BCH 361 Lecture Notes - Lecture 6: Glycogen, Dihydroxyacetone Phosphate, Muscle Biopsy

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9 Nov 2020
BCH 361 Advanced Biochemistry I Fall 2020
Group Discussion Questions
Week 6 (October 19/20)
Case Study
Prepare by reading the case study Murder on the Metabolic Ward” and attempting the following:
a. Answer the questions in the case study
b. Interpret the patient’s data.
You will be given additional questions in class relating to the patient’s data.
Additional questions for study or discussion, time permitting.
1. Although both hexokinase and phosphofructokinase catalyze irreversible steps in glycolysis and the
hexokinase comes first, phosphofructokinase is the rate limiting step of glycolysis. What does this
information suggest about the fate(s) of the G6P formed by hexokinase?
2. Suppose that a microorganism that was an obligate anaerobe suffered from a mutation that
resulted in the loss of triose phosphate isomerase. How would this loss affect the ATP yield of
fermentation? Could such an organism survive?
3. What is the equilibrium ratio of phosphoenolpyruvate to pyruvate under standard conditions when
[ATP]/[ADP] = 10?
4. How would a Mg+2 deficiency affect glycolysis?
5. The 5-carbon sugar xylose has the same structure as glucose except that it has a hydrogen atom at
C-5 instead of a hydroxymethyl group. When xylose is added to a solution of ATP in the presence of
hexokinase, the rate of ATP hydrolysis increases yet, xylose is not phosphorylated. Explain.
6. For the hydrolysis of FBP to F6P, ΔGᵒ’ has been found to be -16.7 kJ/mol. ATP hydrolysis has a ΔG
value of -30.5 kJ/mol. Determine the standard free energy change for phosphorylation of F6P by
ATP. What is the equilibrium constant for this reaction? If the cellular concentrations of [ATP] and
[ADP] are maintained constant at 4 mM and 1.6 mM, respectively, what will be the ratio of
[FBP]/[F6P] when the phosphofructokinase reaction reaches equilibrium?
7. The enzyme aldose reductase catalyzes reactions such as the one shown here. Epalrestat is used as
an inhibitor of this enzyme to prevent cataract formation. Suggest the manner in which this
inhibition occurs (how and where does the inhibitor interact with the enzyme)?
8. The recommended daily allowance for the vitamin niacin is 15 mg per day. How would glycolysis be
affected by niacin deficiency?
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BCH 361 Advanced Biochemistry I Fall 2020
Each group member will be graded individually on their contribution to the group discussion as
indicated on your group’s discussion summary. By working together, your group can maximize the
marks each of you gets. The following rubric will be used:
Grading Rubric for Group Discussion Participation and Contribution
Description of contribution characteristics
Group member’s comments are usually constructive and insightful.
Appropriate terminology is used.
Comments are a good balance of general and specific.
Evidence is almost always used to support opinions.
Group member’s comments are mostly constructive and insightful.
Appropriate terminology is used.
Comments are normally on point but might occasionally be too general or not
relevant to the discussion.
Evidence is often used to support opinions.
Group member’s comments are sometimes constructive and insightful.
Appropriate terminology is normally used.
Comments tend not to be relevant to the discussion.
Evidence is sometimes used to support opinions.
Group member is present but does not contribute meaningfully.
Comments are uninformative.
Topic-appropriate terminology is not used.
Evidence is rarely used to support opinions.
Group member is absent or does not participate.
If a group member is absent, carry on without them, and don’t write their name down on your
submission. Their absence will not impact your grade.
If you are absent or experience unexpected technical difficulties, contact Dr. Johnson ASAP.
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This case study is © 2012 by the National Center for Case Study Teaching in Science, University of
Buffalo, State University of New York.
This case study is an adaptation of:
Murder or Medical Mishap?
Death on the Metabolic Ward
By Nancy M. Boury
Department of Animal Science, Iowa State University, Ames, IA.
Part I
You have been chosen for a very competitive paid under-graduate clinical internship position (uCLIP).
You spent your first weeks becoming a certified nurse assistant (CNA). You will be paid to work as a CNA
at St. Visintainer’s, assisting the nurses on the suspected metabolic disorder’s acute-care floor.
As part of your internship, you will also be allowed to follow Dr. Saccharo as he sees clinic patients. The
doctor is an expert in enzyme deficiency disorders relating to glycolysis. Because you hope to become a
family physician, you’re excited about the opportunity to learn about these rare metabolic disorders. To
prepare for your first day on the metabolic ward, Dr. Saccharo requests that you research normal sugar
metabolism, particularly glycolysis.
Monday Morning at the Metabolic Disorders Clinic
After working all weekend on Dr. Saccharo’s assignment, you feel ready for anything including Monday
morning. As you ride up the elevator with your mentor and fellow interns, Dr. Saccharo asks a few
questions to determine how prepared you are for this morning’s clinic hours.
1. Which glycolytic enzymes catalyze a reaction that produced ATP?
2. Which glycolytic enzyme catalyzes a reaction that breaks the 6-carbon sugar into two 3-carbon
Dr. Saccharo’s Review of Glucose Homeostasis
Your body (particularly your brain) needs glucose as fuel for cell processes. When you eat, your blood
glucose levels will temporarily rise, signaling the pancreas to release insulin. When you have gone
without food for several hours, your pancreas will release glucagon, which triggers the liver to release
glucose from glycogen stores.
If your blood sugars are too high, your blood vessels are damaged and the organs they supply with blood
are damaged as well. Consistently high levels of blood sugars lead to kidney, heart, liver, and brain injury
over time.
If your blood sugars are too low, your brain will starve for energy. As a result, you could pass out, enter a
coma, and potentially die in a matter of hours.
Diabetics either have cells that don’t respond to insulin properly (Type II diabetes, or late-onset) or don’t
have functional insulin produced (Type I diabetes, or juvenile).
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