paracrine signaling

Examples of paracrine signaling in the following topics:

• Forms of Signaling

  • The major types of signaling mechanisms that occur in multicellular organisms are paracrine, endocrine, autocrine, and direct signaling.
  • There are four categories of chemical signaling found in multicellular organisms: paracrine signaling, endocrine signaling, autocrine signaling, and direct signaling across gap junctions .
  • Signals that act locally between cells that are close together are called paracrine signals.
  • Paracrine signals move by diffusion through the extracellular matrix.
  • One example of paracrine signaling is the transfer of signals across synapses between nerve cells.

• Termination of the Signal Cascade

  • Signal cascades convey signals to the cell through the phosphorylation of molecules by kinases.
  • Ligand binding to the receptor allows for signal transduction through the cell.
  • The chain of events that conveys the signal through the cell is called a signaling pathway or cascade.
  • The aberrant signaling often seen in tumor cells is proof that the termination of a signal at the appropriate time can be just as important as the initiation of a signal.
  • Describe the process by which the signal cascade in cell communication is terminated

• Signaling in Yeast

  • Yeasts utilize cell-surface receptors, mating factors, and signaling cascades in order to communicate.
  • The components and processes found in yeast signals are similar to those of cell-surface receptor signals in multicellular organisms.
  • Because yeasts contain many of the same classes of signaling proteins as humans, these organisms are ideal for studying signaling cascades.
  • Therefore, the signaling cascades are also simpler and easier to study, although they contain similar counterparts to human signaling
  • Describe how cell signaling occurs in single-celled organisms such as yeast

• Binding Initiates a Signaling Pathway

  • This type of receptor spans the plasma membrane and performs signal transduction in which an extracellular signal is converted into an intracellular signal.
  • Another complicating element is signal integration of the pathways in which signals from two or more different cell-surface receptors merge to activate the same response in the cell.
  • The effects of extracellular signals can also be amplified by enzymatic cascades.
  • At the initiation of the signal, a single ligand binds to a single receptor.
  • However, activation of a receptor-linked enzyme can activate many copies of a component of the signaling cascade, which amplifies the signal.

• Signaling in Bacteria

  • Bacterial signaling allows bacteria to monitor cellular conditions and communicate with each other.
  • Because the number of cells present in the environment (the cell density) is the determining factor for signaling, bacterial signaling was named quorum sensing.
  • Quorum sensing uses autoinducers as signaling molecules.
  • The peptide autoinducers stimulate more complicated signaling pathways that include bacterial kinases.
  • Describe how cell signaling occurs in single-celled organisms such as bacteria

• Cell Signaling and Cell Growth

  • Cell signaling pathways play a major role in cell division.
  • Cells do not normally divide unless they are stimulated by signals from other cells.
  • Signaling pathways control cell growth.
  • Mutations in these genes can result in malfunctioning signaling proteins.
  • Herceptin therapy helps to control signaling through HER2.

• Methods of Intracellular Signaling

  • The induction of a signaling pathway depends on the modification of a cellular component by an enzyme.
  • They are small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor.
  • Phosphatidylinositol (PI) is the main phospholipid that plays a role in cellular signaling.
  • Termination of the signal occurs when an enzyme called phosphodiesterase converts cAMP into AMP.
  • Explain how the binding of a ligand initiates signal transduction throughout a cell

• Signal Summation

  • Signal summation occurs when impulses add together to reach the threshold of excitation to fire a neuron.

• Visual Processing

  • Visual signals are processed in the brain through several different pathways.
  • Within the nerves, different axons carry different parts of the visual signal.
  • One route takes the signals to the thalamus, which serves as the routing station for all incoming sensory impulses except smell.
  • When visual signals leave the thalamus, they travel to the primary visual cortex at the rear of the brain.
  • From the visual cortex, the visual signals travel in two directions.

• Signaling Molecules

  • Signaling molecules are necessary for the coordination of cellular responses by serving as ligands and binding to cell receptors.
  • Produced by signaling cells and the subsequent binding to receptors in target cells, ligands act as chemical signals that travel to the target cells to coordinate responses.
  • Compare and contrast the different types of signaling molecules:  hydrophobic, water-soluble, and gas ligands