Enzymes
Chapter 2.5
• Enzymes are catalysts for
chemical reactions in
living things
Why Are Enzymes So Important?
Why are we devoting
one whole lecture topic
to a protein molecule?
Nearly all chemical
reactions in
biological cells need
enzymes to make the
reaction occur fast
enough to support
life.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Jumping rope, Meagan E. Klein
Enzymes allow chemical reactions to occur
under tightly controlled conditions.
• Enzymes are catalysts in living
things.
• Enzymes are needed for almost
all processes.
• Most enzymes are proteins
What do enzymes do?
• Enzymes act as
_________ in
cellular reactions.
• Q: What does a
catalyst do?
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Images: Activation energy graph, Wiki
Enzymes…
…are REUSABLE.
They are not
consumed (used up)
in the reactions
they catalyze.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
How do enzymes work?
Enzymes catalyze
reactions by
weakening chemical
bonds, which
________ activation
energy.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Activation energy graph, Wiki
Meet the Enzyme: ___ _______
Important metabolic enzyme that
harnesses energy for biological cells
to use.
Involved in synthesis of adenosine
triphosphate (ATP), from:
- adenosine diphosphate (ADP)
- a phosphate group and
- energy from H+ ion gradient
ATP is the most commonly used
"energy currency" of cells.
Reaction:
(ATP
synthase)
ADP + Pi -------ATP
substrate
substrate
product
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Images: ATP synthase diagram, Tim Vickers
How do you stop
an enzyme?
__denature it!
• Alteration of a protein shape through
some form of external stress
• Example,
by applying heat or changing pH.
• Denatured
protein can’t carry out its
cellular function .
Irreversible egg
protein
denaturation
caused by high
temperature
(while cooking it).
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Factors That Influence Enzyme Activity
• Temperature
• pH
• Cofactors & Coenzymes
• Inhibitors
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Animation of Enzyme, Wiki
What enzymes do I have around the house?
detergents
textiles (fabric)
wine
beer
vinegar
cheeses
corn and wheat syrups
leather
biodegradable plastic
starch into sugar
yeast
Where are they found?
• Enzymes are found in many cleaning and spot removal and odor removal
products.
Enzymes are found in all living foods such as fruits and vegetables as they keep
ripening.
•
•
•
•
Enzymes are found in those agents that cause food spoilage,
Enzymes are found in many food reactions such as yogurt, cheeses, saurkraut,
pickles, fermentations of beer and wine, etc,
Meat tenderizer is an enzyme
milk products for lactose intolerant individuals is treated with lactase, an enzyme
Digestive enzymes are enzymes that break down
food into usable material. The major different
types of digestive enzymes are:
• amylase – breaks down carbohydrates, starches, and sugars which are prevalent in
potatoes, fruits, vegetables, and many snack foods
• 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
• protease – breaks down proteins found in meats, nuts, eggs, and cheese
• pepsin – breaks down proteins into peptides
Enzymes…
• Have names that
usually end in -_____.
-Sucrase
-Lactase
-Maltase
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Animation of Enzyme, Wiki
Go to: http://redirectyourcarbs.com/carbredirect-method/?sid=a1
• Factors Affecting Enzyme Activity
• Temperature - Enzymes are proteins that function optimally at certain temperatures.
They are inactivated or denatured by temperatures above 50 °C to 60 °C. Enzymes are
not inactivated by freezing, but either work slowly or do not work at all.
• pH - Enzymes are sensitive to changes in acidity. For example, the high acidity of stomach
juice is needed for the enzyme pepsin to function, whereas an enzyme called trypsin in
the small intestine requires alkaline surroundings.
• Concentration of Enzyme - If pH and temperature are kept constant, the rate of reaction
is proportional to the amount of enzyme present. The more enzyme there is, the more
reactions that occur.
• Co-Enzymes - Some vitamins and minerals (e.g. copper, zinc, iron) in small quantities
work with enzymes to speed up reactions.
• Enzyme Inhibitors - A pesticide called DDT stops the action of enzymes in insects, thereby
killing them.
How acidic is your body?
• http://scienceforkids.kidipede.com/biology/cells/enzyme.htm
A catalyst lowers activation energy.
• Catalysts are substances that speed up chemical
reactions.
• decrease activation energy
• increase reaction rate
• Disruptions in homeostasis can prevent enzymes from
functioning.
– Enzymes function best in a small range of conditions.
– Changes in temperature and pH can break hydrogen
bonds.
– An enzyme’s function depends on its structure.
Enzymes…
•
are specific for what
they will catalyze.
•
fit with substrate
like a lock and
key____.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
• An enzyme’s structure allows only certain reactants to
bind to the enzyme.
– substrates
– active site
substrates
(reactants)
enzyme
Substrates bind to an
enzyme at certain places called
active sites.
• The lock-and-key model helps illustrate how enzymes
function.
– substrates brought together
– bonds in substrates weakened
Substrates bind to an
enzyme at certain places
called active sites.
The enzyme brings
substrates together and
weakens their bonds.
The catalyzed reaction forms
a product that is released
from the enzyme.
When an enzyme is interacting with
it’s substrate, during the chemical
reaction, together they are referred
to as the …
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Enzyme –substrate complex, UC Davis
Enzymes are like tiny machines within living things.
$
$
$
$
$
$
$
The more cans (substrate), the more $ (product).
The more recycling machines (enzymes), the faster the cans turn into $.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Cofactors & Coenzymes
• Non-protein substances (zinc, iron,
copper, vitamins) are sometimes need
for proper enzymatic activity.
• Coenzyme vs Cofactor: What’s
the difference?
_________ more general term.
Includes inorganic and organic
molecules.
_________ type of cofactor,
But specifically organic
molecules.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Enzyme with Cofactor, Wiki. Ribbon-diagram showing carbonic
anhydrase II. The grey sphere is the zinc cofactor in the active site.
Meet the Enzyme: Catecholase
• Catecholase is present in most _Fruits_____ and
__Vegetables________.
• It is the enzyme that facilitates the ________ of cut or bruised fruits
and vegetables by catalyzing the following reaction:
(______________)
_________ + _____ ----------------- _____________
colorless substrate
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
brown product
Image: Bananas T. Port
Meet the Enzyme: Catecholase
Lemon juice and other acids are used to preserve color in fruit,
particularly apples, by lowering the ____ and removing the copper
(cofactor) necessary for the enzyme to function.
Reaction:
catecholase
catechol
+ O2
----------
colorless substrate
Images: Apples, T. Port; Lemons, André Karwath; Enzyme
with Cofactor, Wiki; pH scale, Edward Stevens, Wiki
polyphenol
brown product
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Meet the Enzyme: Bromelain
• Pineapple contains enzyme bromelain, which can
digest protein
• Jell-O® is made of gelatin, a processed version of a
structural protein called _________ found in many
animals, including humans.
• Collagen = big, fibrous molecule makes skin, bones,
and tendons both strong and elastic.
• Gelatin you eat in Jell-O ® comes from the collagen
in cow or pig bones, hooves, and connective tissues.
(Yummie!)
• Examine 2 containers:
a. In one, canned pineapple was used to make Jell-O® .
b. The other, fresh pineapple was used.
Q: Why is one Jell-O solid and the other liquid?
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Pineapple, Whaldener Endo
Meet the Enzyme:
Bromelain
Bromelain is a ______
enzyme that facilitates
hydrolysis of protein.
Remember, hydrolysis cuts
molecule by adding water…the
reverse of the hydration
synthesis pictured to the left.
(bromelain)
collagen protein + H20 -------------- amino acids
substrate
products
FYI: Bromelain is used as a meat tenderizer. Breaks down
the collagen in meat. So what do you think could happen to
your tongue when you eat fresh pineapple?
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Assignment
See the ScienceProfOnline Virtual Cell
Biology Classroom: Enzymes Lecture for a
printable Word .doc of this assignment.
• At the end of most lectures, I
will give you some type of inclass assignment or homework
to evaluate your
understanding of today’s
topic.
• This assignment will always be
open-book.
• Today you may be completing
an experiment on the topic of
Enzymes.
Image: Accumulation of polyphenol in apple, T. Port
From the Virtual Cell Biology Classroom on ScienceProfOnline.com