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Platelets have no cell nucleus; they are fragments of cytoplasm derived from the megakaryocytes [2] of the bone marrow or lung, [3] which then enter the circulation. Platelets are found only in mammals, whereas in other vertebrates (e.g. birds, amphibians), thrombocytes circulate as intact mononuclear cells. [4]: 3
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. [1] This takes place through a pilus. [2][full citation needed] It is a parasexual mode of reproduction in bacteria. A micrograph displaying Escherichia coli undergoing bacterial ...
Illustration of a bacterium showing chromosomal DNA and plasmids (Not to scale) A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; however, plasmids are ...
In most bacteria the most numerous intracellular structure is the ribosome, the site of protein synthesis in all living organisms. All prokaryotes have 70S (where S= Svedberg units) ribosomes while eukaryotes contain larger 80S ribosomes in their cytosol. The 70S ribosome is made up of a 50S and 30S subunits.
Each half of the chromosome replicated by one replication fork is called a "replichore". (Graphic computer art by Daniel Yuen) A circular chromosome is a chromosome in bacteria, archaea, mitochondria, and chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromosome of most eukaryotes. Most prokaryote chromosomes contain ...
The F-plasmid (first named F by one of its discoverers Esther Lederberg；also called the sex factor in E. coli，the F sex factor, or the fertility factor) [1][2][3] allows genes to be transferred from one bacterium carrying the factor to another bacterium lacking the factor by conjugation. The F factor was the first plasmid to be discovered.
A megakaryocyte (from mega- 'large' karyo- ' cell nucleus ' and -cyte ' cell ') is a large bone marrow cell with a lobated nucleus that produces blood platelets (thrombocytes), which are necessary for normal clotting. In humans, megakaryocytes usually account for 1 out of 10,000 bone marrow cells, but can increase in number nearly 10-fold ...
The genetic material is freely found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. [3]