What do multicellular organisms require in order to function?
precise internal communication
exes of precise internal communication
o Example- animals have nervous systems in which neuronstransmit information electrically and chemically o Plants and animals have hormones as signals between cells andorgans
the process by which cells convert and amplify an extra-cellular signal into an intra-cellular signal
signaling molecules/first messenger
Examples of signaling molecules:
Neurotransmitters (produced by nerve cells) Hormones
First step of signaling
1- Synthesis and release of the signaling molecules
Second step of signaling
2- Transport to target cells
Third step of signaling
3- Reception of the information by target cells
Fourth step of signaling
4- Signal transduction
Fifth step of signaling
5- Response by the cell
Sixth step of signaling
6- Termination of signaling
Examples of cell signaling in unicellular bacteria, protists, fungi–amoeba
Amoeba-like cellular slime mold secretes cAMP (cyclic adenosine monophosphate) when food is scarce, causing other slime molds to come together and form amulticellular slug-shaped colony
Examples of cell signaling in unicellular bacteria, protists, fungi–yeast
Yeast cells send out signals to mate with one another
Examples of cell signaling in unicellular bacteria, protists, fungi–sperm
Sperm have receptors that respond to chemical signalsthat guide the sperm to the egg
- Response by the cell– The activated enzyme can either
- Catalyze the production of large numbers of intracellular signaling molecules, called second messengers2. Or it may activate intracellular enzymes called protein kinases
enzymes that activate specific proteins by transferring phosphate groups to them from ATP
second messengers, like___
cAMP (catalyzed by enzyme called adenylyl cyclase)
mechanism by which cells communicate with each other. One cell secretes ligand, which combines with receptors on a diff cell
What synthesizes ligands?
Either synthesized by neighboring tissue or by
specialized tissue that may be far away
Transport of ligands
by diffusion or via the circulatory system
Reception of the information by target cells
Ligands bind to
receptors on target cells
How can regulatory molecules transmit information to the cell without physically crossing the plasma membrane?
by using systems of interacting integral membrane proteins–Each component in signal transduction acts as a “switch”-activated or inactivated
transmembrane protein with 3
3 domains of receptor
One on extracellular surface, acts as docking site for ligand
Second extending through plasma membrane
Third is “tail” that extends into cytoplasm
When ligand, or first messenger, binds to receptor, how does it activate it?
by changing the
shape of the receptor tail that extends into the cytoplasm
What does the activated receptor do?
changes the conformation of a
second protein, sometimes called G protein,
which then becomes activated. GTP then turns into GDP, which releases energy.
Why is 2nd protein called a G protein?
Called G protein
because when it’s in activated form, it is bound
to guanosine triphosphate (GTP- similar to
What happens after the activated receptor changes the conformation?
Eventually, this causes
activation of a specific enzyme bound to the membrane