alginate gel binding them together to form aggregates

12. Why immobilize?
They can be recovered and reused (enzymes are very expensive)
Reaction is more efficient
Easily separate enzyme and product
Immobilized enzymes are more stable, can better resist changes to pH and temp changes, which reduces the rate at which they are denatured and have to be replaced
Substrates can be exposed to higher enzyme concentrations, which increases rate of reaction

13. Commercial uses
Enzyme-linked immunoabsorbent assays (ELISAs)- detect antibodies to infections
Biological washing powders- enzymes can break down proteins that cause stains
Pectinase- production of alcohol and juice
Lactase- breaks down lactose in milk

14. A2.5.1 Methods of production of lactose-free milk and its advantages
Lactose is the sugar that is present in milk
Lactase breaks it down to glucose and galactose
Lactase (produced in Kluveromyces lactis- a yeast that grows naturally in milk) is extracted from biotech companies and sold to food manufacturers
Lactose-free milk can be produced one of two ways
Add lactase to milk so that the milk contains the enzyme
Immobilizing the enzyme on a surface or in beads of a porous material. The milk is then allowed to flow past the beads. The lactase breaks down lactose, and milk does not contain lactase.

15. Reasons for doing this
Reduce the amount of lactose in milk for people who are lactose intolerant
Galactose and glucose are sweeter than lactose, so less sugar needs to be added to foods containing milk, such as yogurt
Lactose crystallizes during production of ice cream, glucose and galactose are more soluble
Bacteria ferments glucose and galactose more quickly than lactose, so the production of cottage cheese and yogurt is faster.

16. Enzyme Lab

17. Helpful links: