Biochemistry I, CHEM 4400 Exam 3 Fall 2004 Name_____________________
There are 120 possible points, 100 regular points and 20 extra credit points. You pick the extra credit! Be
sure to read all of the questions.
R = 8.315 J/mole*K k = 1.381 x1023J/K h= 6.636 x10-34 J*sec
- (20 points) Enzymes inhibition is a very exciting area of study. Many new pharmaceutical drugs are
developed as specific inhibitors of an enzyme. In class we studied competive, uncompetitive and
mixed reversible inhibitors. We also learned about irreversible inhibitors. Describe each of these
types of inhibition. What type of inhibition do you think would make the best drug? Explain your
reasoning.
- (10 points) Enzymes greatly enhance the rates of reactions by lowering the activation energy of the
reaction. If an enzyme increased the rate of a hydrolysis reaction from 10 uM/min to 800 uM/min at
25C, how much lower is the activation energy for the catalyzed reaction? Consider the
concentration of the reactants to be constant: [S] = 0.1M.
- (10 points) Describe the catalytic triad in the active site of
chymotrypsin. What is it? What does it
do?
- (10 points) The following data was obtained for a new enzyme. Measurements were done at 25C.
Use this data and graph (show your calculations) to determine the following:
- What is the Km for the uninhibited enzyme?
- What is the Vmax for the uninhibited enzyme?
- What is the Km for the inhibited enzyme?
- What type of inhibition does this graph show? Describe the evidence that supports that type
of inhibition
| [S] (mM) |
Velocity (mM s-1 ) no
inhibitor |
Velocity (mMs-1 )
with inhibitor |
| 0.5 |
23.5 |
16.67 |
| 1 |
32.2 |
25.25 |
| 1.5 |
36.9 |
30.49 |
| 2.5 |
41.8 |
37.04 |
| 3.5 |
44 |
38.91 |
(10 points) Using complete sentences in organized paragraphs, fully describe how the following
enzymes are regulated
a. Glycogen phosphorylase
b. Trypsin
(10 points) Using complete sentences and structures as needed, describe the mechanism that your
group presented to the class.
(10 points) Polymers of sugars have three different functions: energy storage, structural support and
information. Discuss the roles that sugars play as information molecules. Give specific examples
and describe these examples in detail.
(5 points) Give an example of an anomeric pair of hexoses. Draw the structures and give the names.
- (10 points) Complete the following table for sugar polymers:
| Polymer |
Monomers |
Linkage |
Function |
|
|
(1->4),
(1->6) |
|
|
|
(1->4) |
|
| Dextran |
|
|
|
| Chitin |
|
|
|
(10 points) Complete the following table:
| Common name |
Short hand
notation |
Structure (show all C-C bonds) |
|
18:29,12
|
|
| Arachidonic acid |
|
|
| Linolenic acid |
|
|
(10 points) What are polar membrane lipids? They are not simply recycled. They are completely
degraded to free sugars, ceramide and phophocholine in one cellular compartment and new polar
membrane lipids are synthesized in a different cellular compartment.
- Where are they degraded?
- Where are they synthesized?
- What happens when an enzyme in the degradation pathway is missing or defective?
Give an example of a missing enzyme for one of the following diseases:
Tay Sach's disease, Gaucher's disease, Fabry's disease, Sandoff's disease, Generalized gangliosidosis
(10 points) Phospholipase A2 cleaves the second fatty acid off of a membrane phospholipid. Often,
this fatty acid is Arachidonic acid and it is the precursor for three different types of eicosanoids.
- What is the function of each of these different eicosoanoids?
- Why doesn't aspirin affect the production of leukotrienes?
(5 points) Name two fat soluble vitamins. Briefly describe why each vitamin is important and what will
happen if there is a deficiency.
(10 points) What is the type of lipids that describes each of the following molecules. Also, indicate
where these molecules are found and briefly describe their function.
