2-4 Chemical Reactions

& Enzymes

A chemical reaction is a change in which one or more substances are converted into new substances.

A + B C + DThe substances

that will be reacting together

are called reactants.

The substances that are produced

are called products.

Chemical reactions where the reactants release energy, often occurs almost instantly.

2H2 + O2 → 2H2O

Chemical reactions where you have to add energy to the reactants will not happen unless you add energy to it.

Burning hydrogen

gas

Oxygen gas

Water

2H2O → 2H2 + O2

Oxygen gas

Burning hydrogen

gas

Water

Exothermic reaction

Endothermic reaction

Energy is used to create chemical reactions no matter which method is used.

+

A B C

Reactants

Energy

Products

Energy changes into… or forms.

So how much ENERGY does it take to start a chemical reaction?

You have to put energy into the equation to get a reaction to work

The amount of ENERGY needed to start a chemical reaction is called the ACTIVATION ENERGY

If enough energy is added, the ball reaches the Activation energy level and the

Chemical Reaction Occurs

Activation Energy

If not enough energy is added, the ball cannot reach the Activation Energy level

and there is NO REACTION.

Chemical A

Chemical B

(Reactant)

(Reactant)

Activation energy

Chemical C

(Product)

When the reaction occurs, ENERGY is RELEASED because the ENERGY is

changing forms.

AB

Product

Energy Releas

ed

ENZYMES

ENZYMES are proteins that help speed up a chemical reaction.

A great example of an enzyme is in your stomach with the enzyme Pepsin.

(which breaks down proteins like in a steak that you eat)

Another word for this (speed up reaction) is called CATALYST

When you eat, your food is still too big to digest properly.

Your stomach can’t absorb the food this way

Your stomach releases an ENZYME called PEPSIN, which breaks down the food

proteins into small monomers which the body absorbs for energy.

If you didn’t have this enzyme, the stomach acids would take days for it to dissolve the food into smaller pieces.

What happens if you don’t eat for days?

1. You’re sluggish / no energy

2. Body systems start to shut down

3. Leads to illness

So the enzyme PEPSIN, speeds up the chemical breakdown of proteins in our

food.

How does it do it? – It lowers the

ACTIVATION ENERGY

AB

Product

Energy Releas

ed

Remember this?

Pepsin lowers the activation level like this.

AB

You don’t need as much energy!!!

Energy Releas

ed

ENZYMES:

1.Speed up a reaction

2. Lower Activation Energy.

3. Are reusable?

Yes, enzymes can be used over an over and over like re-chargeable batteries.

Let’s look at the enzyme “Pepsin” up close…

Pepsin attaches one of the reactants (protein)

PEPSIN

Active site

Pepsin

Substrate (protein)

Where it attaches is called the “Active Site”

The reactant it attaches to is called a *SUBSTRATE*

Pepsin is very specific for one Substrate only! (Just like only 1 key can fit a lock) All

enzymes are specificNote how the curves fit perfectly

together…

PEPSIN

Pepsin

Substrate

When the enzyme and substrate join together, it gets a new name called the:

Enzyme-Substrate Complex

This is when the chemical reaction occurs!

PEPSINPEPSIN

Pepsin

Substrate

Notice that the lock & key curves are the same, yet the chemical reaction makes the new products in that same space.

Pepsin

After the chemical reaction, the new Products (proteins) are made and the Pepsin looks for more Substrate to break down.

Pepsin

The Process Simplified…

Enzyme + Substrate Enzyme Enzyme + Product(s) Substrate

Complex

E + S ESC E + P

Pepsin

+ Pepsin

Pepsin

+

Since enzymes are specific for a certain substrate, there are many enzymes in your

body.

Enzymes were originally named with a “-in” ending (Pepsin).

Later on, scientist started naming the enzymes with a “-ase” ending

Since Carbohydrate sugars are named with a “-ose” ending, there is a enzyme that is specific for each one.

SUGAR NAME ENZYME NAME

Lactose Lactase

Sucrose Sucrase

Maltose Maltase

What I want you to remember from this is:

Sugars – have “ose” endingsEnzymes – have “ase” endings

What could cause enzymes not to work properly?

When an enzyme doesn’t work properly it is said to be Denatured - the active sites on an enzyme change in shape, therefore unabling the enzyme to lock up with a substrate

Pepsin

Pepsin

1. Too high of Acid or Base (pH) in your body

2. Temperature differences (hot / cold) fever, chills

3. Lack of Water / Oxygen

Causes of Denaturation are:

One of the most important reactions in your body involves the enzyme Catalase.

Catalase turns the cell waste product of Hydrogen Peroxide (H2O2) into Water and

Oxygen gas.

The reaction is: 2H2O2 ----> 2H2O + O2 (fix)

Hydrogen

Peroxide----> Water Oxyge

n Gas