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Muuh Cellular Biology
Muuh Cell
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The Muuh environment is too cold for a flexible polymeric biochemistry to operate- even the simplest nonpolar polymers. At 90-110K and Muuh pressures, even the four-carbon butane tends to freeze solid. Nor are self-assembling bilayer membranes possible; the polar bonds involved are too strong, forming ices.

Instead, Muuh biochemistry relies heavily on microscopic solid surfaces, portions of which can be briefly "melted" and re-sculpted using metabolic energy to provide useful catalytic sites. The most important energetic molecule is acetylene (C2H2), which can either be hydrogenated in two stages (to ethene and then ethane) to provide energy, or take part directly in addition or polymerisation reactions.

This system is extremely resistant to low temperatures. Even if the methane solvent freezes, biochemical processes will simply pause. As soon as the temperature rises enough for the solvent to melt and metabolites to flow again, the cell can resume normal operations. High temperatures are far more destructive. The solid surfaces will soften and lose their structure, killing the cell.

Similar solid cell structures are found other, unrelated methane-ethane life, as well as rarer forms of cryogenic life that use liquid nitrogen or neon as a solvent, though obviously the details vary.

Structure

In its most basic form, the Muuh equivalent of the cell consists of two parallel plates of solidified hydrocarbons. Solid pillars join the plates, holding them the correct distance apart. The core of each plate is formed of long chain alkanes, forming a stable base, on which is laid an active surface composed of a mix of aromatic and aliphatic hydrocarbons.

This active surface is the analogue of dissolved proteins on Earth, carrying out the cell's primary functions. The structure of aromatic rings and double bonds on its surface form binding sites for smaller molecules. These smaller molecules, more loosely bound into van der Waals complexes, form a more easily modifiable and flexible structure which provides various dissolved substances.

Amidst the catalytic sites, a network of grooves and channels provide active transport for larger structures, carrying them to necessary locations in the cell. Finally, a series of spikes rise up from each plate. These form a second transport network. The top of each spike is an active transport site, which can move the larger pieces of frozen hydrocarbons around the cell without disrupting the active surface.

There is no membrane at the rim of the cell; molecules can simply diffuse into and out of the space between the plates, but such molecules are likely to impact the plates, where they can be sorted and moved to the necessary locations.

Genetic information is stored in the centre of the cell in a two-dimensional array of biphenyls, terphenyls, and terminal alkenes on each plate. These genetic arrays encode information using complementary pairs, with each plate holding an array the complements the other. A ring of pillars surrounds this "nucleus".

Small plaques of solid alkanes carry information from the nucleus out into the rest of the cell. The plaques are held against the gene array to read the information, then are carried by the spikes to the desired location, where they are held against the surface of the plate. The active surface is then re-sculpted according the information on the plaque.

Replication

Muuh cells can replicate in two ways. The first is layering replication, which begins when genome reading plaques assemble in centre of a cell. The plaques take imprints from the entire genome of each plate, then combine, becoming the beginnings of a third plate in between the existing two. The new plate expands outwards as hydrocarbons precipitate on its outer rim, growing around the pillars, until it is as broad as the old plates. Simultaneously, the pillars grow longer, increasing the space between the new plate and each of the old plate. The result is two cells joined together, each sharing the new plate.

In slide replications, the cell's plates grow at their rim, becoming elongates, but in opposite directions. A sequence of pillars grow along the rim. All the pillars detach, and the two plates slide relative to each other, until the old surface of each plate is facing the newly-grown surface of its counterparts. Genome reading plaques then transfer a copy of the separate genome to the new surface. The result is two cells sharing two elongated plates.

Multicellularity and eversion

Both types of cell replication result in connected cells, sharing one or both plates. This leads to one of the more peculiar aspects of the Muuh biosphere: Multicellular organisms far outnumber unicellular organisms.

Nevertheless, most organisms are still microscopic, being composed of only a handful of cells without tissue differentiation. After reaching a maximum size, these organisms tend to divide, either by the shared plates fracturing, or by the two plates a central cell separating.

When the two plates of a cell separate, the active surface and the genome of each plate becomes exposed to the outside world. The cell is no longer able to reproduce, but the active surface can interact directly with the external environment, gathering or emitting various molecules, sensing, or growing biomaterials. This process, called eversion, is common among Muuh organisms.

Motility

Being in the solid state, Muuh cells and the tissues they make up tend to be rigid, moving only through growth. Macroscopic sessile organisms, like the coral analogues in reef forests, are often entirely solid.

Motile organisms, however, rely on a specific class of "muscle" tissues. The cells making up these tissues are specialised to change the distance between their two plates using jointed pillars that move between folded and straightened configurations.

Most Muuh fauna superficially resemble arthropods, with hard body parts connected by a limited number or flexible joints. However, this resemblance is indeed only superficial — there is no soft flesh hidden under the exoskeleton, only other rigid tissues.

Similar jointed cells are also used in nerves. These nerve cells grow in lines, sharing two plates, and are activated by mechanical stress. When cells at the start of the signal extend, those further down the nerve extend in turn, transmitting a mechanical signal down the plates.
 
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Development Notes
Text by Liam Jones
Initially published on 29 September 2024.

 
 
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