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Enzymes
Enzymes are important biological macromolecules that do work in all living things. Plants,
animals, and prokaryotes all depend on enzymes to break down large molecules or build new
ones. ENZYMES are proteins that act as catalysts and help chemical reactions occur. In
order for these chemical reactions to occur energy is needed. The amount of energy
needed to start a chemical reaction is called the activation energy. A CATALYST is a
substance that speeds up a chemical reaction by reducing the amount of energy needed to
start that reaction. This is called lowering the activation energy. Activation energy can be
thought of as a hill that must be gotten over. When a catalyst acts, it lowers the energy
required to get over the HILL and the reaction can proceed. Enzymes are catalysts because
they speed up chemical reactions by lowering the activation energy of the chemical reaction.
The seemingly simple act of breaking down food molecules to release energy is actually a
series of dozens of chemical reactions. Without enzymes to speed up these reactions,
energy would not be released fast enough to support all but the smallest organisms.
Enzymes are not changed during the chemical reactions that they expedite (speed up) – so
they can be reused over and over again.
“LOCK AND KEY” MODEL OF ENZYME ACTION
A door that is locked needs a key that is just the right shape to fit in that lock. Otherwise
you're stuck outside. Enzymes work in a similar way. Enzymes complete very specific jobs
and do nothing else. They are very specific locks and the compounds they work with are the
special keys. There are four steps in the process of an enzyme action.
(1) An enzyme and a SUBSTRATE are in the same area. The substrate is the biological
molecule that the enzyme will work on.
(2) The enzyme grabs onto the substrate with a special area called the ACTIVE SITE. The
active site is a specially shaped area of the enzyme that fits around the substrate. The
active site is the keyhole of the lock.
(3) A process called CATALYSIS happens. Catalysis is when the substrate is changed. It
could be broken down or combined with another molecule to make something new.
(4) The enzyme lets go. When the enzyme lets go, it returns to normal, ready to do another
reaction. The substrate is no longer the same. The substrate is now called the PRODUCT or
products
ENZYMES AND THEIR ENVIRONMENT
An enzyme may not work if its environment is changed. Enzyme action depends on an exact
fit between the active site of an enzyme and the substrate to which it binds. If anything
were to block the active site or change the shape of the protein (enzyme), it could prevent
the enzyme from working properly.
(1) TEMPERATURE:
Proteins (including enzymes) change shape or DENATURE as temperatures change. Just
think of what happens to an egg (mostly protein) as you cook it or your hair (protein) when
you use a curling iron. Because so much of an enzyme’s activity is based on its shape,
temperature changes can mess up the process and the enzyme won’t work. Proteins change
shape (denature) as temperatures change. Because so much of an enzyme's activity is based
on its shape, temperature changes can mess up the process and the enzyme won't work.
(2) PH LEVELS:
In the same way that temperature can change the shape of proteins, the pH of the
environment does the same thing. Remember that the pH is a measure of how acidic or basic
something is. Proteins denature if the environment is too acid or too basic
(3) ENZYME AND SUBSTRATE CONCENTRATION
The rate of a chemical reaction is affected by the total number of enzymes as well as the
concentration of substrates.
(4) INHIBITORS:
Inhibitors either slow down or stop the activity of an enzyme. They bond to the enzyme –
causing the shape to change. Remember - When the shape changes, the enzyme will not
work the same way. An example of an inhibitors is snake venom, cyanide, and nerve gas from
World War I.
(c) Inhibitor
Enzyme Worksheet
1) What is an enzyme?
2) Enzymes are made of which type of biomolecule?
3) What is a catalyst?
4) Are enzymes catalysts?
5) Why do enzymes generally bind to only one kind of substrate?
6) What is a substrate ?
7) What is the active site?
8) Label A-E on the picture below: active site, substrate, enzyme, product, enzyme-substrate complex
e__________________
9) When the substrate binds to the enzyme it is known as an ________________ _______________
___________________ .
Enzyme A:
Enzyme B:
10) Is enzyme A above breaking down (hydrolysis) or building (synthesizing) a macromolecule? Circle answer.
11) Is enzyme B above breaking down (hydrolysis) or building (synthesizing) a macromolecule? Circle answer.
12) Some examples of enzymes are oxidase, amylase, catalase, and protease. What 3 letters at the end of each
enzyme help us identify enzymes?
13) What is denaturing?
14) What are 4 things that can affect the way enzymes work?
a. _________________________________
b. ________________________________
c. _____________________________________________________________________________
d. __________________________________
Catalyst
Catalyst
Catalyst
15) The diagram above illustrates a biochemical process that occurs in organisms. The substance labeled
“catalyst” is also known as _______________________________ .
(A) a hormone (B) an antibody (C) an enzyme (D) an inorganic compound
16) The effect of pH on a certain enzyme is shown in the graph below.
At what pH would the enzyme above be most effective? __________________________
17) Gastric protease works best in which type of environment, acid or base? See graph above _______________
18) Intestinal protease works best in which type of environment, acid or base? See graph above______________
19) Neither enzyme (see graph above) works well at a pH of ______________________ .
(A) 2
(B) 5 (C) 10
20) Enzymes have an optimum temperature at which they work best. Temperatures above and below this
optimum will decrease enzyme activity. Which graph best illustrates the effect of temperature on enzyme
activity? ____________________________
(a.)
(b.)
(c.)
(d.)