You have been chosen for a very competitive undergraduateclinical internship at St. Visintainer’s Hospital and MetabolicClinic working with Dr. Saccharo, an expert in enzyme deficiencydisorders related to glycolysis. Before your first day Dr. Saccharohas asked that you review the reactions of glycolysis and theconcept of isoenzymes.
Recall that isoenzymes are groups of enzymes that catalyze thesame reaction in that they use the same reactants to product thesame products. They may have different genes, tissue expression,developmental timing of expression, and affinities for theirsubstrates. As an example, phosphofructokinase-1 has 3 isoenzymeforms: PFK-L is expressed in the liver and the gene is found onchromosome 21; PFK-M is expressed in the muscle and the gene isfound on chromosome 12; and PFK-P is expressed in platelets and thegene is found on chromosome 10.
Question 1:
If a person would be deficient in all 3 forms of PFK-1, thisperson 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 wouldbe unregulated.
It is now Monday morning and you are ready to start seeingpatients with Dr. Saccharo.
Patient 1:
Ann is a teenager and avid golfer who was referred to the clinicafter being refused at the blood drive and tiring easily on thehigh school golf course during practice. Ann is examined and ablood sample was obtained for analysis of a glycolysis relatedmetabolic 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 Annhas a defect in glycolysis, what glycolytic enzyme is the mostlikely to have the defect based on the blood metabolicprofile?
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 fatigueand muscle cramps with exercise. She had always blamed herintolerance to exercise on her sedentary lifestyle. However, sherecently joined a gym and after a week of aerobics classes went toher physician, who ordered a series of blood tests. The blood workcame back with abnormal results, leading to her muscle biopsy andreferral to the metabolic clinic. Marie’s blood was subjected tothe same metabolic panel used before with the followingresults:
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 | - |
Marie’s muscle biopsy was also analyzed and showed an excess ofglycogen.
Question 3:
What is the most likely enzyme deficiency forMarie?
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 tocomplete 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 Marie’s blood for this, whatcompound could you add to enable these cells to completeglycolysis?
A.          Glucose
B.          Fructose-1,6-bisphosphate
C.          Insulin
D.         Glucagon
E.          Fructose-6-phosphate
