Mitochondrial Memes (Part 2: Aliens Within)

Part 1: Logos

150px-Biological_classification_L_Pengo_vflip.svgBiologically speaking, you are a member of the species Homo sapiens, (subspecies Homo sapiens sapiens.) Your genus is Homo–this includes all of our near cousins, like Homo neanderthalensis (with whom H. sapiens interbred,) Homo erectus, and the 2+million year old Homo habilis. Your family is hominidae, aka the great apes–chimps, gibbons, orangutans, gorillas, and us. We cannot interbreed with these groups. Your order is primates. The first primates probably evolved 65 million years (or more) ago; their modern members include apes, monkeys, lemurs, and lemur-like creatures like bushbabies.

Your class is mammalia–all animals with hair,[a] three middle ear bones, mammary glands, and a neocortex, at least according to Wikipedia. Most mammals have placentas and don’t lay eggs, but platypuses and echidnas have to be different. The first mammals appeared 225 million years ago.

From there, we head up to the sub-phylum Vertebrata, or all animals with backbones, then to the phylum Chordates, all animals with a nerve cord running down their back (but not necessarily any bones.) Chordates includes all birds, amphibians, reptiles, fish, and obscure creatures like salps, squishy, tubular creatures that look like jelly fish, and sea squirts, basically brainless tubes. Chordates appear to be over 500 million years old.

Next we have the kingdom Animalia, which includes all of the squishy things like sponges, jellyfish, octopuses, earthworms, and starfish, and crunchy things like insects, crabs, and spiders, in addition to us. The first fossil animals are 665 million years old, though older animals may simply not have been fossilized, due to being too soft. All animals are multi-cellular.

Above that, we have the domain Eukaryotes. All Eukaryotes have a nucleus and other organelles enclosed within membranes. Eukaryotes are divided into plants, animals, fungi, and protists, which are generally single-cells and include algae and the malaria parasite.

This is an animal cell, but all Eukaryotes are similar
This is an animal cell, but all Eukaryotes are similar, due to their nucleus (1) enclosed within a membrane (2) and other organelles.

There are two other major domains of life, bacteria and archaea, collectively known as prokaryotes. They have neither nuclei nor any other membrane-bound organelles. As distant cousins go, these guys are pretty distant–the common ancestors of eukaryotes, bacteria, and archaea lived over 1.6 billion years ago, possibly over 2.7 billion years ago (it’s really hard to find fossilized algae and bacteria.)

450px-Phylogenetic_tree.svg

Humming away inside your H. sapiens cells, making energy for you, are mitochondria. You might have heard that your mitochondria can be used to trace your maternal family line, because they 1. Are only passed down from mother to child (eggs have mitochondria but sperm don’t;) 2. Possess their own DNA, referred to as mtDNA or mDNA.

Why do mitochondria have their own DNA?

Because they aren’t human. They aren’t animals; they aren’t even eukaryotes. They’re prokaryotes, like bacteria.

Approximately one or two billion years ago, our ancestor–probably a primitive eukaryote cell–ate a prokaryote. But this prokaryote, by a great stroke of luck, didn’t get digested. Instead it got comfy, settled in, and stuck around. Here’s a helpful graphic to explain the process in more detail:

800px-Serial_endosymbiosis.svg

Yes, chloroplasts are prokaryotic invaders, too.

Mitochondias’ closest living relatives are the other Rickettsiales, an order of proteobacteria, which cause a variety of diseases including Typhus and Q fever. Luckily for us, our mitochondria help keep us alive, rather than kill us.

Part 3: to be named

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