004-Energy & Metabolism

Summary

This lesson explores the chemical basis of life, focusing on energy and metabolism within biological systems through the lens of thermodynamics. Key concepts include Gibbs free energy, enthalpy, and entropy, highlighting their roles in determining whether reactions are spontaneous or non-spontaneous. The importance of coupling reactions to make unfavorable processes favorable is discussed, alongside the vital role of metabolic pathways and enzymes. The interplay between photosynthesis and cellular respiration exemplifies how organisms harness and utilize energy, emphasizing the continual effort to maintain homeostasis while navigating the complexities of biochemical reactions.

Takeaways

• 😀 Energy and metabolism in biological systems are governed by thermodynamics.
• 😀 The first law of thermodynamics states that energy cannot be created or destroyed, only converted.
• 😀 Gibbs free energy (ΔG) represents the energy available to do work in a system.
• 😀 Enthalpy (ΔH) measures the total energy content, while entropy (ΔS) measures disorder in a system.
• 😀 A negative ΔG indicates a spontaneous reaction (exergonic), while a positive ΔG indicates a non-spontaneous reaction (endergonic).
• 😀 Life processes create order (negative change in entropy) and require energy input to maintain this order.
• 😀 Living systems operate away from equilibrium to maintain homeostasis.
• 😀 Unfavorable reactions can be coupled with favorable ones to make the overall process favorable.
• 😀 Metabolic pathways often involve oxidation-reduction (redox) reactions, where electrons are transferred.
• 😀 Enzymes facilitate metabolic reactions, playing a crucial role in biological processes.

Q & A

What is the first law of thermodynamics?

The first law of thermodynamics states that energy can neither be created nor destroyed; it can only be converted from one form to another.

What does Gibbs free energy (ΔG) represent?

Gibbs free energy (ΔG) represents the amount of energy available to do work in a system and is expressed as ΔG = ΔH - TΔS.

How is enthalpy (ΔH) defined in the context of biological systems?

Enthalpy (ΔH) is a measure of the total energy or heat content of the system, with negative changes indicating heat release and positive changes indicating heat absorption.

What does a positive ΔG indicate about a reaction?

A positive ΔG indicates that the final energy of the system is higher than the initial energy, meaning the reaction is non-spontaneous and requires an input of energy.

What role does entropy (ΔS) play in energy changes?

Entropy (ΔS) measures the disorder or randomness of a system; a positive change in entropy indicates that energy is becoming more dispersed.

Why do living systems never reach equilibrium?

Living systems never reach equilibrium because that would imply no net energy change, which is incompatible with the need for continuous energy input and maintenance of order.

How can unfavorable reactions occur in biological systems?

Unfavorable reactions can occur by coupling them with favorable reactions, allowing the overall ΔG to be negative and making the process spontaneous.

What is the significance of redox reactions in metabolism?

Redox reactions involve the transfer of electrons, where oxidation (loss of electrons) and reduction (gain of electrons) occur simultaneously, playing a crucial role in metabolic pathways.

What is homeostasis in the context of living organisms?

Homeostasis refers to the maintenance of stable internal conditions (like pH and temperature) in living organisms, allowing them to function optimally despite external changes.

What are metabolic pathways, and how are they related to enzyme function?

Metabolic pathways are series of biochemical reactions facilitated by enzymes, which accelerate reactions and enable the transformation of substrates into products efficiently.