Cell communication Flashcards
What is the name for chemical transmission between cells
Cell - cell (synapse)
Cell - several cells (paracrine)
Many cells - many cells (endocrine)
Chemical synapse properties
Cell - cell using chemical transmitter
Effect depends on transmitter and the receptor it acts on
One way transmission
Common in nervous system
Sequence of a 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
Alters postsynaptic cell:
‘excitatory’ e.g. impulse generated; muscle contracts; gland secretes
‘inhibitory’: cell is switched off
What is paracrine
-One cell communicates with several cells locally
-Often used by defence cells (inflammation)
-Can be part of a ‘cascade’ of reactions
What is autocrine communications
Where chemical acts on cell releasing it (feedback)
Describe endocrine transmission
Chemical sent to all parts of the body via the blood stream
Hormone acts only on cells with the correct membrane receptor protein (target cells)
Similarities of nerves and hormones
both are used for communication in organisms
Communication by nerves advantages
-Actions are very specific or localised
-Quick impulse transmission
-Suitable for rapid and specific response
Examples of nervous communication
-control of voluntary muscle contractions
-sensory systems
-salivary gland responses
-control of blood pressure
Properties of hormonal communication
-Can affect many cells in different parts of body
-Coordinated, body-wide actions
-Slow to act, but effect persists
Examples of hormonal commmunications
-gastro-intestinal gland responses
-control of metabolism and growth
-regulation of menstrual cycle
What are steroids
Lipids that can pass through the outer cell membrane
Function of steroids
They act on receptors inside the target cell (step 3)
The steroid-receptor complex acts on the DNA in the nucleus to initiate protein synthesis (steps 4, 5, 6)
The protein then alters cell function (step 7)
First messenger
the chemical transmitter which acts on a receptor protein
Some first messengers can pass through the target cell membrane and act on receptors inside the target cell while some cannot enter the cell.
Whycant Peptide transmitters pass through the cell membrane
Peptide and other transmitters cannot pass through the cell membrane because they bind to plasma membrane receptors and set up a series of reactions controlled by ’G-proteins’
These in turn activate 2nd messenger systems such as:
Cyclic AMP (cAMP)
Calcium ions (Ca++)
Why is there a delayed reaction with steroid transmitters
As the protein needs to be produced, takes time
Second messengers:
G-protein and Cyclic AMP - 1
The transmitter binds to a membrane receptor
G-protein is activated by GTP (guanosine triphosphate
ATP (in cytosol) is converted to cyclic AMP by the enzyme adenyl cyclase
Note: Adenyl cyclase is also called adenylate cyclasecAMP activates an enzyme, called protein kinase,
This, in turn activates a specific enzyme which catalyses a chemical reaction
Resulting in formation of molecule, e.g. protein
calcium as a secondary messenger
Transmitter binds to a membrane receptor (step 1)
This activates a G-protein, which activates an enzyme: phospholipase C
This in turn causes opening of Ca2+ channels; Ca2+ enters by diffusion
Ca2+ binds to a protein in the cytosol; here, it is calmodulin
(There are other Ca-binding proteins, such as Troponin, which is involved in muscle contractions)
Ca2+-calmodulin complex acts as a 2nd messenger,
Then which regulates an enzyme which regulates a chemical reaction
….In some cells, the Ca 2+ is released from stores within the cell, but the basic principle is much the same.
