General Biology/Cells/Cell-Cell Interactions

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Cell-cell interactions

with the environment with each other

Cell signaling

Signaling requires
- Signal
- Cell receptor (usually on surface)
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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