Energy, Metabolism, and Enzyme Function in Biological Systems

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Energy is fundamental to all biological processes. It exists in different forms, primarily as kinetic and potential energy.

Kinetic Energy: The energy of motion. Any moving object possesses kinetic energy. For example, a rolling ball or flowing water.
Potential Energy: Stored energy due to an object's position or structure. For example, a rock at the top of a hill or chemical bonds in molecules.
Example: In cells, the chemical bonds of glucose represent potential energy, which can be converted to kinetic energy during cellular respiration.

Thermal Energy: A type of kinetic energy associated with the random movement of atoms or molecules. It is often referred to as heat.
Chemical Energy: A form of potential energy stored in chemical bonds of molecules. It is released or absorbed during chemical reactions.
Example: The breakdown of glucose in cellular respiration releases chemical energy, some of which is lost as thermal energy (heat).

First Law (Law of Energy Conservation): Energy cannot be created or destroyed, only transformed from one form to another.
Second Law: Every energy transfer increases the entropy (disorder) of the universe. Some energy is always lost as heat.
Example: When cells convert chemical energy from food into ATP, some energy is lost as heat, increasing entropy.

Biological reactions can be classified based on their free energy changes.

Exergonic Reactions: Release free energy; products have less free energy than reactants. These reactions are spontaneous.
Endergonic Reactions: Require an input of free energy; products have more free energy than reactants. These reactions are non-spontaneous.
Example: Cellular respiration is exergonic; photosynthesis is endergonic.

Exergonic Reaction Diagram: The free energy of the products is lower than that of the reactants. The difference () is negative.
Endergonic Reaction Diagram: The free energy of the products is higher than that of the reactants. The difference () is positive.

Equation:

Additional info: In diagrams, the y-axis represents free energy, and the x-axis represents the progress of the reaction.

Definition: The sum of all chemical reactions that occur within a living organism to maintain life.
Catabolism: Breakdown of molecules to release energy.
Anabolism: Synthesis of complex molecules from simpler ones, requiring energy.

Definition: The use of energy released from exergonic reactions to drive endergonic reactions.
Example: ATP hydrolysis (exergonic) is coupled to muscle contraction (endergonic).

ATP stands for: Adenosine Triphosphate.
Structure: Consists of an adenine base, a ribose sugar, and three phosphate groups.
Function: ATP stores and transfers energy within cells. It powers cellular work by transferring a phosphate group to other molecules (phosphorylation).
Example: ATP provides energy for muscle contraction, active transport, and biosynthesis.

ATP is continuously regenerated from ADP (adenosine diphosphate) and inorganic phosphate () through cellular respiration.
Equation:

Definition: Enzymes are biological catalysts that speed up chemical reactions without being consumed.
They lower the activation energy required for reactions to proceed.
Example: Amylase catalyzes the breakdown of starch into sugars in the mouth.

Enzymes bind to specific substrates at their active sites, forming an enzyme-substrate complex.
This interaction stabilizes the transition state and decreases the activation energy.
After the reaction, the enzyme releases the product and is free to catalyze more reactions.

Temperature: Each enzyme has an optimal temperature; too high or too low can denature the enzyme or slow the reaction.
pH: Each enzyme has an optimal pH range; deviations can affect enzyme structure and function.
Substrate Concentration: Increasing substrate concentration increases reaction rate up to a point (saturation).
Inhibitors: Molecules that decrease enzyme activity. Can be competitive (bind active site) or noncompetitive (bind elsewhere).