Chapter 11 Cell Communication Essentially the entire chapter with special focus on G protein coupled receptors Understand the basic reasons why cells of a multicellular organism need to communicate 1 Cells can signal to each other and interpret the signals they receive from other cells and the environment function in another 2 Signals are most often chemicals a chemical produced in one cell that can affect the 3 The same set of cell signaling mechanisms show up in diverse species and processes cells of different organisms face similar challenges and have evolved similar mechanisms to face these challenges EX yeast and mammal cells are very distantly related yet have similarities in 4 Communication between microorganisms shows insight into how cells send receive cell signaling and respond to signals Understand the basic method by which cells communicate 1 Local Signaling between neighboring and touching cells Study Guide for Exam IV Dec 3rd Animal cells may communicate by direct contact or by releasing molecules that contact nearby cells a Direct signaling cell junctions that directly contact the cytoplasm of adjacent cells Signaling substances in the cytosol can pass freely between adjacent cells In animal cells gap junctions In plant cells plasmodesmata Cell to cell recognition b Non direct signaling paracrine signaling animal cells communicate using Fall 2015 secreted messenger molecules that travel only short distances Class of local regulators growth factors stimulate nearby target cells to grow and divide EX morphagen received in a concentration gradient by surrounding cells c Synaptic signaling occurs in the animal nervous system when a neurotransmitter is released in response to an electric signal EX taking your hand off a hot pan quickly 2 Long Distance Signaling plants and animals use hormones hormonal signaling In humans Endocrine signaling specialized cells endocrine cells release hormones which travel to target cells via circulatory system blood stream o Receptor Ligand interactions The target cell detects a signaling molecule that binds to a receptor protein on the cell surface causing a shape change A shape change in a receptor is often the initial transduction of a signal The binding between a signal molecule ligand and receptor is highly specific Most signal receptors are plasma membrane proteins 3 types Know the three major types of membrane associated receptors 1 G Protein Coupled Receptors GCPRs cell surface transmembrane proteins 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 cellular response A G protein receptor with a GTP bound to it is in its active state Study Guide for Exam IV Dec 3rd If an animal cell suddenly lost its ability to produce GTP its signaling system would not be able to activate or inactivate the G protein on the cytoplasmic side of the cell membrane 2 Receptor Tyrosine Kinases 3 Ion channel receptors Ligand binds to the ligand binding site of receptor Tyrosine kinase protein Creates dimer structure which is phosphorylated to activate receptor Activated relay proteins can bind to create a cellular response Ligand binds to the closed ion channel receptor located on the membrane Binding causes gate to open and the ion passes the channel cell response o Focus on the G protein coupled receptors o What is the relationship between the receptor and the G protein o Distinguish between GDP and GTP bound G proteins and the nature of activation Know the one type of intracellular receptor Intercellular receptor found in the cytoplasm or nucleus of target cells they are small or hydrophobic chemical messengers that can readily cross the membrane and activate receptors EX steroid and thyroid hormones aldosterone Understand the two major signal transduction mechanisms that we discussed o Phosphorylation cascades results in a conformational change to each protein created because relay molecules in signal transduction pathways are protein kinases which activate and inactivate other proteins by adding a phosphate group to them and transfer phosphates from ATP to protein phosphorylation Fall 2015 Signaling molecule binds to receptor which activates relay molecules Which then activated protein kinase 1 which activated protein kinase 2 which Study Guide for Exam IV Dec 3rd activated protein Creates phosphorylation cascade results active protein and cellular response o Second Messengers small nonprotein water soluble molecules or ions that spread throughout a cell through diffusion Participate in pathways initiated by GCPRs and RTKs Common second messengers cyclic AMP and calcium ions 1 Cyclic AMP adenylyl cyclase converts ATP to cAMP in response to an extracellular signal EX epinephrine G protein coupled receptor G protein adenylyl cyclase cAMP 2 Phospholipase IP3 not common 3 Calcium ion Ca2 calcium binds to calmodulin its concentration inside the cell cytosol is lower than outside the cell cytoplasm thus a small change in calcium ions represents a relatively large percentage change in calcium concentration Phospholipase C inhibitor used to block the release of calcium from the ER Know the three major types of cellular response to signaling and the molecules and cellular machinery involved in each o Nuclear transcription of target genes regulates the synthesis of enzymes or other proteins by turning genes on or off in the nucleus Study Guide for Exam IV Dec 3rd When the final activated molecule in the signal pathway is a transcription factor Growth factor binds to a receptor Through the phosphorylation cascade it entyers the cell to bind with inactive transcription factor then binds to DNA to create a strand of mRNA o Cytoplasmic enzyme activation regulate the activity of enzymes A signal could cause an opening or closing of an ion channel in the plasma membrane or a change in cell metabolism Study Guide for Exam IV Dec 3rd Epinephrine response Binding of epinephrine to G protein receptor activates G protein activates adenylyl cyclase uses ATP to activate Cyclic AMP activates protein kinase A activates phosphorylase kinase and activates glycogen Fall 2015 phosphorylase which produces glucose o Signaling pathways can also affect the overall behavior of a cell EX Signal could lead to cell division Understand the mechanisms involved in differential cellular responses to signaling 1 Amplification of the signal Enzyme cascades amplify the cell s
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