The DNA of a prokaryotic cell consists of a single circular chromosome that is in direct contact with the cytoplasm.

[1][page needed] A prokaryotic cell has three regions: Plants, animals, fungi, slime moulds, protozoa, and algae are all eukaryotic.

The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound organelles (compartments) in which specific activities take place.

[2] The membrane is semi-permeable, and selectively permeable, in that it can either let a substance (molecule or ion) pass through freely, to a limited extent or not at all.

There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments.

Prokaryotic genetic material is organized in a simple circular bacterial chromosome in the nucleoid region of the cytoplasm.

Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection.

Some (such as the nucleus and Golgi apparatus) are typically solitary, while others (such as mitochondria, chloroplasts, peroxisomes and lysosomes) can be numerous (hundreds to thousands).

The capsule may be polysaccharide as in pneumococci, meningococci or polypeptide as Bacillus anthracis or hyaluronic acid as in streptococci.

Capsules are not marked by normal staining protocols and can be detected by India ink or methyl blue, which allows for higher contrast between the cells for observation.

[2] Cells of all organisms contain enzyme systems that scan their DNA for damage and carry out repair processes when it is detected.

The widespread prevalence of these repair processes indicates the importance of maintaining cellular DNA in an undamaged state in order to avoid cell death or errors of replication due to damage that could lead to mutation.

E. coli bacteria are a well-studied example of a cellular organism with diverse well-defined DNA repair processes.

Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.

Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP),[2] a molecule that possesses readily available energy, through two different pathways.

In plant cells, chloroplasts create sugars by photosynthesis, using the energy of light to join molecules of water and carbon dioxide.

This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA.

mRNA molecules bind to protein-RNA complexes called ribosomes located in the cytosol, where they are translated into polypeptide sequences.

In multicellular organisms, cells can move during processes such as wound healing, the immune response and cancer metastasis.

Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins.

[17][16] In August 2020, scientists described one way cells—in particular cells of a slime mold and mouse pancreatic cancer-derived cells—are able to navigate efficiently through a body and identify the best routes through complex mazes: generating gradients after breaking down diffused chemoattractants which enable them to sense upcoming maze junctions before reaching them, including around corners.

Multicellularity has evolved independently at least 25 times,[22] including in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, or Methanosarcina.

Small molecules needed for life may have been carried to Earth on meteorites, created at deep-sea vents, or synthesized by lightning in a reducing atmosphere.

RNA may have been the earliest self-replicating molecule, as it can both store genetic information and catalyze chemical reactions.

The early cell membranes were probably simpler and more permeable than modern ones, with only a single fatty acid chain per lipid.

[31] It evolved some 2 billion years ago into a population of single-celled organisms that included the last eukaryotic common ancestor, gaining capabilities along the way, though the sequence of the steps involved has been disputed, and may not have started with symbiogenesis.

It featured at least one centriole and cilium, sex (meiosis and syngamy), peroxisomes, and a dormant cyst with a cell wall of chitin and/or cellulose.

[36][37] The plants were created around 1.6 billion years ago with a second episode of symbiogenesis that added chloroplasts, derived from cyanobacteria.

[31] In 1665, Robert Hooke examined a thin slice of cork under his microscope, and saw a structure of small enclosures.

[38] To further support his theory, Matthias Schleiden and Theodor Schwann both also studied cells of both animal and plants.