A cell is the smallest form of life.* It is made of a nucleus or nucleoid of DNA floating in cytoplasm, surrounded by a cell membrane.
Protein assumbly is handled by ribosomes, which receive instructions from the DNA:
Cells can be divided into two classes: Prokaryotes and Eukaryotes.
Prokaryotes have a very simple structure with no defined bodies inside. The ribosomes are controlled by a single strand of DNA bunched together in a nucleoid. The cell is covered by a cell membrane which may also have a cell wall and a flagellum, a tentacle-like structure used for locomotion.
Bacteria and archaea, a set of bacteria-like organisms, are made of prokaryote cells. While prokaryotes are single cell organisms, they can cluster together in colonies. All prokaryotes produce asexually.
Eukaryotes have a nucleus for storing DNA, and small, organ-like bodies called organelles. The Golgi body acts like the liver, assembling nutrients like fats and proteins. The mitochondria produce ATP, a chemical used to power the cell. Water is stored in vacuoles. Plant cells have chloroplasts produce energy from sunlight. Plant and fungi cells are covered in a cell wall.
All multicellular organisms have eukaryotic cells. While they all contain the same DNA, they are set to perform specific tasks using only parts of the DNA strand with one exception: stem cells. These cells are unassigned, and can grow into any kind of cell; this makes them extremely useful in medical treatments requiring new tissue.
Eukaryontes reproduce sexually, combining DNA strands from two organisms. Once this new cell is created, it grows and divides much like a prokaryote until it forms a complete organism.
*Viruses are smaller, but are just a strand of DNA covered by a layer of protein. They require a host cell to reproduce, so they are not considered living organisms.
Posted 5066 day ago