Chemical Reactions
& Enzymes
Q! What is Activation Energy?
Many chemical reactions need a source of energy to occur
Activation Energy = the energy needed to
get the reaction going
e.g. What will happen to a pile of wood sitting in a fireplace?
Nothing!
It needs the energy from a lit
match to get the wood burning!
Graph of Energy
Lower energy = faster reaction!
Q! What do Enzymes Do?
Enzymes lower the activation
energy and
speed up
chemical reactions in cells
Q! What type of macromolecule
are Enzymes?
4 macromolecules
lipids
nucleic acids
carbohydrates
proteins
Enzymes are proteins!
Q! How do Enzymes work in
Our Body?
In our body…
1. Enzymes speed up digestion by
breaking down food
2. Enzymes speed up cell respiration
to make ATP
Q! How do Enzymes Work?
Active Site (a groove
that fits a substrate)
Enzyme
Substrate
How Enzymes Work
Enzyme
Substrate
Substrate moves into the
active site
How Enzymes Work
Substrate
Enzyme
Substrate moves into the
active site
How Enzymes Work
Substrate
Enzyme
Substrate moves into the
active site
How Enzymes Work
Substrate
Enzyme
Fits tightly into the
groove!
How Enzymes Work
Product
Enzyme
When the reaction is done,
the products are released
How Enzymes Work
Products
Enzyme
The enzyme is free to start all over!
Q! What is the Lock and Key
Model?
One enzyme fits one substrate
(like one key fits one lock)
Lock and Key Model
Enzymes Summary
Enzymes…
1. Are proteins
2. Lower the activation energy
3. Speed up chemical reactions
4. Are not destroyed or used up
5. Bond to a substrate
6. Are also called catalysts
Cracker Challenge!
1. Take a cracker and lick it. Record how it tastes.
2. Chew it for 10 seconds and again record how it
tastes.
3. Why did the taste of the cracker change?
The cracker became sweeter as
amylase, an enzyme in your saliva,
broke down the starch into sugar!
Enzymes All Around Us
Copy this table in your notes
1
Enzyme
Substrate
Products
2
3
4
5
6
Enzymes All Around Us
Use these products to fill in your table!
Amylases Detergents for dish washing to remove starch
Meat tenderizers (Papain) To soften meat for cooking
Contact lens cleaners (Proteases) To remove proteins on contact lens
to prevent infections.
Fruit juices (Pectinases) To make fruit juices clear
Baby foods (Trypsin) To predigest baby foods
Q! What Conditions to enzymes
depend on?
Enzyme activity is affected 3 things:
1. pH
2. Concentration of substrate
3. Temperature
Q! Hos does pH affect enzymes?
• Stomach enzymes work best at an acidic pH
(pH 2-4)
• Small intestine enzymes work best at a basic
pH (pH 8-9)
(graphs on next slide)
HSA Question:
Cells in the stomach produce pepsin, an
enzyme, to help digest food. Pepsin works
best at a pH of 2. Which of these graphs
most likely shows what will happen to the
activity of pepsin as the pH of the
stomach is increased?
Q! How does the Concentration of
Substrate affect enzymes?
The more substrate that is available, the more
reactions can take place at once.
Substrate
Substrate
E
Substrate
Substrate
E
Substrate
E
Concentration of Substrate
The more substrate that is available, the more
reactions can take place at once.
Substrate
E
Substrate
Substrate
E
E
Concentration of Substrate
The more substrate that is available, the more
reactions can take place at once.
Substrate
E
Substrate
Substrate
E
E
Q! How does Temperature
Affect enzymes?
Some enzymes like it warm…
but some like it hot!
• Enzymes in humans work best at 98F
• Enzymes in thermophilic bacteria work
best at MUCH hotter temperatures!
Temperature
* In general, enzymes work better in warmer
temperatures because the molecules move
more quickly and cause more interactions.
** However, if the temperature gets TOO hot, it
can damage the enzyme so that it stops
working. This is called denaturation.
Q! What is Denaturing?
Denature= when the structure of a protein
changes so that it no longer functions
Can be caused by:
• high temperatures
• changes in pH
Toothpick Demo
I need 1 volunteer to race against time!
Objective: To pick up as many toothpicks as
possible in 15 seconds
Rules:
1. only use one hand
2. only pick up one toothpick at a time
3. NO cheating!
What was the enzyme?
What was the substrate?
The product?
HSA Question:
A researcher is testing the effect of acid rain
on living organisms. She takes a tissue
sample and places it in acid rainwater,
which decreases its pH. As the pH
decreases, what will most likely happen to
the enzyme reaction rates in the cells of
this tissue?
A. They will increase.
B. They will decrease.
C. They will stay the same.
D. They will increase and level off.
HSA Question :
Catalase is an enzyme found in plant and animal cells.
Catalase causes hydrogen peroxide to break down into
water and oxygen. A student conducted an experiment
to determine whether plant and animal cells have the
same amount of catalase. She measured and recorded
the amount of oxygen that is given off by each of the
tissues when mixed with the enzymes.
The student conducted a second experiment. She boiled
the liver tissue completely and added it to the hydrogen
peroxide solution. She observed that little to no oxygen
was released in the second experiment.
Which of these statements best supports the student’s
observations?
A. Exposing catalase to high temperatures makes it inactive.
B. Exposing catalase to high temperatures changes it into a
different enzyme.
C. Boiling liver breaks down hydrogen peroxide faster.
D. Boiling removes oxygen from the liver.