Intracellular communication and signal transduction Flashcards
Cell communication
A signalling cell releases signalling molecules therefore the responding cell has receptor proteins that bind to the signalling molecule
Intracellular signalling molecules
paracrines
NTs
Hormones
Neurohormones
Signal Transduction
A transducer converts energy forms (e.g., pressure to electrical signal).
Signal transduction transmits an incoming signal through the cell membrane to produce a cellular response.
Second messenger systems amplify the original signal through multiplying steps
Messenger Responses
Extracellular messenger (1st messenger) binding to receptors causes:
FAST: Opens/closes ion channels, causing EPSPs or IPSPs.
SLOW: Activates a second messenger system.
Hormone Responses
Hormones can elicit responses through:
Direct gene activation of steroid hormones.
Activation of G-protein coupled receptors.
G-proteins bind GTP (active) and GDP (inactive).
Involved in cyclic AMP and intracellular Ca²⁺ second messenger systems.
Types of hormones
Hydrophilic
Lipophilic
What are lipophilic hormones?
Lipid soluble and water insoluble
Combine with intracellular receptors and activate specific genes to cause the formation of new intracellular proteins
Time taken to response= several hours
Duration of response= depends on how quickly protein is degraded
Examples might include thyroid hormone- amine hormone derived from the amino acid tyrosine
What are hydrophilic hormones?
Extracellular domain
Transmembrane domain
Cytoplasmic domain
water soluble and lipid insoluble
combine with a protein receptor on outside of membrane + activate a second messenger system= altering the activity of pre-existing intracellular proteins; usually proteins
time to response= few mins
duration of response- after hormonal trigger = depends on how quickly the enzyme is inactivated
examples; insulin= peptide hormones
receptors with dynamic structures
Sometimes target cells can form more receptors in response to rising blood levels of that specific hormone
This is called up-regulation
Sometimes prolonged exposure to high concentrations of a hormone desensitizes the target cells so that the cell responds less vigorously.
This involves the loss of receptors and is called down-regulation