Biochemistry: Metabolic Reactions Quiz
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Questions and Answers

Which type of reaction involves the synthesis of large molecules from smaller ones?

  • Endergonic reactions
  • Anabolic reactions (correct)
  • Exergonic reactions
  • Catabolic reactions

In which type of metabolic reaction is energy released?

  • Glycogenolysis
  • Anabolic reactions
  • Photosynthesis
  • Catabolic reactions (correct)

What is the primary role of coenzymes like NAD+ in metabolic processes?

  • Synthesize carbohydrates
  • Store energy in ATP
  • Facilitate oxidative reactions (correct)
  • Catalyze phosphorylation

Which of the following reactions is an example of an anabolic reaction?

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

What is the standard Gibbs free energy change sign for catabolic reactions?

<p>Negative (-∆G) (B)</p> Signup and view all the answers

What is produced when pyruvate is converted through oxidative decarboxylation?

<p>Acetyl CoA, CO2, NADH, and H+ (D)</p> Signup and view all the answers

What role does the TCA cycle primarily play in the body?

<p>It generates most of the energy needed for the brain (C)</p> Signup and view all the answers

What effect does a deficiency in pyruvate dehydrogenase have on the body?

<p>Lactic acidosis due to impaired acetyl CoA formation (C)</p> Signup and view all the answers

How many ATP molecules are generated from one molecule of acetyl CoA during the TCA cycle?

<p>10 ATP (D)</p> Signup and view all the answers

Where does oxidative decarboxylation of pyruvate occur in the cell?

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

Which shuttle mechanism produces 1.5 ATP molecules per cytoplasmic NADH?

<p>Glycerol phosphate shuttle (D)</p> Signup and view all the answers

What is the net result of the oxidation of one molecule of glucose in terms of ATP and CO2 produced?

<p>2 ATP and 4 CO2 (D)</p> Signup and view all the answers

Which complex in the electron transport chain is directly after NADH dehydrogenase?

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

In which part of the mitochondria do the reactions of the electron transport chain occur?

<p>Inner mitochondrial membrane (D)</p> Signup and view all the answers

How many ATP molecules result from the oxidation of one mitochondrial NADH?

<p>2.5 ATP (C)</p> Signup and view all the answers

What does a negative change in free energy (∆G) indicate about a chemical reaction?

<p>The reaction proceeds spontaneously. (B)</p> Signup and view all the answers

What is enthalpy (∆H) a measure of in a chemical reaction?

<p>The heat content change of reactants and products. (A)</p> Signup and view all the answers

How does the standard free energy change (∆G°) relate to additive reactions?

<p>The sum of ∆G° values is additive for consecutive reactions. (D)</p> Signup and view all the answers

What happens when the sum of the ∆G values of individual reactions in a pathway is negative?

<p>The pathway can proceed as written. (C)</p> Signup and view all the answers

What does a positive change in free energy (∆G) signify?

<p>The reaction requires energy input to proceed. (B)</p> Signup and view all the answers

What is the approximate ∆G° for each of the two terminal phosphate groups of ATP?

<p>-7.3 kcal/mol (B)</p> Signup and view all the answers

Which of the following statements regarding the hydrolysis of ATP is correct?

<p>ATP hydrolysis produces energy. (B)</p> Signup and view all the answers

What is the relationship between entropy (∆S) and the disorder of reactants and products?

<p>Entropy is a measure of disorder in the system. (A)</p> Signup and view all the answers

What is the primary function of carbohydrates in cells?

<p>To provide energy through oxidation (B)</p> Signup and view all the answers

Which sugars can be converted to glucose in the liver?

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

What is the net gain of ATP from one molecule of glucose during glycolysis?

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

If oxygen is absent, pyruvate is converted into which of the following during anaerobic respiration?

<p>Alcohol or lactate (A)</p> Signup and view all the answers

Where does glycolysis occur within the cell?

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

What happens to pyruvate if oxygen is present during cellular respiration?

<p>It is oxidized to carbon dioxide and water (D)</p> Signup and view all the answers

Which of the following statements is true regarding lactose intolerance?

<p>Most adults of African and Asian descent are lactase deficient (C)</p> Signup and view all the answers

Which molecule serves as the central pathway for glucose catabolism?

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

What is produced at the end of the oxidative phosphorylation process?

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

Which enzyme catalyzes the conversion of pyruvate to lactate in animals?

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

What is the primary effect of insulin on glycogen metabolism?

<p>Induces glycogen synthesis (B)</p> Signup and view all the answers

What deficiency is responsible for McArdle syndrome?

<p>Glycogen phosphorylase deficiency (C)</p> Signup and view all the answers

Which pathway is characterized by the formation of NADPH and 5-C sugars?

<p>Pentose Phosphate Pathway (C)</p> Signup and view all the answers

What condition is associated with Von Gierke disease?

<p>Severe fasting hypoglycaemia (D)</p> Signup and view all the answers

During prolonged fasting, which organ becomes the major glucose-producing organ?

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

Which of the following substrates is NOT a precursor for gluconeogenesis?

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

What is the primary function of NADPH produced in oxidative reactions?

<p>Fatty acid synthesis (D)</p> Signup and view all the answers

Which hormone is primarily responsible for stimulating glycogen breakdown in the liver?

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

What is the main consequence of G6PD deficiency?

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

Which of the following pathways occurs in the cytosol of the cell?

<p>Pentose phosphate pathway (B)</p> Signup and view all the answers

What is the function of glucagon during low blood glucose levels?

<p>Stimulates glycogen breakdown (A)</p> Signup and view all the answers

Flashcards

Bioenergetics

The branch of biochemistry that focuses on the transfer and utilization of energy in biological systems.

Enthalpy (ΔH)

The measure of change in the heat content of reactants and products.

Entropy (ΔS)

The measure of change in randomness or disorder of reactants and products.

Free energy (ΔG)

A measure of the energetic feasibility of a chemical reaction. It predicts whether a reaction can occur spontaneously.

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Negative ΔG

A reaction will proceed spontaneously if it leads to a net loss of energy. Indicates a favorable reaction.

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Positive ΔG

A reaction will not occur spontaneously, as it requires a net input of energy. Indicates an unfavorable reaction.

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ΔG = 0

Reactants are in equilibrium, meaning the rates of forward and reverse reactions are equal.

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ATP

A high-energy phosphate compound that is essential for many cellular processes.

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Metabolism

The sum of all chemical reactions that take place within an organism to build up and break down molecules, allowing for growth, reproduction, and maintaining life processes.

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Anabolic Reactions

Metabolic reactions that synthesize larger molecules from smaller ones, requiring energy input (Endergonic).

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Catabolic Reactions

Metabolic reactions that break down larger molecules into smaller ones releasing energy (Exergonic).

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Glycolysis

The breakdown of glucose to pyruvate, generating ATP and NADH. It is a key catabolic pathway in carbohydrate metabolism.

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Gluconeogenesis

The synthesis of glucose from non-carbohydrate sources, such as pyruvate, lactate, glycerol, and amino acids. It is a key anabolic pathway in carbohydrate metabolism, primarily occurring in the liver.

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What's the main function of carbohydrates in the body?

Carbohydrates are used as a primary energy source by the body. They can be stored for later use, converted to lipids, or used to build cell structures.

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What is lactose intolerance?

Most adults worldwide lack the enzyme lactase, which is needed to digest lactose in milk. This inability to digest lactose is called lactose intolerance.

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What is glycolysis?

Glycolysis is a metabolic pathway where glucose is broken down into pyruvate, producing energy (ATP) in the process.

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Where does glycolysis take place in the cell?

Glycolysis occurs in the cytoplasm of cells. Glucose is transported into cells by special membrane proteins.

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What determines the fate of pyruvate?

The fate of pyruvate, a product of glycolysis, depends on the availability of oxygen. If oxygen is present, it undergoes aerobic respiration. If oxygen is absent, it undergoes anaerobic respiration.

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What is aerobic respiration?

Aerobic respiration, which requires oxygen, involves breaking down pyruvate to carbon dioxide and water, producing a large amount of energy (ATP).

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What is anaerobic respiration?

Anaerobic respiration occurs when oxygen is limited. It converts pyruvate to lactate or alcohol, producing only a small amount of ATP.

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What are the two phases of aerobic respiration?

The two phases of aerobic respiration are oxidative decarboxylation of pyruvate and the citric acid cycle (Krebs cycle).

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Oxidative Decarboxylation of Pyruvate

A metabolic process in the mitochondria where pyruvate is converted to acetyl-CoA, generating NADH and CO2. Pyruvate dehydrogenase is the enzyme responsible for this reaction.

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Tricarboxylic Acid Cycle (TCA Cycle)

This cycle, also known as the Kreb's cycle, is a central metabolic pathway that occurs inside the mitochondria. It's responsible for generating energy (ATP) and reducing equivalents (NADH and FADH2).

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TCA Cycle and Brain Energy

The TCA cycle plays a crucial role in energy production within the brain. It's the primary source of energy for this vital organ.

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Pyruvate Dehydrogenase Deficiency

A deficiency in pyruvate dehydrogenase can lead to lactic acidosis because pyruvate cannot be converted to acetyl-CoA, resulting in an accumulation of lactic acid.

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TCA Deficiency and Brain Development

This deficiency can result in developmental defects in the brain and nervous system as the TCA cycle, crucial for brain energy production, is disrupted.

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Glycerol Phosphate Shuttle

A transport mechanism that carries electrons from cytoplasmic NADH across the mitochondrial membrane to produce FADH2, yielding 1.5 ATP molecules per NADH.

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Malate-Aspartate Shuttle

A transport mechanism that carries electrons from NADH across the mitochondrial membrane to produce mitochondrial NADH, yielding 2.5 ATP molecules per NADH. This shuttle is more efficient than the glycerol phosphate shuttle.

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Carboxylation of Pyruvate

The process where pyruvate is converted into acetyl-CoA, a key molecule in energy production.

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Electron Transport Chain

The process of generating ATP using the energy from the movement of electrons through a series of protein complexes in the inner mitochondrial membrane.

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Net Products of Glucose Oxidation

The net yield from the complete oxidation of one glucose molecule, including glycolysis, pyruvate oxidation, and the TCA cycle.

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Oxidative Phosphorylation

The process where ATP is generated from the transfer of electrons from NADH and FADH2 during cellular respiration.

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Where does Oxidative Phosphorylation occur?

The reaction that occurs within the inner mitochondrial membrane, where the electron transport chain and ATP synthase reside.

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Anaerobic Respiration (Plants)

A type of respiration that occurs in the absence of oxygen, converting pyruvate to ethanol and carbon dioxide. It's common in yeast cells.

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Anaerobic Respiration (Animals)

A type of anaerobic respiration where pyruvate is converted to lactate. It happens in red blood cells, muscles during exercise, and tissues with limited oxygen.

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Glycogenolysis

The breakdown of glycogen stored in the liver and muscle into glucose for energy release. It's a way to provide glucose when blood sugar is low.

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McArdle Syndrome (Cori Type V)

A genetic condition where skeletal muscle lacks the enzyme to break down glycogen, leading to muscle weakness and cramping after exercise.

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Von Gierke Disease (Cori Type 1a)

A genetic condition where the liver lacks the enzyme to convert glucose-6-phosphate to free glucose, resulting in low blood sugar after fasting.

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Glycogen Metabolism

The process regulated by hormones like insulin, glucagon, and epinephrine, controlling the synthesis and breakdown of glycogen.

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Pentose Phosphate Pathway

Also known as the hexose monophosphate shunt, this metabolic pathway generates NADPH and 5-carbon sugars in the cytosol.

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Irreversible Oxidative Reactions

The first phase of the Pentose Phosphate pathway, generating NADPH and 5-carbon sugars. It's irreversible.

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Reversible Non-oxidative Reactions

The second phase of the Pentose Phosphate pathway, involving reversible reactions that produce essential intermediates like ribose-5-phosphate and glyceraldehyde-3-phosphate.

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G6PD Deficiency

A genetic deficiency in the enzyme glucose-6-phosphate dehydrogenase (G6PD), causing hemolytic anemia due to reduced NADPH production and oxidative damage to red blood cells.

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Gluconeogenesis in Liver and Kidneys

During prolonged fasting, the liver and kidneys contribute to gluconeogenesis. The liver is mainly responsible, but during prolonged fasting, the kidneys become the dominant glucose producing organ.

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Gluconeogenesis: Mitochondrial and Cytosolic Enzymes

Gluconeogenesis requires enzymes from both the mitochondria and cytosol to convert non-carbohydrate sources into glucose.

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Study Notes

Carbohydrate Metabolism

  • Carbohydrates are metabolized to create a variety of organic compounds.
  • Animals consume significant amounts of carbohydrates, which can either be stored, oxidized for energy, converted to lipids for more effective energy storage, or used for creating cellular components.
  • A major role for carbohydrates is to be oxidized and provide energy for metabolic processes.
  • Cells primarily utilize glucose as a source of carbohydrates.
  • Fructose and galactose can be readily converted to glucose within the liver.

Metabolism - Coupling Reactions

  • Some reactions require energy, while others produce it.
  • Coupling reactions are a strategy for initiating energy-requiring reactions by pairing them with energy-releasing reactions.
  • Example of coupling reactions:
    • ATP → ADP -7.3 kcal/mol +3.3 kcal/mol Glucose -> Glu-6-phosphate
    • Phosphoenolpyruvate → Pyruvate -14.8 kcal/mol +7.3 kcal/mol ADP -> ATP

Metabolism

  • Metabolism is the combination of all the biochemical reactions within an organism.
  • It is integral to building cellular components and utilizing energy from the environment.
  • Metabolism is categorized into two types:
    • Anabolic: Synthesis of complex molecules from simpler ones (requires energy)
    • Catabolic: Breakdown of complex molecules into simpler ones (releases energy)

Anabolic Reactions

  • Anabolic reactions involve the synthesis of larger molecules from smaller ones.
  • They require an input of energy and are considered endergonic.
  • Example: Photosynthesis, transforming carbon dioxide and water into carbohydrates, with sunlight as the energy source.
  • The creation of complex biological molecules from simpler precursor molecules consumes energy.

Catabolic Reactions

  • Catabolic reactions are the breakdown of larger molecules into smaller components.
  • Release energy and are called exergonic.
  • Example: Digestion, the breakdown of large food molecules for absorption by the body.
  • These reactions play a role in the breakdown of larger molecules into simpler components, releasing energy as a byproduct.

Stages of Metabolism

  • Stage 1: Hydrolysis of complex molecules (proteins, polysaccharides, lipids) into their constituent building blocks (amino acids, monosaccharides, glycerol, and fatty acids).
  • Stage 2: Conversion of building blocks to acetyl CoA.
  • Stage 3: Oxidation of acetyl-CoA via the citric acid cycle and oxidative phosphorylation.

Glycolysis

  • Glycolysis is the central pathway for glucose catabolism, producing energy.
  • Glucose is broken down into 2 pyruvate molecules, 2 ATP, and 2H+ in the cytoplasm.
  • All cells undergo glycolysis to obtain glucose from diet and other catabolic reactions.
  • The fate of pyruvate depends on the presence of oxygen.
    • With oxygen (aerobic): Pyruvate enters the mitochondria for further oxidation, producing carbon dioxide, water and more energy.
    • Without oxygen (anaerobic): Pyruvate converted into alcohol or lactic acid.
  • Input: 1 glucose, 2 ATP, 2 NAD.
  • Output: 2 pyruvate, 4 ATP, 2 NADH, 2 H2O.

Aerobic Respiration

  • Involves two stages:
    • Oxidative decarboxylation of pyruvate: Removal of CO2 and oxidation.
    • TCA cycle: Series of reactions, resulting in 2CO2 molecules, 1 ATP, and energy-carrying molecules.

Oxidative Decarboxylation of Pyruvate

  • Occurs in the mitochondrial matrix.
  • Pyruvate is converted into acetyl CoA, CO2, NADH and H⁺, through the action of pyruvate dehydrogenase.
  • Products feed into the TCA cycle.

Tricarboxylic Acid (TCA) Cycle

  • Also known as the citric acid cycle or Krebs cycle.
  • Acetyl-CoA is hydrolyzed to acetyl, a series of reactions occur, resulting in the formation of 2 CO2 and 1 ATP.

Energy from Acetyl CoA

  • 3 NADH → 7.5 ATP
  • 1 FADH2 → 1.5 ATP
  • 1 GTP → 1 ATP
  • 10 ATP per oxidized acetyl CoA
  • NADH produced in the cytoplasm is not able to directly pass the mitochondrial membrane. Brain and muscle cells have a specific transport mechanism to get cytoplasmic NADH into the mitochondria and produce more ATP. The liver, heart, and kidney use a different transport mechanism to produce more ATP.

Oxidative Phosphorylation

  • ATP is formed from the transfer of electrons from NADH and FADH2.
  • Takes place in the inner mitochondrial membrane.

Anaerobic Respiration (In Plants)

  • Pyruvate + NADH + H+ → Ethanol + CO2 + NAD+.

Anaerobic Respiration (In Animals)

  • Pyruvate is converted to lactate.
  • Reaction catalyzed by lactate dehydrogenase.

The Cori Cycle

  • Cycle where lactate produced by anaerobic respiration in muscles is carried to the liver, converted back to pyruvate, and subsequently glucose.
  • This glucose is then used by the muscle cells.

Glycogenolysis

  • The breakdown of glycogen into glucose.
  • Occurs in the liver and skeletal muscles.
  • It is NOT the reverse reaction of glycogen synthesis (glycogenesis).

In-born Errors of Carbohydrate Metabolism

  • Genetic defects in enzymes involved in carbohydrate metabolism.
  • Examples: McArdle syndrome (glycogen phosphorylase deficiency) and Von Gierke disease (glucose-6-phosphatase deficiency).

Pentose Phosphate Pathway

  • Also known as the hexose monophosphate shunt.
  • Occurs in the cytosol of cells.
  • Produces NADPH (needed for biosynthetic reactions, example steroid and fatty acid synthesis) and 5-carbon sugars (important for nucleotide synthesis).
  • Divided into two portions:
    • Oxidative reactions: Irreversible reactions.
    • Non-oxidative reactions: Reversible reactions.

G6PD Deficiency

  • Glucose-6-phosphate dehydrogenase deficiency is a hereditary disease causing hemolytic anemia.
  • Reduced NADPH leads to a decrease in glutathione, resulting in damage to red blood cells and hemolysis.

Gluconeogenesis

  • Synthesis of glucose from non-carbohydrate precursors.
  • Precursors include: lactate, glycerol, and certain amino acids.
  • Crucial for maintaining glucose levels during prolonged fasting or carbohydrate deprivation.
  • Requires specific enzymes in both the mitochondrial and cytosolic compartments
  • Key role in providing a continuous supply of glucose to areas such as the brain and active tissues like muscles.

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Test your knowledge of metabolic reactions with this quiz focused on anabolic and catabolic processes, the role of coenzymes, and the TCA cycle. Explore questions about energy production, ATP generation, and the significance of various biochemical pathways. Perfect for students studying biochemistry!

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