cell bio exam

• Cellular receptors


  Proteins either inside a cell or embedded in the plasma membrane that receive a signal

  
• Cellular receptors


  • Specialized integral membrane proteins that allow communication between the cell and the extracellular space
• Modes of cell-cell signaling

  • Direct cell-cell or cell-matrix
  • Indirect: Secreted molecules
• Endocrine signaling


  Signaling molecules (hormones) secreted by endocrine cells and carried through the circulation system to act on target cells at distant body sites
• Paracrine signaling


  Signaling molecules released by one cell act on neighboring target cells (e.g. neurotransmitters)
• Autocrine signaling


  Cells respond to signaling molecules that they themselves produce (e.g. response of the immune system to foreign antigens, and cancer cells)
• Types of ligands


  • Small and hydrophobic ligands (e.g. steroids)
  • Large or hydrophilic ligands (e.g. GABA)
• Cell signaling by steroid hormones

  1. Steroid hormone passes through plasma membrane

  2. Hormone binds to receptor protein in cytoplasm, activating it

  3. Hormone-receptor complex enters nucleus and binds to specific genes

  4. Bound protein stimulates transcription of gene into mRNA

  5. mRNA is translated into a specific protein

  
• Intracellular receptors


  Receptor proteins found in the cytosol or nucleus of target cells that can be activated by small or hydrophobic chemical messengers that can cross the membrane

  
• Three stages of cell signaling

  • Reception
  • Transduction
  • Response

  
• Reception


  The process by which a cell detects a signal in the environment
• Transduction


  The process of activating a series of proteins inside the cell from the cell membrane
• Response


  The change in behavior that occurs in the cell as a result of the signal

  
• Cell-surface receptors


  • Membrane-anchored proteins that bind to external ligand molecules and perform signal transduction, activating an intracellular signal
  • Have an extracellular ligand-binding domain, a transmembrane domain, and an intracellular domain that connects to a signal transduction pathway

  
• Cell signaling


  The process by which a cell responds to a signal in its environment
• Three steps in cell signaling

  1. Reception

  2. Transduction

  3. Response
• Reception


  The process by which a cell detects a signal in the environment
• Transduction


  The process of activating a series of proteins inside the cell from the cell membrane

  
• Response


  The change in behavior that occurs in the cell as a result of the signal
• Reception


  1. Signal molecule binds to receptor protein

  2. Receptor changes shape

  
• Receptor-ligand binding


  • Highly specific
  • Conformational change in receptor is initial transduction of signal
  • Most signal receptors are plasma membrane proteins

  
• Cell communication


  Cell's response to a signal often involves activating or inactivating proteins

  
• Phosphorylation


  Common way to change the activity of a protein
• Protein kinase


  Enzyme that adds a phosphate to a protein
• Phosphatase


  Enzyme that removes a phosphate from a protein
• Receptor types


  • Intracellular receptor
  • Cell surface receptor or membrane receptor
• Membrane receptor subtypes


  • Ion channel linked receptors
  • Enzymatic receptors
  • G protein-coupled receptor

  
• Ion channel linked receptors


  Ion channel that opens in response to a ligand

  
• Enzymatic receptors


  Receptor is an enzyme that is activated by the ligand
• G protein-coupled receptor


  1. protein (bound to GTP) assists in transmitting the signal

  
• 1. protein coupled receptor signaling

  1. G-protein is a switch turned on by the receptor

  2. G-protein then activates an effector protein (usually an enzyme)

  3. Effector protein produces a second messenger

  4. Second messenger generates the cellular response

  
• Second messengers


  cAMP, inositol phosphates, calcium ions (Ca2+)
• Cyclic AMP (cAMP)


  • One of the most widely used second messengers
  • Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal

  
• Intracellular receptors


  • Steroid hormones have a nonpolar, lipid-soluble structure and can cross the plasma membrane to a steroid receptor
  • Usually affect regulation of gene expression

  
• Termination of cell signaling cascade

  1. Degradation of signaling molecules

  2. Dephosphorylation of intermediates of the pathway

  3. When signal molecules leave the receptor, the receptor reverts to its inactive state

  4. Phosphatases remove phosphate groups added by kinases
• Cyclic AMP (cAMP) degradation


  Degraded into AMP by phosphodiesterase
• Cyclic AMP (cAMP)


  A second messenger molecule that plays a crucial role in various cellular processes, including metabolism, cell growth, and gene expression.
• Phosphodiesterase

  The enzyme responsible for degrading cAMP into AMP.
• AMP


  Adenosine Monophosphate, the product of cAMP degradation by phosphodiesterase.