Chapter 13 Bioenergetics part 1

Summary

This chapter delves into bioenergetics and biochemical reactions, emphasizing the application of thermodynamics to biochemistry. It explores metabolism, distinguishing between catabolism (energy-releasing) and anabolism (energy-consuming), and how energy carriers like ATP, NADH, and FADH2 function in these processes. The script covers free energy, equilibrium, and the spontaneity of biochemical reactions, along with common reaction types like hydrolysis, oxidation-reduction, and isomerization. Enzyme mechanisms, nucleophiles, electrophiles, and carbon-carbon bond formation are also discussed, providing a detailed look into the energetic landscape of living systems and biochemical transformations.

Takeaways

• 😀 Metabolism is the sum of all chemical transformations in a cell, involving both anabolism (biosynthesis) and catabolism (degradation).
• 😀 Catabolic reactions break down complex molecules into simpler ones, releasing energy in the form of ATP, NADH, and FADH2.
• 😀 Anabolic reactions build larger macromolecules from smaller precursors, using energy stored in ATP, NADH, NADPH, and FADH2.
• 😀 The laws of thermodynamics apply to living organisms, where energy cannot be created or destroyed, only transformed.
• 😀 Free energy (ΔG) determines the spontaneity of a reaction, with negative ΔG indicating a forward reaction and positive ΔG indicating a reverse reaction.
• 😀 The relationship between free energy and equilibrium constant (K) is exponential, with large changes in K corresponding to small changes in free energy.
• 😀 The actual free energy change in a reaction depends on both standard free energy change and the reaction quotient, which reflects the concentrations of reactants and products.
• 😀 Hydrolysis reactions, such as the breakdown of acid anhydrides, release significant amounts of energy and are strongly favorable in biochemical reactions.
• 😀 Oxidation reactions, such as the complete oxidation of organic compounds like glucose, are highly favorable and provide energy for chemotrophs.
• 😀 Biochemical reactions often involve the transfer of groups (like protons, methyls, or phosphates), nucleophilic attacks, and electron transfers.
• 😀 Isomerization and elimination reactions in cells typically do not involve changes in oxidation states, such as in the conversion of glucose-6-phosphate to fructose-6-phosphate.

Q & A

What are the two main phases of metabolism?

The two main phases of metabolism are catabolism and anabolism. Catabolism is the degradative phase where larger molecules are broken down into simpler products, releasing energy. Anabolism is the biosynthetic phase where smaller molecules are used to build larger macromolecules, consuming energy in the process.

How is energy conserved in catabolic pathways?

Energy in catabolic pathways is conserved in the form of high-energy molecules such as ATP, NADH, NADPH, and FADH₂. These molecules store energy that can be used in anabolic processes.

What does the second law of thermodynamics imply for living organisms?

The second law of thermodynamics states that living organisms must increase the entropy of the universe when they transform energy. This means organisms cannot create or destroy energy but can only convert it from one form to another while releasing heat into the surroundings.

What is the significance of free energy (ΔG) in biochemical reactions?

Free energy (ΔG) determines whether a biochemical reaction is spontaneous. A negative ΔG means the reaction is spontaneous and will proceed forward, while a positive ΔG indicates a reaction will proceed in the reverse direction or is non-spontaneous.

How does the equilibrium constant (K_eq) relate to standard free energy change (ΔG°)?

The equilibrium constant (K_eq) is related to the standard free energy change (ΔG°) through an exponential relationship. A large K_eq (greater than 1) corresponds to a negative ΔG°, indicating a favorable reaction, while a small K_eq (less than 1) corresponds to a positive ΔG°, indicating an unfavorable reaction.

What is the difference between standard free energy change (ΔG°) and actual free energy change (ΔG)?

Standard free energy change (ΔG°) is measured under standard conditions, while actual free energy change (ΔG) accounts for the current concentrations of reactants and products in a cell. ΔG reflects the spontaneity of a reaction under physiological conditions.

Why are hydrolysis reactions typically favorable in biochemical systems?

Hydrolysis reactions are typically favorable because they release energy, making them spontaneous. For example, the breakdown of ATP into ADP and phosphate is a highly favorable reaction due to the release of energy.

What types of reactions are common in biochemical systems involving carbon-carbon bonds?

Common reactions involving carbon-carbon bonds in biochemical systems include aldol condensations, Claisen ester condensations, and decarboxylation of beta-keto acids. These reactions often involve nucleophilic attack on electrophilic carbonyl groups.

How do nucleophiles and electrophiles interact in biochemical reactions?

Nucleophiles are electron-rich species that attack electrophilic centers, which are electron-deficient. In biochemical reactions, nucleophiles (like negatively charged oxygen or sulfur groups) react with electrophilic centers (such as carbonyl carbon or protonated amine groups) to form new bonds.

What role do cofactors like NAD+ and FAD play in biochemical reactions?

NAD+ and FAD serve as universal electron carriers in redox reactions. They accept and donate electrons during oxidation and reduction processes, playing a crucial role in energy transfer during cellular respiration and other metabolic pathways.