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ENZYMES
Life’s Little Regulators
Ch. 2.4
ENZYME
Molecule, usually protein, that acts
as a biological catalyst. The name of
an enzyme usually ends in –ase.
CATALYST
Substance that speeds up a reaction
but is not changed or used up by
that reaction. Can be used over and
over again.
Enzyme Manufacture
•Enzymes are made by protein
synthesis
•DNA in the nucleus is transcribed into
RNA
•Ribosomes are assembled in the cytoplasm
•Protein is made at the ribosome & enters
the ER
•Protein is “finished” in the Golgi
“Finished” protein is an enzyme!
(but remember, not all proteins are enzymes!)
Where are enzymes?
Enzymes are usually in cells. They can be:
•proteins in the cytoplasm
•proteins in an organelle
•proteins in the membranes of cells or
organelles.
•Enzymes can also be secreted by cells into
an organism’s body, such as those in your
mouth, your stomach, and your intestines.
How an enzyme works:
Vocabulary:
Active site – place on an enzyme where
another molecule bonds and is changed
- what “disappears” when an
enzyme is denatured
Substrate – the molecule that bonds to the
enzyme and is changed by the reaction
there; the reactant
enzyme
How an enzyme works
1. The substrate and the enzyme
bond together.
2. A reaction occurs that changes
the substrate to something new (a
product).
3. The enzyme is NOT changed
and reacts again with a new
substrate molecule.
Enzymes and substrates fit
together more like a
“handshake”. Each slightly
changing to make the fit better
once they contact each other.
http://www.hillstrath.on.ca/moffatt/bio3a/digestive/enzanim.htm
“Real” Example
*Pepsin is an enzyme in the stomach.
Protein is the substrate.
Amino acids are the products.
Enzymes are sensitive to their
environment.
*denatured enzymes – when
enzymes lose their structure so
they don’t work; called
denatured
Notice the process is often reversible when
favorable conditions are re-established.
*Enzymes will not work right if:
*pH too low or too high (lysosomes,
your stomach, your small intestine)
*temperature too high (or sometimes
too low); (fever)
*there are other causes, too.
Reaction Rate
How fast the reaction occurs.
In “real life” enzymatic reactions happen at
the rate of thousands of times per second, per
enzyme molecule!
There are thousands of enzyme molecules
per cell and trillions of cells!!!!!!
http://www.bbc.co.uk/education/asguru/biology/02biologicalmolecul
es/01proteins/11enzymes/03enzymes_b/index.shtml
Reaction rate can be affected by many things.
•Increasing temperature increases reaction
rate.
•Increasing concentration increases reaction
rate. (Increasing concentration means adding
more substrate or more enzyme.)
Reaction rate can be measured by measuring
how fast a product is formed or a substrate
(reactant) is used up.
http://www.wellesley.edu/Biology/Concepts/Html/initialvelocity.html
How does an enzyme affect the
reaction rate?
Enzymes make reactions happen
easier. For a living organism, this
means the reaction takes less
energy to get started. The
energy needed to get a reaction
started is called the activation
energy. Enzymes lower the
activation energy.
Inhibitors
Some enzyme reactions are
slowed down by molecules called
inhibitors.
http://www.bbc.co.uk/education/asguru/biology/02biologicalmolecules/01proteins/11enzym
es/03enzymes_b/index.shtml
Summary:
Enzymes are proteins that act as catalysts.
Catalysts are molecules that speed up reactions
without being changed or used up.
Enzymes have an active site where the substrate binds
to form the product.
Enzymes can be denatured by changes in the
environment.
Enzymes work by lowering the activation energy of the
reaction.
http://www.lewport.wnyric.org/JWANAMAKER/
animations/Enzyme%20activity.html