Cells are the smallest units of life. They are a closed system, can self-replicate, and are the building blocks of our bodies. In order to understand how these tiny organisms work, we will look at a cell’s internal structures.
We will focus on eukaryotic cells, cells that contain a nucleus. Prokaryotic cells, cells that lack a nucleus, are structured differently.
A cell consists of two major regions, the cytoplasm and the nucleus. The nucleus is surrounded by a nuclear envelope and contains DNA in the form of chromosomes. The cytoplasm is a fluid matrix that usually surrounds the nucleus and is bound by the outer membrane of the cell. Organelles are small structures within the cytoplasm that carry out functions necessary to maintain homeostasis in the cell. They are involved in many processes, for example energy production, building proteins and secretions, destroying toxins, and responding to external signals.
Organelles are considered either membranous or non-membranous. Membranous organelles possess their own plasma membrane to create a lumen separate from the cytoplasm. This may be the location of hormone synthesis or degradation of macromolecules. Non-membranous organelles are not surrounded by a plasma membrane. Most non-membranous organelles are part of the cytoskeleton, the major support structure of the cell. These include: filaments, microtubules, and centrioles.