Biology

• Ways cells communicate


  • Direct contact with other cells
  • Chemical signaling from a distance
• Juxtacrine signaling


  Cells communicate by cell-to-cell contact
• Juxtacrine signaling


  • Interactions between antigen presenting cells and T-cells in animal immune systems
  • Plasmodesmata between plant cells
• Paracrine signaling


  Cells communicate over short distances by using local regulators that target cells in the vicinity of the signal-emitting cell
• Paracrine signaling


  • Neurotransmitters
  • Plant immune response
  • Quorum sensing in bacteria
  • Morphogens in embryonic development
• Endocrine signaling


  Signals released by one cell type can travel long distances to target cells of another cell type
• Endocrine signaling


  • Insulin
  • Human growth hormone
  • Thyroid hormones
  • Testosterone
• Signal transduction pathways link signal reception with cellular responses
• Many signal transduction pathways include protein modification and phosphorylation cascades
• Ligand


  A chemical messenger that is recognized by a receptor protein in a target cell
• Ligand-binding domain


  A specific chemical messenger which can be a peptide, a small chemical, or protein, in a specific one-to-one relationship
• G protein-coupled receptor protein


  A common type of receptor protein
• Ligand-gated channels


  Binding of ligand to receptors that serve as ligand-gated channels can cause the channel to open or close
• Signaling cascades


  Relay signals from receptors to cell targets, often amplifying the incoming signals, resulting the appropriate responses by the cell, which could in include cell growth, secretion of molecules, or gene expression
• Second messengers


  Molecules that can relay and amplify the intracellular signal, such as cyclic AMP (cAMP) or calcium ions
• Signal transduction pathways


  Influence how the cell responds to its environment
• Signal transduction pathways


  May result in changes in gene expression and cell function which may alter phenotype or result in programmed cell death (apoptosis)
• Changes in signal transduction pathways

  Can alter cellular responses
• Mutations in any domain of the receptor protein or in any component of the signaling pathway may affect the downstream components by altering the subsequent transduction of the signal
• Chemicals that interfere with any component of the signaling pathway may activate or inhibit the pathway
• Negative feedback mechanisms


  Maintain homeostasis for a particular condition by regulating physiological processes
• Positive feedback mechanisms


  Amplify responses and processes in biological organisms
• Stages of the cell cycle

  • Interphase (G1, S, G2)
  • Mitosis
  • Cytokinesis
• A cell can enter a stage (G0) where it no longer divides, but it can reenter the cell cycle in response to appropriate cues
• Non-dividing cells may exit the cell cycle or be held at a particular stage in the cell cycle
• Mitosis


  Ensures the transfer of a complete genome from a parent cell to two genetically identical daughter cells
• Mitosis


  • Plays a role in growth, tissue repair, and asexual reproduction
  • Alternates with interphase in the cell cycle
  • Occurs in a sequential series of steps (prophase, metaphase, anaphase, telophase)
• A number of internal controls or checkpoints regulate progression through the cell cycle
• Interactions between cyclins and cyclin-dependent kinases control the cell cycle
• Disruptions to the cell cycle may result in cancer and/or programmed cell death (apoptosis)