BIOLOGY EXAM 4 STUDY GUIDE Chapter 11 Cell Communication why cells of a multicellular organism need to communicate cells can signal to each other and interpret the signals they receive from other cells and the environment signals are most often chemicals that are produced in one cell that can affect the function of another cell the molecular details of cell signaling are similar in organisms whose last common ancestor was a billion years ago EX yeast and mammal cells are very distantly related yet share many similarities in cell signaling communication among microorganisms provides some insight into how cells send receive and respond to signals types of cells communication Local Signaling type of communication between neighboring or touching cells animal cells may communicate by direct contact or by releasing molecules that contact nearby cells Direct Contact cell junctions directly connect the cytoplasm of adjacent cells signaling substances in the cytosol can pass freely between adjacent cells 1 gap junctions in animal cells 2 plasmodesmata in plant cells cell cell recognition Non Direct Contact paracrine signaling animal cells communicate using secreted messenger molecules that travel only short distances growth factors stimulate nearby target cells to grow and divide are one class of such local regulators in animals EX morphagen received in a concentration gradient by surrounding cells synaptic signaling occurs in the animal nervous system when a neurotransmitter is released in response to an electric signal how a neuron signal is passed an electrical signal triggers the release of neurotransmitters which are diffused across the synapse to the target cell EX taking your hand off of a hot pan quickly GPCRs Long Distance Signaling hormone signaling chemicals used by plants and animals in humans endocrine signaling specialized cells endocrine cells release hormones which travel to target cells via the circulatory system blood stream method by which cells communicate Earl W Sutherland discovered how the hormone epinephrine acts on cells suggested that cells receiving signals went through these three processes 1 reception receptor ligand interaction the target cell detects a signaling molecule that binds to a receptor protein a shape change in a receptor is often the initial transduction of the signal the binding between a signal molecule on the cell surface causing it to change shape ligand and the receptor is highly specific most signal receptors are plasma membrane proteins 3 main types 1 G protein coupled receptors cell surface transmembrane receptors that work with the help of a G protein G protein when inactive it binds to the activated receptor GDP becomes energy rich GTP which will activate the enzyme to create a specific cellular response a G protein receptor with GTP bound to it is in its active state if an animal cell suddenly lost the ability to produce GTP its signaling system would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane 2 receptor tyrosine kinases ligand binds to the ligand binding site of receptor tyrosine kinase proteins creates dimer structure which is phosphorylated to activate the activated relay proteins can bind to create a cellular response 3 ion channel receptors ligand binds to the closed ion channel receptor located on the binding causes the gate to open and ions pass through channel cell receptor membrane response intracellular receptors found in the cytoplasm or nucleus of target cells they are small or hydrophobic chemical messengers can readily cross the membrane and activate receptors ex steroid and thyroid hormones aldosterone 2 transduction phosphorylation and second messengers 1 A signal molecule binds to a receptor 2 A conformational change in the signal receptor complex activates an enzyme 3 Second messenger molecules are released 4 Protein kinases are activated 5 Target proteins are phosphorylated the binding of the signaling molecule to a receptor initiates a signal transduction pathway the first step in a chain of molecular interactions like falling dominoes the receptor activates another protein which activates another and so on until the protein producing the response is activated cascades of these molecular interactions relay signals from receptors to often occurs in multiple steps multistep pathways greatly amplify a signal provide more opportunities for coordination and regulation of the cellular response not all intercellular signals require transduction EX a lipid soluble signal would be processed without transduction target molecules in the cell phosphorylation cascade results in a conformational change to each protein created because relay molecules in signal transduction pathways are protein kinases protein kinases activate inactivate other proteins by adding a phosphate group to them and transfer phosphates from ATP to protein phosphorylation signaling molecule binds to receptor which activates relay molecule which activates protein kinase 1 which activated protein kinase 2 creates phosphorylation cascade results in active protein and cellular etc response second messengers are small nonprotein water soluble molecules or ions that spread throughout a cell by diffusion participate in pathways initiated by GPCRs and RTKs common ones are cyclic AMP cAMP adenylyl cyclase enzyme converts ATP to cAMP in protein coupled receptor G protein adenylyl cyclase cAMP response to an extracellular signal EX epinephrine G phospholipase C IP3 not as common calcium ions CA2 calcium binds to calmodulin its concentration in the cytosol is lower than the concentration outside the cell thus a small change in number of calcium ions represents a relatively large percentage change in calcium concentration phospholipase C an inhibitor used to block the release of calcium from the edoplasmic reticulum 3 response nuclear and cytoplasmic responses the transduced signal triggers a specific response in the target cell output response the cell s response to an extracellular signal nuclear response transcriptional a signal transduction pathway leads to regulation of one or more cellular activities many signaling pathways regulate the synthesis of enzymes or other proteins usually by turning genes on or off in the nucleus this is the case when the final activated molecule in the signaling pathway is a transcription factor controls gene expression cytoplasmic response enzyme activation other pathways
View Full Document
Unlocking...