intercellular communication - lacking in most prokaryotes/protists
- uses many different molecules to communicate
- dissolved gasses like nitric oxide can also be used as signals
- signal molecules either attached to surface, secreted through plasma membrane, or released by exocytosis
- receptor proteins - have 3D shapes that fit the shape of a specific signal molecule
- signal molecule and receptor protein bind, changing the shape of the protein
- change in protein shape >> response within the cell
- hard to find, can make up less than 0.01% of a cell's mass
- immunochemistry - uses antibodies to target/isolate specific molecules/proteins
- molecular genetics - intentionally creates mutations in genes
- receptor malfunction is very evident, more easily seen
- determines relationship between protein structures and cellular functions
types of cell signaling - 4 basic mechanisms for communication between cells
- autocrine signaling - cells sending signals to themselves; may reinforce developmental changes
- direct contact - when cells are actually close enough to touch each other
- paracrine signaling - released molecules that only influence cells in close vicinity
- endocrine signaling - uses hormones, which lasts longer in the circulatory system
- synaptic signaling - used by animals' nervous systems
- neurotransmitters - don't travel through the circulatory system; released by nerve cells to very close target cells
- chemical synapse - association of a neuron and its target cell
- neurotransmitters pass across the synaptic gap, last very briefly
second messengers - substances used to relay message from receptors to inside the cytoplasm
- alter the behavior of certain proteins by binding to them, changing their shape
- cyclic AMP (cAMP) - used by all animal cells
- produced by adenylyl cyclase when started by G-protein
- activates the alpha-kinase enzyme, adding phosphates to certain proteins
- works in muscle cells to make more glucose available
- calcium ion - serves as 2nd messengers though found in low levels inside the cell
- levels are much higher outside the cell
- gated channels controlled by G-proteins allow Ca++ in to start certain activities
- IP3 made from phospholipids and phospholipase binds to ER to let Ca++ into the cytoplasm
- binds to calmodulin (148-amino-acid protein w/ 4 binding sites for C++) to activate other proteins
protein kinase cascades - chains of protein messengers used to relay messages to the nucleus
- usually starts w/ phosphorylating a stage 1 protein
- each stage protein activates a large number of proteins in the next stage, and so forth
- different signals may use some of the same messengers, but ultimately have different targets
- vision amplification cascade - starts w/ light activating rhodopsin (a G-protein)
- rhodopsin activates hundreds of transducin (another G-protein)
- each transducin causes phosphodiesterase enzyme to change thousands of cyclic GMP
- human rod cells sensitive enough to detect brief flashes of just 5 photons
- cell division amplification cascade - starts w/ phosphorylating ras (a protein kinase)
- ras proteins activate series of phosphorylation, leading to division
- 1/3 of cancers involve a mutation in the ras protein gene, causing unrestrained growth
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