Carbohydrate Metabolism Overview
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Questions and Answers

What is the definition of metabolism?

Metabolism is the sum total of the chemical reactions of biomolecules in an organism.

What are the two main categories of metabolic reactions?

  • Phosphorylation and Dephosphorylation
  • Catabolism and Anabolism (correct)
  • Glycolysis and Gluconeogenesis
  • Oxidation and Reduction

    • What is a metabolic pathway?

    A metabolic pathway is a sequence of reactions where the product of one reaction becomes the substrate for the next reaction.

    What are metabolites?

    <p>Metabolites are intermediates in metabolic pathways.</p> Signup and view all the answers

    Metabolic pathways can only proceed in a linear fashion.

    <p>False (B)</p> Signup and view all the answers

    Which of the following is NOT a coenzyme involved in metabolism?

    <p>ATP (A)</p> Signup and view all the answers

    What is the role of NAD+ in metabolism?

    <p>NAD+ acts as a biological oxidizing agent.</p> Signup and view all the answers

    What is the role of coenzyme A (CoA) in metabolism?

    <p>Coenzyme A activates metabolites by forming thioester bonds, making them more reactive.</p> Signup and view all the answers

    ATP is a low-energy compound.

    <p>False (B)</p> Signup and view all the answers

    What is phosphorylation?

    <p>Phosphorylation is the addition of a phosphoryl (PO32-) group, also known as inorganic phosphate, to a molecule.</p> Signup and view all the answers

    Hydrolysis of ATP to ADP releases energy.

    <p>True (A)</p> Signup and view all the answers

    What is substrate-level phosphorylation?

    <p>Substrate-level phosphorylation is the formation of ATP by direct transfer of a phosphoryl group from a high-energy intermediate to ADP.</p> Signup and view all the answers

    What is oxidative phosphorylation?

    <p>Oxidative phosphorylation is the process of ATP production that uses the energy released from the electron transport chain to drive the phosphorylation of ADP.</p> Signup and view all the answers

    What is the main purpose of glycolysis?

    <p>Glycolysis is the first stage of glucose metabolism, breaking down glucose into pyruvate.</p> Signup and view all the answers

    Glycolysis is an aerobic process.

    <p>False (B)</p> Signup and view all the answers

    What is the immediate product of glycolysis?

    <p>Pyruvate (B)</p> Signup and view all the answers

    Glycolysis yields a net gain of 2 ATP molecules per glucose molecule.

    <p>True (A)</p> Signup and view all the answers

    What happens to pyruvate in aerobic conditions?

    <p>In aerobic conditions, pyruvate is further oxidized in the citric acid cycle, producing a significant amount of ATP.</p> Signup and view all the answers

    Hexokinase is the enzyme responsible for converting glucose to glucose-6-phosphate in glycolysis.

    <p>True (A)</p> Signup and view all the answers

    The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate is the rate-limiting step in glycolysis.

    <p>True (A)</p> Signup and view all the answers

    What is the role of glyceraldehyde-3-phosphate dehydrogenase in glycolysis?

    <p>Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, a key step in energy production.</p> Signup and view all the answers

    What is the role of phosphoglycerate kinase in glycolysis?

    <p>Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP, generating ATP.</p> Signup and view all the answers

    What is the role of pyruvate kinase in glycolysis?

    <p>Pyruvate kinase catalyzes the final step of glycolysis, transferring a phosphate group from phosphoenolpyruvate to ADP, producing ATP and pyruvate.</p> Signup and view all the answers

    What is gluconeogenesis?

    <p>Gluconeogenesis is the biosynthesis of new glucose from non-carbohydrate precursors.</p> Signup and view all the answers

    Gluconeogenesis is the reverse of glycolysis.

    <p>False (B)</p> Signup and view all the answers

    Where does gluconeogenesis primarily take place?

    <p>Gluconeogenesis primarily occurs in the liver and kidneys.</p> Signup and view all the answers

    Gluconeogenesis is an endergonic process.

    <p>True (A)</p> Signup and view all the answers

    What is the Cori cycle?

    <p>The Cori cycle is a metabolic pathway where lactate produced in muscles during anaerobic glycolysis is transported to the liver, where it is converted back to glucose, which then can be used by the muscles.</p> Signup and view all the answers

    The citric acid cycle is a linear pathway.

    <p>False (B)</p> Signup and view all the answers

    The citric acid cycle is amphibolic, meaning it participates in both anabolism and catabolism.

    <p>True (A)</p> Signup and view all the answers

    What is the role of the pyruvate dehydrogenase complex in the citric acid cycle?

    <p>The pyruvate dehydrogenase complex catalyzes the conversion of pyruvate to acetyl-CoA, the two-carbon unit that enters the citric acid cycle.</p> Signup and view all the answers

    What is the role of citrate synthase in the citric acid cycle?

    <p>Citrate synthase combines acetyl-CoA with oxaloacetate to form citrate, the first step in the citric acid cycle.</p> Signup and view all the answers

    What is the role of aconitase in the citric acid cycle?

    <p>Aconitase catalyzes the isomerization of citrate to isocitrate, a key step in the citric acid cycle.</p> Signup and view all the answers

    What is the role of isocitrate dehydrogenase in the citric acid cycle?

    <p>Isocitrate dehydrogenase catalyzes the oxidation of isocitrate to α-ketoglutarate, producing NADH and CO2.</p> Signup and view all the answers

    What is the role of α-ketoglutarate dehydrogenase in the citric acid cycle?

    <p>α-ketoglutarate dehydrogenase catalyzes the oxidation of α-ketoglutarate to succinyl-CoA, releasing CO2 and producing NADH.</p> Signup and view all the answers

    What is the role of succinyl-CoA synthetase in the citric acid cycle?

    <p>Succinyl-CoA synthetase converts succinyl-CoA to succinate, generating GTP (which is equivalent to ATP).</p> Signup and view all the answers

    What is the role of fumarase in the citric acid cycle?

    <p>Fumarase catalyzes the hydration of fumarate to L-malate, adding water to the molecule.</p> Signup and view all the answers

    What is the role of malate dehydrogenase in the citric acid cycle?

    <p>Malate dehydrogenase catalyzes the oxidation of L-malate to oxaloacetate, regenerating the starting compound of the citric acid cycle.</p> Signup and view all the answers

    Study Notes

    Carbohydrate Metabolism

    • Metabolism is the sum of the biochemical reactions in an organism, including coordination, regulation, and energy needs.
    • It consists of two major parts: catabolism and anabolism.
    • Catabolism: the breakdown of larger molecules into smaller ones, releasing energy (oxidative process).
    • Anabolism: the synthesis of larger molecules from smaller ones, requiring energy (reductive process).
    • Metabolic pathways are sequences of reactions where the product of one reaction becomes the substrate for the next.
    • Linear, cyclic, branched (converging/diverging), and spiral pathways are different types of metabolic pathways.
    • Metabolites are intermediates in metabolic pathways.

    Terminology of Metabolism

    • Photosynthesis: 6 CO2 + 6 H2O → C6H12O6 + 6 O2 (anabolic)
    • Respiration: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O (catabolic)

    Role of Oxidation and Reduction in Metabolism

    • Oxidation-reduction (redox) reactions involve electron transfer.
    • Oxidation: loss of electrons (reducing agent).
    • Reduction: gain of electrons (oxidizing agent).

    Oxidation and Reduction in Metabolism (Example: Ethanol)

    • NAD+ + 2e- + H+ → NADH(reduced)
    • CH3CH2OH (ethanol) + NAD+ → CH3CHO (acetaldehyde) + NADH + H+
    • CH3CHO(acetaldhyde) + NADH + H+ → CH3CH2OH(ethanol) + NAD+

    Oxidation and Reduction in Metabolism (Example: Pyruvate)

    • NADH + H+ + pyruvate → lactate + NAD+

    Metabolic Pathways

    • Enzymes: groups of noncovalently associated enzymes that catalyze two or more sequential steps in a metabolic pathway.
    • Multienzymes (components of a metabolic pathway): coordinated groups of enzymes that carry out these functions.
    • Coenzymes: organic molecules that assist enzymes in their function.
    • ATP (adenosine triphosphate): produced or used in metabolic pathways for energy.

    Metabolism Regulation

    • Feedback inhibition: the product of a pathway inhibits an earlier step in the pathway.
    • Feed-forward activation: a metabolite produced early in the pathway activates an enzyme further down the pathway.

    Coenzymes

    • NAD+/NADH: electron carriers involved in redox reactions.
    • NADP+/NADPH: electron carriers involved in biosynthesis, similar to NADH.
    • FAD/FADH2: electron carriers; accept one or two electrons at a time.
    • Coenzyme A (CoASH): activates metabolites.

    NAD+/NADH

    • Nicotinamide adenine dinucleotide (NAD+) is a coenzyme.
    • Acts as a biological oxidizing agent.
    • Consists of a nicotinamide portion.
    • NAD+ is a two-electron oxidizing agent that is reduced to NADH.

    NADP+/NADPH

    • Nicotinamide adenine dinucleotide phosphate (NADP+) is a coenzyme.
    • NADP+ acts as a biological oxidizing agent and is reduced to form NADPH, which is involved in reductive biosynthesis processes.
    • It differs from NAD+ by a phosphate group on its ribose.

    FAD/FADH2

    • Flavin adenine dinucleotide (FAD) is an important coenzyme, accepting one or two electrons at a time , involved in oxidation-reduction reactions.

    Coenzyme A

    • Coenzyme A (CoASH) is a coenzyme that acts as a carrier for acetyl and other acyl groups in metabolic pathways.
    • The thioester bond in acetyl-CoA is a high-energy bond; hydrolysis releases energy.

    ATP - High-Energy Compound

    • ATP is an essential high-energy bond-containing compound.
    • Phosphorylation of ADP to ATP requires energy input.
    • Hydrolysis of ATP to ADP releases energy.

    High-Energy Bonds in ATP

    • Phosphoanhydride bonds in ATP are high-energy bonds.
    • These bonds release or require convenient amounts of energy in reactions.
    • Couple reactions use energy released by one reaction (such as ATP hydrolysis) to provide energy for another reaction.

    Couple Reactions - Example

    • Energy release from ATP hydrolysis can drive other energy-requiring reactions.
    • Various examples of coupled reactions (energy-requiring and releasing reactions) are mentioned in the provided text in context with glucose.

    Breakdown of Glucose to Generate Energy (Respiration)

    • Two processes: anaerobic respiration and aerobic respiration.
    • Anaerobic respiration: glycolysis → fermentation (lactic acid or alcohol).
    • Aerobic respiration: glycolysis → oxidative decarboxylation → citric acid cycle → oxidative phosphorylation.

    Aerobic Respiration Stages

    • Oxidative decarboxylation of pyruvate.
    • Citric acid cycle(TCA cycle).
    • Oxidative phosphorylation/electron transport chain(ETC).

    Glycolysis

    • The first stage of glucose metabolism.
    • Converts 1 glucose molecule into 2 pyruvate molecules.
    • Involves 10 enzymatic steps.
    • Has two phases (energy investment and energy recovery).
    • Generates a net gain of 2 ATP molecules, 2 NADH+H+ molecules per glucose molecule.
    • In anaerobic conditions, pyruvate is converted into lactate(muscle cells) or ethanol (yeast/bacteria).

    Glycolysis- Detailed Stages

    • Glucose is phosphorylated—initiating the glycolysis pathway.
    • Glucose-phosphate is isomerized to fructose-6-phosphate
    • Fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate.
    • Fructose-1,6-bisphosphate is split into two 3-carbon fragments.
    • Dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate.
    • Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate, with an oxidation-reduction reaction involving NAD+ and NADH.
    • 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate, and ATP is produced.
    • 3-phosphoglycerate is converted to 2-phosphoglycerate.
    • 2-phosphoglycerate is dehydrated to phosphoenolpyruvate.
    • Phosphoenolpyruvate is converted to pyruvate, producing ATP.

    Fates of Pyruvate

    • Aerobic conditions: pyruvate enters the citric acid cycle.
    • Anaerobic conditions: pyruvate is converted to lactate(muscles) or ethanol (yeast and bacteria).

    Glycolysis Control Points

    • Glucose-6-phosphate.
    • Fructose-6-phosphate.
    • Fructose-1,6-bisphosphate.
    • Glyceraldehyde-3-phosphate.
    • 1,3-bisphosphoglycerate.
    • 3-phosphoglycerate.
    • 2-phosphoglycerate.
    • Phosphoenolpyruvate.
    • Pyruvate.

    ATP Production

    • ATP is produced by substrate-level phosphorylation during glycolysis (steps 7 and 10).
    • 1,3-bisphosphoglycerate and phosphoenolpyruvate are high-energy intermediates involved in substrate-level phosphorylation to generate ATP.
    • Oxidative phosphorylation is the process of ATP production in the electron transport chain.

    Anaerobic Metabolism of Pyruvate

    • Under anaerobic conditions, the most important pathway for regenerating NAD+ is the reduction of pyruvate to lactate by lactate dehydrogenase.
    • This occurs in muscle tissue under strenuous exercise when oxygen supply is limited.

    Alcoholic Fermentation

    • Decarboxylation of pyruvate to acetaldehyde occurs, followed by reduction to ethanol.
    • Pyruvate decarboxylase catalyzes decarboxylation, requiring Mg2+ and thiamine pyrophosphate (TPP).
    • Alcohol dehydrogenase catalyzes the conversion to ethanol.

    Gluconeogenesis

    • The process of synthesizing glucose from non-carbohydrate precursors.
    • It involves a different set of enzymes than those used in glycolysis, and some steps are irreversible, so it has to go through alternative steps that bypass those irreversible steps in glycolysis.
    • Includes 9 steps that occur mainly in liver and kidney.
    • Used to maintain blood glucose levels when glycogen stores are depleted.

    Gluconeogenesis - Different Steps

    • Conversion of pyruvate to Oxaloacetate, through pyruvate carboxylase enzyme.

    Controlling Glucose Metabolism

    • Glycolysis and gluconeogenesis are not simultaneously active.
    • Regulation of cellular activity of both pathways ensures enough ATP availability to the cell.
    • Cori cycle: cycling of glucose between muscle and liver via glycolysis and gluconeoesis, maintaining blood glucose levels and handling lactate from muscle under anerobic condition.

    The Citric Acid Cycle (TCA Cycle)

    • Circular pathway involving eight reactions.
    • Acetyl-CoA is needed to begin the cycle.
    • Eight enzymes are involved.
    • Generates 3 NADH, 1 FADH2, 2 CO2, and 1 GTP (equivalent to 1 ATP) per acetyl-CoA molecule.

    Citric Acid Cycle Steps

    • Formation of Citrate.
    • Isomerization to Isocitrate.
    • First oxidation reaction: Formation of α-Ketoglutarate and CO2
    • Second oxidation reaction: Formation of Succinyl-CoA and CO2
    • Formation of Succinate.
    • Formation of Fumarate: FAD-linked oxidation.
    • Formation of L-Malate
    • Regeneration of Oxaloacetate: Final oxidation step.

    Regulation of TCA Cycle

    • Various steps have control points where the reactions are regulated.

    Fluorocitrate

    • A potent poison that inhibits mitochondrial oxidative metabolism.
    • Blocks the Krebs cycle by inhibiting aconitase.

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    Chapter 3 Carbohydrate Metabolism PDF

    Description

    This quiz explores the fundamentals of carbohydrate metabolism, including metabolic pathways, catabolism, and anabolism. Understand key processes such as photosynthesis and respiration, as well as the importance of oxidation-reduction reactions in metabolism. Test your knowledge on these critical biochemical reactions.

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