Biochemistry Carbohydrates Metabolism 2
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Questions and Answers

What does the term 'amphibolic' refer to in the context of the TCA cycle?

  • It involves only catabolic reactions.
  • It is a cycle that only produces energy and CO2.
  • It describes the synthesis of glucose exclusively.
  • It involves anabolic and catabolic reactions in the same pathway. (correct)

Which of the following enzymes plays a regulatory role in the TCA cycle?

  • Amylase
  • Pepsin
  • Citrate synthase (correct)
  • Lactate dehydrogenase

Which amino acid is formed from oxaloacetate and is integral to nitrogen metabolism within the TCA cycle?

  • Aspartate (correct)
  • Serine
  • Alanine
  • Glutamate

What effect does high ATP concentration have on the TCA cycle?

<p>It inhibits the cycle at specific steps due to high ATP:ADP ratio. (D)</p> Signup and view all the answers

Which of the following is NOT a precursor needed for lipid metabolism through the TCA cycle?

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

Which of the following pathways directly feeds into the TCA cycle?

<p>Glycolysis (C), Lipid metabolism (D)</p> Signup and view all the answers

Where does the TCA cycle primarily take place within the cell?

<p>Mitochondrial matrix (C)</p> Signup and view all the answers

What is the main purpose of the TCA cycle?

<p>Oxidize acetyl-CoA and produce energy-rich molecules (A)</p> Signup and view all the answers

In the context of energy production, how much ATP is generated from one molecule of NADH?

<p>3 ATP (D)</p> Signup and view all the answers

Which coenzymes are reduced during the TCA cycle?

<p>NADH and FADH2 (C)</p> Signup and view all the answers

Which metabolic processes are interconnected with the TCA cycle?

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

Which of the following statements is FALSE regarding the TCA cycle?

<p>It is an anabolic process. (B)</p> Signup and view all the answers

What is produced at the end of one complete turn of the TCA cycle?

<p>Three NADH and one FADH2 (A)</p> Signup and view all the answers

Where do the reactions of the TCA cycle primarily occur?

<p>Mitochondria (C)</p> Signup and view all the answers

Which enzyme is responsible for converting pyruvate to Acetyl CoA?

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

What is the primary location for gluconeogenesis in the body?

<p>Liver and kidney (D)</p> Signup and view all the answers

Which substance is NOT a major precursor for gluconeogenesis?

<p>Fructose (C)</p> Signup and view all the answers

What function does pyruvate carboxylase serve in gluconeogenesis?

<p>Converts pyruvate to oxaloacetate (C)</p> Signup and view all the answers

Which of the following statements about gluconeogenesis is true?

<p>It is the reverse of glycolysis with alternate enzymes. (D)</p> Signup and view all the answers

Which enzyme functions to regulate gluconeogenesis?

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

What is a consequence of failure in gluconeogenesis?

<p>Potential fatal consequences (A)</p> Signup and view all the answers

What is the primary function of the mitochondrial inner membrane?

<p>Impedes the movement of almost all molecules (A)</p> Signup and view all the answers

Which specialized phospholipid is abundant in the mitochondrial inner membrane?

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

How many complexes are involved in the electron transport chain?

<p>4 (C)</p> Signup and view all the answers

What do NADH and FADH2 donate to the electron transport chain?

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

What is generated as a result of the electron transport chain's function?

<p>Hydrogen ion gradient (A)</p> Signup and view all the answers

What is the reaction that frequently occurs with water molecules in a solution?

<p>Splitting into hydroxyl and hydrogen ions (B)</p> Signup and view all the answers

What drives the ATP synthesis in the ATP synthase complex?

<p>Hydrogen ion gradient (D)</p> Signup and view all the answers

Which force is responsible for the return of hydrogen ions into the mitochondrial matrix?

<p>Proton motive force (D)</p> Signup and view all the answers

What happens to hydrogen ions as they travel through the electron transport chain?

<p>They are pumped out of the mitochondrial matrix (B)</p> Signup and view all the answers

What is formed when a hydrogen ion (H+) combines with a hydroxyl ion (OH-)?

<p>Water (H2O) (C)</p> Signup and view all the answers

What term refers to the potential energy stored in the hydrogen ion gradient?

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

Which component of the electron transport chain does NOT directly accept electrons from NADH?

<p>Complex II (D)</p> Signup and view all the answers

What does the high protein content of the inner membrane primarily facilitate?

<p>The functionality of the electron transport chain (A)</p> Signup and view all the answers

What voltage across the mitochondrial inner membrane results from the hydrogen ion gradient?

<p>Negative voltage (C)</p> Signup and view all the answers

What are cristae in the context of the mitochondrial inner membrane?

<p>Folds in the membrane (B)</p> Signup and view all the answers

Which substances are utilized in the synthesis of steroids and fatty acids within the TCA cycle?

<p>Acetyl-CoA and glycerol (D)</p> Signup and view all the answers

What is the result of the oxidation of acetyl-CoA in the TCA cycle?

<p>Release of energy, CO2, and water (D)</p> Signup and view all the answers

Which regulatory factors inhibit the TCA cycle when ATP levels are high?

<p>High concentrations of acetyl-CoA and NADH (C)</p> Signup and view all the answers

Which amino acid is formed from oxaloacetate through transamination and contributes to nitrogen metabolism?

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

Which of the following statements best describes the amphibolic nature of the TCA cycle?

<p>It integrates both anabolic and catabolic processes. (B)</p> Signup and view all the answers

What is the main purpose of the tricarboxylic acid (TCA) cycle?

<p>To oxidize acetyl-CoA for energy production (C)</p> Signup and view all the answers

Which molecule acts as a precursor in the biosynthesis of many compounds within the TCA cycle?

<p>Acetyl-CoA (A)</p> Signup and view all the answers

Which energy-rich molecules are produced during the TCA cycle?

<p>NADH and FADH2 (D)</p> Signup and view all the answers

In which cellular compartment does the TCA cycle primarily occur?

<p>Mitochondrial matrix (D)</p> Signup and view all the answers

How is acetyl-CoA formed from pyruvate?

<p>By the enzymatic action of pyruvate dehydrogenase (A)</p> Signup and view all the answers

What role does the electron transport chain play in relation to the TCA cycle?

<p>It reoxidizes NADH and FADH2 produced in the TCA cycle (D)</p> Signup and view all the answers

Which tissues have a significant capacity for the TCA cycle?

<p>Liver and brain tissue (B)</p> Signup and view all the answers

How many ATP equivalents are produced from one molecule of NADH during metabolism?

<p>3 ATP (A)</p> Signup and view all the answers

Where does gluconeogenesis primarily occur in the body?

<p>Liver (D)</p> Signup and view all the answers

What enzyme is responsible for converting pyruvate into oxaloacetate during gluconeogenesis?

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

Which of the following is a major precursor for gluconeogenesis?

<p>Lactate (C)</p> Signup and view all the answers

Which enzyme does NOT regulate gluconeogenesis?

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

What is a key function of gluconeogenesis?

<p>To provide glucose when carbohydrate is unavailable (B)</p> Signup and view all the answers

Which component of the electron transport chain receives electrons from both NADH and FADH2?

<p>Coenzyme Q (C)</p> Signup and view all the answers

Which of the following statements about citrate synthase is true?

<p>It catalyzes the formation of citrate from acetyl CoA and oxaloacetate. (C)</p> Signup and view all the answers

What is the primary function of the inner mitochondrial membrane?

<p>To prevent the entry of all ions and large molecules (A)</p> Signup and view all the answers

Which specialized phospholipid is particularly abundant in the mitochondrial inner membrane?

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

What is the composition of the mitochondrial inner membrane in terms of protein content?

<p>76% (C)</p> Signup and view all the answers

What generates the proton motive force within the mitochondria?

<p>The hydrogen ion concentration gradient and voltage (D)</p> Signup and view all the answers

Which of the following best describes what happens to the hydrogen ions (H+) during the electron transport chain process?

<p>They are pumped out of the matrix into the inter-membrane space (A)</p> Signup and view all the answers

What role do NADH and FADH2 play in the electron transport chain?

<p>They provide electrons for the process (C)</p> Signup and view all the answers

What is the result of a hydrogen ion recombining with a hydroxyl ion?

<p>Water (H2O) (B)</p> Signup and view all the answers

What function does ATP synthase serve in the mitochondria?

<p>It generates ATP by using the proton motive force (B)</p> Signup and view all the answers

Which complexes do electrons pass through in the electron transport chain?

<p>Complex I, II, III, IV (C)</p> Signup and view all the answers

What initiates the proton motive force in the mitochondria?

<p>Electron transport and hydrogen ion pumping (C)</p> Signup and view all the answers

Which of the following is NOT a function of the mitochondrial inner membrane?

<p>Storing excess glucose (D)</p> Signup and view all the answers

How does the electron transport chain contribute to ATP synthesis?

<p>By establishing a hydrogen ion gradient used for ATP synthesis (A)</p> Signup and view all the answers

What does the cristae in the inner mitochondrial membrane functionally contribute to?

<p>Enhancing the capacity for ATP production (A)</p> Signup and view all the answers

What key factor creates the voltage across the mitochondrial inner membrane?

<p>The concentration of hydrogen ions (D)</p> Signup and view all the answers

Flashcards

What is the 'amphibolic' role of the TCA cycle?

The TCA cycle is a metabolic pathway involved in both the breakdown of carbohydrates and lipids (catabolism), and the building of essential molecules like amino acids, lipids, and certain components of blood (anabolism).

What is catabolism in the context of the TCA cycle?

The TCA cycle breaks down acetyl-CoA, releasing energy in the form of ATP, CO2, and water. This energy is used to power cellular processes.

What is anabolism in the context of the TCA cycle?

The TCA cycle uses intermediates to create essential molecules like amino acids, fatty acids, and heme (for haemoglobin).

What enzymes regulate the TCA cycle?

Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase are key enzymes that regulate the TCA cycle by controlling the rate of its reactions.

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How does ATP level affect the TCA cycle?

When ATP levels are high, the TCA cycle slows down due to the inhibition of key enzymes like citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase. This ensures that energy production is balanced with cellular needs.

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What is the Citric Acid Cycle?

The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid cycle, is a metabolic pathway that takes place in the mitochondria of eukaryotic cells. It's a central hub for energy production, oxidizing acetyl-CoA derived from carbohydrates, fats, and proteins.

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What happens during the TCA cycle?

The TCA cycle is a crucial step in cellular respiration. Acetyl-CoA, produced from the breakdown of glucose, fatty acids, and some amino acids, enters the cycle. Through a series of reactions, it's oxidized, generating high-energy electron carriers (NADH and FADH2) and releasing carbon dioxide as a byproduct.

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What's the main product of the TCA cycle?

The TCA cycle is a cyclical pathway that generates high-energy electron carriers, NADH and FADH2. These carriers are then used in the electron transport chain to produce ATP, the cell's primary energy currency.

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Where does the TCA cycle occur?

The TCA cycle takes place in the mitochondrial matrix. This is the innermost compartment of the mitochondria, where enzymes involved in the cycle are located.

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What kind of process is the TCA cycle?

The TCA cycle is a catabolic pathway, meaning it involves the breakdown of molecules. It's involved in the degradation of acetyl residues, which are derived from various sources like carbohydrates, fats, and proteins.

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Can the TCA cycle be considered anabolic?

The TCA cycle can also be considered an anabolic pathway as its intermediates can be used to synthesize various compounds needed by the cell. These include amino acids, glucose, and heme.

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How much ATP is produced from 1 glucose molecule?

Each NADH molecule produced in the TCA cycle yields 3 ATP molecules through oxidative phosphorylation. Each FADH2 molecule produces 2 ATP molecules.

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What is the importance of the TCA cycle in cellular metabolism?

The TCA cycle is a key regulator of cellular metabolism. It plays a role in integrating the metabolism of carbohydrates, fats, and proteins. By its various metabolic intermediates, it also provides precursors for biosynthesis processes.

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Gluconeogenesis

The process of creating glucose from non-carbohydrate sources like lactate, pyruvate, amino acids, glycerol, and propionate.

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Gluconeogenesis Location

The liver and kidneys are the primary sites where gluconeogenesis occurs.

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Pyruvate to Oxaloacetate

Pyruvate carboxylase is a mitochondrial enzyme that converts pyruvate to oxaloacetate, a key step in gluconeogenesis.

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Glycolysis

The process of converting glucose to pyruvate, a central pathway for energy production.

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Citric Acid Cycle (TCA Cycle)

The citric acid cycle (TCA cycle) is a series of reactions that generate energy (ATP) from glucose. It takes place in the mitochondria of cells.

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Electron Transport Chain

The movement of electrons through a series of protein complexes in the mitochondria, leading to ATP production.

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Pyruvate Dehydrogenase

The enzyme that converts pyruvate to acetyl CoA, a key step in cellular respiration.

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TCA Cycle Regulation

A regulatory mechanism in the TCA cycle where specific enzymes control the rate of the cycle, preventing excessive energy production.

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What are the key features of the mitochondrial inner membrane?

The inner membrane of the mitochondria is highly impermeable to most molecules due to the absence of porins and the presence of cardiolipin, a specialized phospholipid. It is also densely packed with proteins, making up 76% of its composition, and is folded into numerous cristae.

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What is the electron transport chain (ETC) and what is its function?

The electron transport chain (ETC) is a series of protein complexes embedded in the inner mitochondrial membrane. It plays a vital role in converting the energy stored in NADH and FADH2 molecules into usable ATP energy.

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How does the electron transport chain generate a hydrogen ion gradient?

The four protein complexes (I-IV) of the ETC sequentially transfer electrons from NADH and FADH2. During this process, a crucial hydrogen ion gradient is established across the inner mitochondrial membrane.

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Where are the protons (H+) pumped by the electron transport chain?

The ETC complexes pump hydrogen ions (protons) from the mitochondrial matrix, the space inside the inner membrane, into the intermembrane space between the two mitochondrial membranes. This creates a higher concentration of hydrogen ions in the intermembrane space.

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What is the proton motive force and what creates it?

The proton motive force is the energy stored in the hydrogen ion gradient across the mitochondrial inner membrane. It arises from both the concentration difference of protons and the electrical potential difference across the membrane.

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How is ATP synthesized using the proton motive force?

ATP synthase, a large protein complex embedded in the inner membrane, harnesses the proton motive force to generate ATP. The flow of protons back into the matrix provides the energy for ATP synthase to attach a phosphate group to ADP, forming ATP.

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What is the role of NADH and FADH2 in the electron transport chain?

NADH and FADH2 are electron carriers that deliver high-energy electrons to the ETC. These electrons travel through the four complexes of the ETC, releasing energy along the way. The energy released is used to pump hydrogen ions across the membrane.

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What are the roles of Complex I and Complex II in the electron transport chain?

Complex I accepts electrons from NADH and pumps protons. Complex II receives electrons from FADH2 and does not directly pump protons. Both complexes contribute to the proton gradient.

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What are the roles of Complex III and Cytochrome c in the electron transport chain?

Complex III receives electrons from Coenzyme Q and pumps protons. Cytochrome c, a small mobile protein, carries the electrons from Complex III to Complex IV.

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What is the role of Complex IV in the electron transport chain?

Complex IV is the final electron acceptor in the ETC. It receives electrons from cytochrome c and uses them to reduce oxygen (O2) into water (H2O). This process also pumps protons, contributing to the gradient.

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What is the significance of the proton motive force in ATP synthesis?

The ETC is a highly efficient system that converts the energy stored in electrons into a useable form (ATP). The proton motive force drives the synthesis of ATP, highlighting the importance of this gradient.

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Why is the mitochondrial inner membrane important for cellular energy production?

The inner mitochondrial membrane is highly selective, allowing only specific molecules to cross. The electron transport chain, embedded within this membrane, is a crucial component of cellular energy production.

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What is the importance of the cristae in the mitochondrial inner membrane?

The inner mitochondrial membrane folds into cristae, increasing its surface area to accommodate the numerous proteins involved in the ETC and ATP synthesis. These folds enhance the efficiency of energy production.

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Explain the energy flow from electrons to ATP in mitochondria.

The ETC generates a proton gradient across the inner mitochondrial membrane. This gradient is used by ATP synthase to produce ATP, the main energy currency of the cell. The energy flow from electrons to protons and ultimately to ATP is a remarkable feat of biological machinery.

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Why is the electron transport chain significant in cellular respiration?

The ETC is a fundamental process in cellular respiration, responsible for generating the majority of ATP required for cellular functions. Understanding the ETC is crucial for comprehending the mechanisms of energy production in living organisms.

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Study Notes

Module Information

  • Module: Biochemistry
  • Topic: Carbohydrates metabolism 2

Learning Outcomes

  • Identify key carbohydrate metabolic pathways, including the Krebs cycle and gluconeogenesis
  • Describe metabolic regulation
  • Explain the interconnection between metabolic pathways

Quick Recap

  • Glucose is degraded to pyruvate via glycolysis
  • Pyruvate enters the mitochondria and is converted to acetyl-CoA
  • Acetyl-CoA is metabolized by the TCA cycle
  • The TCA cycle produces energy-rich molecules NADH and FADH2
  • NADH and FADH2 are converted to ATP

Tricarboxylic Acid Cycle (TCA Cycle)

  • Also known as the citric acid cycle or Krebs cycle
  • Occurs in the mitochondria
  • Oxidizes acetyl-CoA, producing NADH and FADH2
  • Coenzymes NADH and FADH2 are reoxidized via electron transport chain
  • Carbohydrates, lipids, and proteins are ultimately broken down to acetyl-CoA or intermediates in this cycle

Site of Synthesis

  • TCA cycle occurs primarily in the liver
  • Enzymes are located in the mitochondrial matrix, often attached to the inner membrane or cristae
  • Enzymes of the respiratory chain are also found in this location

Mitochondrial Compartments

  • Outer membrane
  • Intermembrane space
  • Inner membrane
  • Cristae
  • Matrix (central space)

Pyruvate Oxidized to Acetyl CoA

  • Pyruvate is oxidized to Acetyl CoA in the mitochondria
  • This process involves pyruvate dehydrogenase
  • Results in the production of CO2, NADH, and Acetyl CoA
  • Pyruvate converted to Acetyl CoA, then enters the TCA cycle
  • 1 NADH = 3 ATP
  • 1 FADH2 = 2 ATP
  • GTP = ATP

Catabolic and Anabolic Processes

  • Catabolic: The cycle degrades acetyl residues from carbohydrates, fats, and proteins.
  • Anabolic: Intermediates in the TCA Cycle are used to synthesize other compounds.

Amphibolic Role of TCA Cycle

  • The TCA cycle is amphibolic, meaning it plays a role in both catabolism and anabolism

Anabolic Role

  • Amino acid metabolism: Several glycogenic amino acids enter the TCA cycle via transamination reactions.
  • Lipid metabolism: Acetyl-CoA and glycerol are essential for steroid and fatty acid synthesis; and TCA cycle intermediates are crucial for porphyrin, hemoglobin, cytochrome, and other haemoprotein synthesis
  • Nitrogen metabolism: Aspartate, formed from oxaloacetate via transamination, is involved in argininosuccinate and purine synthesis.

Catabolic Role

  • The oxidation of acetyl-CoA in the TCA cycle produces energy, CO2, and water.

Regulation of TCA Cycle

  • Cellular ATP demands control the cycle's rate
  • Regulation occurs via enzymes: citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase
  • High ATP/ADP and NADH/NAD+ ratios inhibit the cycle

The Mitochondrial Inner Membrane Structure and Function

  • Highly impermeable to most molecules, due to lack of porins
  • Strengthened by cardiolipin
  • High protein content (76%)
  • Folded into cristae

Role of the Electron Transport Chain (ETC)

  • ETC, or respiratory chain, is used to convert high-energy electrons from NADH and FADH2 into ATP energy.
  • Electrons are passed through four complexes (I-IV).

Hydrogen Ion Gradient

  • Water molecules dissociate into H+ and OH- ions
  • H+ ions are pumped out of the matrix into the intermembrane space of the mitochondria, producing a gradient.

ATP Synthase & Proton Motive Force

  • ATP synthase uses the hydrogen ion gradient to produce ATP.
  • Hydrogen ions flow back into the matrix, generating energy for ATP production.

Electron Transport Chain Routes

  • Electrons from NADH travel through complex I, then proceed through Coenzyme Q, complex III, cytochrome c, and complex IV, eventually reacting with oxygen to form water.
  • Electrons from FADH2 enter the ETC at complex II before proceeding through the rest of the chain in a similar way

Anaerobic Respiration (Lactic Acid/Ethanol Fermentation)

  • Occurs when oxygen is not available
  • Breakdown of glucose to produce ATP without using oxygen, producing either lactic acid or ethanol

Gluconeogenesis

  • The synthesis of glucose from non-carbohydrate sources (e.g., lactate, pyruvate, amino acids, glycerol)
  • Pathway largely mirrors the reversed glycolysis pathway, with bypassed steps regulated by specific enzymes

Gluconeogenesis Locations

  • Primarily takes place in the cytosol
  • Also occurs to a lesser degree in the liver and kidney matrix

Gluconeogenesis Reactions

  • Reactions of gluconeogenesis reverse glycolytic pathways to produce glucose
  • Specific enzymes bypass glycolysis-specific reactions to allow glucose production

Quizzes (Answers)

  • Quiz 1: Reactions of the TCA cycle occur in the mitochondria
  • Quiz 2: Pyruvate is converted to acetyl-CoA by pyruvate dehydrogenase
  • Quiz 3: The exact number of ATP generated by glucose metabolism needs to be calculated; it is likely to be 30-32.
  • Quiz 4: Citrate synthase is one of the three regulatory enzymes in the TCA cycle
  • Quiz 5: Malate dehydrogenase is one of the three regulatory enzymes in the TCA cycle

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Carbohydrates Metabolism 2 PDF

Description

This quiz covers key carbohydrate metabolic pathways, including the Krebs cycle and gluconeogenesis. You'll explore metabolic regulation and the interconnections between various metabolic pathways, focusing on the breakdown of glucose and the production of energy-rich molecules.

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