AP Bio Unit 4 Cell Communication

Direct communication…

a. Cell-to-cell contact

• Immune cells, such as antigen presenting cells, helper and killer T cells.

• Plasmodesmata in plants allow materials to be transported from cell to cell.

• Gap junctions in animals in cardiac muscle allow materials to be transported from cell to cell so all the cells in the heart function in unison.

Local distance signaling…

• secreting cell and target cell are close by; use local regulators.

  • nerve cells and neurotransmitters, cytokines, chemokines, yeast mating, quorum sensing, and morphogens gradient

Long distance signaling…

• secreting cell and target cell are far apart

  • hormones

Local regulators…

• signaling molecules that act on nearby cells through short-distance diffusion.

• Yeast mating factors, neurotransmitters, plant immune response.

Cell communication using local regulators…

• neurotransmitters

• yeast mating factors

• plant immune response

• quorum sensing

• morphogen gradient in embryonic development 

Morphogen gradient…

• diffusable substances which can form gradients in tissues

• allows cell to read both direction and distance from the organizing centers (cells that produce the morphogens)

• most are proteins

Excitatory neurotransmitters…

• open Na+ channels

• brings neuron towards threshold

Inhibitory neurotransmitters…

• Opens K+ and Cl- channels

• brings neuron away from threshold

Quorum Sensing…

• use chemical messengers by microbes to communicate with near cells and to regulate specific pathways in response to population density.

• bacteria release a chemical (auto inducers) into their surrounding which is small organic molecules so bacteria’s can do cell-to-cell communication.

Action potentials…

• are impulses, electrical signals, along neurons

• membranes are polarized by the establishment of electrical potentials across the membranes.

Membrane potential…

• difference between the charges on either side

• maintained by action of Na/K pump and large proteins and anions

Resting potential…

• due to actions of sodium potassium pump

• high concentration of Na and Chlorine outside

• high concentration K inside

• More positive outside, more negative inside

Depolarization…

• reduction of membrane potential

• sodium floods into cell as sodium channels open, making it more positive on the inside and more negative outside.

Action potential…

• causes depolarization

• results in Na moving in, and reset by K moving out

Repolarization…

• sodium channels close, and diffuse in different directions.

• potassium channels open and potassium floods out the cell and Cl- channels open allowing them to enter.

• putting the charge back to more positive outside the cell and negative inside the cell.

Hyperpolarization…

• potassium channels are slow to close, making too much leave, and increasing the membrane potential.

• chlorine is still entering the cell, as more potassium leaves.

Synapse…

• transmission of information between neurons occurs across synapses.

• involves chemical messengers called neurotransmitters

• short distance communication-using local regulators that target cells within vicinity of emitting cells.