CONCEPT 12. Cell signalling & responding to the environment

• The cellular response is triggered by an extracellular signal, which can be a chemical or physical stimulus.
• What is positive feedback?

  Positive feedback increases the change or output resulting in the amplification of a reaction's result.
• What is negative feedback?

  Negative feedback reduces the change or output, resulting in the reduction of a reaction's products bringing the system back to a stable state.
• What are the steps of cell-to-cell communication?

  • Signal perception: signal is detected by a target cell, binding to a receptor protein either on the surface or inside the cell
  • Intracellular signal transduction: the signal is transformed into a form that can bring about specific cellular responses.
  • Cellular response. the cell performs an action in response
• Why is cell-to-cell communication essential?

  Ensure that crucial activities occur in the right cells, at the right times and in proper coordination with other activities occurring in the cell.
• What are endocrine signals?

  Signals that are distributed throughout the body and carried through circulation systems such as the bloodstream to act on target cells at distance body sites. An example of an endocrine sign is a hormone.
• What is paracrine signal?

  Signals that are released into the extracellular fluid to bind receptors on nearby cells. These signals have a localised effect.
• What is a synaptic signal?

  A signal that is transmitted electronically along nerve axon cells, releasing a chemical signal, a neurotransmitter, to be detected by an adjacent cell
• What is a contact dependent signal?

  A signal that is membrane bound and detected by a target cell that is in contact with the signalling cell
• What are autocrine signals?

  Signals that bind to the receptors on the same cell that secretes them
• What are Juxacrine/contact-dependent signals?

  Signals that bind to adjacent cells
• What feature of steroids allow them to activate intracellular receptors?

  Steroids are small, hydrophobic molecules and can, therefore, pass through the plasma membrane to activate intracellular receptors.
• Without the appropriate receptor, a cell will be deaf to the signal. By reducing the types of receptors a cell possesses, a cell restricts the types of signals it response to allowing for specificity.
• Types of receptors:

  Enzyme-linked receptor, GPCR, Ligand-gated ion channel, intracellular receptor
• Where is an enzyme-linked receptor located?

  Plasma membrane
• Where are GPCRs located?

  Plasma membrane
• Where are ligand-gated ion channels located?

  Plasma membrane
• Where are intracellular receptors located?

  Cytosol or nucleus
• What occurs when an enzyme-linked receptor is activated?

  Phosphorylation of an intracellular protein
• What occurs when a GPCR is activated?

  Binds to a G protein
• What occurs when a ligand-gated ion channel is activated?

  Ion channel is opened
• What occurs when an intracellular receptor is activated?

  Transcription of specific genes are turned on
• What extracellular factors do plants respond to?

  Carbon dioxide concentration, red light, blue light, water, nutrients, temperature, pathogens, and herbivores.
• How is specificity achieved in a signal transduction pathway?

  A cell must possess the corresponding receptor to a signal in order to respond