22) Explain in words, what is the difference between endocrine, paracrine, and synaptic signaling?
23) Explain each of the following methods of cell-cell communication: a. Direct Contact: Signaling (Antigen Presenting Cell) Recognition (Major Histocompatibility Cell) The MHC is a protein on the surface of a cell that helps the immune system identify foreign cells or substances. Tight Junctions/Gap Junctions/Anchoring Junctions With gap junctions neighboring cells are connected through their cytoplasm in the gap and can send signals. b. Communication over short distances: Neurotransmitters/synaptic signaling Synaptic signaling is where nerve cells release a signal (neurotransmitter) which binds to receptors on nearby cells. Paracrine signaling Paracrine signaling is where a signal is released from a cell and has an effect only on the the neighboring cells. *Quorum sensing (bacteria)- on Bonnie Bassler TED talk Quorum sensing is the regulation of gene expression in response to fluctuations in cell-population density. Quorum sensing bacteria produce and release chemical signal molecules called autoinducers that increase in concentration as a function of cell density. c. Communication over long distances: Endocrine signaling Endocrine is where hormones are released from a cell and they travel through the circulatory system to other cells 13
throughout the body. Used in plants and animals Insulin (what is one way in which insulin acts?) Insulin is a hormone that attaches to an RTK and causes the enzyme to phosphorylate a protein which then causes glucose to be converted into glycogen. Glucagon (what is one way in which glucagon acts?) This has the same effect for a variety of cells and this signal raises blood sugar by breaking down stored glycogen into glucose by turning on the genes that make enzymes that synthesize glucose Epinephrine (what is one way in which epinephrine acts?) It is a signal which is released during stress. It has different effects for different cells depending on their coactivators. Describe signal transduction G-protein linked receptors G protein receptors receive ligands on the outside of the cell which activates a signal transduction on the inside of the cell. It isn’t an immediate cell response, it goes through a chain of reactions. First the GDP is phosphorylated into GTP which causes the G protein to phosphorylate and be activated. The G protein releases its alpha part which then goes and activates other proteins in the cell, which activate others through protein kinases until a cell response is achieved.