Enzymes

They are biological catalysts and globular proteins.
Each type of enzyme catalyses a specific reaction.

Enzymes can be re-used.

Metabolism consists of many enzyme reactions.

The reactions are either anabolic (builds up) or catabolic (breaks down).

To increase the rate of a reaction you could:

• Increase the temperature. (More kinetic energy = more collisions.
• Increase the concentration of reactants.
• Increase the surface area : volume ratio.
• Add a catalyst (like an enzyme).

All of these factors allow a larger number of successful collisions per unit time.

Enzyme/Substrate Complexes.

This is when a substrate combines with an enzyme. When more of these occur, the rate of reaction increases. In this complex, the chance of a reaction happening is larger than normal.

Collisions need to occur in a specific orientation for them to be successful. Enzymes have a specific shape which can "hold on" to the substrate and then changes its shape slightly to combine the two substances together in a specific orientation.

Activation Energy

This is the minimum amount of energy required for substrates to react. The higher the activation energy, the harder it is for the substrates to react. Enzymes lower the activation energy which makes it easier for reactions to occur. Enzymes don't change the energy level of a substrate.

Lock and Key (Fischer 1890)

The substrate binds into the enzyme's active site (3-12 amino acids) and the shape of the active site fits the substrate, so they are complementary. The shape of the enzyme is dependent on the specific R groups of the amino acids. These may bond with the substrate.

Induced Fit (Koshland 1959)

The substrate causes a change in the shape of the enzyme, and the amino acids in the active site form a specific arrangement for the enzyme to carry out its catalytic function.

Measuring Enzyme Activity

To measure enzyme activity, you can use the amount of substrate used against time or the amount of product made in time. Being measured over time, it identifies the changes in the rate of reaction. To measure the activity, the initial rate of reaction needs to be calculated.

Enzyme activity is affected by:

• Temperature
• Enzyme Concentration
• Substrate Concentration
• pH

Temperature
The optimum temperature on this graph is 40 ˚C

When you increase the temperature, there is more kinetic energy so there are more successful collisions per unit time. This means more enzyme/substrate complexes.

When the temperature goes past it's optimum point, there is still more kinetic energy, but H bonds break as well as other bonds causing the enzyme to lose it's shape, becoming denatured.

Enzyme Concentration

More enzymes = more collisions per unit time.

This means more enzyme/substrate complexes

It reaches a maximum rate of reaction because of limiting factors. In this case, the concentration of the substrate.

Substrate Concentration

More substrate = more collisions per unit time.

This means more enzyme/substrate complexes which means a faster rate of reaction.

It reaches a maximum rate because of limiting factors. In this case, the concentration of enzymes. Active sites are saturated with substrates so the reaction can't occur any faster.

pH

Above or below the optimum pH, the enzyme loses it's shape and denatures. This is because ionic bonds break due to changes in pH.

Denatured enzymes mean no enzyme/substrate complexes which lowers the rate of reaction dramatically.