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?

It inhibits the cycle at specific steps due to high ATP:ADP ratio. Signup and view all the answers

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

Oxaloacetate Signup and view all the answers

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

Glycolysis Signup and view all the answers

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

Mitochondrial matrix Signup and view all the answers

What is the main purpose of the TCA cycle?

Oxidize acetyl-CoA and produce energy-rich molecules Signup and view all the answers

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

3 ATP Signup and view all the answers

Which coenzymes are reduced during the TCA cycle?

NADH and FADH2 Signup and view all the answers

Which metabolic processes are interconnected with the TCA cycle?

Glycolysis and gluconeogenesis Signup and view all the answers

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

It is an anabolic process. Signup and view all the answers

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

Three NADH and one FADH2 Signup and view all the answers

Where do the reactions of the TCA cycle primarily occur?

Mitochondria Signup and view all the answers

Which enzyme is responsible for converting pyruvate to Acetyl CoA?

Pyruvate dehydrogenase Signup and view all the answers

What is the primary location for gluconeogenesis in the body?

Liver and kidney Signup and view all the answers

Which substance is NOT a major precursor for gluconeogenesis?

Fructose Signup and view all the answers

What function does pyruvate carboxylase serve in gluconeogenesis?

Converts pyruvate to oxaloacetate Signup and view all the answers

Which of the following statements about gluconeogenesis is true?

It is the reverse of glycolysis with alternate enzymes. Signup and view all the answers

Which enzyme functions to regulate gluconeogenesis?

Pyruvate carboxylase Signup and view all the answers

What is a consequence of failure in gluconeogenesis?

Potential fatal consequences Signup and view all the answers

What is the primary function of the mitochondrial inner membrane?

Impedes the movement of almost all molecules Signup and view all the answers

Which specialized phospholipid is abundant in the mitochondrial inner membrane?

Cardiolipin Signup and view all the answers

How many complexes are involved in the electron transport chain?

4 Signup and view all the answers

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

Electrons Signup and view all the answers

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

Hydrogen ion gradient Signup and view all the answers

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

Splitting into hydroxyl and hydrogen ions Signup and view all the answers

What drives the ATP synthesis in the ATP synthase complex?

Hydrogen ion gradient Signup and view all the answers

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

Proton motive force Signup and view all the answers

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

They are pumped out of the mitochondrial matrix Signup and view all the answers

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

Water (H2O) Signup and view all the answers

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

Electrochemical potential Signup and view all the answers

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

Complex II Signup and view all the answers

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

The functionality of the electron transport chain Signup and view all the answers

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

Negative voltage Signup and view all the answers

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

Folds in the membrane Signup and view all the answers

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

Acetyl-CoA and glycerol Signup and view all the answers

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

Release of energy, CO2, and water Signup and view all the answers

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

High concentrations of acetyl-CoA and NADH Signup and view all the answers

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

Aspartate Signup and view all the answers

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

It integrates both anabolic and catabolic processes. Signup and view all the answers

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

To oxidize acetyl-CoA for energy production Signup and view all the answers

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

Acetyl-CoA Signup and view all the answers

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

NADH and FADH2 Signup and view all the answers

In which cellular compartment does the TCA cycle primarily occur?

Mitochondrial matrix Signup and view all the answers

How is acetyl-CoA formed from pyruvate?

By the enzymatic action of pyruvate dehydrogenase Signup and view all the answers

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

It reoxidizes NADH and FADH2 produced in the TCA cycle Signup and view all the answers

Which tissues have a significant capacity for the TCA cycle?

Liver and brain tissue Signup and view all the answers

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

3 ATP Signup and view all the answers

Where does gluconeogenesis primarily occur in the body?

Liver Signup and view all the answers

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

Pyruvate carboxylase Signup and view all the answers

Which of the following is a major precursor for gluconeogenesis?

Lactate Signup and view all the answers

Which enzyme does NOT regulate gluconeogenesis?

Pyruvate phosphorylase Signup and view all the answers

What is a key function of gluconeogenesis?

To provide glucose when carbohydrate is unavailable Signup and view all the answers

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

Coenzyme Q Signup and view all the answers

Which of the following statements about citrate synthase is true?

It catalyzes the formation of citrate from acetyl CoA and oxaloacetate. Signup and view all the answers

What is the primary function of the inner mitochondrial membrane?

To prevent the entry of all ions and large molecules Signup and view all the answers

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

Cardiolipin Signup and view all the answers

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

76% Signup and view all the answers

What generates the proton motive force within the mitochondria?

The hydrogen ion concentration gradient and voltage 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?

They are pumped out of the matrix into the inter-membrane space Signup and view all the answers

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

They provide electrons for the process Signup and view all the answers

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

Water (H2O) Signup and view all the answers

What function does ATP synthase serve in the mitochondria?

It generates ATP by using the proton motive force Signup and view all the answers

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

Complex I, II, III, IV Signup and view all the answers

What initiates the proton motive force in the mitochondria?

Electron transport and hydrogen ion pumping Signup and view all the answers

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

Storing excess glucose Signup and view all the answers

How does the electron transport chain contribute to ATP synthesis?

By establishing a hydrogen ion gradient used for ATP synthesis Signup and view all the answers

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

Enhancing the capacity for ATP production Signup and view all the answers

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

The concentration of hydrogen ions Signup and view all the answers

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

Link to TCA Cycle (Oxidative Phosphorylation)

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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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.