Questions and Answers
What is the primary consequence of aldolase B deficiency in fructose metabolism?
Which statement correctly describes the function of fructokinase in fructose metabolism?
How does a deficiency in aldolase B affect thermodynamics in the cell?
According to the second law of thermodynamics, how do cells maintain order?
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What reaction characteristic is indicated by a positive change in free energy (ΔG)?
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What occurs when the change in free energy (ΔG) is zero?
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Which of the following best describes fructose 1-phosphate accumulation in the cell?
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If compound A has a higher free energy than compound B, what can be inferred if the ΔG of A → B is -5 kcal/mol?
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Which of the following statements is true regarding catabolic reactions?
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Why are fats considered more energy dense than carbohydrates?
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In oxidation-reduction reactions, what happens to carbon-hydrogen bonds?
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How does fatty acid oxidation stimulate gluconeogenesis?
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What is a key difference between fructokinase deficiency and aldolase B deficiency?
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What is the consequence of aldolase B deficiency upon fructose ingestion?
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Which of the following is a symptom associated with aldolase B deficiency?
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Which process is NOT affected by low levels of ATP?
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What is the primary function of catabolic reactions in the body?
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Why are fats considered to be more energy dense compared to carbohydrates?
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What is the role of NADPH in anabolic reactions?
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What occurs during oxidative reactions associated with catabolic pathways?
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What is the main outcome of gluconeogenesis?
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How does a deficiency in ATP affect cellular function?
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What is primarily affected by the Na+/K+ ATPase when ATP levels are low?
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What are the predominant fuel sources during catabolism?
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Study Notes
Metabolism Overview and Objectives
- Aldolase B deficiency has severe effects compared to fructokinase deficiency due to significant ATP depletion after fructose, sucrose, or sorbitol ingestion.
- Energetic imbalances in cells do not violate the first and second laws of thermodynamics; cells maintain energy balance through heat generation that increases overall entropy.
- Spontaneity of a reaction can be predicted by its change in free energy (𝚫G); negative 𝚫G indicates a spontaneous reaction, while positive requires energy input.
- Exergonic reactions release energy (negative 𝚫G), while endergonic reactions absorb energy (positive 𝚫G).
- Coupling endergonic reactions with ATP hydrolysis makes them thermodynamically favorable, allowing otherwise unfavorable reactions to proceed.
Disorders of Fructose Metabolism
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Fructokinase deficiency:
- Autosomal recessive disorder leading to fructose accumulation in urine.
- Generally benign, affecting approximately 1 in 30,000 live births.
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Aldolase B deficiency:
- Autosomal recessive disorder, prevents conversion of fructose 1-P into glyceraldehyde and dihydroxyacetone phosphate.
- More severe than fructokinase deficiency, affects around 1 in 20,000 live births.
- Symptoms include renal dysfunction, hyperuricemia, hypoglycemia, lactic acidemia, liver failure, jaundice, and can lead to death upon ingestion of fructose.
Metabolism and Thermodynamics
- The first law of thermodynamics states that energy is conserved; it cannot be created or destroyed.
- The second law indicates that entropy in a system increases over time; cells increase order while balancing entropy changes in their environment.
- A decrease in cellular entropy necessitates the release of heat to maintain overall energy balance.
Chemical Reactions and Free Energy
- Gibbs free energy (G) indicates the work potential of a reaction; 𝚫G changes as reactions occur.
- At equilibrium, 𝚫G equals zero; reactions with negative 𝚫G proceed spontaneously, while positive 𝚫G reactions need energy input.
- ATP deficiency disrupts critical cellular functions, including enzyme activity and ion balance, leading to cell swelling and potential rupture.
Metabolic Pathways
- Metabolic pathways consist of anabolic (storage) and catabolic (mobilization) reactions.
- High glucose levels lead to storage for future energy needs; conversely, low glucose levels trigger mobilization of stored energy.
- ATP/NADH/NADPH generation is vital for maintaining metabolic processes.
Intermediary Metabolism
- Pathways are interlinked; regulated and reversible steps play crucial roles in metabolic control.
- Key reactions include hydrolysis of complex molecules in catabolic processes and synthesis of complex products in anabolic reactions.
- Catabolic reactions: Breakdown of molecules (e.g., proteins to amino acids) and oxidation reactions generating ATP.
- Anabolic reactions: Synthesis of complex products from simpler substrates, requiring energy input typically involving NADPH for high-energy electrons.
Energy Density of Fats vs. Carbohydrates
- Fats are more energy dense than carbohydrates due to greater hydrogen content and higher caloric yield per gram.
- In a typical 70 kg male: approximately 30 kg of muscle and 10 kg of fat illustrate fuel reserves during metabolic processes.
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Description
This quiz focuses on key concepts of metabolism relevant to the M2P Course. It covers topics such as energy in the cell, aldolase B and fructokinase deficiencies, and the laws of thermodynamics. Additionally, it addresses spontaneous reactions and the distinction between exergonic and endergonic reactions.