1. Describe the allosteric regulation and the covalent modification (phosphorylation/dephosphorylation, if available!) of the following enzymes: a) Phosphofructokinase-1. b) Phosphofructokinase 2/Fructose-phosphatase 2 c) Hexokinase. d) Pyruvate kinase. e) Glycogen phosphorylase. f) Glycogen synthase. g) Pyruvate carboxylase and PEP carboxykinase.

OneClass: 1. Describe the allosteric regulation and the covalent modification (phosphorylation/dephos...

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Case Study Section 2 â glycolysis
Based on âMonday at the Metabolic Clinic, Adventures in Glycolysisâ by Nancy Boury (National Center for Case Study Teaching in Science)

Background:
You have been chosen for a very competitive undergraduate clinical internship at St. Visintainerâs Hospital and Metabolic Clinic working with Dr. Saccharo, an expert in enzyme deficiency disorders related to glycolysis. Before your first day Dr. Saccharo has asked that you review the reactions of glycolysis and the concept of isoenzymes.

Recall that isoenzymes are groups of enzymes that catalyze the same reaction in that they use the same reactants to product the same products. They may have different genes, tissue expression, developmental timing of expression, and affinities for their substrates. As an example, phosphofructokinase-1 has 3 isoenzyme forms: PFK-L is expressed in the liver and the gene is found on chromosome 21; PFK-M is expressed in the muscle and the gene is found on chromosome 12; and PFK-P is expressed in platelets and the gene is found on chromosome 10.

Question 1:
If a person would be deficient in all 3 forms of PFK-1, this person would .
A. Have lower than normal glycogen stores.
B. Have more mitochondrial activity than normal.
C. Be dead.
D. Produce more energy per glucose molecule because glycolysis would be unregulated.

It is now Monday morning and you are ready to start seeing patients with Dr. Saccharo.

Patient 1:
Ann is a teenager and avid golfer who was referred to the clinic after being refused at the blood drive and tiring easily on the high school golf course during practice. Ann is examined and a blood sample was obtained for analysis of a glycolysis related metabolic panel. The results of her panel is below (levels: + = normal, - = decreased; ++= increased):
Blood Metabolic Panel
Blood Glucose +
Glucose-6-phosphate ++
Fructose-6-phosphate ++
Fructose-1,6,bisphosphate ++
Glyceraldehyde-3-phosphate ++
1,3-bisphosphoglycerate ++
Phosphoenolpyruvate ++
Pyruvate -
ATP -
Red Blood Cell Concentration -
Question 2:
Assuming that Dr. Saccharo is correctly assuming that Ann has a defect in glycolysis, what glycolytic enzyme is the most likely to have the defect based on the blood metabolic profile?
A. Hexokinase
B. Phosphofructokinase
C. Triose Phosphate Isomerase
D. Pyruvate Kinase
E. Aldolase

Patient 2:
Marie is a 32-year-old mother of three complaining of fatigue and muscle cramps with exercise. She had always blamed her intolerance to exercise on her sedentary lifestyle. However, she recently joined a gym and after a week of aerobics classes went to her physician, who ordered a series of blood tests. The blood work came back with abnormal results, leading to her muscle biopsy and referral to the metabolic clinic. Marieâs blood was subjected to the same metabolic panel used before with the following results:
Blood Metabolic Panel
Blood Glucose +
Glucose-6-phosphate ++
Fructose-6-phosphate ++
Fructose-1,6,bisphosphate -
Glyceraldehyde-3-phosphate -
1,3-bisphosphoglycerate -
Pyruvate -
ATP -
Red Blood Cell Concentration -

Marieâs muscle biopsy was also analyzed and showed an excess of glycogen.

Question 3:
What is the most likely enzyme deficiency for Marie?
A. Hexokinase
B. Phosphofructokinase
C. Triose Phosphate Isomerase
D. Pyruvate Kinase
E. Aldolase

Question 4:
If you wanted to test the ability of red blood cells to complete glycolysis what compound would you try to detect?
A. Fructose-6-phosphate
B. Aldolase
C. Pyruvate
D. Phosphofructokinase
E. Dihydroxyacetone phosphate

Question 5:
If you used a sample of Marieâs blood for this, what compound could you add to enable these cells to complete glycolysis?
A. Glucose
B. Fructose-1,6-bisphosphate
C. Insulin
D. Glucagon
E. Fructose-6-phosphate

Patient 3:
Leo is a 25-year-old accountant that is not anemic, has perfect teeth, but has experienced two fainting spells recently. One happened after accidentally drinking a non-diet soda; the other after eating ânaturally sweetenedâ fruit salad. His dentist referred him to Dr. Saccharoâs clinic. Dr. Saccharo suspects Leo may have Hereditary Fructose Intolerance (HFI) and has recommended a closely monitored fructose tolerance test.

Hereditary Fructose Intolerance is a recessive disorder where individuals lack a functional copy of one isoform of the enzyme aldolase, specifically Aldolase B (also known as fructose-1-phosphate aldolase). In the liver, fructose is phosphorylated by Fructokinase to fructose-1-phosphate, then is cleaved by Aldolase B to glyceraldehyde and dihydroxyacetone phosphate. Fructose-1-phosphate is also a known allosteric inhibitor of Glycogen Phosphorylase, the primary enzyme responsible for releasing glucose from glycogen.

Question 6:
As compared to a normal individual that consumes fructose, a person with HFI who ingested fructose would have (select all that apply):
A. High levels of blood fructose
B. High levels of blood fructose-1-phosphate
C. High levels of blood glucose
D. Low levels of blood fructose
E. Low levels of blood glucose

That afternoon Leo undergoes the fructose tolerance test with the following results:

Question 7:
Based on the results of the test, what was the effect of giving Leo the intravenous fructose?
A. A rise in blood glucose levels
B. A decrease in blood glucose levels
C. An increase in glycogen stores
D. A rapid drop in blood pressure

However there were complications: Soon after the test Leo orders and drinks a cup of tea, but after half the cup Leo passes out. Dr. Saccharo orders two sequential blood glucose checks. The first was 50 mg/dl and 15 minutes later Leoâs blood glucose was down to 40 mg/dl. With those results Dr. Saccharo injected something into Leoâs IV and within minutes Leo was back to normal.

Question 8:
From these results does it appear that Leo has HFI?
A. Yes
B. No
C. It is unclear from the results

Question 9:
What did Dr. Saccharo inject into Leoâs IV line?
A. Insulin
B. Glucagon
C. Glucose
D. Fructose
E. Phosphofructokinase

Dr. Saccharo puts Leo on a restricted diet and orders follow-up visits.

Question 10:
Which of the following foods/ingredients would Leo NOT be allowed to eat?
A. Artificial sweeteners
B. High starch foods, such as potatoes
C. Sweet tea made with cane sugar
D. Any dairy products

Dr. Saccharo puts Leo on a restricted diet and orders follow-up visits.

Case Study Section 2 â glycolysis
Based on âMonday at the Metabolic Clinic, Adventures in Glycolysisâ by Nancy Boury (National Center for Case Study Teaching in Science)

Background:
You have been chosen for a very competitive undergraduate clinical internship at St. Visintainerâs Hospital and Metabolic Clinic working with Dr. Saccharo, an expert in enzyme deficiency disorders related to glycolysis. Before your first day Dr. Saccharo has asked that you review the reactions of glycolysis and the concept of isoenzymes.

Recall that isoenzymes are groups of enzymes that catalyze the same reaction in that they use the same reactants to product the same products. They may have different genes, tissue expression, developmental timing of expression, and affinities for their substrates. As an example, phosphofructokinase-1 has 3 isoenzyme forms: PFK-L is expressed in the liver and the gene is found on chromosome 21; PFK-M is expressed in the muscle and the gene is found on chromosome 12; and PFK-P is expressed in platelets and the gene is found on chromosome 10.

Question 9:
What did Dr. Saccharo inject into Leoâs IV line?
A. Insulin
B. Glucagon
C. Glucose
D. Fructose
E. Phosphofructokinase

indigolocust876

16. Muscle glycogen cannot contribute directly to blood glucose levels because:

A. Muscle glycogen cannot be converted to glucose-6-phosphate

B. Muscle lacks glucose-6-phosphatase

C. Muscle contains no glycogen phosphoyrlase

D. Muscle lacks phophoglucoisomerase

_____17. Which of one of the following tissues requires insulin for glucose transport into the cell?

A. Brain

B. Liver

C. Skeletal muscle

D. Red blood cells

_____18. The mobilization of triaclyglycerol-bound fatty acids from adipose tissue and their subsequent oxidation by muscle mitochondria require all of the following compounds except:

A. Serum albumin

B. Carnitine

C. Acetyl CoA carboxylase

D. Hormone sensitive lipase

_____19. Which one of the following reactions is unique to gluconeogenesis?

A. Lactate Â® pyruvate

B. PhosphoenolpyruvateÂ® pyruvate

C. OxalacetateÂ® Phosphoenolpyruvate

D. 1,3bisphosphoglycerate Â® 3-phosphoglycerate

_______20. A newborn vomits after each feeding of milk-based formula and doesnât gain weight. Biochemical testing reveals a sever deficiency of galactose-1-phosphate uridyltransferase. If this condition goes untreated, which of the following is the likely outcome for this patient?

A. Benign disease except for cataract formation

B. Chronic emphysema appearing in early adulthood

C. Chronic renal failure appearing in adolescence

D. Death in infancy

E. Gastrointestinal symptoms that remit with puberty

Case Study Section 2 â glycolysis
Based on âMonday at the Metabolic Clinic, Adventures in Glycolysisâ by Nancy Boury (National Center for Case Study Teaching in Science)

Background:
You have been chosen for a very competitive undergraduate clinical internship at St. Visintainerâs Hospital and Metabolic Clinic working with Dr. Saccharo, an expert in enzyme deficiency disorders related to glycolysis. Before your first day Dr. Saccharo has asked that you review the reactions of glycolysis and the concept of isoenzymes.

Recall that isoenzymes are groups of enzymes that catalyze the same reaction in that they use the same reactants to product the same products. They may have different genes, tissue expression, developmental timing of expression, and affinities for their substrates. As an example, phosphofructokinase-1 has 3 isoenzyme forms: PFK-L is expressed in the liver and the gene is found on chromosome 21; PFK-M is expressed in the muscle and the gene is found on chromosome 12; and PFK-P is expressed in platelets and the gene is found on chromosome 10.

Patient 1:
Ann is a teenager and avid golfer who was referred to the clinic after being refused at the blood drive and tiring easily on the high school golf course during practice. Ann is examined and a blood sample was obtained for analysis of a glycolysis related metabolic panel. The results of her panel is below (levels: + = normal, - = decreased; ++= increased):
Blood Metabolic Panel
Blood Glucose +
Glucose-6-phosphate ++
Fructose-6-phosphate ++
Fructose-1,6,bisphosphate ++
Glyceraldehyde-3-phosphate ++
1,3-bisphosphoglycerate ++
Phosphoenolpyruvate ++
Pyruvate -
ATP -
Red Blood Cell Concentration -

Question 2:
Assuming that Dr. Saccharo is correctly assuming that Ann has a defect in glycolysis, what glycolytic enzyme is the most likely to have the defect based on the blood metabolic profile?
A. Hexokinase
B. Phosphofructokinase
C. Triose Phosphate Isomerase
D. Pyruvate Kinase
E. Aldolase

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