The cell and its environment

The cell within the organism

The cell and its organelles

How cells communicate with their environment and vice versa

Three modes of distribution of first messengers

Different types of first messengers

Different types of cell membrane receptors

Different types of intracellular (nuclear) receptors

the phospholipid bilayer

Headgroups of phospholipids and non-bilayer arrangements of (phospho)lipids in an aqueous

environment

Phospholipid bilayers are efficient barriers that allow for a « privileged » intracellular

environmont

Because of the impermeable membrane, cells require transmembrane proteins in order to

communicate and interact with their environment

Epithelial cells in particular make extensive contacts with adjacent cells via specialized cellular junctions

Tight junctions seal the intercellular space of epithelial cellular sheets (selective barrier), an essential function for selective transport of solutes (for instance nutrient uptake in the intestine)

Adherens junctions protect the cell against physical agression (tension forces in particular). They play an important role in the

maintenance of tissue integrity

Adhesion molecules, in particular the integrins, also interact with cellular matrix. Collagen is an important component

with both structural and cell interaction functions

Fibronectin is an important ligand for integrins, it has a prime role in connecting cells with the extracellar matrix.

Laminin, an important component of the basal lamina (basement membrane) plays a bridging role between cells (through binding with integrins) and their matrix (through

binding with other components).

This drawing nicely illustrates how the different components of the extracellular matrix form a dense matrix to which cells firmly attach

Integrins bind to proteins of the extracellular matrix. This often occurs in focal adhesion complexes, where numerous proteins attach to each other, and importantly, to the actin cytoskeleton

Glycosaminoglycans also have their place in the extracellular matrix. These long and highly charged sugar chains attract water

and have the important capacity, unlike collagens, to resist compression

Cartilage of the synovial joint is a beautiful example of how proteins (collagen and aggregan) and glycosaminoglycans (hyaluronan, KS and CS) act together to resist to both tension (during flexion of the joint)

and compression (static weight bearing of the joint). The importance of all this is best explained by people who suffer from rhumatoid arthritis or arthrosis.

Finally, cell-cell and cell-matrix interactions are important

- to maintain tissue integrity and because adhesion molecules act like « classic » receptors and signal into the cell, they also play a role in

- maintaining the cell in a differentiated state- providing a survival signal that protects the cells against apoptosis

DNA versus RNA, a better way to stock genetic information (less prone to alterations)

Coding sequence and non-coding (template) sequenceTranscription and translation,