Cell communication

direct communication

direct exchange of materials and interaction of cell surface molecules

indirect communication

two non contacting cells using signals

paracrine

release of chemical signal from one cell, detected by another closely located cell

autocrine

release of chemical signal from one cell, detected by the same cell

neural

release of neurotransmitters across a synapse between two closely located neurons

endocrine

long distance, hormonal signaling

signal molecules

AA and its derivatives, steroids, proteins, peptides

Glutamic acid

AA excitatory transmitter

GABA

AA derivative inhibitory transmitter

epinephrine

AA derivative increases blood glucose

Ligands

signals- dont change anything unless bonded to a receptor

AA and its derivatives interact with

polar + hydrophilic (water soluble), signals that cannot cross the membrane

Steroids interact with

non-polar + hydrophobic (lipid soluble) signals that can cross the membrane

step 1 signaling process

reception, signal molecule binds

step 2 signaling process

transduction pathway in cell

step 3 signaling process

response

1) alteration of enzyme function

2) alteration of gene expression

transduction cascade

consists of kinase enzymes that catalyzes phosphate group, changes it shape, activates

phosphotase

enzymes that remove phosphate groups/reduce enzyme activity

advantages to transduction cascades

1. amplified signal

2. divergence of multiple cellular processes

3. various signals can control the cascade

second messenger

act to trigger the transduction cascade, intermediaries between receptor and cascade

3 principal second messengers

1. cyclic AMP

2. calcium ions Ca2+

3. IP3

cyclic amp cycle

ATP looses 2 phosphate groups w/ adenylyl cyclase, cyclizes ribose-phosphate=cyclic AMP, phosphodiesterase adds H20 and linearizes the ribose-phosphate into AMP

Types of transmembrane receptors

1. g-protein-linked (epinephrine)

2. tyrosine-kinase (insulin)

3. ligand-gated ion channels (calcium)

g-protein receptors

linked to relay proteins and bind guanosine di/tri-phosphate

g-protein receptors ligand binds and…

g-protein can now bind and GDP → GTP, activate/inhibit an adj. enzyme to create cAMP, once hydrolyzed cycle reverses

kinase component of tyrosine kinase receptor

part of the receptor

target protein component of tyrosine kinase receptor

separate from receptor

Dimerization

connection of two separated parts (kinases) when ligand binds

once dimerized kinase…

moves a phosphate from ATP to an AA (tyropsine)

autophosphorylation

kinase receptor phosphorylates itself

ATP → ADP in tyrosine kinase

phosphorylates dimer and therefore activates relay proteins

kinase signaling and gene expression

reception (signal attaches), transduction (phosphorylation cascade), activates transcription factors in nucleus, creates mRNA

calcium second messenger

binds to calmodulin, kinase triggers kinase cascade

increase intracellular calcium by

1. facilitated diffusion through ion channels

2. release of calcium from intracellular stores

release of calcium from intracellular stores

regulated by signal cascade using IP3- activated by g-protein or protein-kinase

phospholipase C

breaks down PIP2 → DAG + IP3 (second messenger)

termination of Ca2+ signaling

removed from cytosol by pumps into outside, mitochondria, SER, w/ use of ATP

variations of signaling

1. single response

2. branch point, two responses

3. cross-talk btwn two pathways

4. same signal, diff response on diff receptor

steroid hormones control

1. gene expression

2. intracellular signaling/cross-talk

steroid hormones pathway

1. diffusion into cell

2. binds to receptor, change in conformation

3. moves into nucleus aided by protein

4. controls gene expression