Understanding Energy Metabolism Pathways

BS161 In Class Activity – Introduction to Energy Metabolism Getting started Learning Objectives * Compare and contrast anabolic and catabolic pathways * Explain how an unfavorable reaction can become favorable in a cell and why this is required in metabolic pathways * Explain how the same enzyme would catalyze a reaction in opposite directions in different cell types or cell compartments From the PCA Insert below your entire figure from part B of the PCA: Key features of anabolic and catabolic pathways Activity 1: Anabolic and catabolic pathways and energetics Objectives: compare and contrast anabolic and catabolic pathways. 1. The ΔG for the complete oxidation of glucose is -2800 kJ/mol. 1. Write out the summary reaction for glucose oxidation (cellular respiration) (no need to describe exact stoichiometry): highlight 2. Based on the PCA model, the reactions of glucose oxidation and other catabolic pathways are energetically favorable / energetically unfavorable (highlight one) and can be coupled to production of __atp____ and ___heat___. 2. The ΔG for glucose synthesis from CO2 and H2O, without energetic coupling, is +2800 kJ/mol. 1. Write out the summary reaction for building glucose in photosynthetic cells: Hint: this is the opposite of glucose oxidation in cellular respiration. However, please note: glucose is NOT a direct product of photosynthesis, so this is a summary reaction of photosynthesis and additional reactions needed to build glucose. 6CO2 + 6H2O + light energy = C6H12O6 + 6O2 2. Based on the PCA model, the uncoupled process of glucose synthesis and other anabolic pathways are energetically favorable / energetically unfavorable (highlight one) and must be coupled to consumption of __atp____ and ___nadph___. Activity 2: Specific coupled reactions in metabolic pathways Objective: compare and contrast anabolic and catabolic pathways Use ideas from the PCA (including your figure on anabolic and catabolic pathways) and the reactions shown in this activity to fill in the blanks and develop explanations. 1. Reaction 1. A simplified diagram of the citric acid cycle from cellular respiration, summarizing inputs and outputs, is shown below on the left. Details for one reaction in the citric acid cycle are shown on the right. Note, you do not need to understand the details of this specific pathway to answer the questions below. You do not need to memorize details of the citric acid cycle. 1. Write out the reaction from the Citric acid cycle shown at above right (all reactants and products): ___Isocitrate _+ NAD^+______ → __ketoglutarate + NADH + CO2_____ 2. Recognizing redox. 1. In the above reaction, which carbon in IC (see light blue numbers in the reaction) is being oxidized to produce AKG? Carbon 1 / Carbon 2 / Carbon 3 (highlight one) is being oxidized because __loses electrons _____ (refer to changes in bonds to carbon during the reaction). 2. What happens to NAD+ in the reaction? NAD+ is being oxidized / reduced (highlight one) because __gains electrons_____. 3. Reaction 1 produces NADH that will be used by later steps to power ATP production in the electron transport chain. 1. Based on the coupled reaction, this reaction is likely part of a(n) anabolic / catabolic (highlight one) pathway because __reaction involves breaking down isocitrate and releasing energy in form of NADH_____. 2. What would happen to NADH production by this reaction if IC were substantially decreased? Explain your answer, referring to principles of equilibrium. Decreasing IC would shift equilibrium toward maintaining IC levels rather than producing NADH 4. Based on the model of the citric acid cycle, how might cells maintain sufficient concentrations of IC (isocitrate)? Regulate enzyme activity to slow down or speed up conversion of isocitrate, or help maintain balance of high ATP and NADH levels 2. Reaction 2. A simplified diagram of the Calvin cycle of photosynthesis, summarizing inputs and outputs, is shown below on the left. Details for one reaction in the Calvin cycle are shown on the right. Note, you do not need to understand all the details of this specific pathway to answer the questions below. You do not need to memorize details of the Calvin cycle. 1. Write out the reaction from the Calvin cycle shown at above right (all reactants and products): __1,3 bisphosphoglycerate + NADPH + H^+________ → __glyceraldehyde-3-phosphate + pi_____ 2. Recognizing redox. 1. In the above reaction, which carbon in BPG (see light blue numbers in the reaction) is being reduced to produce G3P? Carbon 1 / Carbon 2 / Carbon 3 (highlight one) is being reduced because ___gains electrons____ (refer to changes in bonds to carbon during the reaction). 2. What happens to NADPH in the reaction? NADPH is being oxidized / reduced (highlight one) because __donates electrons_____. 3. Reaction 2 is part of a multistep pathway used to store energy in the form of sugars. 1. Based on the coupled reaction, this reaction is likely part of a(n) anabolic / catabolic (highlight one) pathway because __Sugars use ATP and NADPH for energy_____. 2. Would plants be able to use the Calvin cycle to make sugar if no NADPH were present in the cell? Explain your answer, referring to principles of equilibrium. highlight 4. Based on the model of the Calvin cycle, how might cells maintain sufficient concentrations of BPG (1,3 bisphosphoglycerate)? highlight Activity 3: Effect of substrate and product concentrations on reactions Objectives: * Explain how an unfavorable reaction can become favorable in a cell and why this is required in metabolic pathways. * Explain how the same enzyme would catalyze a reaction in opposite directions in different cell types or cell compartments The enzyme lactate dehydrogenase catalyzes the reaction below. 1. Based on the above diagram, write out the reaction (all reactants and products) in the space below for the reaction as it occurs from left to right. ______Pyruvate + NADH^+ + H^+____ → _______NAD^+ + Lactate______ 2. What enzyme catalyzes the reaction as it occurs from right to left? Lactate Dehydrogenase This reaction is reversible, meaning the reaction has a ΔG very close to 0. Both liver and muscle cells have the lactate dehydrogenase enzyme to perform this reaction, but the direction of the reaction (forward or reverse) depends on specific substrate and product concentrations in those cells. For reasons we will explore in the next class, if muscle cells do not have enough oxygen, NADH concentrations are increased. Table 1 below shows that different directions of the reaction are favorable in different cell types. Table 1: Energetics of reactions catalyzed by lactate dehydrogenase in two cell types. Cell Type Reaction net ΔG for the reaction as written under cellular conditions Muscle with low oxygen Pyruvate + NADH + H+ → Lactate + NAD+ ΔG < 0 Liver Lactate + NAD+ → Pyruvate + NADH + H+ ΔG < 0 3. Use the ΔG values in the table above to answer questions about the differences in metabolism between muscle and liver cells. 1. Is the reaction at equilibrium in either cell type? Yes / no (highlight one) because ___They are both favorable___. 2. In muscle cells with low oxygen, the reaction pyruvate -> lactate / lactate -> pyruvate (highlight one) is more likely to occur, because __Pyruvate is the substrate and Lactate is the product____. 3. In liver cells, the reaction pyruvate -> lactate / lactate -> pyruvate (highlight one) is more likely to occur, because __Lactate is the reactant and pyruvate is the product____. 4. Review the reaction occurring in muscle cells with low oxygen (see Table 1). 1. The conversion of pyruvate to lactate increases the concentrations of __NADH____ and ___H___. 2. Considering Le Chatelier’s Principle, how do the changes in molecule concentrations described above affect the ΔG of the reaction to convert pyruvate to lactate? This makes the reaction more energetically favorable / less energetically favorable (highlight one) because __The delta G would increase above a negative____. 3. For reasons we will discuss in the next class, muscle cells need to convert pyruvate to lactate under low oxygen conditions. In order for this reaction to continue, muscle cells must maintain certain relative concentrations of reactants and products. Propose how muscle cells could maintain the favorable concentrations of lactate and pyruvate: 1. In order for the concentration of pyruvate to remain relatively high / low (highlight one) in muscle cells, cells could ______. 2. In order for the concentration of lactate to remain relatively high / low (highlight one) in muscle cells, cells could ______. OPTIONAL additional practice on this topic: Consider the following coupled reaction that takes place as part of a set of reactions called glycolysis. This is a multi-step pathway that is part of cellular respiration. A simplified diagram of glycolysis summarizing inputs and outputs is shown below on the left. Details for one reaction in glycolysis are shown on the right. This is the same reaction seen in Activity 2, Reaction 2, but with the direction reversed. This reaction illustrates the use of energy from food to make NADH. Note, you do not need to understand all the details of this specific pathway to answer the questions below. 1. Based on the above diagram, write out the reaction (all reactants and products) in the space below. ____G3P+NAD+Pi______ → _____NADH+H+BPG________ 2. Under normal cellular conditions, the overall coupled reaction to convert G3P and NAD+ to BPG and NADH + H+ has a ΔG of -1.3 kJ/mol. This means the reaction is energetically favorable / unfavorable (highlight one). 3. However, as seen above, the favorability of a reaction depends on the concentrations of substrates and products. Based on that idea, if the concentration of NAD+ increases and the concentration of NADH decreases, the reaction will become more / less (highlight one) energetically favorable. 4. If the cellular concentration of NAD+ was so low that the ΔG of the overall reaction became positive, would the cell be able to make BPG and NADH? Yes / No (highlight one), because ___It would be unfavorable___. Using ideas throughout today’s ICA and Le Chatelier’s Principle, address the following: 5. The ability of catabolic pathways to oxidize carbon atoms in food molecules as an energy source requires the cell to maintain high / low (highlight one) concentrations of NAD+ and high / low (highlight one) concentrations of NADH because __The NAD would lower the NADH which keeps the delta G low ____. 6. The ability of cells to produce activated phosphorylated metabolic intermediates as part of pathways and to synthesize macromolecules in anabolic pathways requires cells to maintain high / low (highlight one) concentrations of ATP and high / low (highlight one) concentrations of ADP because __ATP provides the energy needed for anabolic reactions _____. 7. The ability of cells to do cellular respiration relies on maintaining appropriate concentrations of the substrates and reactants needed for overall glucose oxidation. Based on the summary reaction for glucose oxidation from Activity 1 Part A, explain why your cells require you to eat and breathe: To help maintain the energy production for the cell to function. Eating provides the glucose needed and breathing supplies the oxygen needed for cellular respiration. 8. The ability of plant cells to do photosynthesis relies on maintaining appropriate concentrations of the substrates and reactants needed for overall glucose production (As noted before, glucose is NOT a direct product of photosynthesis, so we are referring to photosynthesis and additional reactions needed to build glucose). Based on the summary reaction for glucose production from Activity 1 Part B, explain why plant leaves must exchange gas with the atmosphere and absorb materials through their roots: they must perform anabolic reactions to perform photosynthesis. They take more simple molecules and turn them into more complex molecules. They will absorb the CO2 and H2O turn it into simple sugars in order to then make starch. This is the favorable process.

BS161         In Class Activity – Introduction to Energy Metabolism        
Getting started

Learning Objectives
* Compare and contrast anabolic and catabolic pathways
* Explain how an unfavorable reaction can become favorable in a cell and why this is required in metabolic pathways
* Explain how the same enzyme would catalyze a reaction in opposite directions in different cell types or cell compartments

From the PCA
Insert below your entire figure from part B of the PCA: Key features of anabolic and catabolic pathways

Activity 1: Anabolic and catabolic pathways and energetics
Objectives: compare and contrast anabolic and catabolic pathways.

1. The ΔG for the complete oxidation of glucose is -2800 kJ/mol. 
   1. Write out the summary reaction for glucose oxidation (cellular respiration) (no need to describe exact stoichiometry): 
highlight
   2. Based on the PCA model, the reactions of glucose oxidation and other catabolic pathways are energetically favorable / energetically unfavorable (highlight one) and can be coupled to production of __atp____ and ___heat___.

2. The ΔG for glucose synthesis from CO2 and H2O, without energetic coupling, is +2800 kJ/mol. 
   1. Write out the summary reaction for building glucose in photosynthetic cells:
Hint: this is the opposite of glucose oxidation in cellular respiration. However, please note: glucose is NOT a direct product of photosynthesis, so this is a summary reaction of photosynthesis and additional reactions needed to build glucose. 
6CO2 + 6H2O + light energy = C6H12O6 + 6O2             
   2. Based on the PCA model, the uncoupled process of glucose synthesis and other anabolic pathways are energetically favorable / energetically unfavorable (highlight one) and must be coupled to consumption of __atp____ and ___nadph___.

Activity 2: Specific coupled reactions in metabolic pathways
Objective: compare and contrast anabolic and catabolic pathways

Use ideas from the PCA (including your figure on anabolic and catabolic pathways) and the reactions shown in this activity to fill in the blanks and develop explanations.
1. Reaction 1. A simplified diagram of the citric acid cycle from cellular respiration, summarizing inputs and outputs, is shown below on the left. Details for one reaction in the citric acid cycle are shown on the right. Note, you do not need to understand the details of this specific pathway to answer the questions below. You do not need to memorize details of the citric acid cycle.

1. Write out the reaction from the Citric acid cycle shown at above right (all reactants and products):

___Isocitrate _+ NAD^+______   →   __ketoglutarate + NADH + CO2_____

2. Recognizing redox.
   1. In the above reaction, which carbon in IC (see light blue numbers in the reaction) is being oxidized to produce AKG? Carbon 1 / Carbon 2 / Carbon 3 (highlight one) is being oxidized because __loses electrons _____ (refer to changes in bonds to carbon during the reaction).
   2. What happens to NAD+ in the reaction? NAD+ is being oxidized / reduced (highlight one) because __gains electrons_____.

3. Reaction 1 produces NADH that will be used by later steps to power ATP production in the electron transport chain.
1. Based on the coupled reaction, this reaction is likely part of a(n) anabolic / catabolic (highlight one) pathway because __reaction involves breaking down isocitrate and releasing energy in form of NADH_____.
2. What would happen to NADH production by this reaction if IC were substantially decreased? Explain your answer, referring to principles of equilibrium. Decreasing IC would shift equilibrium toward maintaining IC levels rather than producing NADH

4. Based on the model of the citric acid cycle, how might cells maintain sufficient concentrations of IC (isocitrate)? Regulate enzyme activity to slow down or speed up conversion of isocitrate, or help maintain balance of high ATP and NADH levels

2. Reaction 2. A simplified diagram of the Calvin cycle of photosynthesis, summarizing inputs and outputs, is shown below on the left. Details for one reaction in the Calvin cycle are shown on the right. Note, you do not need to understand all the details of this specific pathway to answer the questions below. You do not need to memorize details of the Calvin cycle.

1. Write out the reaction from the Calvin cycle shown at above right (all reactants and products):

__1,3 bisphosphoglycerate + NADPH + H^+________   →   __glyceraldehyde-3-phosphate + pi_____

2. Recognizing redox.
   1. In the above reaction, which carbon in BPG (see light blue numbers in the reaction) is being reduced to produce G3P? Carbon 1 / Carbon 2 / Carbon 3 (highlight one) is being reduced because ___gains electrons____ (refer to changes in bonds to carbon during the reaction).
   2. What happens to NADPH in the reaction? NADPH is being oxidized / reduced (highlight one) because __donates electrons_____.

3. Reaction 2 is part of a multistep pathway used to store energy in the form of sugars.
1. Based on the coupled reaction, this reaction is likely part of a(n) anabolic / catabolic (highlight one) pathway because __Sugars use ATP and NADPH for energy_____.
2. Would plants be able to use the Calvin cycle to make sugar if no NADPH were present in the cell? Explain your answer, referring to principles of equilibrium. highlight

4. Based on the model of the Calvin cycle, how might cells maintain sufficient concentrations of BPG (1,3 bisphosphoglycerate)? highlight

Activity 3: Effect of substrate and product concentrations on reactions
Objectives:  
* Explain how an unfavorable reaction can become favorable in a cell and why this is required in metabolic pathways.
* Explain how the same enzyme would catalyze a reaction in opposite directions in different cell types or cell compartments

The enzyme lactate dehydrogenase catalyzes the reaction below.

1. Based on the above diagram, write out the reaction (all reactants and products) in the space below for the reaction as it occurs from left to right. 
______Pyruvate + NADH^+ + H^+____   →   _______NAD^+ + Lactate______

2. What enzyme catalyzes the reaction as it occurs from right to left? Lactate Dehydrogenase

This reaction is reversible, meaning the reaction has a ΔG very close to 0. Both liver and muscle cells have the lactate dehydrogenase enzyme to perform this reaction, but the direction of the reaction (forward or reverse) depends on specific substrate and product concentrations in those cells. For reasons we will explore in the next class, if muscle cells do not have enough oxygen, NADH concentrations are increased. Table 1 below shows that different directions of the reaction are favorable in different cell types.

Table 1: Energetics of reactions catalyzed by lactate dehydrogenase in two cell types.
Cell Type
	Reaction
	net ΔG for the reaction as written under cellular conditions
	Muscle with low oxygen
	Pyruvate + NADH + H+    →     Lactate + NAD+
	ΔG < 0
	Liver
	Lactate + NAD+ → Pyruvate + NADH + H+
	ΔG < 0

3. Use the ΔG values in the table above to answer questions about the differences in metabolism between muscle and liver cells.
   1. Is the reaction at equilibrium in either cell type? Yes / no (highlight one) because ___They are both favorable___. 
   2. In muscle cells with low oxygen, the reaction pyruvate -> lactate / lactate -> pyruvate (highlight one) is more likely to occur, because __Pyruvate is the substrate and Lactate is the product____. 
   3. In liver cells, the reaction pyruvate -> lactate / lactate -> pyruvate (highlight one) is more likely to occur, because __Lactate is the reactant and pyruvate is the product____.

4. Review the reaction occurring in muscle cells with low oxygen (see Table 1).
   1. The conversion of pyruvate to lactate increases the concentrations of __NADH____ and ___H___.
   2. Considering Le Chatelier’s Principle, how do the changes in molecule concentrations described above affect the ΔG of the reaction to convert pyruvate to lactate? This makes the reaction more energetically favorable / less energetically favorable (highlight one) because __The delta G would increase above a negative____.
   3. For reasons we will discuss in the next class, muscle cells need to convert pyruvate to lactate under low oxygen conditions. In order for this reaction to continue, muscle cells must maintain certain relative concentrations of reactants and products. 
Propose how muscle cells could maintain the favorable concentrations of lactate and pyruvate:
1. In order for the concentration of pyruvate to remain relatively high / low (highlight one) in muscle cells, cells could  ______.

2. In order for the concentration of lactate to remain relatively high / low (highlight one) in muscle cells, cells could  ______.

OPTIONAL additional practice on this topic:
Consider the following coupled reaction that takes place as part of a set of reactions called glycolysis. This is a multi-step pathway that is part of cellular respiration. A simplified diagram of glycolysis summarizing inputs and outputs is shown below on the left. 
Details for one reaction in glycolysis are shown on the right. This is the same reaction seen in Activity 2, Reaction 2, but with the direction reversed. This reaction illustrates the use of energy from food to make NADH. Note, you do not need to understand all the details of this specific pathway to answer the questions below.

1. Based on the above diagram, write out the reaction (all reactants and products) in the space below. 
____G3P+NAD+Pi______   →   _____NADH+H+BPG________

2. Under normal cellular conditions, the overall coupled reaction to convert G3P and NAD+ to BPG and NADH + H+ has a ΔG of -1.3 kJ/mol.  This means the reaction is energetically favorable / unfavorable (highlight one).

3. However, as seen above, the favorability of a reaction depends on the concentrations of substrates and products. Based on that idea, if the concentration of NAD+ increases and the concentration of NADH decreases, the reaction will become more / less (highlight one) energetically favorable.

4. If the cellular concentration of NAD+ was so low that the ΔG of the overall reaction became positive, would the cell be able to make BPG and NADH?  
Yes / No (highlight one), because ___It would be unfavorable___.

Using ideas throughout today’s ICA and Le Chatelier’s Principle, address the following: 
5. The ability of catabolic pathways to oxidize carbon atoms in food molecules as an energy source requires the cell to maintain high / low (highlight one) concentrations of NAD+ and high / low (highlight one) concentrations of NADH because __The NAD would lower the NADH which keeps the delta G low ____.

6. The ability of cells to produce activated phosphorylated metabolic intermediates as part of pathways and to synthesize macromolecules in anabolic pathways requires cells to maintain high / low (highlight one) concentrations of ATP and high / low (highlight one) concentrations of ADP because __ATP provides the energy needed for anabolic reactions _____.

7. The ability of cells to do cellular respiration relies on maintaining appropriate concentrations of the substrates and reactants needed for overall glucose oxidation.  Based on the summary reaction for glucose oxidation from Activity 1 Part A, explain why your cells require you to eat and breathe:  To help maintain the energy production for the cell to function. Eating provides the glucose needed and breathing supplies the oxygen needed for cellular respiration.

8. The ability of plant cells to do photosynthesis relies on maintaining appropriate concentrations of the substrates and reactants needed for overall glucose production (As noted before, glucose is NOT a direct product of photosynthesis, so we are referring to photosynthesis and additional reactions needed to build glucose). 
Based on the summary reaction for glucose production from Activity 1 Part B, explain why plant leaves must exchange gas with the atmosphere and absorb materials through their roots:  they must perform anabolic reactions to perform photosynthesis. They take more simple molecules and turn them into more complex molecules. They will absorb the CO2 and H2O turn it into simple sugars in order to then make starch. This is the favorable process.

Transcript for:Understanding Energy Metabolism Pathways

Transcript for:
Understanding Energy Metabolism Pathways