Create a selective boundary.
Lipid bilayers separate inside from outside while embedded proteins control exchange and signaling.
Side 149
Cell Biology
The cell as an organized physical system: compartments, membranes, molecular machines and signaling networks coordinate transport, metabolism, shape, growth and reproduction.
membrane→compartment→transport→signal→cell behavior
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16working concepts
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SS-1.0standard
Cells organize chemistry through membranes and compartments.
Spatial organization changes reaction conditions, transport requirements and regulatory possibilities.
Separate genome regulation from much of cytoplasmic activity.
Nuclear transport controls access between transcriptional and cytoplasmic machinery.
Couple metabolism to electrochemical gradients.
Internal membranes organize energy conversion and metabolite exchange.
Route proteins and lipids through compartments.
ER, Golgi, vesicles and lysosomes create a regulated trafficking network.
Movement across membranes is selective and energy-dependent.
Concentration, charge and molecular size determine whether transport can occur spontaneously or requires machinery.
Move down a concentration gradient.
Small or membrane-permeable molecules can cross without direct energy input.
Provide selective passive pathways.
Channels can be gated by voltage, ligands, stretch or other signals.
Bind and move specific solutes.
Transporters can mediate facilitated diffusion or couple one gradient to another.
Use energy to move against a gradient.
Active transport creates the electrochemical differences that power many other cellular processes.
Dynamic filaments organize shape, transport and force.
Actin, microtubules and intermediate filaments provide different mechanical and transport functions.
Support shape change and contractility.
Actin networks drive crawling, cytokinesis and cortical mechanics.
Create polarized tracks and structural support.
Motor proteins move cargo along microtubules and build mitotic spindles.
Convert chemical energy into directed movement.
Myosins, kinesins and dyneins transport cargo or generate force.
Connect cells to neighbors and matrix.
Adhesion molecules transmit both mechanical load and biochemical signals.
Cells sense conditions, grow, divide and sometimes die.
Cell-cycle control integrates internal integrity with extracellular signals.
Convert external cues into intracellular responses.
Receptor pathways amplify, filter and integrate information.
Coordinate DNA replication and division.
Checkpoints delay progression when key events are incomplete or damaged.
Separate duplicated chromosomes.
Spindle mechanics and checkpoint signaling reduce segregation errors.
Execute regulated cell death.
Programmed death removes damaged or unnecessary cells without the same inflammatory disruption as uncontrolled rupture.
A cell is organized by boundaries and flows. Compartmentation makes incompatible processes coexist, while transport and signaling coordinate them into one functioning system.