3.1_ Energy Transfers and Coupled Reactions

Energy Fundamentals

• Potential Energy

  • Refers to stored energy that can be used to do work.

  • Biological potential energy includes energy stored in chemical bonds of glucose, lipids, etc.

Reactions in Biological Systems

• Spontaneous Reactions

  • Do not require energy input.

• Nonspontaneous Reactions

  • Require energy to proceed.

• Maintaining homeostasis requires significant energy from both spontaneous and nonspontaneous reactions.

Thermodynamic Principles

First Law of Thermodynamics

• Energy cannot be created or destroyed; it can only change forms.

Second Law of Thermodynamics

• The universe tends towards increased disorder (entropy).

• Energy transfer often results in loss of useful energy (not in a usable form).

Energy Transfers in Life

• Energy is dissipated to the environment at every stage, leading to efficiency losses.

• Large, rapid energy transfers produce significant heat, posing challenges for homeostasis.

  • Energy Pathway: The Sun → Glucose → ATP → Cellular Reactions

Chemical Reaction Dynamics

Energy Inputs for Reactions

• All chemical reactions need some energy input.

Types of Reactions

• Endothermic Reactions

  • Absorb energy (energy is absorbed).

• Exothermic Reactions

  • Release energy (product stock releases energy).

  • Activation Energy (Ea) is still required for these reactions to proceed.

Coupled Reactions

• Coupling an exothermic reaction with a desired reaction helps overcome activation energy barriers.

• Energy from the exothermic reaction drives the coupled reaction, enhancing efficiency.

ATP: The Energy Currency

Structure of ATP

• Composed of adenine, ribose, and three phosphate groups.

• High-energy bonds between the phosphate groups store energy available for cellular work.

Using ATP

• ATP → ADP + P (Inorganic phosphate) + Energy

• 31 kJ/mol of energy is used in coupled reactions; glucose combustion provides 2805 kJ/mol.

Phosphorylation Process

• Phosphorylation

  • Involves transfer of an inorganic phosphate group to ADP to form ATP.

  • Reaction: ADP + Pi + Energy → ATP + H2O

• Types of Phosphorylation

  • Substrate-Level Phosphorylation: ATP formed in cytoplasm using energy from high-energy substrates.

  • Oxidative Phosphorylation: Most ATP produced in mitochondria via electron transfer and H+ ion gradient.

Redox Reactions

• Redox: Involves oxidation (loss of electrons) and reduction (gain of electrons).

• Energy released as electrons are transferred from less electronegative to more electronegative atoms.

Energy Carriers

• NAD+ & NADH: Key roles in capturing and transferring electrons during redox reactions, facilitating energy storage and release.

• FAD and FADH2: Another set of electron carriers that function similarly to NAD+ and NADH.

Metabolism Overview

• Metabolism: Sum of all catabolic (breaking down) and anabolic (building up) reactions in a cell or organism.

• Involves nutrients and substrates like glucose, carbon dioxide, and other minerals for growth and energy.