Enzymes

Enzymes Enzymes are substances that are necessary

for most of the chemical reactions that occur in living cells.

Chemical reactions that occur in the body are done in small steps. In some of these small steps, the enzyme works on the reaction to help it take place, rearranging the molecules involved.

Enzymes Are Biological Catalysts• Enzymes are proteins that carry out most

catalysis in living organisms.– Unique three-dimensional shape enables an

enzyme to react with specific substrates.– Because the enzyme itself is not changed or

consumed in the reaction, only a small amount is needed, and can then be reused.

Enzyme names Usually end in “-ase” like isomerase

Most enzymes are used within the cell, but some are used outside of the cell. Example: Digestive enzymes

Free Energy• Free energy refers to the amount of energy

actually available to break and subsequently form other chemical bonds.– in a cell - amt of energy contained in a molecules

chemical bonds• Energy involved in chemical reactions:

• endergonic - any reaction that absorbs free energy

• exergonic - any reaction that releases free energy

Activation Energy

• Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.

• catalyst - substance that lowers the activation energy

• Enzymes are catalysts.

Activation Energy and Catalysis

How do enzymes work?

• An enzyme reacts only with specific substrates (Another word for reactants)

– Active site- the part of an enzyme that actually

interacts with the reactants

Enzyme Active Site• Amino acid side chains interact, metal ions,• Various types of polar, non-polar, ionic interactions

Enzymes

• Most enzymes are globular proteins with one or more active sites.– Substrates bind to the enzyme at these active

sites, forming an enzyme-substrate complex.

How Does It Fit? 2 Models Old – Lock and Key Model – the active site

only fits certain substrates. Newer – Induced Fit Model – Enzyme

changes shape in reaction to being exposed to the substrate.

• Lock and Key Analogy: lock = enzyme, key = substrate.

Induced Fit Model

Control of enzyme activity:• Concentration of enzyme and substrate molecules

• Temperature

• pH

Enzymes - Activity• Enzyme and substrate concentrations

Enzymes - Activity• Temperature and pH effect enzyme action

Enzymes - Activity• Temperature and pH effect enzyme action