Introduction to Metabolism and Bioenergetics

Anabolic Pathways (Anabolism)

Anabolism is the process of building larger, more complex molecules from smaller building blocks. Photosynthesis is a classic example, as it uses small molecules like carbon dioxide and water to build glucose. These are endergonic reactions, meaning they require an input of energy to proceed, resulting in a positive change in free energy ($\Delta G > 0$).

Exam Tip: Remember the relationship between the pathway type and the sign of $\Delta G$.

• Catabolism $\rightarrow$ Breaking down $\rightarrow$ Releases energy $\rightarrow$ Negative $\Delta G$
• Anabolism $\rightarrow$ Building up $\rightarrow$ Requires energy $\rightarrow$ Positive $\Delta G$

Bioenergetics and Thermodynamics

Bioenergetics is the study of how energy is transformed within these biological systems. To understand bioenergetics, we must apply the laws of thermodynamics within the context of open systems. Unlike a "closed" system (like a sealed thermos) that prevents the exchange of matter or energy, living cells are open systems that constantly exchange both matter and energy with their environment.

The First Law of Thermodynamics

The First Law states that energy cannot be created or destroyed, only transformed from one form to another. For example, a cell might transform the potential energy stored in the chemical bonds of a molecule into kinetic energy (movement) or thermal energy (heat).

The Second Law of Thermodynamics and Entropy

The Second Law states that every energy transformation increases the total entropy, or disorder, of the universe. While organisms can create local order (decreasing entropy within themselves), they do so by releasing heat into their surroundings, which increases the overall disorder of the universe.

Calculating Free Energy

The energy available to do work in a system is measured by the free energy change ($\Delta G$). This is calculated using the following formula: