Membrane Signalling 1 Flashcards
Why do cells communicate ?
To allow coordinated modification of short and long term responses that determine functional properties of a cell
Cell to cell communication involves integration of multiple signals
- receptor
- transduction
- response
Function of plasma membranes
- separates and protects a cells components from the environment
- provides a permeability barrier
Constituents of plasma membrane
- Lipid
- proteins
- carbohydrates
Examples of plasma membrane proteins involved in cell signalling
- Transporters such as NA+ pump = actively pumps Na+ out of cells and K+ in.
- Receptors such as PDGF receptor = binds extracellular PDGF and as a consequence, generates intracellular signals that cause the cell to grow and divide
- Enzymes such as adenylate cyclase = catalyses the production of intracellular cyclic AMP in response to extracellular signal
Roles of membranes in cell communication
- maintain electrical potential
- function as sites for recognition
- organise chemical reactions
What are the three basic types of cell communication ?
- direct intercellular communication via cytoplasmic bridges
- secreted chemical signals
- anchored extracellular messenger
Cytoplasmic bridges / Gap Junctions
- Link the interior of adjacent cells, allow direct and rapid intercellular communication.
- Passage of small molecules.
- proteins, nucleic acids and polysaccharides cannot pass through gap junctions
Composition of gap junctions
- connexin have 4 membrane spanning domains, they are the major protein in gap junctions
- six connexin = a connexon
Gap junctions are composed of two aligned connexons which form an aqueous pore between the two cells
Functional roles of gap junctions
ELECTRICAL COUPLING ALLOWS :
- movement of ions
- movement between neurons
- found at electrical synapses
- action potential that occurs is one cell is passed onto the next. This allows non delayed sync of cardiac muscle and single unit smooth muscle
METABOLIC COUPLING ALLOWS :
- sharing of metabolites
- allows metabolites/ signals to spread to where they are needed
- the movement of 2nd messengers such as CAMP allowing multiple cells to respond as one
Chemical Signals
There are two types of chemical signal and therefore two types of receptors :
- cell surface receptors = chemical A cannot pass through the membrane so needs a cell surface receptor to send the signal to the inside of the cell
- intracellular receptors = chemical B can pass through the cell membrane so needs a receptor inside the cell.
Three types of chemical signals
- hormones
- neurotransmitters
- local mediators
Anchored extracellular messenger
- least common type
- involves association of proteins on the surface of 2 neighbouring cells.
- mechanism for keeping alike cells together within a tissue.
- initialisation of fertilisation
Response to infection - the recognition of cell surface carbohydrate on neutrophils
- lectin proteins are made by endothelial cells in response to chemical signals from the site of infection
- lectins recognise sugars present on the surface of neutrophils circulating in the blood.
- the neutrophils bind to the blood vessel wall and eventually migrate out of the bloodstream between the endothelial cells into the tissue at the site of infection
