General Biology/Cells/Cell-Cell Interactions

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

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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.