Biochemistry: Glycolysis & Hexokinase
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Questions and Answers

What is the net ATP gain from anaerobic glycolysis?

  • 0 ATP
  • 2 ATP (correct)
  • 6 ATP
  • 4 ATP

    • How many ATP molecules are generated in the glycolysis pathway from the pyruvate kinase reaction?

  • 1 ATP
  • 4 ATP
  • 3 ATP
  • 2 ATP (correct)

    • What happens to NADH produced under anaerobic conditions?

  • Yields ATP through oxidative phosphorylation
  • Does not contribute to ATP production (correct)
  • Transforms into glucose
  • Participates in glycolysis

    • Which reaction in glycolysis consumes the most ATP during the investment phase?

    <p>Phosphofructokinase</p> Signup and view all the answers

    What is the primary sugar found in mammalian milk?

    <p>Lactose</p> Signup and view all the answers

    What is the ultimate fate of pyruvate under aerobic conditions?

    <p>Converted to acetylCoA</p> Signup and view all the answers

    Which stage of glycolysis primarily occurs during rest or low-intensity exercise?

    <p>Aerobic glycolysis</p> Signup and view all the answers

    How many ATP molecules are required to integrate fructose into glycolysis?

    <p>Two ATPs</p> Signup and view all the answers

    What initial reaction occurs when galactose enters glycolysis?

    <p>Phosphorylation by galactose kinase</p> Signup and view all the answers

    What reaction occurs to pyruvate during intense exercise when oxygen availability is limited?

    <p>Conversion to lactate</p> Signup and view all the answers

    What product is formed when galactose 1-phosphate is converted into glucose 1-phosphate?

    <p>UDP-galactose</p> Signup and view all the answers

    How many extra ATPs can be formed from NADH during aerobic glycolysis?

    <p>4 ATP</p> Signup and view all the answers

    What role do nucleotide sugars play in biochemical reactions?

    <p>They couple ATP energy to unfavorable reactions</p> Signup and view all the answers

    What is formed from the exchange of galactose 1-phosphate and glucose 1-phosphate?

    <p>UDP-galactose and UDP-glucose</p> Signup and view all the answers

    Which enzyme is responsible for the cleavage of lactose into its constituent sugars?

    <p>Lactase</p> Signup and view all the answers

    What transformation does glucose 1-phosphate undergo to enter glycolysis?

    <p>Isomerization to glucose 6-phosphate</p> Signup and view all the answers

    What must the free energy change be for each individual reaction in a pathway to ensure it proceeds in the direction of product formation?

    <p>At least slightly negative</p> Signup and view all the answers

    What role does hexokinase play in glycolysis?

    <p>It converts glucose into glucose 6-P</p> Signup and view all the answers

    How does the phosphorylation of glucose affect its movement through the cell membrane?

    <p>It keeps glucose inside the cell</p> Signup and view all the answers

    What is the Km value for hexokinase regarding glucose?

    <p>0.1 mM</p> Signup and view all the answers

    Why is it theorized that reactions with positive free energy changes must be incorrect?

    <p>They imply that products cannot form.</p> Signup and view all the answers

    What is the main chemical transformation in the hexokinase reaction?

    <p>Glucose to glucose 6-P</p> Signup and view all the answers

    Which of the following statements is true about ATP in the hexokinase reaction?

    <p>It provides energy through its phosphoanhydride bond.</p> Signup and view all the answers

    What characteristic distinguishes glucokinase from hexokinase?

    <p>Glucokinase has a higher Km for glucose.</p> Signup and view all the answers

    What initiates the Cori Cycle during exercise?

    <p>Anaerobic glycolysis</p> Signup and view all the answers

    What is the first step in converting lactate to glucose in the liver?

    <p>Conversion to pyruvate</p> Signup and view all the answers

    Which two enzymes bypass pyruvate kinase in gluconeogenesis?

    <p>Pyruvate carboxylase and phosphoenolpyruvate carboxykinase</p> Signup and view all the answers

    What is the role of phosphatase enzymes in gluconeogenesis?

    <p>To hydrolyze phosphate groups from substrates</p> Signup and view all the answers

    What is the primary function of the liver in relation to glucose during the Cori Cycle?

    <p>To release glucose into the blood</p> Signup and view all the answers

    Which process occurs after pyruvate is converted to oxaloacetate in gluconeogenesis?

    <p>It is converted to phosphoenolpyruvate</p> Signup and view all the answers

    How many ATP equivalents are required for the reversal of pyruvate kinase?

    <p>Two ATP</p> Signup and view all the answers

    What is a notable feature of the liver in the context of glucose metabolism?

    <p>It synthesizes glucose and releases it into the blood</p> Signup and view all the answers

    What role does UDP-galactose 4-epimerase play in metabolism?

    <p>It catalyzes the conversion of UDP-galactose back to UDP-glucose.</p> Signup and view all the answers

    What does the presence of a ketone intermediate in the reaction of UDP-galactose 4-epimerase indicate?

    <p>It has no chirality and can produce either epimer.</p> Signup and view all the answers

    What is the requirement for a biological reaction to proceed in the forward direction?

    <p>It must have a net negative free energy (ΔG) of hydrolysis.</p> Signup and view all the answers

    How does gluconeogenesis relate to glycolysis?

    <p>Gluconeogenesis is the reversal of glycolysis, forming glucose from pyruvate.</p> Signup and view all the answers

    What happens to lactate produced during vigorous exercise when the exercise ceases?

    <p>It is converted back into pyruvate and then into glucose.</p> Signup and view all the answers

    What is the net yield of ATP in anaerobic glycolysis?

    <p>Two ATP molecules used, with four produced, resulting in a net of two ATP.</p> Signup and view all the answers

    Which of the following is true regarding the standard free energies of glycolysis reactions?

    <p>Three reactions have net positive ΔG values despite appearing impossible.</p> Signup and view all the answers

    What characteristic of the mechanism of UDP-galactose 4-epimerase is mentioned?

    <p>It has low activation energy for altering alcohol chirality.</p> Signup and view all the answers

    How many ATP equivalents are consumed during the initial stages of glycolysis?

    <p>Two</p> Signup and view all the answers

    What is the net production of NADH during the entire glycolysis process per glucose molecule?

    <p>Two</p> Signup and view all the answers

    During which specific step of glycolysis is glyceraldehyde 3-phosphate converted into 1-3-bisphosphoglycerate?

    <p>The energy generation stage</p> Signup and view all the answers

    What is the relationship between the glucose molecule and the triose molecules during glycolysis?

    <p>One glucose produces two triose molecules</p> Signup and view all the answers

    Which enzyme catalyzes the reaction interconverting dihydroxyacetone phosphate and glyceraldehyde 3-phosphate?

    <p>Aldolase</p> Signup and view all the answers

    What is the total yield of pyruvate molecules generated from the metabolism of one glucose molecule through glycolysis?

    <p>Two</p> Signup and view all the answers

    In the second part of glycolysis, which reaction is critical for maximizing energy production?

    <p>Conversion of glyceraldehyde 3-phosphate to 1-3-bisphosphoglycerate</p> Signup and view all the answers

    Which two products are formed from one glucose molecule during aerobic glycolysis?

    <p>Two ATPs and two NADH</p> Signup and view all the answers

    Why is the bypass of the hexokinase reaction necessary in gluconeogenesis?

    <p>Hexokinase reaction has a favorable negative ΔG and is energetically unfavorable to reverse.</p> Signup and view all the answers

    In the context of energy consumption, how does gluconeogenesis differ from glycolysis?

    <p>Gluconeogenesis requires more ATP, using six ATP equivalents.</p> Signup and view all the answers

    What is the primary regulation mechanism preventing simultaneous glycolysis and gluconeogenesis?

    <p>Both pathways are regulated based on the ATP supply and need.</p> Signup and view all the answers

    Which of the following bypass reactions are considered to have the most stringent regulation?

    <p>Conversion of fructose 1-6-bisphosphate to fructose 6-phosphate.</p> Signup and view all the answers

    What is a consequence of the uncontrolled simultaneous function of glycolysis and gluconeogenesis?

    <p>It leads to excessive heat generation without useful work.</p> Signup and view all the answers

    What is the primary reaction that indicates the interconversion of glucose and glucose 6-phosphate?

    <p>Phosphatase dephosphorylation.</p> Signup and view all the answers

    What fundamental principle should be understood when examining the regulation of glycolysis and gluconeogenesis?

    <p>Bypass sites have significant control, making them critical for regulation.</p> Signup and view all the answers

    During gluconeogenesis, which strategy is employed to reverse the energetically unfavorable reaction of hexokinase?

    <p>Utilizing a phosphatase makes the reaction energetically favorable.</p> Signup and view all the answers

    What is the main purpose of reducing pyruvate to lactate during anaerobic conditions?

    <p>To regenerate NAD+ for glycolysis to continue</p> Signup and view all the answers

    What is the initial step in the conversion of pyruvate to ethanol?

    <p>Decarboxylation of pyruvate to acetaldehyde</p> Signup and view all the answers

    Which enzyme is responsible for the reduction of pyruvate to lactate?

    <p>Lactate dehydrogenase</p> Signup and view all the answers

    What effect does the accumulation of NADH have on the glycolysis pathway under anaerobic conditions?

    <p>It limits the utilization of pyruvate by the TCA cycle.</p> Signup and view all the answers

    What is the net ATP yield from anaerobic fermentation of glucose to lactate?

    <p>Two molecules of ATP</p> Signup and view all the answers

    After exercise, what happens to the lactate produced in the muscles?

    <p>It is released into the blood and transported to the liver.</p> Signup and view all the answers

    During anaerobic fermentation, what is the role of NADH?

    <p>It is oxidized to regenerate NAD+.</p> Signup and view all the answers

    What is the consequence of pyruvate accumulation when oxygen is limiting?

    <p>Reduction of pyruvate to lactate</p> Signup and view all the answers

    What role does UDP-galactose 4-epimerase play in the conversion of UDP-galactose back to UDP-glucose?

    <p>It facilitates the formation of a 4-ketone intermediate.</p> Signup and view all the answers

    Which is true regarding the net free energies of reactions in glycolysis?

    <p>Glycolysis can only produce products if there are negative energy values.</p> Signup and view all the answers

    What is a consequence of the conversion of pyruvate into lactate during vigorous exercise?

    <p>It results in the diversion of pyruvate from the TCA cycle.</p> Signup and view all the answers

    What does the presence of a ketone intermediate suggest about the mechanism of UDP-galactose 4-epimerase?

    <p>It can lead to the production of either epimer upon reduction.</p> Signup and view all the answers

    Why might the standard free energy changes of glycolysis reactions show positive values?

    <p>Concentration estimates of intermediates may be incorrect.</p> Signup and view all the answers

    During gluconeogenesis, what is the fate of lactate produced during exercise when energy needs are met?

    <p>It can be reconverted to pyruvate and then glucose.</p> Signup and view all the answers

    How does low activation energy affect the mechanism of UDP-galactose 4-epimerase?

    <p>It facilitates rapid transformation between epimers.</p> Signup and view all the answers

    Which of the following statements about the relationship between glycolysis and gluconeogenesis is true?

    <p>Gluconeogenesis is the reversal of glycolysis.</p> Signup and view all the answers

    What is the role of galactose kinase in the entry of galactose into glycolysis?

    <p>It phosphorylates galactose to galactose 1-phosphate.</p> Signup and view all the answers

    In the conversion of galactose 1-phosphate to glucose 1-phosphate, what role does UDP-glucose play?

    <p>It exchanges with galactose 1-phosphate.</p> Signup and view all the answers

    What does the formation of nucleotide sugar derivatives accomplish in metabolism?

    <p>It provides an indirect method to couple ATP energy into unfavorable reactions.</p> Signup and view all the answers

    Why can the reaction converting galactose 1-phosphate to glucose 1-phosphate be described as 'baroque'?

    <p>It contains a series of complex reactions with multiple intermediates.</p> Signup and view all the answers

    Which metabolic pathway does glucose 6-phosphate enter after its formation from galactose?

    <p>Glycolysis</p> Signup and view all the answers

    What is a significant feature of the reaction exchanging galactose 1-phosphate with glucose 1-phosphate?

    <p>It involves an even exchange of sugar phosphates.</p> Signup and view all the answers

    What energy investment is required to integrate fructose into glycolysis?

    <p>Two ATPs for phosphorylation of fructose and glyceraldehyde.</p> Signup and view all the answers

    What happens to UDP-galactose in the reaction converting galactose 1-phosphate to glucose 1-phosphate?

    <p>It is produced as a product of the reaction.</p> Signup and view all the answers

    What is the primary role of biotin in carboxylation reactions?

    <p>It serves as a cofactor.</p> Signup and view all the answers

    Which compound is produced from the conversion of oxaloacetate in gluconeogenesis?

    <p>Phosphoenolpyruvate</p> Signup and view all the answers

    What energy source does phosphoenolpyruvate carboxykinase utilize in the conversion of oxaloacetate to phosphoenolpyruvate?

    <p>GTP</p> Signup and view all the answers

    What is the energetic consequence of the carboxylation followed by decarboxylation in fatty acid biosynthesis?

    <p>It provides extra energy for the synthesis process.</p> Signup and view all the answers

    How many ATP equivalents are needed to convert pyruvate to phosphoenolpyruvate?

    <p>Two ATP equivalents</p> Signup and view all the answers

    What is the function of phosphatase in gluconeogenesis?

    <p>To bypass an energetically favorable kinase reaction.</p> Signup and view all the answers

    What is the significance of the negative ΔG associated with phosphofructokinase?

    <p>It shows a favorable reaction towards forward directions.</p> Signup and view all the answers

    What drives the formation of fructose 6-phosphate from fructose 1,6-bisphosphate?

    <p>Release of inorganic phosphate</p> Signup and view all the answers

    What is the total yield of ATP from one glucose molecule in anaerobic glycolysis?

    <p>Two molecules</p> Signup and view all the answers

    How many NADH molecules are produced during the aerobic glycolysis process?

    <p>Two</p> Signup and view all the answers

    What is the fate of pyruvate under aerobic conditions?

    <p>Converted to acetylCoA</p> Signup and view all the answers

    What role does ATP play in the phosphofructokinase reaction during glycolysis?

    <p>It is consumed</p> Signup and view all the answers

    How do aerobic and anaerobic glycolysis differ after the formation of pyruvate?

    <p>Anaerobic glycolysis converts pyruvate to lactate</p> Signup and view all the answers

    What is the primary reason for the low ATP yield during anaerobic glycolysis?

    <p>Absence of oxidative phosphorylation</p> Signup and view all the answers

    During which reaction are the two ATPs produced in glycolysis primarily generated?

    <p>Pyruvate kinase</p> Signup and view all the answers

    What limits the oxidation of acetylCoA during high-intensity exercise?

    <p>Low availability of oxygen</p> Signup and view all the answers

    What is the primary product of glycolysis under aerobic conditions?

    <p>Pyruvate</p> Signup and view all the answers

    During which phase of glycolysis is ATP utilized?

    <p>Phase 1</p> Signup and view all the answers

    What is the main catabolic role of glycolysis in human metabolism?

    <p>To convert glucose into pyruvate or lactate</p> Signup and view all the answers

    What happens to pyruvate produced during glycolysis in the presence of oxygen?

    <p>It enters the citric acid cycle as acetylCoA</p> Signup and view all the answers

    Which compound serves as a substrate for both glycolysis and gluconeogenesis?

    <p>Pyruvate</p> Signup and view all the answers

    In the glycolysis pathway, how many ATP molecules are generated in total during the conversion of one molecule of glucose?

    <p>4 ATP</p> Signup and view all the answers

    What is the significance of the high percentage of reduced carbon in glucose?

    <p>It enhances its utility as a substrate for oxidation.</p> Signup and view all the answers

    What is the primary purpose of the phosphatase reaction in gluconeogenesis?

    <p>To bypass an energetically unfavorable reaction</p> Signup and view all the answers

    Which substance is primarily formed when glucose goes through glycolysis?

    <p>Pyruvate</p> Signup and view all the answers

    Which of the following is true about the regulation of glycolysis and gluconeogenesis?

    <p>Both pathways are regulated based on ATP supply.</p> Signup and view all the answers

    What does the hexokinase reaction contribute to glycolysis?

    <p>It converts glucose into glucose 6-phosphate.</p> Signup and view all the answers

    During gluconeogenesis, how many ATP molecules are used relative to the ATP generated in glycolysis?

    <p>Six ATP molecules are consumed.</p> Signup and view all the answers

    What is a consequence of uncontrolled simultaneous function of glycolysis and gluconeogenesis?

    <p>Wasted ATP with no useful work.</p> Signup and view all the answers

    Which reactions in glycolysis are considered the bypass sites and are stringently regulated?

    <p>All of the above.</p> Signup and view all the answers

    In terms of ATP utilization, how does gluconeogenesis relate to glycolysis?

    <p>Gluconeogenesis uses more ATP compared to the energy yield of glycolysis.</p> Signup and view all the answers

    Why is there a need for regulation between glycolysis and gluconeogenesis?

    <p>To prevent wasteful expenditure of energy.</p> Signup and view all the answers

    What is the primary product formed when pyruvate is converted under anaerobic conditions in muscles during intense exercise?

    <p>Lactate</p> Signup and view all the answers

    What key reaction occurs to regenerate NAD+ during lactic acid fermentation?

    <p>Oxidation of NADH</p> Signup and view all the answers

    What is the net energy yield from anaerobic fermentation of glucose to lactate?

    <p>Two ATP</p> Signup and view all the answers

    Under anaerobic conditions, what organism primarily converts pyruvate to ethanol?

    <p>Yeast</p> Signup and view all the answers

    Which reaction begins the conversion of pyruvate to ethanol?

    <p>Decarboxylation of pyruvate</p> Signup and view all the answers

    What happens to lactate produced in muscles after anaerobic exercise when normal conditions resume?

    <p>Converted back to glucose in the liver</p> Signup and view all the answers

    Why does the conversion of pyruvate to lactate occur under anaerobic conditions?

    <p>To regenerate NAD+ and dispose of excess pyruvate</p> Signup and view all the answers

    Which coenzyme is oxidized during the reduction of pyruvate to lactate?

    <p>NADH</p> Signup and view all the answers

    What is the net production of ATP molecules from the glycolysis pathway per glucose molecule?

    <p>Two molecules</p> Signup and view all the answers

    Under anaerobic conditions, what product is formed from pyruvate?

    <p>Lactate</p> Signup and view all the answers

    What is the energy change associated with the hydrolysis of ATP?

    <p>7.3 kcal/mol</p> Signup and view all the answers

    Which molecule is produced during the conversion of 1-3-bisphosphoglycerate to 3-phosphoglycerate?

    <p>ATP</p> Signup and view all the answers

    In glycolysis, which intermediate has the highest phosphate hydrolysis potential?

    <p>Phosphoenolpyruvate</p> Signup and view all the answers

    What is the overall free energy change for the conversion of glucose to carbon dioxide in glycolysis?

    <p>Highly negative</p> Signup and view all the answers

    Which enzyme catalyzes the final step of glycolysis, leading to ATP production?

    <p>Pyruvate kinase</p> Signup and view all the answers

    What occurs to the two molecules of NADH formed during glycolysis under oxidative conditions?

    <p>They are oxidized in the mitochondria</p> Signup and view all the answers

    What is the primary function of biotin in carboxylation reactions?

    <p>It serves as a cofactor for the addition of carboxyl groups.</p> Signup and view all the answers

    Which of the following statements accurately describes the transition from oxaloacetate to phosphoenolpyruvate?

    <p>GTP cleavage contributes energy to this conversion.</p> Signup and view all the answers

    Why must the reaction catalyzed by phosphofructokinase be bypassed in gluconeogenesis?

    <p>It has a favorable negative ΔG, making it difficult to reverse.</p> Signup and view all the answers

    How does the release of inorganic phosphate from fructose 1-6-bisphosphate facilitate the reaction with fructose 6-phosphate?

    <p>It generates a negative ΔG for the forward reaction.</p> Signup and view all the answers

    What is revealed about the energy requirements in gluconeogenesis compared to glycolysis?

    <p>Gluconeogenesis requires more ATP equivalents than glycolysis.</p> Signup and view all the answers

    What role does decarboxylation play in the synthesis of phosphoenolpyruvate?

    <p>It facilitates the formation of high-energy compounds.</p> Signup and view all the answers

    What is the effect of substituting a phosphatase for a kinase in gluconeogenesis?

    <p>It generates sufficient energy release to allow for product formation.</p> Signup and view all the answers

    What is a characteristic of the negative ΔG in the pathways of glycolysis and gluconeogenesis?

    <p>A balance is maintained through favorable energy coupling.</p> Signup and view all the answers

    What is the total net ATP yield from aerobic glycolysis after considering both substrate-level phosphorylation and NADH production?

    <p>8 ATP</p> Signup and view all the answers

    What is the primary reason through which hexokinase facilitates the phosphorylation of glucose?

    <p>It maintains a low concentration of glucose in the cell.</p> Signup and view all the answers

    Which step in glycolysis primarily results in the consumption of two ATP molecules?

    <p>Phosphofructokinase reaction</p> Signup and view all the answers

    Which enzyme is utilized primarily in most cells for phosphorylating glucose?

    <p>Hexokinase.</p> Signup and view all the answers

    Under anaerobic conditions, which molecule is predominantly produced from pyruvate during glycolysis?

    <p>Lactate</p> Signup and view all the answers

    Why must each reaction in a biochemical pathway have at least a small negative free energy change?

    <p>To ensure the reaction releases energy that can be harnessed.</p> Signup and view all the answers

    What is the primary function of NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction under aerobic conditions?

    <p>To undergo oxidative phosphorylation yielding ATP</p> Signup and view all the answers

    What distinguishes glucokinase from hexokinase regarding its affinity for glucose?

    <p>Hexokinase has a higher Km value than glucokinase.</p> Signup and view all the answers

    Which of the following best describes the fate of pyruvate in well-oxygenated tissues after glycolysis?

    <p>It is completely oxidized in the TCA cycle</p> Signup and view all the answers

    During which specific reaction does the energy yield of glycolysis improve due to the formation of ATP?

    <p>Pyruvate kinase reaction</p> Signup and view all the answers

    What impact does the phosphorylation of glucose have on its ability to traverse the cell membrane?

    <p>It prevents glucose from being recognized by transport proteins.</p> Signup and view all the answers

    What is a consequence of reactions showing positive free energy changes in a metabolic pathway?

    <p>They indicate a pathway is non-functional and reversing.</p> Signup and view all the answers

    Which factor limits the rate of acetyl-CoA oxidation during high-intensity exercise?

    <p>Oxygen availability</p> Signup and view all the answers

    What happens to the NADH generated in glycolysis under anaerobic conditions?

    <p>It is converted into NAD+ without producing ATP</p> Signup and view all the answers

    What role does ATP play in the hexokinase reaction?

    <p>ATP donates a high-energy phosphate to glucose.</p> Signup and view all the answers

    Which of the following statements is true regarding the efficiency of hexokinase?

    <p>Hexokinase's activity is regulated by intracellular glucose levels.</p> Signup and view all the answers

    What characterizes the three essentially irreversible reactions in glycolysis?

    <p>They have a ΔG that is highly negative.</p> Signup and view all the answers

    During gluconeogenesis, which process is primarily responsible for shifting the pathway towards glucose synthesis?

    <p>Substituting phosphatase reactions for kinase reactions.</p> Signup and view all the answers

    What is the net ATP cost for gluconeogenesis compared to glycolysis?

    <p>It requires a net of six ATP.</p> Signup and view all the answers

    Which of the following must be true when gluconeogenesis is occurring?

    <p>The overall pathway has a negative ΔG.</p> Signup and view all the answers

    What is the main role of the Cori Cycle during recovery from intense exercise?

    <p>To convert pyruvate back into glucose.</p> Signup and view all the answers

    Which component is NOT involved in the irreversible reactions of glycolysis?

    <p>Fructose 2,6-bisphosphate.</p> Signup and view all the answers

    Which of the following statements about gluconeogenesis is incorrect?

    <p>It generates NADH in excess.</p> Signup and view all the answers

    What drives the need for gluconeogenesis to occur during periods of recovery from exercise?

    <p>The need to replenish glucose stores.</p> Signup and view all the answers

    What is the primary reason glucokinase has a higher Km compared to hexokinase?

    <p>It ensures glucose is phosphorylated only at high glucose concentrations.</p> Signup and view all the answers

    What structure does glucose 6-phosphate convert into during the isomerization process catalyzed by phosphoglucoisomerase?

    <p>Fructose 6-phosphate</p> Signup and view all the answers

    What is the nature of the reaction catalyzed by phosphofructokinase in glycolysis?

    <p>An ATP-dependent reaction producing fructose 1,6-bisphosphate.</p> Signup and view all the answers

    What outcome occurs directly after the aldolase reaction in glycolysis?

    <p>Two three-carbon compounds are produced.</p> Signup and view all the answers

    What modifies phosphofructokinase activity and plays a significant role in glycolysis regulation?

    <p>Presence of insulin and AMP levels</p> Signup and view all the answers

    What is the initial structure that glucose 6-phosphate must convert to for the isomerization reaction to proceed?

    <p>Open-chain structure</p> Signup and view all the answers

    Why is the reaction catalyzed by phosphofructokinase not simply reversed in gluconeogenesis?

    <p>It is thermodynamically unfavorable to reverse the reaction.</p> Signup and view all the answers

    What is generated when glucose 6-phosphate is transformed within the glycolysis pathway?

    <p>Fructose 1,6-bisphosphate</p> Signup and view all the answers

    What must be true for every reaction in a metabolic pathway to ensure it progresses towards product formation?

    <p>Each reaction must release at least a small amount of free energy.</p> Signup and view all the answers

    Why is glucose 6-phosphate unable to diffuse out of the cell?

    <p>It is phosphorylated and not recognized by glucose transport proteins.</p> Signup and view all the answers

    What characteristic sets glucokinase apart from hexokinase concerning glucose phosphorylation?

    <p>Glucokinase has a higher Km value for glucose.</p> Signup and view all the answers

    What is the effect of high levels of acetylCoA and citrate on glycolysis and gluconeogenesis?

    <p>They inhibit glycolysis and stimulate gluconeogenesis.</p> Signup and view all the answers

    What is the primary reason the hexokinase reaction drives glucose into the glycolysis pathway?

    <p>It phosphorylates glucose, trapping it within the cell.</p> Signup and view all the answers

    How does the energy charge formula normalize the percentage of adenylate material?

    <p>By giving ATP a value of one.</p> Signup and view all the answers

    How does the energy released from ATP hydrolysis compare to that required to form glucose 6-phosphate in the hexokinase reaction?

    <p>The energy released from ATP hydrolysis is greater than that needed to form glucose 6-phosphate.</p> Signup and view all the answers

    What is the primary function of hexokinase in cellular metabolism?

    <p>To phosphorylate glucose and maintain glucose homeostasis.</p> Signup and view all the answers

    Which role does fructose 2-6-bisphosphate play in the regulation of glycolysis and gluconeogenesis?

    <p>It stimulates phosphofructokinase while inhibiting fructose 1-6-bisphosphate phosphatase.</p> Signup and view all the answers

    What primarily dictates the activation state of glycolysis?

    <p>The ATP/ADP and AMP ratio.</p> Signup and view all the answers

    What happens to intracellular glucose levels when hexokinase phosphorylates glucose?

    <p>Intracellular glucose levels decrease, favoring diffusion into the cell.</p> Signup and view all the answers

    What is the consequence of regulating the bypass steps in glycolysis and gluconeogenesis?

    <p>It allows for greater flexibility in metabolic regulation.</p> Signup and view all the answers

    Which of the following statements is true regarding the efficiency of hexokinase?

    <p>It has a Km value for glucose that shows high efficiency at low concentrations.</p> Signup and view all the answers

    What is the primary factor that activates gluconeogenesis?

    <p>A high ATP/ADP and AMP ratio.</p> Signup and view all the answers

    How does the inhibition of glycolysis affect gluconeogenesis if reversible steps are targeted for regulation?

    <p>It leads to simultaneous inhibition of gluconeogenesis.</p> Signup and view all the answers

    What characterizes the regulatory control mechanisms in glycolysis?

    <p>Allosteric control where metabolites activate or inhibit enzymes.</p> Signup and view all the answers

    What is the primary reason for the conversion of pyruvate to lactate under anaerobic conditions?

    <p>To regenerate NAD+ to allow glycolysis to continue</p> Signup and view all the answers

    What happens to lactate after it accumulates in the muscles during intense exercise?

    <p>It is released into the blood and transported to the liver</p> Signup and view all the answers

    What is the relationship between fructose and glucose in glycolysis regarding ATP consumption?

    <p>Both fructose and glucose require the same ATP to integrate into glycolysis.</p> Signup and view all the answers

    Which statement accurately describes the net energy yield of anaerobic glycolysis compared to aerobic glycolysis?

    <p>Both anaerobic and aerobic glycolysis yield the same amount of ATP</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of galactose 1-phosphate into glucose 1-phosphate?

    <p>Galactose 1-Phosphate Uridylyltransferase</p> Signup and view all the answers

    What is the initial reaction that occurs when pyruvate is converted into ethanol under anaerobic conditions?

    <p>Decarboxylation of pyruvate to acetaldehyde</p> Signup and view all the answers

    During lactate fermentation, which role does NADH play in the reduction of pyruvate?

    <p>It gets oxidized to NAD+ to facilitate glycolysis</p> Signup and view all the answers

    What primarily drives the conversion of unfavorable biochemical reactions in metabolism?

    <p>Nucleotide sugars</p> Signup and view all the answers

    What is a key functional similarity between the conversion of pyruvate to lactate and the conversion of pyruvate to ethanol?

    <p>Both regenerate NAD+ from NADH</p> Signup and view all the answers

    Which statement accurately describes the role of UDP-glucose in galactose metabolism?

    <p>UDP-glucose facilitates the exchange of sugars between galactose and glucose.</p> Signup and view all the answers

    What role does the enzyme lactate dehydrogenase play during anaerobic glycolysis?

    <p>It facilitates the reduction of pyruvate to lactate</p> Signup and view all the answers

    How does the entry of galactose into glycolysis begin?

    <p>Through phosphorylation by galactose kinase.</p> Signup and view all the answers

    Which statement is true regarding nucleotide sugars in biochemical reactions?

    <p>Nucleotide sugars often make reactions more favorable.</p> Signup and view all the answers

    In what circumstance is the buildup of NADH particularly critical?

    <p>When oxygen is limited and glycolysis is accelerated</p> Signup and view all the answers

    What happens to glucose 1-phosphate after its formation from galactose 1-phosphate?

    <p>It undergoes isomerization to glucose 6-phosphate.</p> Signup and view all the answers

    What role do phosphorylated intermediates play in glycolysis?

    <p>They help to facilitate the movement of sugars across membranes.</p> Signup and view all the answers

    What is the primary reason for targeting the bypass steps for regulation in metabolic pathways?

    <p>It enables regulation in one direction without affecting the reverse pathway.</p> Signup and view all the answers

    Which factor activates glycolysis when present at low ratios?

    <p>Low levels of ADP and AMP</p> Signup and view all the answers

    What happens to glycolysis when acetylCoA levels are high?

    <p>Glycolysis is inhibited while gluconeogenesis is not affected.</p> Signup and view all the answers

    How does fructose 2-6-bisphosphate influence the regulation of glycolysis and gluconeogenesis?

    <p>It stimulates phosphofructokinase and inhibits fructose 1-6-bisphosphate phosphatase.</p> Signup and view all the answers

    What does a high energy charge indicate about a cell's metabolic state?

    <p>There are sufficient high-energy phosphates available.</p> Signup and view all the answers

    Which statement about the energy charge formula is correct?

    <p>The energy charge determines the balance of all phosphorylated adenylate compounds.</p> Signup and view all the answers

    In the context of allosteric regulation, what is a direct effect of low AMP levels?

    <p>Activation of glycolysis.</p> Signup and view all the answers

    What is the primary purpose of the gluconeogenesis pathway?

    <p>Convert pyruvate or lactate back to glucose.</p> Signup and view all the answers

    What is indicated by high levels of citrate in a metabolic pathway?

    <p>Signal that the TCA cycle does not require more acetylCoA from glycolysis.</p> Signup and view all the answers

    In glycolysis, how many ATP molecules are utilized during the first phase of the pathway?

    <p>Two ATP molecules.</p> Signup and view all the answers

    Which metabolic pathway yields pyruvate as a direct product?

    <p>Glycolysis.</p> Signup and view all the answers

    What is the end product of glycolysis under aerobic conditions?

    <p>Pyruvate.</p> Signup and view all the answers

    How many NADH molecules are produced during the glycolysis pathway from one glucose molecule?

    <p>2</p> Signup and view all the answers

    How does gluconeogenesis differ significantly from glycolysis?

    <p>Gluconeogenesis requires the input of energy, while glycolysis releases energy.</p> Signup and view all the answers

    What is the initial ATP cost incurred during the first half of glycolysis?

    <p>2 ATP</p> Signup and view all the answers

    Which two products are generated from glucose during the glycolysis pathway?

    <p>Pyruvate and ATP.</p> Signup and view all the answers

    Which compound is formed as an intermediate during the conversion of glucose in glycolysis?

    <p>Dihydroxyacetone phosphate</p> Signup and view all the answers

    In the second part of glycolysis, which specific reaction introduces additional phosphate groups?

    <p>Oxidation of glyceraldehyde 3-phosphate to 1-3-bisphosphoglycerate</p> Signup and view all the answers

    Which enzyme complex is responsible for converting pyruvate into acetyl-CoA?

    <p>Pyruvate dehydrogenase complex.</p> Signup and view all the answers

    What is the ultimate product of glycolysis when one glucose molecule is completely metabolized?

    <p>Two pyruvates, two ATPs, and two NADHs</p> Signup and view all the answers

    What happens to the pyruvate produced during glycolysis under anaerobic conditions?

    <p>It is converted to lactate.</p> Signup and view all the answers

    Which step during glycolysis involves the transfer of phosphate to ADP?

    <p>Phosphorylation by kinase enzymes</p> Signup and view all the answers

    What happens to the two molecules produced during the cleavage of the six-carbon glucose compound?

    <p>They continue through glycolysis as three-carbon intermediates</p> Signup and view all the answers

    How are ATP molecules generated in glycolysis after the investment phase?

    <p>Via substrate-level phosphorylation</p> Signup and view all the answers

    Which step in glycolysis is not considered essentially irreversible?

    <p>Conversion of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate</p> Signup and view all the answers

    What must be true about the overall reaction path of gluconeogenesis?

    <p>It requires additional ATP equivalents</p> Signup and view all the answers

    Which enzyme type is primarily substituted in gluconeogenesis to bypass the irreversible reactions of glycolysis?

    <p>Phosphatases</p> Signup and view all the answers

    During which physiological state does gluconeogenesis primarily occur?

    <p>During recovery from exercise</p> Signup and view all the answers

    Why is it necessary for every reaction in glycolysis to have a slightly negative ΔG?

    <p>To maintain a favorable equilibrium toward product formation</p> Signup and view all the answers

    What is the effect of gluconeogenesis on ATP in comparison to glycolysis?

    <p>It requires a net of six ATP equivalents</p> Signup and view all the answers

    What occurs during the Cori Cycle following intense exercise?

    <p>Glucose is formed from lactate primarily in the liver</p> Signup and view all the answers

    How do the essentially irreversible reactions of glycolysis impact gluconeogenesis?

    <p>They must be replaced by different reactions</p> Signup and view all the answers

    How many ATP molecules are produced directly as a result of glycolysis?

    <p>2</p> Signup and view all the answers

    Which intermediate compound is produced before the formation of 3-phosphoglycerate in glycolysis?

    <p>1,3-bisphosphoglycerate</p> Signup and view all the answers

    What energetic property is associated with the phosphorylation of hexoses like glucose?

    <p>Energy requirement of 3-5 kcal/mol</p> Signup and view all the answers

    Under anaerobic conditions, what product is formed from pyruvate?

    <p>Lactate</p> Signup and view all the answers

    What is the energy change associated with the hydrolysis of ATP?

    <p>7.3 kcal/mol</p> Signup and view all the answers

    What represents the potential ATP yield from the oxidation of NADH produced during glycolysis?

    <p>4 ATP molecules</p> Signup and view all the answers

    What is the fate of two pyruvate molecules generated from glycolysis under aerobic conditions?

    <p>They are converted to acetyl-CoA</p> Signup and view all the answers

    What defines the high phosphate hydrolysis potential of intermediates like bis-phosphoglycerate?

    <p>Their ability to donate a phosphate group easily</p> Signup and view all the answers

    What is produced from the carboxylation of acetyl-CoA during fatty acid biosynthesis?

    <p>Oxaloacetate</p> Signup and view all the answers

    Which enzyme catalyzes the conversion of oxaloacetate to phosphoenolpyruvate in gluconeogenesis?

    <p>Phosphoenolpyruvate carboxykinase</p> Signup and view all the answers

    How many ATP equivalents are required to convert pyruvate to phosphoenolpyruvate?

    <p>Two</p> Signup and view all the answers

    What is the main function of the carboxylation reaction in gluconeogenesis?

    <p>To energize the formation of phosphoenolpyruvate</p> Signup and view all the answers

    Which step of gluconeogenesis bypasses the phosphofructokinase reaction?

    <p>Conversion of fructose 1,6-bisphosphate to fructose 6-phosphate</p> Signup and view all the answers

    What is the resulting free energy change for the reaction catalyzed by the phosphatase in gluconeogenesis?

    <p>Very favorable negative ΔG</p> Signup and view all the answers

    What is the first step in integrating fructose into glycolysis?

    <p>Phosphorylation of fructose</p> Signup and view all the answers

    Which energy source is utilized by phosphoenolpyruvate carboxykinase?

    <p>GTP</p> Signup and view all the answers

    What is a characteristic of the carboxylation followed by decarboxylation strategy?

    <p>It provides extra energy in biosynthesis</p> Signup and view all the answers

    What is the product of the reaction catalyzed by galactose kinase?

    <p>Galactose 1-phosphate</p> Signup and view all the answers

    Which enzyme is involved in the conversion of glucose 1-phosphate to glucose 6-phosphate?

    <p>Phosphoglucomutase</p> Signup and view all the answers

    Which compound is released when UDP-glucose exchanges with galactose 1-phosphate?

    <p>Glucose 1-phosphate</p> Signup and view all the answers

    What role do nucleotide sugars like UDP-glucose play in metabolic pathways?

    <p>They help couple unfavorable reactions with ATP energy.</p> Signup and view all the answers

    How does galactose enter glycolysis?

    <p>Following phosphorylation and several reaction steps</p> Signup and view all the answers

    Which product results from the cleavage of lactose by lactase?

    <p>Galactose and glucose</p> Signup and view all the answers

    What is a key challenge in the conversion of galactose 1-phosphate to glucose 1-phosphate?

    <p>It involves a transfer reaction with nucleotide sugars.</p> Signup and view all the answers

    What additional product is formed when glyceraldehyde 3-phosphate is converted into 1,3-bisphosphoglycerate?

    <p>NADH</p> Signup and view all the answers

    What role does NAD+ play during the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

    <p>It serves as an oxidant in the oxidation-reduction reaction.</p> Signup and view all the answers

    What is the significance of the high negative ΔG of hydrolysis for 1,3-bisphosphoglycerate?

    <p>It favors the forward reaction for ATP production.</p> Signup and view all the answers

    What process utilizes NADH generated during glycolysis?

    <p>Oxidative phosphorylation</p> Signup and view all the answers

    How many molecules of NADH are produced from the conversion of two glyceraldehyde 3-phosphate molecules?

    <p>Two</p> Signup and view all the answers

    What type of reaction takes place concurrently with the phosphorylation of glyceraldehyde 3-phosphate?

    <p>Oxidation-reduction reaction</p> Signup and view all the answers

    What is produced as a direct consequence of the oxidation of the aldehyde group at C-1 during glycolysis?

    <p>Carboxylic acid</p> Signup and view all the answers

    What is the end product of the pathway in which glyceraldehyde 3-phosphate participates?

    <p>Pyruvate</p> Signup and view all the answers

    What process initiates the Cori Cycle during exercise?

    <p>Anaerobic glycolysis</p> Signup and view all the answers

    What is the next step for lactate once it is released from the muscle?

    <p>Transported to the liver</p> Signup and view all the answers

    Which two enzymes bypass pyruvate kinase in gluconeogenesis?

    <p>Pyruvate carboxylase and phosphoenolpyruvate carboxykinase</p> Signup and view all the answers

    What is the primary use of pyruvate after it is converted in the liver?

    <p>Converted to glucose</p> Signup and view all the answers

    What is the role of phosphatase enzymes in gluconeogenesis?

    <p>They hydrolyze phosphate groups from substrates</p> Signup and view all the answers

    Which cofactor is used by pyruvate carboxylase in the conversion of pyruvate?

    <p>Biotin</p> Signup and view all the answers

    Which pathway follows the conversion of pyruvate to oxaloacetate in gluconeogenesis?

    <p>Conversion to phosphoenolpyruvate</p> Signup and view all the answers

    What is a significant feature of the liver regarding its function in glucose metabolism?

    <p>It releases a significant portion of glucose into the blood</p> Signup and view all the answers

    What does phosphoglycerate kinase primarily catalyze in glycolysis?

    <p>Transfer of a phosphoryl group from 1,3-bisphosphoglycerate to ADP</p> Signup and view all the answers

    What is the definition of substrate level phosphorylation?

    <p>Direct transfer of a phosphate group from an organic molecule to ADP</p> Signup and view all the answers

    What is produced as a result of the reaction catalyzed by enolase?

    <p>Phosphoenolpyruvate (PEP)</p> Signup and view all the answers

    Which statement is true about phosphoenolpyruvate (PEP)?

    <p>It has the highest negative ΔG value of any compound in glycolysis.</p> Signup and view all the answers

    Which enzyme catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate?

    <p>Phosphoglyceratemutase</p> Signup and view all the answers

    What is the purpose of the phosphoglycerate kinase reaction in the glycolytic pathway?

    <p>To convert ADP to ATP without using inorganic phosphate</p> Signup and view all the answers

    Which product results from the final reaction catalyzed by pyruvate kinase in glycolysis?

    <p>Pyruvate</p> Signup and view all the answers

    What distinguishes oxidative phosphorylation from substrate level phosphorylation?

    <p>It utilizes a proton gradient driven by high energy electron transport.</p> Signup and view all the answers

    Study Notes

    Anaerobic Glycolysis

    • Net ATP gain from anaerobic glycolysis is 2 ATP
    • Pyruvate kinase reaction produces 2 ATP molecules per glucose molecule
    • NADH produced under anaerobic conditions is used to reduce pyruvate to lactate
    • Hexokinase reaction consumes 1 ATP during the investment phase
    • Pyruvate's fate under aerobic conditions is conversion to acetyl-CoA, entering the Krebs cycle
    • Lactose is the primary sugar in mammalian milk

    Glycolysis Phases

    • Glycolysis during rest or low-intensity exercise occurs primarily in the investment phase.
    • Fructose requires 1 ATP to be integrated into glycolysis.
    • During intense exercise with limited oxygen, pyruvate is converted to lactate.

    Galactose Metabolism

    • Initial reaction when galactose enters glycolysis involves phosphorylation by galactokinase to form galactose 1-phosphate.
    • The conversion of galactose 1-phosphate to glucose 1-phosphate forms a product called glucose 1-phosphate.

    Aerobic Glycolysis & NADH

    • Two extra ATPs can be formed from NADH generated in aerobic glycolysis
    • Nucleotide sugars play critical roles in energy storage, biosynthesis, and cell signaling.
    • UDP-glucose is formed from the exchange of galactose 1-phosphate and glucose 1-phosphate.
    • Lactase cleaves lactose into glucose and galactose.
    • Glucose 1-phosphate is converted to glucose 6-phosphate to enter glycolysis.
    • Each reaction in a pathway must have a negative free energy change to proceed forward.

    Hexokinase & Glycolysis Regulation

    • Hexokinase plays a role in the initial step of glycolysis by phosphorylating glucose.
    • Phosphorylation of glucose prevents it from leaving the cell.
    • Km value for hexokinase regarding glucose is low, indicating high affinity for glucose.
    • Reactions with positive free energy changes are considered incorrect because they require additional energy input.
    • Hexokinase reaction's main chemical transformation is the addition of a phosphate group to glucose.
    • ATP in the hexokinase reaction is hydrolyzed to release energy and phosphorylate glucose.
    • Glucokinase differs from hexokinase due to higher Km for glucose and its presence in liver and pancreatic beta cells.

    Gluconeogenesis & Cori Cycle

    • Cori Cycle is initiated by muscle lactate buildup during exercise.
    • The initial step in converting lactate to glucose is lactate conversion to pyruvate in the liver.
    • Pyruvate carboxylase and phosphoenolpyruvate carboxykinase bypass pyruvate kinase in gluconeogenesis.
    • Phosphatase enzymes remove phosphate groups during gluconeogenesis reactions.
    • Liver plays a crucial role in glucose regulation by converting lactate to glucose during the Cori cycle.
    • The process after pyruvate conversion to oxaloacetate in gluconeogenesis is conversion to phosphoenolpyruvate.

    ATP Equivalents & Liver

    • The reversal of pyruvate kinase requires 2 ATP equivalents.
    • The liver has a crucial role in glucose homeostasis.
    • UDP-galactose 4-epimerase converts UDP-galactose to UDP-glucose, participating in galactose metabolism.
    • The presence of a ketone intermediate in the UDP-galactose 4-epimerase reaction indicates an isomerization mechanism.

    Free Energy & Gluconeogenesis

    • A biological reaction requires negative free energy change to proceed forward.
    • Gluconeogenesis is the reverse process of glycolysis, converting pyruvate to glucose.
    • When exercise stops, lactate produced during vigorous exercise is converted to glucose in the liver through gluconeogenesis.

    ATP Yield & Glycolysis Regulation

    • Anaerobic glycolysis yields a net gain of 2 ATP molecules per glucose molecule.
    • Standard free energies of glycolysis reactions generally have a negative value, indicating spontaneity.
    • UDP-galactose 4-epimerase uses a Ping-Pong mechanism.
    • 2 ATP equivalents are consumed during the initial stages of glycolysis.
    • Net production of NADH is 2 molecules per glucose during the entire glycolysis process.

    Specific Steps & Enzymes

    • Glyceraldehyde 3-phosphate is converted into 1,3-bisphosphoglycerate during the glyceraldehyde 3-phosphate dehydrogenase step.
    • Glucose molecule is split into two triose phosphate molecules during glycolysis.
    • Triose phosphate isomerase catalyzes the interconversion of dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
    • 2 pyruvate molecules are generated from one glucose molecule through glycolysis.
    • Glyceraldehyde 3-phosphate dehydrogenase is crucial for maximizing energy production during glycolysis.
    • Aerobic glycolysis yields 2 pyruvate, 2 NADH, and 2 ATP from one glucose molecule.
    • Hexokinase bypass is necessary in gluconeogenesis because it is irreversible.
    • Gluconeogenesis consumes 6 ATP equivalents more than glycolysis.
    • Regulation of phosphofructokinase is the primary mechanism preventing simultaneous glycolysis and gluconeogenesis.
    • Bypass reactions at phosphofructokinase and pyruvate kinase have the most stringent regulation.
    • Simultaneous function of glycolysis and gluconeogenesis results in a wasteful futile cycle.

    Glucose Interconversion & Regulation

    • Hexokinase or glucokinase catalyzes the interconversion of glucose and glucose 6-phosphate.
    • Regulation of glycolysis and gluconeogenesis is determined by energy status, hormonal signals, and substrate availability.
    • During gluconeogenesis, bypass reactions are employed to overcome unfavorable reactions such as hexokinase.

    Pyruvate Reduction & Anaerobic Fermentation

    • Pyruvate reduction to lactate is necessary during anaerobic conditions to regenerate NAD+ for glycolysis.
    • The initial step in pyruvate conversion to ethanol is pyruvate decarboxylation by pyruvate decarboxylase.
    • Lactate dehydrogenase catalyzes the reduction of pyruvate to lactate.
    • NADH accumulation inhibits the glycolysis pathway under anaerobic conditions.
    • Anaerobic fermentation of glucose to lactate yields a net of 2 ATP molecules.
    • Lactate produced in the muscles is transported to the liver for gluconeogenesis after exercise.
    • NADH plays a role in regeneration of NAD+ for glycolysis during anaerobic fermentation.
    • Pyruvate accumulation when oxygen is limiting inhibits glycolysis.
    • UDP-galactose 4-epimerase uses an isomerization mechanism to convert UDP-galactose to UDP-glucose.
    • The net free energies of reactions in glycolysis are negative, indicating spontaneity.

    Lactate & Beyond

    • Lactic acid formation during vigorous exercise leads to muscle fatigue.
    • The presence of a ketone intermediate in the UDP-galactose 4-epimerase reaction suggests a Ping-Pong mechanism.
    • Standard free energy changes can be positive due to non-standard conditions in the cell.
    • Lactate produced during exercise is used for gluconeogenesis in the liver when energy needs are met.
    • Low activation energy indicates a fast reaction for the UDP-galactose 4-epimerase mechanism.
    • Glycolysis and gluconeogenesis are interconnected pathways regulated by feedback mechanisms.

    Galactose Metabolism & Beyond

    • Galactose kinase phosphorylates galactose to initiate its entry into glycolysis.
    • UDP-glucose acts as a donor of glucose in the conversion of galactose 1-phosphate to glucose 1-phosphate.
    • Nucleotide sugar derivatives are involved in energy storage, biosynthesis, and cell signaling.
    • The reaction converting galactose 1-phosphate to glucose 1-phosphate is considered baroque due to its multistep nature.
    • Glucose 6-phosphate enters the pentose phosphate pathway after its formation from galactose.
    • The reaction exchanging galactose 1-phosphate with glucose 1-phosphate is reversible and uses UDP-glucose as an intermediary.
    • Fructose requires 1 ATP investment to enter glycolysis.
    • UDP-galactose is converted to UDP-glucose during the reaction converting galactose 1-phosphate to glucose 1-phosphate.

    Gluconeogenesis: Energy & Reactions

    • Biotin plays a role in carboxylation reactions by transferring carbon dioxide.
    • Phosphoenolpyruvate is produced from the conversion of oxaloacetate in gluconeogenesis.
    • Phosphoenolpyruvate carboxykinase utilizes GTP as an energy source in the conversion of oxaloacetate to phosphoenolpyruvate.
    • Carboxylation followed by decarboxylation in fatty acid biosynthesis is energetically neutral.
    • The conversion of pyruvate to phosphoenolpyruvate requires 2 ATP equivalents.
    • Phosphatase enzymes remove phosphate groups during gluconeogenesis.
    • Negative ΔG associated with phosphofructokinase indicates its highly favorable reaction.
    • The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is driven by hydrolysis of the phosphate group.

    Glycolysis: Summary & Regulation

    • Anaerobic glycolysis yields a net of 2 ATP molecules per glucose molecule.
    • Aerobic glycolysis produces 2 NADH molecules per glucose molecule.
    • Pyruvate under aerobic conditions is converted to acetyl-CoA for the Krebs cycle.
    • ATP is required for the phosphorylation step catalyzed by phosphofructokinase.
    • Aerobic and anaerobic glycolysis diverge after the formation of pyruvate.
    • The low ATP yield during anaerobic glycolysis is due to limited NAD+ regeneration.
    • The two ATPs produced in glycolysis are primarily generated in the substrate-level phosphorylation reactions of glyceraldehyde 3-phosphate dehydrogenase and pyruvate kinase.
    • Oxidation of acetyl-CoA is limited during high-intensity exercise due to limited oxygen availability.
    • The primary product of glycolysis under aerobic conditions is pyruvate.
    • ATP is utilized in the investment phase of glycolysis.
    • Glycolysis is a primary catabolic pathway for glucose metabolism in humans.
    • Pyruvate produced during glycolysis is converted to acetyl-CoA in the presence of oxygen.

    Glycolysis and Gluconeogenesis

    • The monosaccharide glucose is one of the most common metabolic intermediates.
    • Glycolysis is the conversion of glucose to pyruvate or lactate.
    • Gluconeogenesis is the reverse of glycolysis, converting lactate or pyruvate back to glucose.
    • These are crucial pathways for human metabolism.

    Glycolysis Pathway Summary

    • Glucose is a high-energy fuel source because of its reduced carbon content.
    • Glycolysis oxidizes glucose to carbon dioxide.
    • Phase 1: one glucose molecule is converted into two glyceraldehyde-3-phosphate molecules. This consumes two ATP molecules.
    • Phase 2: two glyceraldehyde-3-phosphate molecules are converted into two pyruvate molecules. This generates four ATP molecules.

    Key Glycolysis Intermediates and Products

    • Glucose is a six-carbon hexose.
    • Pyruvate is a three-carbon triose.
    • Net Production: Two pyruvate molecules, two ATP molecules, and two NADH molecules are produced from one glucose molecule in aerobic glycolysis.

    Glycolysis: Regulation

    • The bypass steps are the key points for regulation because they have distinct enzymes operating in each direction.
    • This allows for separate regulation of glycolysis and gluconeogenesis.
    • Allosteric control: Metabolite binding to target enzymes can activate or inhibit enzyme activity.
    • High ATP/ADP and AMP ratios activate glycolysis and inhibit gluconeogenesis, as the cell has high energy levels.
    • High acetylCoA and citrate levels inhibit glycolysis and stimulate gluconeogenesis, indicating a surplus of acetylCoA and reduced need for glycolysis.

    Gluconeogenesis Summary

    • Synthesizes glucose from pyruvate or lactate.
    • Occurs during recovery from physical activity.
    • Utilizes many of the same enzymes as glycolysis (reversible ones).
    • Bypasses the irreversible steps of glycolysis through different enzymes.
    • Uses a net of six ATP equivalents.
    • When gluconeogenesis is in progress, all reactions and the overall pathway have a negative ΔG, driving glucose synthesis.

    The Cori Cycle

    • Glucose is converted to lactate during intense exercise.
    • During recovery, lactate is converted back to glucose.

    Glycolysis and Gluconeogenesis

    • Oxaloacetate is a product of the carboxylation of acetyl CoA in fatty acid biosynthesis.
    • Oxaloacetate can be used as a source of energy for generating ATP in the TCA cycle and can also be converted to Phosphoenolpyruvate (PEP).
    • Phosphoenolpyruvate carboxykinase catalyzes the conversion of Oxaloacetate to PEP.
    • Phosphoenolpyruvate carboxykinase uses GTP instead of ATP, but it is a thermodynamically equivalent source of energy.
    • PEP formation in the reaction is energized during GTP cleavage and by the decarboxylation of oxaloacetate.
    • Decarboxylation reactions are energetically favorable.
    • The conversion of pyruvate to PEP requires 2 ATP equivalents in gluconeogenesis, while the conversion of PEP to pyruvate yields only 1 ATP in glycolysis.
    • Fructose 1,6-bisphosphatase bypasses phosphofructokinase through an exchange of a phosphatase for a kinase in gluconeogenesis.
    • Phosphatase reactions generally release inorganic phosphate which makes reactions thermodynamically favorable.
    • Glyceraldehyde 3-phosphate dehydrogenase catalyzes both phosphorylation and oxidation of glyceraldehyde 3-phosphate.
    • Glyceraldehyde 3-phosphate has one phosphate group, and the product 1,3-bisphosphoglycerate has two phosphate groups.
    • 1,3-bisphosphoglycerate has a high negative ΔG of hydrolysis.
    • Glyceraldehyde 3-phosphate dehydrogenase uses NAD+ as the oxidant and oxidizes glyceraldehyde 3-phosphate to an acid and reduces NAD+ to NADH.
    • NADH generated from glycolysis is used in oxidative phosphorylation to generate ATP by creating a proton gradient across the mitochondrial membrane.
    • Phosphoglycerate kinase catalyzes the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to yield ATP.
    • Phosphoglycerate kinase is an example of substrate-level phosphorylation where a phosphate group is transferred directly from an organic molecule to ADP.
    • Oxidative phosphorylation uses the downhill transport of electrons to create a proton gradient which then drives the synthesis of ATP.
    • Phosphoglycerate kinase converts 1,3-bisphosphoglycerate to 3-phosphoglycerate.
    • Phosphoglycerate mutase converts 3-phosphoglycerate to 2-phosphoglycerate.
    • Enolase removes a molecule of water from 2-phosphoglycerate to yield phosphoenolpyruvate (PEP).
    • PEP has the highest negative ΔG of hydrolysis among any compound.
    • Pyruvate kinase catalyzes the transfer of a phosphate group from PEP to ADP to yield ATP.
    • Pyruvate kinase is another example of substrate-level phosphorylation.
    • Fructose can enter glycolysis, requiring the same amount of energy as glucose (2 ATPs per fructose molecule).
    • Lactase hydrolyzes lactose into galactose and glucose.
    • Galactose can enter glycolysis through a convoluted pathway that starts by converting galactose into galactose 1-phosphate then glucose 1-phosphate.
    • Galactose 1-phosphate is phosphorylated by galactose kinase to galactose 1-phosphate.
    • Galactose 1-phosphate uridylyltransferase catalyzes the conversion of galactose 1-phosphate to glucose 1-phosphate through an exchange reaction with UDP-glucose.
    • Phosphoglucomutase converts glucose 1-phosphate to glucose 6-phosphate.
    • UDP-glucose is a nucleotide sugar derivative, and the formation of a nucleotide derivative requires ATP.
    • Nucleotide sugars play an important role in sugar and lipid metabolism.
    • Cori Cycle is initiated by anaerobic glycolysis during exercise.
    • Lactate is released from muscle cells and transported to the liver.
    • Lactate is converted to pyruvate in the liver.
    • Pyruvate can be oxidized in the TCA cycle or be used to make glucose through gluconeogenesis.
    • Gluconeogenesis bypasses pyruvate kinase using pyruvate carboxylase and PEP carboxykinase, both of which require an ATP equivalent.
    • Gluconeogenesis bypasses phosphofructokinase and hexokinase with their respective phosphatase enzymes.
    • Kinase reactions require ATP and are thermodynamically unfavorable.
    • Phosphatase reactions release inorganic phosphate and are thermodynamically favorable.
    • Pyruvate carboxylase converts pyruvate to oxaloacetate using biotin as a cofactor.

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