Geiler Alfaro

THE CELL

English scientist Robert Hooke (1635-1703) observed fine cuts of cork under a microscope, and noticed the presence of small cells, similar to those of a honeycomb, which he called cellulas, which in Latin means "little cells".

The cell is the fundamental unit of living beings that contains all the material necessary to maintain vital processes such as growth, nutrition and reproduction. It is found in a variety of shapes, sizes and functions.

Its size is so small that the micrometer or micron (um) is used as a unit to measure its dimensions (1 um is one thousandth of a millimeter).

New observation and analysis techniques have been added to microscopy, such as those provided by molecular biology, which have allowed for rapid and continuous progress in understanding the functioning of the cellular organization; however, much remains to be discovered.

Next, we will review cell theory; its three central ideas underpin all the scientific knowledge built up to now about cells.

CELL THEORY

The cells were discovered by the English scientist Robert Hooke and about 200 years later, thanks to the improvement of microscopes and the observations of many scientists, among whom Schleiden and Schwann stood out, the true importance of this discovery was understood and it was postulated cell theory. This is still in force and maintains that:

The cell is the structural or anatomical unit of all living things. All organisms, from the simplest to the most complex, are made up of one or more cells.

The cell is the functional or physiological unit of living beings. In it all the processes that living beings carry out, such as nutrition, waste removal and respiration, among others, occur.

The cell is the reproductive or origin unit of living beings. All cells come from pre-existing cells.

CELL TYPES

Depending on the complexity they show, there are two types of cells: prokaryotes and eukaryotes. The former correspond to bacteria and the latter, which are more complex, make up the rest of living organisms.

There are several differences between both types of cells, but the main one is the presence or absence of a cell nucleus. This is a usually spherical structure, made up of a double membrane, which contains the genetic material inside: DNA. Prokaryotes have no nucleus (pro = before, karyon = nucleus, in ancient Greek), while eukaryotes do (nucleus = true).

PROKARYOTIC CELLS

Prokaryotic cells are simpler than eukaryotes. These cells are surrounded by a membrane, called the plasma membrane, and inside it is the cytoplasm. The plasma membrane regulates the passage of substances from the exterior to the interior of the cells, and vice versa, the cytoplasm, meanwhile, is a kind of semi-transparent, gelatinous fluid, formed mainly by water and proteins.

EUKARYOTIC CELLS

All animals, plants and fungi are eukaryotic organisms, in addition to algae and protozoa, such as amoebae. The distinctive feature of eukaryotic cells is the presence of structures formed by membranes.

The basic components of all eukaryotic cells are the plasma membrane, the cell nucleus, and the cytoplasm.

In addition, three types of structures are distinguished inside eukaryotic cells. In general, these structures are called organelles and each one has a specific function.

Membrane-less structures, such as ribosomes, centrosomes, and the cytoskeleton.
Endomembrane system, which are the interconnected membranous structures and vesicles, the main ones are the endoplasmic reticulum, the Golgi apparatus, the vacuoles and the lysosomes.
Energy transducing organelles; they are the mitochondria and the chloroplasts.

Next, the structure of eukaryotic cells in general is described.