Reading Tutorial: Enzyme Lab
Schedule
for Next Week:
·
4-5:00
p.m.: Reading tutorial, pp. 77-85 (if time left, comments on Lab Report)
·
5:00.:
Quiz
·
5:15:
Enzyme Lab
You can pick up 1 extra point for next week’s quiz by
detecting, and submitting to me in writing on or before 4 p.m., 3 typos on pp.
77-85. You can pick yet another point
by detecting one logical error in the text.
Introduction: You get proficient in playing,
bridge, harmonica, by playing.
Similarly, you get good at reading texts by reading. If you read a great deal of literature for
pleasure as a child your struggle is half over. If you want to do well, in that case, you will. A second ingredient for reading well is
motivation. If you really want to do
well, you can, even if you wasted your life until now watching TV. In that case, you must develop reading
skills as if your life depends on them, giving this everything you have
got. To do that, you should catch up on
reading for pleasure. And, learn how to
read well. This is the goal of this
tutorial—to illustrate reading well for people who really wish to improve their
readings skills. At first, this kind of
reading appears enormously difficult, but the sweet thing is that, after a
while, you get really good at it. You
begin by working like crazy, and then, by and by, you begin to understand
everything you read, effortlessly!
-->To get the most out of this
tutorial, try to answer the following questions in writing before next
week. Read one paragraph at a time,
without looking at my questions. Then,
close the book and try to answer the questions for that one paragraph. Then go
back to the paragraphs, making sure your answers make sense. If still stuck, consult your Raven text or
Wikipedia for clarifications about unclear points.
Please read P. 77, parag. 1 and study the reaction as many times as necessary for complete comprehension. 1. Now, try to capture the key points with a single drawing and an explanation (no chemical formulas are needed):
See hard copy in class
Question: Why is this reaction important in this lab?
This reaction is the basis for
today’s entire lab
Parag. 2. Read, close book, then answer. 1. What do enzymes do? Enable a reaction? 2. Are all enzymes made of proteins? 3. Why are enzymes needed in very minute quantities only?
1. No, they speed it up
tremendously (millions of times faster, often). 2. No, a few are made of RNA. 3. Because they remain intact and
can be re-used.
____________
Parag. 3. 1. Can enzymes facilitate any reaction? Give an example. 2. Typically, which is bigger, the enzyme or its substrates? 3. How and why can an enzyme’s capacity to halt reactions be destroyed? 4. Destruction by heat is called?
1. No they are specific. Sucrase: only hydrolyses sucrose. Key/lock with its 3D structure. 2. Enzyme much bigger, e.g., sucrase, 100 of
amino acids, vs. a disaccharide. 3. Heating, acidity, other conditions can
alter the 3D structure of the enzyme, so the lock/key mechanism of
enzyme/substrate no longer works. 4. Denaturing.
P. 78, (full) parag. 1. 1. Summarize the entire parag. with a single graph.
See hard copy in class
Parag. 2. 1. Name the enzyme that breaks lactose? That makes DNA polymers? 2. Could you likewise guess the names of all enzymes?
1. Lactase, DNA polymerase 2. Most but not all; a few have unique
names.
Parag.
3: 1. Goal of this lab? 2. In this lab,
what is our source of enzyme? A pure
preparation? 3. Why does yeast need
this enzyme?
1.
Stated goal: Examine nature of enzyme action.
2. Not pure. Living baking yeast
in water. 3. Sucrose is too big to
enter yeast cell, but glucose, fructose (Mono-S) can enter. (But there is an
unexplained contradiction here: Sucrase
is far bigger than sucrose; how does it get out?)
Parag.
4. 1. What will we do in lab
today? 2. Components of experimental
design?
2. Effects of
pH, temperature; boiling, substrate concentrations (what’s the saturation
point?) on sucrase’s rate of action. 2.
This paragraph of the manual is a bit confusing. Let me give you its intended meaning. a. Problem: the light on my computer screen is out. b. Initial hypothesis: Leela, my dog, disconnected the plug. c. Test prediction: The plug is out of the
socket, and by reconnecting it (this is the independent variable, the cause of
the other variable), the computer screen will display again (this is the
dependent variable) and I’ll see the words I’m typing again.
Parag. 5. 1. Why does our old friend reducing-sugar Benedict resurfaces resurface again? 2. How can you gauge the speed/strength of the reaction? 3. Could we use another reaction? Why did we choose Benedict?
Sucrose is a non-reducing disaccharide, so it leaves the copper alone. Sucrase, our hero, breaks sucrose down to 2 reducing monosaccharides, fructose and glucose. 2. (0 blue), 1 green, 2 yellow, 3 orange, 4 red. 3. Yes, Barfoed for Mono-S. But this would not give us color gradations.
p. 79. Lab Objectives: Now, if you read well to this point, you should be able to answer questions 1-11 or understand the questions this lab poses. Try this!
p. 80, parag. 1. Why do we add the sucrose at the same time to all solutions of the same test (e.g., pH)?
1. We are measuring the speed of
the reactions, so we want to start them all simultaneously (analogy: in a race,
all runners start at the same time).
p. 81. A. Effects of pH. 1. Just to be sure you remember your high school days? Another name for pH 3 is? pH 11 is? 2. Describe, in your own words, the logic of the pH experiment. 3. Graph 8.1 measures what on X axis—draw this. Measures what on Y-axis? What units?
1. Acid/ base (pH is an inverse
logarithmic scale, so 3 is 100X more acidic (more H+ ions) than
5. 7 is neutral (H+=OH-),
neither acid nor base. 2. Five tubes of sucrase, ranging in pH from 3 to
11. Add sucrose to each, for 10
min. Now, transfer each of 5 to a
Benedict solution, agitate, and heat for 3 min. Record results in Table.
3. pH (draw on board) / Reaction rate (blue, green, yellow, orange,
red). The 1 ml transfer provides a
control—would the color have changed anyway?
B. Effects of temperature. 1. What’s the X-axis of Graph 8.2? Write the appropriate units. 2. Why do we heat the sucrose and sucrase separately first?
1. Temperature; use a ruler to mark
0 to 100 degrees. 2. If we don’t, some
reaction will take place at room temperatures, and we don’t want that.
C. Effects of Denaturation. 1. What’s the point of this odd experimental design? 2. What values go on the X-axis?
1. This is like playing Heads or
Tails. We want to show that heat only
impacts sucrase (table sugar does get destroyed by heat, turning to caramel,
but at higher temperatures than 100○C). So, this is
really a kind of Punnett Square:
|
|
Sucrose |
||
|
Room Temp |
Boiled |
||
|
Sucrase |
Room Temp |
+? |
+? |
|
Boiled |
_ |
-? |
|
2. The 4 combinations above.
D. Effects of Substrate Concentration. 1. X-axis of p. 84? 2. What are the controls here?
1. Relative (not absolute, we don’t know the
concentration of the sucrose solution) sucrose concentrations: 0, 6%, 16%, 30%,
50%. 2. To begin with, 0 concentration of sucrose is a control, expecting to
yield no reaction. If the blue color
changes here, the entire experiment is useless and must be repeated. 2. We only test one ml of each
solution. This is another control. We want to make sure that they change color
owing to the Benedict Test, not owing to the passage of time.