11) Cell Communication

• Cell signalling

  • One signal is converted to another (eg extracellular to intracellular)
  • ⤷ Amplification is a result of a intracellular cascade mechanism
  • Key in homeostasis, cell function, gene expression, enzyme activity, cytoskeleton organisation, gene transcription and apoptosis

  
• One signalling molecule can induce multiple responses depending on the proteins produced or function the cells have
• Types of cell communication: 

  • Autocrine: Cell communicates with self by releasing hormones to environment and target receptor is on itself
  • Paracrine: Cell signal travels a short distance (ECM/Synapse) to reach neighbouring receptor 
  • Endocrine: Cell signals travel long distance through the blood
  • Juxtacrine: Two cells communicate with each other through synapses
• Types of cell surface receptors

  • ion channels
  • Enzyme-linked cell surface receptor
  • GPCR cell surface receptor
• The shape of the receptor determines which ligand it will bind to
• GPCRs cell surface receptors:

  • Largest cell surface receptors 

  ⤷ 7 transmembrane domains in membrane 

  • Ligands bind to receptors activating the trimeric domain (eg: Rhodopsin - photosensitive receptor) 

  
• Enzyme-linked cell surface receptors:

  • Receptor has an intrinsic catalytic domain (such as kinase or phosphatase)
  • Enzyme is activated by ligand binding (eg: Insulin receptors) 

  
• Ion Channel Linked Receptors:

  1. Ligand binding opens ion channels
  2. ions pass through channel and are impermeable to the cell membrane
  3. Changes membrane potential
  4. ⤷ Important for many processes (eg Ca2+ in muscles)

  
• Hormones

  • Chemical messengers that are carried throughout our blood to key organs

  ⤷ Their effect is carried out by secondary messengers

  ⤷ Involved in Cell growth and differentiation, wound healing, digestion, response to infection

  ⟶ Hormone imbalances can lead to PCOS, diabetes etc
• Hormones bind to receptors to start a signalling cascade

  • Intracellular receptors are activated by hydrophobic ligands across the cell mb (allowing direct contact with the nuclei)
  • Transmembrane/cell surface receptors: Hormone induces change after activating the receptor

  ⤷ the signals are mediated by 2nd messengers