Cell signaling

G protein couples receptors (GPCR)

the G-protein acts as on/off switch

Receptor Tyrosine Kinases (RTKs)

membrane receptors that attach phosphates to tyrosines which triggers a response

Ion channel receptors

Channel proteins that allow molecules or ions to enter or leave a cell

RTK step 1

before signaling molecule binds, the receptors begin as polypeptides

Structure of Polypeptides

extracellular ligand-binding sites, alpha helix spanning the membrane, intracellular tails consisting of tyrosine

RTK step 2

2 receptor polypeptides with move closer to each other and form a structure called dimer through the process of dimerization

RTK step 3

dimerization activates the tyrosine kinase region of the polypeptide. tyrosine will add a phosphate from ATP to a tyrosine of a tail on another polypeptide

RTK step 4

the receptor is fully activated and is recognized by a relay protein. the relay protein will each bind to a specific phosphorylated tyrosine, which will alter the structure and activate the relay protein to trigger the transduction pathway, leading to a specific cellular response.

what is a relay protein

a protein that receives and passes a message

what is required for effective cell signaling?

ligand, receptor protein, transduction pathway

ligand

a signaling molecule that binds to a specific receptor protein. it can be hydrophobic (can pass) or hydrophilic (can't pass)

transduction pathway

produces cellular response

receptor location for hydrophobic ligands

intracellular for hydrophobic ligands (can pass)

receptor location for hydrophilic ligands

cell surface receptor for hydrophilic ligands (can't pass)

intracellular receptor location

nucleus or cytoplasm

4 basic mechanisms for cellular communication

direct contact, paracrine signaling, endocrine signaling, synaptic signaling

direct contact

molecules on the surface of one cell are recognized by the receptors of the adjacent cell

example of direct contact

gap junction or plasmodesmata; still allows for flow of information and communication

paracrine signaling

it is short lived and can be destroyed by extracellular organisms; secretion of one cell can affect the cells in immediate areas

example of paracrine signaling

growth factors, local regulators in animals stimulate the nearby target cells to grow and divide

synaptic signaling

short distance; transmission of neurotransmitters from a nerve cell across synaptic gaps to target cells, such as muscle and nerve cells

endocrine signaling

A type of long-distance signaling in which hormones are secreted into the blood stream

hormone

a molecule that is usually a peptide or steroid that is produced in one part of an organism and triggers a specific reaction in target tissues or organs some distance away

endocrine gland

a ductless gland that secrets hormones into the extracellular space which is diffused into the circulatory system

exocrine gland

a gland that releases its secretion through its ducts

example of exocrine glands

sweat glands, oil glands, digestive glands

autocrine signaling

cells send signals to themselves; secreting signals will bind to specific receptors on the cells own membrane