55) Types of plasma membrane receptors, receptors associate

• G protein coupled receptors

  3 subunits (alpha, beta, gamma) alpha has 3 isoforms. Extracellular substances bind and transmit signals to an intracellular molecule called a G protein
• Acetylcholine receptors


  When acetylcholine binds, it opens ligand-gated sodium channels in the cell membrane. Sodium ions then enter the muscle cell, initiating a sequence of steps that finally produce muscle contraction
• Receptors with enzymatic activity (tyrosine kinase)

  Used by insulin receptors and also epidermal growth factor. When signalling molecules bind, they cause neighbouring receptors to associate with each other, forming cross-linked dimers. Cross-linking activates the tyrosine kinase activity in these receptors through phosphorylation
• Integrins


  Involved in cell adhesion
• Intracellular receptors


  • Type 1 (in cytosol)
  • Type 2 (in nucleus)
• Type 1 intracellular receptors

  Used by steroid hormones
• Type 2 intracellular receptors

  Used by thyroid hormones, vitamin D and retinoic acid