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UI BIOL 1411 - Cell Communication/Signaling

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BIOL 1411 1st Edition Lecture 8Outline of Last Lecture 1. More cell membrane functions and details2. Transporting substances through membrane3. DiffusionOutline of Current Lecture 1. Active transport2. Macromolecules leaving the cell3. Cell responding to their environment4. Receptors sense signals Current Lecture- Active transporto Moves substances in one direction, (low concentrationhigh)o Three kinds of transporter proteins Uniporters- Glucose transporter- Transports one substance in one direction Symporters- Transports two different substances in the same direction- Glucose-Na+ symporter Antisymporters- Na+-K+ pumpo Present in all cellso Important for maintaining membrane potential o Higher [Na+] outside of cell; higher [K+] inside cello Antiporter Pumps Na+ out of cell against gradient Pumps K+ into cell against gradient These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Uses ATP energy directly (primary active transport) to pump both ions- Other ion pumps- Transports two different substances in opposite directionso Requires ATP energy Primary active transport- Direct hydrolysis of ATP provides energy  Secondary active transport - Energy comes from an ion concentration gradient that is established by primary active transport- The Glucose-Na+ symporter- Found in intestinal and kidney cells- Glucose is transported across the membrane against concentration gradient - Simultaneous diffusion of Na+ (down its concentration gradient) provides the energy to move glucose moleculeso Works in parallel to Na+-K+ pump- How do large molecules leave the cell?o Macromolecules (proteins, polysaccharides, nucleic acids) are too large to cross the plasma membraneo Must be taken in or secreted by means of membrane vesicleso Endocytosis Plasma membrane surrounds the extracellular material and invaginates, forminga vesicle Phagocytosis - Membrane extension and engulfment into huge vesicles - Molecules or entire cells are engulfed- A food vacuole or phagosome forms, which fuses with a lysosomeo Exocytosis  Material in vesicles is expelled (secreted) from a cell by fusion with the plasma membraneo Pinocytosis  Small dissolved substances or fluids Vesicles are much smaller in phagocytosis o Receptor mediated endocytosis  Highly specific Involves receptor proteins-integral membrane proteins- which bind to specific substances  Receptors are in regions of the plasma membrane called coated pits—coated with other proteins such as clathrin on cytoplasmic side Chapter 7: Cell Signaling and Communication- Chunk 1: Big picture here is this section is to understand that cells must respond to their environment o All cells process information (signals) from the environment Chemical- A nutrient, waste, ion, hormone Physical stimulus- Light, sound, or temperature o Signals can come form outside the organism or from other cells within the organism  In multicellular organisms, signals may be transmitted over a short or a great distanceo To detect and respond to a signal, a cell (target) must have a specific receptor that can detect it.o When a cell detects a signal, it initiates a signal transduction pathway—sequence of molecular events and chemical reactions—that lead to a response to the signalo Signals travel to target by diffusiono Plants: plasmodesmata allow long distance transporto Components of signal transduction pathway The Signal The receptor of the signal  The response to the signal- Initiated by receptor- Transduced and amplified by other cellular molecules- Ultimately causes change in target cell-Common themes in signal transduction pathways- Specificity o Receptor proteins have very specific binding sites for chemical signal molecules (=ligands)- Ligand binding causes receptor protein to change shapeo Shape change activates receptor (e.g. kinase activity)- Activated receptor alters function of a responder protein.o The signal is amplified – more than one responder molecule in cell- Response is executedo Responder activates/deactivates other cellular effectorso Cell activity is altered- Chunk 2: Receptors sense signalso Binding is reversible o Ligand is not changed by bindingo The receptor alternates between active and inactive conformationso Many behavior altering drugs work by binding ligand-binding site of receptor proteins in brain cells1. Ion Channel Receptors- Transmembrane channel proteins that allow ions to enter of leave cell - Signals (bind to or change an extracellular domain)o Chemical ligands such as hormones or neurotransmitterso Electric charge differenceso Sensory stimuli such as light, sound, pressure2. Protein Kinase Receptors- Transmembrane proteins that also have a cytoplasmic kinase domain that catalyzes phosphorylation of themselves and/or other proteinso A phosphate is transferred from ATP to the proteinshape change to “active state”- Exampleo Mammalian insulin receptor Phosphorylates itself and other insulin response substrates Initiates insertion of glucose transporters into the plasma membrane3. G protein-linked Receptors - Seven transmembrane domain proteins with a cytoplasmic domain that binds a G proteino When extracellular domain binds ligand, the shape of the cytoplasmic regionchanges and exposes a binding site for a G proteino G Proteins Mobile membrane proteins with three subunits. They bind GDP and GTP (guanosinediphosphate and triphosphate. No signal: inactive state, has GDP bound, no interaction with receptor  Signal binding to receptor: becomes active by binding with receptor and exchange of GDP for GTP- G proteins can either activate or inhibit an effectoro Heart muscle cells: Epinephrine (adrenalin) binds to G protein-linked receptor and activates an enzyme to produce cylic AMP – cAMPo Smooth muscle cells Epinephrine binding to G protein-linked receptor inhibits the enzyme for cAMP synthesis o cAMP is a second messenger that in turn activates diverse effectors - Same signal (epinephrine as different effects on different target cells depending on the G protein involved 4. Cytoplasmic receptors- Bind ligands that can cross the plasma membrane- Ligand binding causes receptor to change shape- allows it to enter nucleus, where is affects gene expressiono The receptor is responder and


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