Case 6 - Glycolysis and Exercise Spring 2021 PDF

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This home work involves looking at the biochemical process of glycolysis...

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Introduction to Biochemistry and Molecu lar Biology Molecular BCMB 3100 57248

Case Study Spring 2021

Case 6: Gly Glycolysis colysis and Exerc Exercise ise

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Take-Home P Point oint The breakdown and building of carbohydrates by an organism (e.g., human) involves a series of chemical reactions called metabolic pathways. The directionality of each reaction in a pathway depends on the free energy and relative concentrations of reactants and products available. The observable “flux” of a pathway is the net result of forward and reverse processes. Enzymes control rates of forward and reverse reactions in a pathway, and their activity is highly regulated. Enzyme-mediated regulatory mechanisms allow pathways to be sensitive and responsive to the needs of the organism. In metabolic pathways, a favorable process is often used to drive a less favorable process.

Learning Objective Objectivess 1. Describe how glucose is imported into, used by, and stored within skeletal muscle cells, including how these processes are regulated. 2. Summarize the answers to the following questions for any given reaction in glycolysis:  What is the ΔG for the reaction under typical physiological conditions?  Is the reaction readily reversible under typical physiological conditions?  What enzyme catalyzes the reaction and what type of reaction is occurring?  Is the enzyme regulated; if so, how? 3. Explain how some reactions can be endergonic under standard conditions and exergonic under intracellular conditions. 4. Apply your knowledge of the reactions in glycolysis to answer the questions above about a chemical reaction that is new to you (i.e., that we’ve not considered in class). 5. Explain how coupling facilitates thermodynamically unfavorable reactions. For example, how do ATP hydrolysis and NAD+ reduction drive less favorable reactions? 6. Describe substrate-level phosphorylation and explain why 1,3-bisphosphoglycerate and phosphoenolpyruvate are substrates for substrate-level phosphorylation.

Updated by Amy Medlock (Fall 2017). Updated by Jin Kyu Lee (Fall 2020)

7. 8. 9. 10.

Describe the metabolic differences between normal and cancer cells. Summarize how muscle cells release glucose from glycogen during exercise and how this process is regulated. Describe a disease of carbohydrate metabolism and relate the observed symptoms to a specific enzyme deficiency. Explain the testing required for diagnosis of a disease in carbohydrate metabolism and why certain treatment options are recommended for individuals who are diagnosed.

Introduction Glycolysis is a critical metabolic pathway shared by virtually every cell. Exercise is important for human health. During exercise, glucose is an important fuel for processes within muscle cells, including transcription, translation, primary active transport for maintaining ion gradients (through the Na+/K+ ATPase and Ca+2 ATPase), and muscle contraction (using myosin ATPase).

Pa Part rt I 1. Glucose requires a protein for transport into the cell. In most cells, glucose moves across the plasma membrane via glucose transporters (GLUTs). A) Why does Glucose need transporter to cross the cell membrane?

B) List GLUTs with their tissue distribution.

GLUT GLUT GLUT GLUT GLUT

1 2 3 4 5

All mammalian tissues Liver and Pancreatic beta cells All mammalian tissues Muscle and fat cells Small intestine

C) Which glucose transporter (GLUT) is responsible for transport of glucose into muscle and fat cells?

D) What molecule regulates transport of GLUT protein to the cell surface in muscle and fat cells?

2. Glucose is catabolized (i.e., broken down) in glycolysis, a metabolic pathway with ten chemical reactions, each catalyzed by a distinct enzyme. A) Complete the table below for all ten reactions. Underneath each enzyme, indicate the type of reaction in parentheses. An example is provided for the first step.

Substrates

ΔG (kJ/mol)

Enzyme (type of reaction)

Products

hexokinase (phosphorylation)

glucose 6-phosphate + ADP + H+

-33.5

Fructose 6-phophate Fructose 1,6-bisphophate + ADP + H+

-2.5 -22.2

1

glucose + ATP

2 3

Glucose 6-phosphate Fructose 6-phophate+ATP

Phosphoglucose isomerase Phophofructokinase

4

Fructose 1,6-bisphophate

Aldolase

5

Dihydroxyacetone phosphate

Triose phosphate isomerase

glyceraldehyde 3-phosphate

2.5

6

glyceraldehyde 3-phosphate + Pi + NAD+

Glyceraldehyde 3-phosphate dehydrogenase

1,3-bisphosphoglycerate + NADH + H+

1.7

7

1,3-bisphosphoglycerate + ADP

Phosphoglycerate kinase

3-phosphoglycerate + ATP

1.3

8

3-phosphoglycerate

Phosphoglycerate mutase

2-phosphoglycerate

9

2-phosphoglycerate

enolase

10

Phosphoenolpyruvate + ADP + H+

Pyruvate kinase

Dihydroxyacetone phosphate + glyceraldehyde 3-phosphate

Phosphoenolpyruvate + H2O Pyruvate +ATP

-1.3

.8 -3.3 -16.7

B) In the table above, highlight in yellow the number of the three most energetically favorable steps under typical cellular conditions. Explain below why each step is so energetically favorable.

C) In the table above, highlight in teal the enzymes that are regulated in glycolysis. Regulated enzymes often catalyze essentially irreversible reactions. D) In general, what does it mean for an enzyme to be regulated? Hint: Think back to kinetics and inhibition. E) For each of the regulatory enzymes, list their effector molecules and the effect those molecules have upon the enzymes to control glycolysis.

F) Consider the step that involves an oxidation-reduction reaction. Why is oxidation of the aldehyde carbon energetically favorable? Hint: The correct answer is not that it’s favorable because the change in free energy is largely negative; that is the definition of favorable. G) Referring to Figure 16.3, explain in your own words how glyceraldehyde 3-phosphate dehydrogenase overcomes the energetically unfavorable process of phosphorylation after oxidation.

3. The enzyme aldolase catalyzes the following reaction in the glycolytic pathway:

The ΔG°′ for the reaction is +23.8 kJ mol−1, whereas the ΔG in the cell is −1.3 kJ mol−1. Explain how the reaction can be endergonic under standard conditions and exergonic under intracellular conditions.

4. ATP can be produced by two processes: substrate-level phosphorylation and oxidative phosphorylation. How do the processes differ? Which process occurs in glycolysis? Support your claim with evidence from Figure 15.7.

5. In tumor cells, mitochondrial function is still normal, but little mitochondrial oxidative phosphorylation (OXPHOS) continues in tumor cells. In order to satisfy the metabolic requirements of both energy and materials for rapidly proliferating cells, ~85% of the glucose is processed to lactate via glycolytic pyruvate even in the presence of oxygen and ~5% of the glucose is metabolized by oxidative phosphorylation. This process, known as the Warburg Effect, has been studied extensively. How Does it Benefit Cancer Cells? Answer the question briefly (3 or 4 sentences), referencing reliable sources. Leave your citation.

Pa Part rt II Skeletal muscle cells use a mixture of carbohydrates and lipids to make ATP for normal function. At rest and during low intensity exercise, skeletal muscle predominately uses fatty acids. As exercise intensity increases, skeletal muscle predominately utilize glucose, as shown in the diagram below. Not shown below – but of note – is that at moderate intensity exercise for long duration (about an hour), skeletal muscle switches from predominately using glucose to using fatty acids.

© Health24 (2017). Ross Tucker, University of Cape Town, Sports Science Institute of South Africa. Downloaded from http://www.health24.com/Fitness/Exercise/Fueled-byfat-fat-burning-101-20120721.

6. When skeletal muscles metabolize glucose, the pyruvate that is produced via glycolysis has several potential fates. A) What is the main fate of pyruvate in skeletal muscle when oxygen is limited, such in the first minute of high intensity exercise? What is the purpose of this reaction in muscle during exercise?

B) What is the main fate of pyruvate in skeletal muscle when oxygen is plentiful, such as during moderate intensity exercise? What pathway does this molecule then enter, and how does the further metabolism of this compound result in ATP synthesis?

7. Glucose can be stored in several tissues/organs in the human body. A) What tissues/organs are the two major sites of glucose storage in the body? Do these tissues/organs contribute to blood glucose levels?

B) In what form is glucose stored in the body? Summarize the structure and size of this molecule.

C) Briefly describe the process by which glucose is released from its stored form to be utilized by glycolysis. Does this process require ATP? Insert your answer

8. Muscle phosphorylase is the key regulatory enzyme of glycogenolysis in muscles. Several important regulators of the enzyme are listed below. Describe how each one controls glycogenolysis. A) ATP

B) AMP

C) glucose 6-phosphate

D) Ca2+

E) epinephrine

9. A 10-year-old boy presents with muscle fatigue and cramping during the first five minutes of vigorous exercise. His parents report that he has recently joined a soccer team, but has been unable to keep up with the other kids. This child has dark brown urine following practice due to rhabdomyolysis. The child undergoes an ischemic forearm exercise test which shows no elevation in blood lactate levels. A muscle biopsy shows normal glycogen stores. He is diagnosed with glycogen storage disease type V, known as McArdle disease. A) What is McArdle disease?

B) Which enzyme is deficient in McArdle disease?

C) Outline the effects that the enzyme deficiency has on metabolism during exercise and relate these to the observed symptoms (cramps, fatigue, and dark brown urine).

10. Several diagnostic tests were used to diagnosis this child. Explain the ischemic forearm exercise test and the results of the test for this child.

11. What are the treatment options for an individual with McArdle disease?

Pa Part rt III - LUW Reflectio Reflection n

(A) What are the two most important things you LEARNED from this case study?

(B) What are you still UNCLEAR about?

(C) What WORK will you do after class to clarify it?...