Cell Communication

Direct Contact

Direct contact is through cell junctions in animal cells, and plasmodesmata in plant cells. Signaling substances and other material dissolved in the cytoplasm can pass freely between adjacent cells

Examples include, immune cells which are antigen presenting cells (APCs) communicating to T cells through direct contact

Local Regulators

Local regulators a secreting cell will release chemical messages (local regulators/ligands) that travel a short distance the extracellular fluid

The chemical messages will cause a response in a target cell

• Paracrine Signaling 

  • This type of signailing invovles secreotry cells releasing local regulars which are languids (chemical messages). These local regulators release through exocytosis to an adjacent cell.  

• Synaptic signaling

  • This occurs in animal nervous system. Neurons secret neurotransmitters (messages) that diffuse across the synaptic cleft to the target cell. This target cell with get this message, leading to the activation of it's receptor and in result leading to a cellular response.

Long Distance Signaling 

• • This signaling occurs within hormones, occuring in animals and plants.

    • Plants: they release homones through into their vestular tissue, this includes the xylem and phloem or into the air where it will reach the target tissues. Thus, leading to a cellular response. 

    • Animals: they use endocrine signaling, this means signaling through the organs and blood. Specialized cells release homones into the circulatory systems until they reach the target cell.

  • Example of animal cell long distance signaling:

    • Insulin is released by the pancreas and it then transported to the blood where it will circulated untill it reaches a target cell.

Cell Signaling

1. Reception

2. Transduction

3. Response

1.Reception

• The ligand binds to the receptor (a macromolecule that binds to a signal molecule)

• These receptors can be found in two different locations, this includes outside the cell or inside

• Once the ligand binds to the receptor this leads to a conformational change that allows the receptor to interact with other molecules 

• Initiating a transduction signal

• These receptors are specific to what ligands can bind to them

• Types of Receptors

Plasma membrane Receptors= found on the plasma membrane of cells

• Ligands that bind to them are usually polar, water-soluble, and large

• Most common type of receptor 

• Ex. GPCR (G-protein coupled receptor) and Ligand gated ion channels

Intracellular receptors= found within the cell

• Found in cytoplasm and nucleus of target cell

• Hydrophobic molecules such as steroids, hormones, and gasses usually bind here.

2. Transduction

• This stage is where the extracellular signal is converted into an intracellular signal that leads to a cellular response

• Sequence of changes with occur this is called a signal transduction pathway (STP)

  • STP regulates protein activity through the cell with protein kinase replaying signal inside the cell by phosphorylation and protein phosphatase dephosphorization which shuts off the pathways

  • One can think about Kinase as the "turn on" of a switch and Phosphatase as the "turn off"

3. Response

• The final molecule will convert the signal into a response that will alter a cellular process

• The cellular processes include:

  • membrane permeability, metabolic process, and gene activation