Cell Adhesion + Diffusion

Tunneling nanotubes

• thin, membranous cellular connections that act as channels for material exchange between cells, transferring a variety of cargos including ions, organelles, and even viruses

• TNTs are dynamic, with varying lengths that can change as the cells move, and their formation is influenced by factors like cell density, and adhesion

Cell Recognition

• One cell specifically recognizes and binds to another cell of a certain type

Cell Adhesion

The connection between the two cells is strengthened

Two Types of Cell Adhesion

• Homotypic

• Heterotypic

Homotypic adhesion

The same molecule extends from both cells and bind to each other

Heterotypic

• Different molecules binds together from the two cells

Cell Junctions

Cell Junctions are specialized structures that hold cells together

Tight Junctions

• Tight junctions form a tight seal between cells, forming a “quilted seal”, helping ensure directional movement of materials

• Blocks the movement of dissolved materials through the space between epithelial cells

Epithelial Cells

Something being an epithelial cell means it is a tightly packed cell that forms a physical barrier

Desmosomes 

• Hold Cells together while still alowing materials to move around in the intercellular space

Intercellular space

The intercellular space is the gap that separates adjacent cells in tissues

Gap Junctions

• Form tunnels between adjacent cells so they can communicate by exchanging small molecules

Extracellular Matrix (ECM)

A macromolecule rich gel outside of cells

How do cell membranes adhere to the ECM?

Through adhesion receptors called Integrins

Integrin

• Transmembrane proteins that attach to the Extracellular Matrix and actin microfilaments inside of the cell

How can cells move within a tissue?

By the binding and reattaching of Integrin receptors to the ECM

Selective Permeability

• Some substances are able to pass through, but not others

Diffusion

The process of random movement of a solute from a region of high concentration to a region of low concentration

Equilibrium

• Particles move randomly in solution, where they are evenly distributed, they are in equilibrium

• Even when in equilibrium, molecules continue to diffuse 

Size + Mass - Diffusion Rate

smaller, less massive molecules move faster

Temperature of Solution: Diffusion Rate

Higher temperatures → faster diffusion

Density of solution: Diffusion Rate

Higher density → Slower diffusion

Concentration Gradient: Diffusion Rate

The higher the concentration gradient(difference), the faster the diffusion

Surface Area : Distance Ration - Diffusion Rate

The greater the ratio of surface area to distance, → faster diffusion

Passive Transport

• the movement of molecules across a biological membrane from an area of high concentration to an area of low concentration,

• does not require energy from the cell

• Simple diffusion (for small, non-polar molecules like gases)

• Facilitated diffusion (using carrier proteins or channels for larger or charged molecules)

• osmosis