Key concepts in biology Study Guide

Enzymes are biological catalysts, which are typically proteins that speed up the rate of biochemical reactions without being used up. They achieve this by lowering the activation energy required for a reaction to occur. The fundamental principle of enzyme action is known as the 'lock and key' hypothesis, which describes their high degree of specificity. Each enzyme has a unique, three-dimensional region called the active site. This active site is precisely shaped to complement specific substrate molecules, much like a lock accommodates only its particular key. When a substrate molecule (the key) binds to the active site (the lock) of its corresponding enzyme, an enzyme-substrate complex is formed. Within this complex, the enzyme facilitates the chemical reaction, converting the substrate into products. Once the reaction is complete, the products are released from the active site, and the enzyme is free to catalyse further reactions with more substrate molecules. The precise fit ensures that only the correct substrate can bind, making enzymes highly specific to the reactions they catalyse.

Advances in microscope technology, particularly the development of electron microscopes, have revolutionised our understanding of cell structure and function. Early light microscopes, while groundbreaking, were limited by the wavelength of visible light, meaning they could not resolve structures smaller than approximately 200 nanometres. This limitation meant that many tiny internal cell components, or organelles, remained invisible or appeared as indistinct blobs. The introduction of the electron microscope overcame this hurdle. Instead of light, electron microscopes use a beam of electrons, which have a much shorter wavelength. This allows for significantly higher magnification and resolution, revealing intricate details of organelles such as mitochondria, endoplasmic reticulum, and ribosomes. With this unprecedented clarity, scientists could observe the precise morphology and arrangement of these sub-cellular structures, leading to a deeper understanding of their individual roles and how they collectively carry out complex cellular processes. For example, seeing the cristae within mitochondria clarified their role in increasing surface area for cellular respiration, and observing ribosomes on the endoplasmic reticulum revealed their function in protein synthesis for secretion.