cell communication

cell communication

done in multicellular organisms to coordinate activity, energy production & use

• done through using signaling molecules to “talk”

  • signaling systems evolved in early prokayrotes & adapted for use in single/multi cellular eukaryotes

how do multi cellular organisms communicate

through chemical messengers (ligands, hormones, neurotransmitter)

• specific molecules are secreted from one cell & travel to bind on receptors on the target cell which then causes an effect

juxtacrine signaling

signaling through direct contact

• pass molecules through gap junctions (animal cells) & plasmodesmata (plant cells)

• can also occur by interaction of cell-surface moelcuels

autocrine signaling

cell releases signal molecule that binds to receptors on the same cell’s surface to produce an effect

paracrine signaling

only occurs in animals: cell releases chemical messenger molecule into extra cellular fluid that surrounds cells & molecule binds to receptors on nearby cells to cause physiological effects

• ex. pdgf (blood clotting)

synaptic signaling

occurs only in animals: nerve cells release chemical messenger (neurotransmitter) into synaptic gap —- neurotransmitter diffuses across gap & binds to receptors

• very fast process

endocrine signaling

cells of endocrine gland produce chemical messengers (hormone) — hormone travels through blood stream to target cell (binds to surface or intracellular receptors)

• occurs in plants & animals

adrenal glands

type of endocrine signaling

• adrenal glands near kindeys & secrete hormones — adrenaline

• well feeling threatened synaptic signaling occurs leading to gland to release adrenalin

  • leads to fight or flight

stages of cell signaling

1. signal reception

2. signal transduction

3. cellular response

signal reception

chemical messenger binds to receptors on/in target cell

• bind causes receptor to change shape — can act as gated ion channel or enzyme

• like lock & key of enzyme & substrate

signal molecules that bind to intracellular receptors

if signal molecules is small/non-polar/hydrophobic it can pass through non-polar regions of plasma membrane & bind to receptors in cytoplasm

• ex. testosterone & estrogen

signal molecules that bind to cell-surface receptors

if signal molecule is charged/hydrophilic/big it won’t pass the plasma membrane

• ex. majority of signal molecules

types of membrane receptors

• g-protein linked receptors

• tyrosine kinase receptors: (phosphorylates another molecule — leads to phosphorylation cascade)

  • first two: when signal molecule binds a 2nd messenger is formed

• gated ion channel receptor

signal transduction

when shape of receptor is changed it triggers signal transduction

• each step a molecule is changed (many times inactive enzyme to active (cascade), many times is phosphorylation

• at each step the signal can be amplified

cellular response

1. activation of enzyme

2. opening of specific ion channel

3. gene turned off//on

second messenger

small non-protein, water soluble molecule or ion

• relay message from receptor to inside the cell

• can cause amplification

  • ex. cyclic amp (cAMP)

paracrine signaling — release of nitric oxide (NO)

endotheliac cells secrete NO which crosses the membrane of neighboring smooth muscle cells & leads to activation of enzyme + formation of 2nd messenger

• result = increased blood flow through the arteriole

testosterone secretion by testes

endocrine signaling: intracellular receptors

• testosterone is secreted — crosses plasma membrane & binds to receptor — leads to genes being turned on