#prokaryotes

evolution

prokaryotes (organisms that make up domains bacteria and archaea) have incredible evolutionary success, which has allowed them to become the most widespread organisms on earth. their small size and insanely rapid reproduction rates is one trait that has allowed them this success - because of how quickly they can reproduce, there is a very short span of time between evolution. this plus frequent mutations equal super saiyan evolution speeds!

prokaryotes also have a wide range of adaptations, which allows them to live in a wide variety of environments, including very extreme ones.

so what are prokaryotes?

prokaryotes are single-celled organisms with no nucleus or membrane-bound organelles. as far as we know, they are the first organisms to inhabit earth. because they have been around for literally billions of years, they have incredible diversity.

prokaryotes are itty-bitty, even compared to eukaryotic cells. they typically range from 0.5-5 micrometers. one notable exception, however, is Thiomargarita namibiensis, which can be up to 750 micrometers (bigger than a poppy seed).

what do they look like??

there are three common shapes that prokaryotes come in: cocci (circular/ovular. little orb guys.), bacilli (rod shaped, think bacteria depictions in media. the beauty standard, if you will.), and spirilla (wiggly corkscrew guys. can also resemble commas or coils).

cocci can hang out alone or form chains with their buddies; sometimes they'll bunch up like grapes. bacilli like to be alone, but sometimes they'll form polite little lines with each other to make long rods. spirilla can be found alone or in chains.

cell surface structures

almost all prokaryotes have a cell wall, which holds its shape and prevents it from exploding into smithereens in hypotonic (low osmotic pressure) environments. prokaryotic cell walls are made of peptidoglycan. archaeabacteria are the weirdos in this, their cell walls are made of polysaccharides and proteins.

bacteria can be sorted by differences in their cell-wall, identified through a process called gram stain. i'll probably make a mini-post talking about gram stain and link it here when i do.

most prokaryotes also have some sort of sticky layer on the outside, called a capsule (or, if less organized, a slime layer). these, as you may have figured out, allow prokaryotes to stick to things. they can also prevent dehydration.

many prokaryotes are capable of taxis - this means they are able to purposefully move in a specific direction in response to external stimuli. the most common structure used for this is a flagellum, which look like little wiggly tails. if you've ever played spore you are probably familiar with these things, and just like in spore they can be pretty much anywhere on an organism.

internal structures

as mentioned above, prokaryotes do not have a nucleus or membrane bound organelles. they're actually pretty simple organisms overall. they usually only have one circular chromosome contained inside of their nucleoid (which is different from a nucleus). additionally, they have DNA molecules that can replicate independently called plasmids.

reproduction

most prokaryotes reproduce via binary fission, which means the cell doubles itself and then the doubles double themselves and then so on and so forth. think like the game 2048.

"but b!" you say, "what about genetic diversity?? if they're just making clones of themselves then there is none!" that is correct! that's where mutations come into play. since there is no exchange of alleles in asexual reproduction, prokaryotes heavily rely on random mutations.

there is another phenomenon that can occur called genetic recombination, which is when you mash together dna from two different organisms. "but... but there's no sex??" correct again! instead, transformation, conjugation, and transduction is how this swap happens. i may go into more detail about this in a mini-post - i will link it here if i do so.

i also wanna make a quick note about dna transfer between different species, which my textbook refers to as "horizontal gene transfer" which sound like one hell of a euphemism to me personally. (for clarification's sake, horizontal gene transfer is a scientific term).

metabolism

the are four major "modes" that prokaryotes acquire nutrition: photoautotroph, chemoautotroph, photoheterotroph, and chemoheterotroph. photo- means light, and chemo- means chemicals. this combined with autotrophs referring to organisms that can create their own food and heterotrophs referring to organism who source food externally makes it relatively simple to interpret these terms. a prokaryote may fall under one or multiple of these categories.

there are also differences in how prokaryotes interact with oxygen. obligate aerobes need oxygen to live and reproduce, while obligate anaerobes are poisoned by oxygen and must get chemical energy through other means.

often prokaryotic cells will work together to carry out metabolic processes that cannot be completes by a lone cell. as these cells band together they may form what is called a biofilm, which recruits even more cells and makes the colonies even bigger.