From Newsgroup: talk.origins
What would it be like to walk around inside a cell? (In this example,
and human ovum.) This exercise may help you comprehend/intuit/appreciate
its workings better.
*The Scale*
If a nucleotide were the size of a tennis ball, a canonical amino acid
would match a golf ball, averaging 37 and 17 atoms respectively.
A mature human oocyte (ovum) is 7km diameter sphere, with a nucleus of
up to 2km, cell membrane roughly 0.5rCo0.7 metres thick.
*The City*
The interior is extremely crowded, but not solidrComore like a dense,
moving fog of machinery.
There is no empty space at human scale; movement happens through
constantly shifting gaps.
Objects range from grapefruit-sized to skyscraper-sized, with the
overwhelming majority being small-to-medium machines.
*The Inhabitants*
A. Individual folded proteins (the dominant population), grapefruit raA
soccer ball size; 100rCo300 amino acid; ~10-|-|rCo10-|-# of them. They are everywhere: cytoplasm, cortex, perinuclear region, appearing like a
dense swarm of autonomous robots, continuously bumping, binding, releasing.
B. Protein complexes (functional teams), e.g., transcription factors, spliceosomes, signalling hubs; millions to tens of millions. Form
temporary clusters, especially near the nucleus, cytoskeletal tracks,
membrane regions. They are delivery trucks or small rooms that briefly assemble, disassemble, and reassemble elsewhere.
C. Ribosomes (protein factories); hundreds of thousands to millions.
Dense in cytoplasm, sparse in nucleus; often found in clusters
(polysomes). Factories the size of small buildings, many operating in parallel, with raw materials constantly arriving and finished products immediately released into the crowd.
D. Cytoskeletal assemblies (infrastructure - actin filaments;
microtubules); hundreds of metres to kilometres. Forming dynamic
highways and scaffolding; continuously assembled and dismantled.
Suspension bridges and rail lines that reconfigure in real time while
traffic continues. With cargo hauled by motor proteins (themselves ~1 m machines walking hand-over-hand).
E. Organelles. E.g. Mitochondrion (power & control district); ~1rCo2 km
long, ~300rCo500 m wide; tens to hundreds; outer wall: 0.6m thick, inner
wall: another 0.6 m thick, folded into cristae (folded walls forming
canyons and terraces tens of metres high). Enzymes: thousands of soccer-ball-scale machines embedded in the walls; proton gradients
become pressure differentials; ATP synthase machines are rotary
turbines. Energy is not rCLstoredrCY but continuously generated and spent. A hydroelectric plant built inside a mountain, with internal tunnels
forcing flow in one direction only.
Or, the endoplasmic reticulum (manufacturing & logistics zone); several kilometres of interconnected sheets and tubes, ~20rCo50m sheets. A
continuous membrane studded with ribosomes (~25m factories). Interior
(lumen); oxidising environment, chaperones everywhere, quality-control checkpoints. Proteins are synthesised, folded, checked, rejected or
forwarded. A vast industrial park with assembly lines running directly
into enclosed inspection halls.
F. Nuclear interior (1.3rCo2 km inner sphere; chromatin fibres of 10rCo30m thickness, thousands of kilometres long, tightly folded. Transcription factories in ~50rCo100 m clusters, dozens to hundreds active at any time.
A dense industrial core, with massive cable bundles routed through
specialised production districts.
*The Wall*
~0.6m thick lipid bilayer (fluid, deformable), with embedded proteins of
many sizes 1rCo10m. Receptors, channels, pumps, adhesion molecules;
thousands per 100m-# of membrane. A living wall studded with doors,
valves, sensors, antennae, and rotating machines, all subtly drifting laterally. Nothing is fixed in place.
Just beneath the membrane: the cortical zone, a protein meshwork
~50rCo100m inward from the membrane. Comprises actin filaments (1rCo2 m
thick, hundreds of metres long); cross-linkers, regulatory proteins
Provides mechanical stiffness, shape control, polarity establishment,
signal amplification. A dense geodesic lattice pressed up against the
city wall, constantly tightening, loosening, and rearranging.
*The Experience*
Proteins occupy ~30rCo40% of volume. Water is the remaining rCLairrCY. Nothing is dilute. Diffusion is like walking through a packed stadium, not
drifting in space. Weak interactions matter; spatial organisation
matters; timing and localisation are as important as sequence.
A living, self-modifying megacity rCo kilometres wide rCo built entirely of moving molecular machines, with no central controller. Upon
fertilisation, going on to divide and differentiate countless times to assemble a human.
*The Control*
For example, a city "block" is not executing a single rCLprogram.rCY
Instead, thousands of overlapping processes; no master clock; no central dispatcher. Control arises from: concentration gradients, proximity,
binding affinities, mechanical constraints. Information is embodied, not broadcast.
*The Conclusion*
For me, to marvel, and more. And you?
_____
Source: ChatGPT
Also: The Inner Life of the Cell Animation
https://www.youtube.com/watch?v=wJyUtbn0O5Y
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