Part of the cell · pH, osmotic and redox homeostasis
Holding the internal balance
Not labelled on the cell picture.
Keeping acidity, water pressure and chemical reactivity inside the cell within the narrow band where its machinery works.
Proteins in the model: 26
Part of the model's 1051 proteins. Each group below is a book group, counted in the working count after the repeats and non-first-cell groups were removed. The proteins are not yet matched gene by gene.
| Group | Proteins |
|---|---|
| DNA repair group | 4 |
| Osmoregulation | 5 |
| Cytoskeleton pathway | 5 |
| Osmosis regulation | 4 |
| pH regulation | 4 |
| Temperature regulation | 4 |
Its pathways
- Thiol redox controlatlas pathway3
- Not yet placed in a pathwayto sort2
If it fails
The internal setpoint drifts, which at 95 °C is not survivable.
Internal balance lost · within the current generation
What it depends on
- Pulling nutrients in from outsideIon transport and solute exchange maintain intracellular pH, osmolarity, and nutrient balance.Book pp. 502–504
- Building and maintaining the membraneSelective membrane permeability allows internal conditions to differ from the surroundings.Book pp. 500–501, 504
- Turning hydrogen into usable energyEnergy supply supports pumps and other active maintenance processes.Book pp. 499, 504
What it supplies
- Mineral ions (not a separate group in the tree)pH and ion buffering constrain metal availability and prevent damaging imbalances.Book pp. 504
- Reading genes into RNA, Building proteins and folding themCompatible pH, ionic strength, and redox conditions support RNA and protein function.Book pp. 183–225, 504
Dependencies are curated from the book at the level of the map’s systems and are not measured protein contacts. See all systems together.
How it is built and controlled
Counts from UniProt annotations of this group’s proteins.
Its place in the control layer
None of this group’s proteins appear in the information, signaling, regulation, machine-signal or assembly lists.
From the control-layer pages. Which genes a regulator controls is mostly inferred from related bacteria, because Aquifex has no genetic system for testing it directly.
Origins
What needs to be explained
How were stable internal conditions maintained in compartments while sustaining material and energy flow?
What needs explaining. Explain the coupling of transport and reactions that maintains viable internal conditions under environmental fluctuations.
Hurdles
- H-BAL-1Compatible operating rangesThe problem. Enzymes, RNAs and membranes each work only within limited ranges of pH, salt and temperature, and those ranges must overlap.Why it is hard. Conditions that suit one component often damage another, especially at the high temperatures where Aquifex lives.Chemistry before lifeStage 0: Not yet addressed by experimentShown: not yet addressed by experiment.In the books: 77 open problems on cellular homeostasis ↗
- H-BAL-2Exchange without collapseThe problem. The cell must take in resources while keeping its internal pH, water balance and ion gradients.Why it is hard. Every opening for nutrients is also a route for losing ions and water; cells control this with pumps, channels and compatible solutes.The integrated cellStage 2: One step shown on its ownShown: Simple fatty-acid vesicles let some nucleotides in while keeping larger molecules inside.In the books: 77 open problems on cellular homeostasis ↗
- H-BAL-3FeedbackThe problem. When conditions drift, the cell must detect the change and trigger a correction.Why it is hard. Feedback needs a sensor, a signal and a response, each a dedicated molecule, linked in the right way.Information and controlStage 0: Not yet addressed by experimentShown: not yet addressed by experiment.In the books: 77 open problems on cellular homeostasis ↗
- H-BAL-4Energy budgetThe problem. Maintenance (pumping ions, repairing damage, replacing molecules) consumes a large share of a cell's energy, and enough must remain for growth and division.Why it is hard. If maintenance costs exceed supply, the cell cannot grow; the energy system and the maintenance systems depend on each other.The integrated cellStage 0: Not yet addressed by experimentShown: not yet addressed by experiment.In the books: 77 open problems on cellular homeostasis ↗
- H-BAL-5Self-maintained internal conditionsThe problem. The cell must keep its own internal pH, ion levels and water balance, with pumps, channels and regulators specified by its genes.Why it is hard. An environment cannot hold the inside of a cell constant; the cell has to do it with encoded machinery from the start.Information and controlStage 0: Not yet addressed by experimentShown: not yet addressed by experiment.In the books: 77 open problems on cellular homeostasis ↗
Scope. Homeostasis overlaps the other categories because it is an outcome of their coordination. Shared components should not be counted as additional independent proteins merely because they serve several functions.
Experimental progress. Structural and functional experiments on MgtE link magnesium-dependent channel gating with magnesium homeostasis, providing a concrete example of regulated ion uptake.
What would strengthen a natural account. Steps shown to work together under plausible early-Earth conditions, without a chemist choosing the reagents, purifying the products or changing conditions between steps, would strengthen a natural account of origins in proportion to what they explain. Loss of a claimed dependency or discovery of functional alternatives would weaken the corresponding design argument. Gaps in the record do not supply a numerical likelihood for either explanation.
Observations. Viable pH, osmotic and redox ranges depend on regulated transport and reactions. Feedback can connect disturbance to compensating activity.
Hallmarks that apply.
- H36 Homeostatic regulation: Viable pH, osmotic and redox ranges depend on regulated transport and reactions.
- H37 Feedback control: Feedback can connect disturbance to compensating activity.
- H40 Cross-domain constraint satisfaction: Internal conditions affect enzyme function and membrane energetics together.
The author’s conclusion. The coordinated features give the author a positive reason to consider design within the wider cellular architecture. For this local system alone, they do not establish that design is uniquely the best historical explanation. The conservative inference is that the system contributes to a cumulative design case, with its weight conditional on the comparative evidence and on how much plausible natural pathways explain.
From the book article Cellular Homeostasis, with its scientific references.
How it was discovered
- 1961Peter Mitchell proposes that cells store energy as gradients of ions across membranes (Nobel Prize 1978).Mitchell, Nature 191:144–148 (1961)
- 1964Laurent, Moore and Reichard discover thioredoxin in E. coli as the hydrogen donor for making DNA building blocks.Laurent, Moore & Reichard, Journal of Biological Chemistry 239:3436–3444 (1964)
- 1975The three-dimensional structure of E. coli thioredoxin is determined.Holmgren et al., PNAS 72:2305–2309 (1975)
Each hurdle above is sorted by kind and by how far experiments have got (see “How hurdles are sorted” at the top).
All parts of the cell side by side: origins hub. The book articles:
- Cellular Homeostasis: system page · full description · origins