CHEMICAL REACTIONS AND ENZYMES

Mr. ChapmanBiology 30

Chemical Reactions and Life Inside the human body, as well as all other

organisms, there are millions of chemical reactions going on all the time.

Chemical reactions that occur in the cells of organisms need to occur quickly, accurate, and precisely. Many factors affect the rate of a chemical reaction, but one thing especially helps when we are dealing with living organisms.

Factors Affecting Rates of Reaction (sounds like Chem, huh?)1. Temperature – an increase in

temperature increases the rate of a chemical reaction.

2. Concentration – a higher concentration of reactants increases the rate of a chemical reaction.

3. Surface area – an increased surface area increases the rate of a chemical reaction.

This orange has a higher surface area than an orange

that has not been cut.

Most Importantly For Us...4. Enzymes and Catalysts

Remember from when we read about chemical reactions (pages 52 and 53 of the text) that all chemical reactions have an activation energy.

The purpose of an enzyme or a catalyst is to lower that activation energy.

Remember Catalysts:1. A catalyst is a chemical that controls the

rate of the reaction. 2. A catalyst DOES NOT alter or change the

products of the reaction.3. The catalyst remains unchanged after the

reaction.4. A catalyst does not add energy to the

reaction; it lowers the EA barrier.

Enzymes and Catalysts

The goal of enzymes and catalysts is to lower this hump. If this is accomplished, reactions will occur faster.

Notice that with the catalyst, the activation energy for the reaction is lower. The activation energy for the

reaction is how much energy is needed to get the reaction going.

Enzymes Enzymes are basically catalysts that

exist in living organisms. An enzyme’s job is to speed up and organize chemical reactions in a cell.

If you could sum up an enzyme in one sentence, it should be:

Enzymes are protein catalysts that serve in biological reactions.

How do Enzymes Work?1. Enzyme function is actually very simple. The specific

reactants that an enzyme works on are called substrates.

2. When the substrate binds to the enzyme, the entire thing is called the enzyme-substrate complex.

3. The enzyme weakens the bonds of the substrate, allowing the products to form more easily.

4. The products are released from the enzyme, which is then free to bind a new substrate.

Each enzyme fits a certain kind of reactant, a.k.a. substrate.

The enzyme is like a lock and the substrate is like a key. Hence, this is the lock and key model of enzymatic activity.

Enzymes can also disassemble large reactants.

Active Site The active site of an enzyme is the

place where the reactants go in the enzyme.

Due to the shape and structure of their active sites, each enzyme can only recognize one type of substrate.

Induced-Fit Model The induced-fit model suggests that

some substrates don’t fit perfectly into the active site, but that the active site surrounds the substrate and makes it fit.

Now That I Know How it Works... How Can I Destroy It? There are 2 ways to destroy (or denature) an enzyme:

1. Place it under high temperatures. Enzymes work best around normal physiological temperature (37 °C for humans), and a few degrees either way can destroy them.

2. Enzymes become denatured by acid. Since enzymes are proteins, putting them in acid can ruin the hydrogen bonding that gives them their shape.