Chemical Signaling

What is quorum sensing?

The method that single-celled organisms used to communicate: each organism secretes their own chemical signals (auto-inducers), once enough organisms are gathered, these signals are detected and processes begin.

What is an example of quorum sensing?

Bioluminescence in the marine bacteria vibrio fischeri:

1. Once there is enough bacteria, more autoinducers are released

2. Once there are enough autoinducers, the expression of genes needed for luminescence are signaled (seen in squid).

What are receptors?

Proteins with binding sites for specific signaling chemicals (ligands, ex. hormones, neurotransmitters, drugs, antigens)

Example: Calcium can be a ligand of troponin in order to initiate muscle contraction

What are cytokines?

Ligands that start intracellular signaling to regulate cell function

What are 3 types of hormones?

Proteins, steroids, amines

What are 5 types of neurotransmitters?

Amines (ex. dopamine), peptides (ex. endorphins), nitrous oxide, acetylcholine, purines (ex. atp)

What are intracellular receptors?

Receptors that reside inside the cell membrane and usually affect gene expression

(ex. Sex hormones bind to intracellular receptors that initiate changes in gene expression - sex hormones are steroids (lipids) so they are hydrophobic, passing easily through the membrane)

What are transmembrane receptors?

Receptors that must have hydrophobic AND hydrophilic regions to stay embedded in the cell membrane.

What are signal transduction pathways?

The binding of a signaling chemical to a receptor that sets off a sequence of responses in the cell - the process that transmembrane receptors rely on, since they are stuck in place.

What are three examples of how transmembrane receptors work (signal transduction pathways)?

1. G protein-coupled receptors: G protein disassembles itself into 3 subunits after ligands bind to the receptors: alpha, beta, gamma. These subunits then initiate cellular responses.

2. Epinephrine binds to G protein-coupled receptors in liver cells. This pathway modifies ATP to make cylic AMP (cAMP) → glycogen break down activates → glucose released into blood → faster fight/flight response

3. Insulin binds to transmembrane receptors, whose tails located inside the cell are enzymes called tyrosine kinase. Binding initiates the formation of glucose transporters on the membrane to increase intake of glucose into cell.