Metabolism Overview M2P Course 2024

Questions and Answers

What is the primary consequence of aldolase B deficiency in fructose metabolism?

Prolonged ATP deficiency (correct)

Normal ATP levels

Enhanced glucose conversion

Increased ATP synthesis

Which statement correctly describes the function of fructokinase in fructose metabolism?

It reduces the rate of fructose entry into hepatocytes.

It directly depletes ATP levels.

It increases the levels of inorganic phosphate.

It catalyzes the reaction converting fructose to fructose 1-phosphate. (correct)

How does a deficiency in aldolase B affect thermodynamics in the cell?

It leads to many reactions becoming thermodynamically unfavorable. (correct)

It makes all reactions thermodynamically favorable.

It increases the availability of ATP for cellular processes.

It creates a permanent state of equilibrium.

According to the second law of thermodynamics, how do cells maintain order?

By consuming energy from the environment. Signup and view all the answers

What reaction characteristic is indicated by a positive change in free energy (ΔG)?

The reaction requires an input of energy to occur. Signup and view all the answers

What occurs when the change in free energy (ΔG) is zero?

The reaction is at equilibrium. Signup and view all the answers

Which of the following best describes fructose 1-phosphate accumulation in the cell?

It causes phosphate depletion. Signup and view all the answers

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?

The reverse reaction B → A will have a ΔG of +5 kcal/mol. Signup and view all the answers

Which of the following statements is true regarding catabolic reactions?

Catabolic reactions generate energy by breaking down molecules. Signup and view all the answers

Why are fats considered more energy dense than carbohydrates?

Fats contain more carbon-hydrogen bonds per molecule. Signup and view all the answers

In oxidation-reduction reactions, what happens to carbon-hydrogen bonds?

Oxidation decreases C-H bonds. Signup and view all the answers

How does fatty acid oxidation stimulate gluconeogenesis?

By providing acetyl-CoA that activates gluconeogenic enzymes. Signup and view all the answers

What is a key difference between fructokinase deficiency and aldolase B deficiency?

Fructokinase deficiency has no serious symptoms while aldolase B deficiency does. Signup and view all the answers

What is the consequence of aldolase B deficiency upon fructose ingestion?

Accumulation of fructose 1-P in the liver. Signup and view all the answers

Which of the following is a symptom associated with aldolase B deficiency?

Hypoglycemia. Signup and view all the answers

Which process is NOT affected by low levels of ATP?

Triglyceride breakdown. Signup and view all the answers

What is the primary function of catabolic reactions in the body?

To generate ATP from complex molecules Signup and view all the answers

Why are fats considered to be more energy dense compared to carbohydrates?

Fats have a higher number of carbon-hydrogen bonds Signup and view all the answers

What is the role of NADPH in anabolic reactions?

To provide high energy electrons for the synthesis of complex products Signup and view all the answers

What occurs during oxidative reactions associated with catabolic pathways?

Release of energy stored in complex molecules Signup and view all the answers

What is the main outcome of gluconeogenesis?

Synthesis of glucose from non-carbohydrate precursors Signup and view all the answers

How does a deficiency in ATP affect cellular function?

It causes impairment in critical enzyme reactions Signup and view all the answers

What is primarily affected by the Na+/K+ ATPase when ATP levels are low?

Osmotic balance in cells Signup and view all the answers

What are the predominant fuel sources during catabolism?

Fats and carbohydrates Signup and view all the answers

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

Fructokinase deficiency:
- Autosomal recessive disorder leading to fructose accumulation in urine.
- Generally benign, affecting approximately 1 in 30,000 live births.
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.