Enzymes
Enzymes Thursday, September 20, 2012 9:01 AM • • • •
Large proteins that catalyze chemical reactions in cells They are very specific, and do not get consumed in the reaction Have an "active site" which is an area to which the substrate binds The precise atomic arrangement in/of the active site is needed for this interaction which recognizes a specific substrate • Within a split second of binding, the substrate is converted to product and the enzyme molecule can bind the next substrate molecule Mechanisms of Enzyme Action • Enzymes are said to lower the activation energy for the reaction. • What does this mean? • How can an enzyme lower the activation energy? • Two basic mechanisms: •
Juxtaposition of substrate molecules
•
Inducing stress in the substrate- physical stress, i.e hydrolyze sucrose a bond needs to be broken, substrate binds to enzyme, enzyme pulls on covalent bond so it breaks • With enzyme lower activation energy
•
Non-Protein Portions of Enzymes • Called co-factors in enzyme action- located somewhere near the active site • Most commonly these are vitamins or minerals that are part of our nutritional requirements •
These cofactors often participate in the catalytic process and are essential for the biological activity of the enzyme
Regulation of Enzyme Activity •
In addition to the active site, most enzymes also have a different site, called the “Allosteric Site” •
The binding of an allosteric regulator to this site, will alter the 3D structure of the enzyme and thus affect its biological activity. •
An allosteric regulator can either enhance or decrease enzyme activity
•
The regulator is often an end product of a series of reactions, or it can be a product of another reaction series. • In a chain of substrates ( A -->B -->C) F is an allosteric effector and bonds to the allosteric site; the concentration of F goes down over time Other factors that affect enzyme activity •
Temperature
•
pH- indication of hydrogen ion concentration
•
Inhibitors
•
Denaturation is a change in the 3D structure of the enzyme and loss of biological
activity. •
Any of the above factors can lead to this.
Inhibitors of enzyme action - two basic types: •
Competitive -compete with the substrate to bind to the active site (e.g. antibiotics) Do not destroy the enzyme, once their concentration goes down the enzyme is active again •
•
Non-competitive - bind to a different site (e.g. heavy metals such as lead &
mercury) •
Bind to an alternate site on the enzyme molecule but when it binds it twists the enzyme out of shape changing it irreversibly, enzyme not functional
Large proteins that catalyze chemical reactions in cells They are very specific, and do not get consumed in the reaction Have an "active site" which is an area to which the substrate binds The precise atomic arrangement in/of the active site is needed for this interaction which recognizes a specific substrate • Within a split second of binding, the substrate is converted to product and the enzyme molecule can bind the next substrate molecule Mechanisms of Enzyme Action • Enzymes are said to lower the activation energy for the reaction. • What does this mean? • How can an enzyme lower the activation energy? • Two basic mechanisms: •
Juxtaposition of substrate molecules
•
Inducing stress in the substrate- physical stress, i.e hydrolyze sucrose a bond needs to be broken, substrate binds to enzyme, enzyme pulls on covalent bond so it breaks • With enzyme lower activation energy
•
Non-Protein Portions of Enzymes • Called co-factors in enzyme action- located somewhere near the active site • Most commonly these are vitamins or minerals that are part of our nutritional requirements •
These cofactors often participate in the catalytic process and are essential for the biological activity of the enzyme
Regulation of Enzyme Activity •
In addition to the active site, most enzymes also have a different site, called the “Allosteric Site” •
The binding of an allosteric regulator to this site, will alter the 3D structure of the enzyme and thus affect its biological activity. •
An allosteric regulator can either enhance or decrease enzyme activity
•
The regulator is often an end product of a series of reactions, or it can be a product of another reaction series. • In a chain of substrates ( A -->B -->C) F is an allosteric effector and bonds to the allosteric site; the concentration of F goes down over time Other factors that affect enzyme activity •
Temperature
•
pH- indication of hydrogen ion concentration
•
Inhibitors
•
Denaturation is a change in the 3D structure of the enzyme and loss of biological
activity. •
Any of the above factors can lead to this.
Inhibitors of enzyme action - two basic types: •
Competitive -compete with the substrate to bind to the active site (e.g. antibiotics) Do not destroy the enzyme, once their concentration goes down the enzyme is active again •
•
Non-competitive - bind to a different site (e.g. heavy metals such as lead &
mercury) •
Bind to an alternate site on the enzyme molecule but when it binds it twists the enzyme out of shape changing it irreversibly, enzyme not functional
