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Objectives
- Describe what a metabolic pathway is, provide examples
- Discuss the concepts of energy and thermodynamics as they relate to biochemical reactions
Key points
- Cells transform energy and matter in a series of enzyme-mediated reactions that make up a metabolic pathway
- a pathway is when the product of one reaction acts as the substrate for a subsequent reaction
- reactions that break down molecules are catabolic
- reactions that synthesize molecules are called anabolic
- chemical energy is a form of potential energy represented by the bonds between atoms
- laws of thermodynamics govern the process of energy transformation in a cell
- energy is neither created nor destroyed
- a reaction only proceeds spontaneously if it results in increased entropy
- in biology we talk about energy in terms of the change in net free energy, ΔG
- reactions that require net input of energy have positive ΔG, endergonic
- reactions that release potential energy have negative ΔG, exergonic
- endergonic and exergonic reactions are coupled
Questions for Practice
- Define the phrase metabolic pathway.
- What is the difference between endergonic and exergonic reactions?
- What is ΔG, and what is the significance of its sign (positive vs. negative)?
- What is energy? Provide examples of the cellular use of energy.