4.3: Eukaryotic Compartmentalization
One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles, such as the nucleus and mitochondria, that carry out specialized functions. Since biological membranes are only selectively permeable to solutes, they help create a compartment with controlled conditions inside an organelle. These microenvironments are tailored to the organelle's specific functions and help isolate them from the surrounding cytosol.
For example, lysosomes in the animal cells maintain an acidic environment compared to the surrounding cytosol. This helps the lysosomal enzymes to digest cellular debris. Similarly, pH regulation within mitochondria helps in the synthesis of energy molecules.
Additionally, some proteins require an oxidative environment for proper folding and processing, but the cytosol is generally reductive. Therefore, these proteins are produced by ribosomes in the endoplasmic reticulum (ER), which maintains the necessary environment. Proteins are then transported to their final destination within the cell through membrane-bound vesicles.
The genetic material of eukaryotic cells is compartmentalized within the nucleus, surrounded by a double membrane called the nuclear envelope. Small pores in the envelope control which molecules or ions can enter or leave the nucleus. For instance, messenger RNA (mRNA) exits the nucleus through these pores to take the genetic instructions encoded in the DNA to the ribosomes, where they can be translated into protein.
Therefore, compartmentalization allows the execution of many different functions with greater efficiency within the same cell by concentrating the required components in a confined space and segregating them from the rest of the cell.