Enzyme Test Review
Define the following vocabulary words:
Catalyst
_________compounds that make a reaction happen faster by reducing activation energy.
Entropy
_________disorder in a system.
Endergonic reaction ________ a reaction that requires the input of energy in order to happen – Ex.
contracting muscles, making proteins
Exergonic reaction ________ a reaction that releases energy - Ex. respiration, breaking ATP into ADP
ATP
________the energy created and used by the cell. This is a form of chemical energy.
Activation energy
Active site
____the minimum amount of energy needed to break (or build) the bonds between
molecules. When the bonds are broken/built the reaction can happen.
________area in the enzyme where the substrate attaches.
Enzyme-substrate complex ______the molecule that is created when the substrate bonds to the enzyme at
the active site.
Induced fit ___when the enzyme folds around the substrate to make a better fit. This makes the enzyme
work more efficiently.
Allosteric enzyme ____an enzyme that has an ‘active’ (on) and an ‘inactive’ (off) version.
Allosteric site _____location on the allosteric enzyme where the noncompetitive inhibitor attaches.
Allosteric inhibitor ___ a noncompetitive inhibitor that attaches to the allosteric site. Once attached, the
enzyme changes shape, the substrate no longer fits correctly and the enzyme is
turned off.
Allosteric activator ____a protein that attaches to the allosteric site, changes the shape of the enzyme to
make it a better fit with the substrate, causing the enzyme to work faster.
Cofactor ___a molecule (like zinc or iron or a matching enzyme – called a coenzyme) that works with the
enzyme to make it more efficient.
Feedback inhibition ___when a biochemical pathway makes enough product, the product build up until it
attaches to the enzyme’s allosteric site, turning the enzyme off. When enough of
the product is used up, the allosteric site opens up and the enzyme begins working
again.
Compare/contrast how competitive and noncompetitive inhibitors decrease an enzyme’s activity.
A competitive inhibitor sits within an enzyme’s active site, keeping the substrate from fitting properly,
decreasing the enzyme’s activity. A noncompetitive inhibitor attaches to the enzyme at a location other
than the active site. This changes the overall shape of the enzyme, which again decreases an enzyme’s
efficiency.
I have an enzyme that has an ‘active’ and an ‘inactive’ form. What kind of enzyme is this? How
could I get this enzyme’s activity to increase above normal? (Be specific in your answer).
An enzyme with an active and an inactive form is an allosteric enzyme. You would add an allosteric
activator to the allosteric site. This would change the shape of the active site, giving the substrate a better
fit within the active site. This would increase the enzyme’s activity above normal.
How are allosteric enzymes related to feedback inhibition?
Allosteric enzymes are used to shut down a cell’s production of a particular material to keep too much from
being made.
Why would a cell want to ‘shut down’ production of a product it normally uses? How would it use
feedback inhibition to do this?
A cell needs to be as energy efficient as possible. This means making and storing the exact amount of a
product that the cell will need, to make or store more than that is a waste of energy and resources. If the
correct amount of product has been made/stored, the cell will shut down production.
In feedback inhibition, if the product being made through a biochemical pathway build up enough, the
product bonds to the enzyme’s allosteric site and shut the pathway off.
Explain the ATP-ADP cycle.
The cell bonds a PO4 (phosphate) to an ADP (adenine diphosphate) molecule creating stored energy – ATP
(adenine triphosphate). When the cell needs energy, it breaks the ATP apart, creating an ADP and a PO 4
molecule releasing energy for the cell to use. The cell then bonds the PO4 back onto the ADP, creating a new
ATP, replacing the energy used.
A cell needs to break sucrose down into fructose and glucose for energy. How would the enzyme
sucrase do this?
The substrate binds to the enzyme sucrase at the active site. The enzyme folds around the substrate
creating a better fit (induced fit). The sucrase stresses the bond between the glucose and the fructose until
it breaks apart. When the bonds are broken, the monosaccharides are released allowing the enzyme to
start again.
pH
Product created
2
4
6
8
10
0.2g
1.3g
4.6g
6.5g
2.9g
A biologist was experimenting with a new enzyme. Based on the data above, what is the
“optimum pH’ of this enzyme? How do you know? What is happening to the enzyme on either
side of this pH?
The optimum pH for this enzyme is 8. This can be determined because the enzyme creates the most product
(6.5g) at pH 8. Enzymes are held together by ionic bonds (+ and -). At low pHs there are more H+ ions in
the solution. These interfere with the enzyme’s ionic bond, making them break apart. At high pHs there
are more OH- ions in the solution. These also interfere with the enzyme’s ionic bond, again, making them
break apart. The closer you get to the optimum pH, the less the bonds are interfered with and the more
efficiently the enzyme can work.
Temp. oC.
10
30
50
70
90
110
Product
created
0.9g
1.4g
3.6g
5.8g
6.2g
4.4g
A biologist was experimenting with a new enzyme. How do you explain the results collected
above?
Enzymes are temperature sensitive. When the temperature is low, the enzyme works more slowly. As
temperature increases, the enzyme begins to work more quickly. When the temperature reaches optimum
(90oC) in this case, the enzyme works at peak efficiency. As temperature increases beyond optimum, the
enzyme begins to break down, decreasing efficiency.