_{This image has a hidden subtlety I only touch on briefly today... for now}

About a week ago, I posted A journey down the tree of life from the very beginning right down to humans. It was pretty wild.

When I found this site I had a dozen ideas that I could do to both educate and learn for myself to appreciate life on a whole new level. So with that introduction to the tree, now it's time to begin a series looking at each stage that we went through to get to humans.

Following that I might even go in different directions if there cause for curiosity. But humans are a long way off, so let's start with:

Archaea

This is one of those regions of life people typically shy away from. If it's tiny, it must be bacteria. Bacteria is far more familiar a term. But bacteria are a whole different domain to archaea. For those of you who forgot school, check the picture to see just how far off they are from being even remotely similar to each other.

In fact there are three distinct domains (although this surprisingly has some grey areas):

• Eukarya is one domain. here is everything you know, pretty much; reptiles, amphibians, insects, jellyfish, birds, chimps.
• Bacteria is the dirty invisible stuff that makes you die
• Archaea is sometimes considered a link between the two, and also considered the most ancient, and perhaps original form of life.

_{(As usual in science this has actually been challenged in numerous ways, something again I could dig into deeper at a later date)}

Prokaryote

One reason Archaea are so easy to ignore, aside from their size, is that it's really difficult to define them in simple terms. According to wiki, they are:

...typically characterized by membrane lipids that are branched hydrocarbon chains attached to glycerol by ether linkages.

This doesn't help at all, does it? But by looking at bacteria, we can see what's going on. Both bacteria and archaea are prokaryotic. This means they are both unicellular, and they do not have a nucleus - the control center of cells that are found only in the Eukaryotic domain. They also lack other organelles like the mitrochondria - 'the power house' of eukaryotic cells.

This might make you wonder how they exist at all. It's kind of like saying they don't have a brain or heart. But then, neither do jellyfish so that argument is void.

You see, life doesn't have to exist the way we happen to feel comfortable with. Prokaryotes have I guess a similar set up, in that they have what's called a nucleoid region, which looks like just an area where the nucleus would have lives but decided it had better places to be. Inside, there's DNA acting in a 'similar way' to our own. It leads to the transcription of RNA and proteins, while also copying itself and dividing as you should very well be familiar with.

This, is bizarrely similar to mitochondria, which also have their own separate DNA and replicates as bacteria does. This lead to the idea of endosymbiosis, that mitochondria is bacteria trapped within a cell, but that is a whole thing we can cover some other day. Or just ask @suesa.

So, a prokaryote is a lifeform without all this junk that eukaryotic life has. But that still doesn't separate bacteria from Archaea. Once more, wiki does not help here, pointing out that unlike archaea:

(bacteria's) membranes are made of unbranched fatty acid chains attached to glycerol by ester linkages

And this is why the issue remains. Morphologically, bacteria and archaea are basically identical. It's only when you get down to the niggly details that there is such a substantial world apart. In fact until fairly recently, they were both joined as one, called 'archaebacteria', coined by Carl Woese.

Biochemistry

It all comes down to the cell walls. In bacteria, their cell walls are made up of something called 'peptidoglycan' made of sugar and amino acids. Archaea on the other hand have cells walls made from Pseudopeptidoglycan, and sometimes other things that are not peptidoglycan. I love that the word 'dog' is in there.

Bacteria's walls are made from unbranched fatty acid chains, whereas Archaea's are made from branched hydrocarbon chains. Additionally, these chains are attached differently; bacteria with ester bonds, archaea with ether bonds. The difference here is basically that bacteria's ester bonds have a slightly more complex structure than ether bonds:

Without digging too deeply into the chemistry - I am supposed to be going out tonight after all - Archaea basically seem to be built differently right at the core of their being, but they also share similarities between both Bacteria and Eukaryote domains.

Life

Archaea also tend to lead different lives to the other two domains. Typically, archaea are found in extreme environments, shunned by their more complex counterparts, presumably. They love hot springs and highly acidic environments, deep inside humans and the bottom of oceans. In fact, in every 'Surviving the extremes' episode that I've written, we typically end up pushing the limits to where only single-celled life can survive, and much of those are indeed Archaea.

Bacteria on the other hand are basically ubiquitous, including extreme environments. Eukaryotes on the other hand are pretty pathetic and only live in temperate zones.

HOWEVER...

Fairly recently, archaea have also been found in fairly modest environments such as soils and marshlands, even inside plankton in the oceans, so they are proving to be much more diverse than first thought and are further breaking down the walls between domains. In fact, the branch of life for archaea is rapidly growing and showing an increasing amount of connections to the other two domains even to this day.

There's still much to learn!

Moving on

So basically, if tl;dr, archaea really look like bacteria, reproduce like bacteria and behave and life like bacteria, but they're built on different chemistry. So in that sense comparing them to bacteria would be like saying I'm the same as a wax model. In many ways I'd be inclined to agree.

Well, that covered basically zero of the tree, having not zoomed in on any branches at all, but that's the fun of discovery I suppose, it takes time! Until next time, thanks for reading =)

Images Sources: _{Bacteria | Ether vs Ester | Original image... from a website proving God lol}

References: _{Domain | Colorado Lecture | Prokaryote | Archaea | Diversity of Archaea | Archaea growing taxonomic tree}