User:Tyleryan/sandbox

Original- "Chemotaxis"

Eukaryotic chemotaxis
The mechanism that eukaryotic cells employ is quite different from that in bacteria; however, sensing of chemical gradients is still a crucial step in the process. Due to their size, prokaryotes cannot detect effective concentration gradients; therefore, these cells scan and evaluate their environment by a constant swimming (consecutive steps of straight swims and tumbles). In contrast, the size of eukaryotic cells allows for the possibility of detecting gradients, which results in a dynamic and polarized distribution of receptors; induction of these receptors by chemoattractants or chemorepellents results in migration towards or away from the chemotactic substance.

Eukaryotic chemotaxis
The mechanism of chemotaxis that eukaryotic cells employ is quite different from that in bacteria; however, sensing of chemical gradients is still a crucial step in the process. Due to their small size, prokaryotes cannot directly detect a concentration gradient. Instead, prokaryotes sense their environments temporally, constantly swimming and redirecting themselves each time they sense a change in the gradient.

Eukaryotic cells are much larger than prokaryotes and have receptors embedded uniformly throughout the cell membrane. Eukaryotic chemotaxis involves detecting a concentration gradient spatially by comparing the asymmetric activation of these receptors at the different ends of the cell. Activation of these receptors results in migration towards chemoattractants, or away from chemorepellants.

It has also been shown that both prokaryotic and eukaryotic cells are capable of chemotactic memory. In prokaryotes, this mechanism involves the methylation of receptors called methyl-accepting chemotaxis proteins (MCPs). This results in their desensitization and allows prokaryotes to "remember" and adapt to a chemical gradient. In contrast, chemotactic memory in eukaryotes can be explained by the Local Excitation Global Inhibition (LEGI) model. LEGI involves the balance between a fast excitation and delayed inhibition which controls downstream signaling such as Ras activation and PIP3 production.