EnzymesSBI 4U

September 14th, 2012

What are Enzymes?

Enzymes are …

Enzymes are proteins (tertiary or quarternary) that catalyze (i.e., increase the rates of)

chemical reactions

What is a Catalyst? A substance that increases the rate

of a chemical reaction without itself undergoing any permanent chemical change

In catalyzed reactions, the reactants are converted into products faster than they would be without the catalyst

All reactions require Activation Energy Activation Energy is defined as the energy

that must be overcome in order for a chemical reaction to occur

Heat provides activation energy for most reactions

Temperature is key! Even though an increase in temperature is

needed for most reactions to occur, too much heat can denature proteins, causing them to lose their function!

Therefore, catalysts allow reactions to proceed at suitable rates at moderate temperature by reducing the activation energy needed to catalyze reactions

What does an enzyme act on? An enzyme acts on a substrate A susbtrate is the reactant that an enzyme

acts on when it catalyzes a chemical reaction The substrate binds to a particular site on the

enzyme to which it is attracted

Enzymes are very specific as to which substrate they bind to – they usually don’t bind to isomers of their substrate

The names of enzymes usually end in –ase. For example: amylase (found in saliva), lactase (found in small intestine)

The Process of an Enzyme-Catalyzed Reaction1. Substrate binds to the enzyme at the active

site (located on the enzyme)2. Substrate’s functional groups functional

groups come close to the functional groups of a number of amino acids as the substrate approaches the active site. This allows the protein to change its shape, thereby better accommodating the structure – induced-fit model

3. The attachment of the enzyme’s active site creates the enzyme-substrate complex

How do Temperature and pH affect Enzyme Activity? Temperature – if temperature increases

beyond the critical point, the protein structure can be disrupted and the enzyme can lose its function

Thus, every enzyme has an optimal temperature at which it works best

Ex: most human enzymes work best at normal body temperature 37 C, while those archaebacteria work best at above 100 C

Ph – Like temperature, enzymes work best at an optimal pH. Ex: Pepsin works best in an acidic environment with a Ph of 2

Cofactors & Coenzymes Cofactors “helper molecules” – non-protein

compounds that are bound to a protein and required for the protein’s biological activity. Cofactors are usually enzymes themselves. Example: vitamins & minerals

Cofactors include zinc and manganese ions Coenzymes – derivatives of vitamins. Also

help with catalysis