Systems: biology of the cell Flashcards
(15 cards)
What do cells need to do? What do they do to accomplish this?
Cells must:
Divide (and know when to stop)
Move and sometimes stay put
Differentiate into the correct cell types
Function properly (physiologically and structurally)
To accomplish this, they need to:
Communicate with one another
Stick together (adhesion)
Become polarised (having directionality, e.g., front/back or top/bottom)
What is auto-organisation and an example?
This section shows how complex tissues can self-organize based on simple physical principles:
💡 Example: Hydra regeneration
Hydra can regenerate from a small group of cells – showing auto-organisation.
What is the differential Adhesion Hypothesis (Steinberg, 1963)?
Cells sort themselves based on how strongly they stick (adhere) to each other.
Like fluids with different surface tensions, cells with stronger mutual adhesion clump together.
Leads to tissue separation and pattern formation.
What is the cellular Potts model? (Graner and glazier 1992)
A computational method to model cell behavior.
Simulates how cells adhere, round up, and sort.
Can test the hypothesis of differential adhesion.
What are the 3 key cell surface mechanics?
Adhesion-driven tension
Area conservation
Cortical tension (from cytoskeleton)
What is molecular correlate, what makes up self organisation?
🧬 Molecular Correlate:
Adhesion is mediated by cadherins, membrane proteins that bind cells together.
📌 Take-home message:
Simple rules + adhesion differences → self-organisation.
Computational models help test biological ideas.
What are unique features from the plant body plan?
Plant cells don’t move or change neighbors.
No cell sorting like in animals.
They rely on growth, polarity, and signals to shape tissues.
Where do complex plant forms arise from?
Gene regulation
Soil/environmental interactions
Ecological context
What is auxin and the questions explored around it?
Auxin is a hormone that directs plant growth.
Moves directionally through PIN transporters (membrane proteins).
Polar auxin flow creates gradients that give cells instructions.
Questions explored:
Are auxin transporters enough to form patterns?
Are auxin gradients stable in growing tissues?
What does modelling auxin show in plants?
Shows that coordinated direction of PINs is critical.
Dynamic flows of auxin result in stable root growth.
Auxin gradients provide positional information, even during growth.
Take-home message:
Plants use directional transport and polarity to auto-organize.
Similar to animal tissues, gradients guide development.
What is single cell motion – The Keratocyte Example?
Animal cells move by reshaping their actin cytoskeleton.
G-actin → polymerizes to F-actin
ARP2/3 complex creates side branches for movement
How is polarity controlled through small G-proteins?
Proteins like Cdc42, Rac, and Rho:
Control front/back polarity
Are molecular switches (GTP-bound = active)
What is the int
eraction model?
Cdc42 & Rac active at the front
Rho active at the rear
Fast cytoplasmic diffusion, slower membrane diffusion = stable patterns
Take-home message:
Patterns and polarity arise from protein interactions and diffusion dynamics.
Cells are dynamic, constantly changing shape and reacting to their environment.
What does systems biology do?
Putting It All Together
Combines imaging, models, and experiments to study:
Shape formation
Polarity
Movement
Response to stimuli/conflict
Example: How a cell resolves shape conflicts when hitting a wall.
What are the 6 final conclusions of systems biology?
Cells self-organise through simple principles: adhesion, polarity, signaling.
Computer models help us test biological ideas and make predictions.
In animals, cell sorting relies on differential adhesion.
In plants, morphogenesis depends on polarised signaling (e.g., auxin flow).
Both plant and animal cells form patterns using similar strategies:
- Polarity
- Diffusion
- Feedback loops
Systems biology helps us connect molecular mechanisms to whole-cell and tissue behavior.
