Enzyme Regulation

Chemical Reactions Thousands of chemical reactions occur in living organisms every second. Energy is required to start each reaction= activation energy. Enzymes reduce the amount of activation energy required to start a reaction.

ENZYMES All enzymes are very large proteins made of chains of amino acids linked together by peptide bonds. Function of Enzymes: Enzymes are catalysts. Catalysts speed up chemical reactions by lowering the activation energy. Catalysts are not changed in the reaction. Each enzyme is very specific= only reacts with a few types of molecules (substrate

Lock and Key Model: The enzyme and substrate fit together. The enzyme changes the substrate into products. The enzyme releases the products and is able to bond with the next substrate.

The activity of enzymes is strongly affected by Changes in pH Changes in temperature Amount of time Concentration of reactants Concentration of enzyme

Many enzymes require cofactors 1. some enzymes have tightly bound helpers called coenzymes or cofactors 2. Cofactors can be single metal ions (Mg, Zn, Co, Mn, etc) 3. Cofactors can be small organic molecule called

Inhibitors slow down rate of reaction of enzyme when necessary I. Competitive Inhibitors Compete with substrate for active site Shape similar to substrates / prevents access when bonded

[EXAMPLE] Methanol Poisoning Methanol CH 3 OH is a competitive inhibitor CH 3 OH can bind to dehydrogenase whose true substrate is C 2 H 5 OH A person who has accidentally swallowed methanol is treated by being given large doses of C 2 H 5 OH C 2 H 5 OH competes with CH 3 OH for the active site

Non-competitive Inhibitors Chemical does not have to resemble the substrate Binds to enzyme other than at active site This changes the enzyme's active site and prevents access to it

Irreversible Inhibition Chemical permanently binds to the enzyme or massively denatures the enzyme Nerve gas permanently blocks pathways involved in nerve message transmission, resulting in death Penicillin, the first of "wonder drug" antibiotics, permanently blocks pathways certain bacteria use to assemble their cell wall component (peptidoglycan)

1. Consider Regulatory problem of cell: thousands of enzymes, each with a "mind of its own". Yet cell needs overall stability. 2. Example: synthesis of a certain amino acid. Reaction scheme looks like this: 3. Suppose supply of E in cell increases (e.g. eat a meal rich in E). How to shut down synthesis of E?

1. Suppose supply of E in cell increases (e.g. eat a meal rich in E). How to shut down synthesis of E? 2. Cell's answer: Enzyme 1 is reversibly inhibited by E. Note that E is not the substrate, and chemically so different that it cannot bind to active site. How does E shut down Enzyme 1? 3. Enz 1 is a special type of enzyme called an allosteric enzyme. It causes feedback inhibition. Allosteric enzymes contains two distinct subunits, one with active site (binds substrate A and catalyzes reaction), one with allosteric site (binds E).

Allosteric Inhibition simulation

1. When E binds, causes shape change in the enzyme, this is transmitted to block activity of active site. 2. Net result: whole pathway is turned on or off as a unit by end-product. Called Feedback inhibition. Crucial to cell regulation.