< General Biology < Cells

General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material

Cell-cell interactions

Cells interact with the environment and with each other.

Cell signaling

  • Signaling requires
    • Signal
    • Cell receptor (usually on the surface of a membrane)
  • Signaling is important in:
    • Response to environmental stimuli
    • Sex
    • Development
  • Major area of research in biology today

Types of signaling

  • Direct contact (e.g., gap junctions between cells)
  • Paracrine: Diffusion of signal molecules in extracellular fluid; highly local
  • Endocrine: Signal (hormone) molecule travels through circulatory system
  • Synaptic: neurotransmitters

Types of signal molecules

  • Hormones: chemically diverse
    • Steroid
    • Polypeptide
    • Vitamin/amino acid derived
  • Cell surface proteins/glycoproteins
  • Ca2+, NO
  • Neurotransmitter
    • Several hundred types
    • Some are also hormones e.g. Estrogen, progesterone

Receptor molecules

  • Intracellular
    • Protein that binds signal molecule in cytoplasm
    • Bound receptor may act as:
  • Gene regulator
  • Enzyme
  • Cell surface
    • Gated ion channels (neurotransmitter receptor)
    • Enzymic receptors
    • G protein-linked receptors
Cell surface protein
  • Tissue identity
    • glycolipids
    • MHC proteins
  • Immune systems
    • distinguish self from not-self
  • Intercellular adhesion
    • permanent contact
    • help form sheets of cells, tissues
    • may permit signaling
Example: G proteins
  • Transmembrane surface receptor binds signal molecule
  • Conformational change allows binding of G protein on cytoplasmic side
  • G protein binds GTP, becomes activated
  • G protein activates intracellular signal cascade
    • Change in gene expression
    • Secrection
    • Many other possible consequences

Communicating junctions

  • Gap junctions
    • animals
    • small molecules and ions may pass
  • Plasmodesmata
    • plants
    • lined with plasma membrane
    • permit passage of water, sugars, etc.

Gap junctions

This text is based on notes very generously donated by Dr. Paul Doerder, Ph.D., of the Cleveland State University.

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