Cell Communication Flashcards
What is a gap junction?
- Gap junctions allow flow of current from cell to cell - allows rapid transmission
- Electrical transmission
- Linked cells can act together as one unit - a syncytium
What are the 3 modes of chemical transmission between cells?
- Cell to cell -> synapse
- Cell to several cells -> paracrine
- Many cells to many cells -> endocrine
What does the resulting effect depend on in cell to cell chemical transmission (i.e. at a chemical synapse)?
The type of neurotransmitter
The receptor the neurotransmitter acts on
What is the sequence of events that occurs at a chemical synapse?
- Impulse arrives at terminal of presynaptic cell
- Transmitter released from storage vesicles
- Transmitter diffuses in synaptic cleft
- Transmitter binds to receptor on postsynaptic cell
- Transmitter alters the postsynaptic cell: excitatory or inhibitory
What is paracrine communication?
- One cell communicates with several cells locally
- Often used by defence cells
- Can be part of a ‘cascade’ of reactions
What is autocrine communication?
- When chemical acts back on cell releasing it
What is endocrine transmission?
- Chemical sent to all parts of the body via the bloodstream
- Hormone acts only on cells with the correct membrane receptor protein (target cells)
What are the main differences between neural and hormonal communication?
Neural communication: actions often very specific and localised, quick impulse transmission (>100m/s), suitable for rapid transmission
Humoral communication (hormonal): can affect many cells in different parts of the body, co-ordinated body-wide actions, slow to act but effect persists
What are some examples of neural communication?
- Control of voluntary muscle contractions
- Sensory systems
- Salivary gland responses
- Control of blood pressure
What are some examples of endocrine communication?
- Gastro-intestinal gland responses
- Control of metabolism and growth
- Regulation of menstrual cycle
What is the ‘first messenger’ in cell communication?
The first messenger is the chemical transmitter which acts on a receptor protein. Some can pass through the cell membrane and act on receptors within the cell. Others cannot enter the cell.
What type of molecule are steroid hormones?
Lipids
Which type of hormone can pass through the cell membrane?
Steroid hormones - they are lipids (lipophilic)
Where are the receptors for steroid hormones located?
Inside the target cell
Why can peptide transmitters not pass through the cell membrane?
They are not lipophilic
Where are receptors for peptide transmitters located?
On the cell membrane
What is cAMP?
Cyclic AMP - a 2nd messenger
Describe the sequence of events in GPCR activation via receptor binding
GPCR = G-protein coupled receptor
- The transmitter binds to the GPCR
- G protein is activated by GTP
- ATP is converted to cAMP by the enzyme adenyl cyclase
- cAMP activates protein kinase
- Protein kinase phosphorylates a specific enzyme (activates it) which catalyses a chemical reaction, resulting in the formation of a molecule (protein)
Describe how calcium can act as a 2nd messenger
- Transmitter binds to a membrane receptor (GPCR)
- This activates a G protein, which activates an enzyme: phospholipase C
- This causes opening of Ca2+ channels, Ca2+ enters cell
- Ca2+ binds to protein in the cytosol (e.g. calmodulin)