Chemical Reactions All living organisms grow, reproduce, eat and use energy, and interact with their environment – we need these things to be living! How do we do this? With chemical reactions!

Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals The chemicals that enter the reaction are the REACTANTS The chemicals produced by the reaction are the PRODUCTS

Label the products and reactants: A + B AB Na+ + Cl- NaCl 2 H2 + O2 2 H2O

Chemical Reactions Whenever a chemical reaction takes place, energy is released or absorbed (taken in). An endothermic reaction is one in which energy is absorbed (get cool/cold) An exothermic reaction is one in which energy is released (get warm/hot)

Let’s think… Some reactions are spontaneous: If you open a soda and leave it out for a while, what happens to all the fizz?

Let’s think… And, some reactions are non-spontaneous: Now, how easy would it be to put all of those bubbles (carbonation) back in?

Chemical Reactions and Energy Some chemical reactions are NON-spontaneous, which means that they are not automatic and need another energy source in order to occur.

Chemical Reactions and Energy Activation energy is the energy required for a chemical reaction to occur

Chemical Reactions Let’s say you’re making a cake. You mix up all the ingredients – does the cake bake itself automatically? No. Why not? It needs heat! (Heat is energy).

Enzymes A catalyst is a substance that speeds up the rate of a chemical reaction by lowering the activation energy. By decreasing the activation energy, reactions can occur faster, and spontaneously!

Enzymes How do organisms take care of non-spontaneous reactions? We have enzymes!

Enzymes Enzymes are specific PROTEINS that act as biological catalysts. They are never used up in a reaction and can be used over and over.

Enzymes Enzymes are used in all sorts of bodily reactions. They help cells build molecules or take them apart (as needed). Ex. lipase breaks down lipids Ex. lactase breaks down lactose

Some examples… • lactase – breaks down lactose (milk sugars) • diastase – digests vegetable starch • sucrase – digests complex sugars and starches • maltase – digests disaccharides to monosaccharides (malt sugars) • invertase – breaks down sucrose (table sugar) • glucoamylase – breaks down starch to glucose • alpha-glactosidase – facilitates digestion of beans, legumes, seeds, roots, soy products, and underground stems

Enzymes Most of their names end in the letters A S E. Examples: lactase, lipase, protease, pepsin, trypsin

Enzymes and Substrates Enzymes have specific shapes and SHAPE dictates FUNCTION! The unique shape of the enzyme means that it is only useful in one reaction and it can only bond with a few other molecules.

Enzymes and Substrates The substance that the enzyme bonds to is called the substrate, and the site where it binds is called the active site.

Mechanism of Action Enzymes have a site where reactants can be brought together  the “active site” Enzymes must bind to the reactants – called the substrate Form the enzyme – substrate complex Products are formed

Enzymes and Substrates Think of a key – it only fits into one lock. We use a “lock-and-key” analogy to describe the relationship between an enzyme and its substrate.

Four Things You Should Know About Enzymes 1. They are proteins 2. They are reusable 3. They are specific – they only work in one reaction 4. They are pH and temperature sensitive

Shape and Function Remember that shape is crucial (think about the key). If the key was sitting in an acid it might corrode, and if it was sitting in heat it might melt. Enzymes are the same way! They are only useful in certain conditions.

Optimal Conditions Enzymes are affected by their environment, such as by pH, temperature, and other chemicals, and they function best under OPTIMUM or OPTIMAL (best, ideal, prime) conditions.

Denatured Enzymes If conditions aren’t right, enzymes may become denatured (broken down).

Denatured Enzymes When enzymes are denatured (by heat or pH), they change shape and don’t function correctly – that means they don’t work anymore.

Four Things You Should Know About Enzymes 1. They are proteins 2. They are reusable 3. They are specific – they only work in one reaction 4. They are pH and temperature sensitive