BIOL 1411 1st Edition Lecture 8 Outline of Last Lecture 1 More cell membrane functions and details 2 Transporting substances through membrane 3 Diffusion Outline of Current Lecture 1 Active transport 2 Macromolecules leaving the cell 3 Cell responding to their environment 4 Receptors sense signals Current Lecture Active transport o 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 pump o Present in all cells o Important for maintaining membrane potential o Higher Na outside of cell higher K inside cell o 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 directions o 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 molecules o 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 membrane o Must be taken in or secreted by means of membrane vesicles o Endocytosis Plasma membrane surrounds the extracellular material and invaginates forming a 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 lysosome o Exocytosis Material in vesicles is expelled secreted from a cell by fusion with the plasma membrane o 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 distance o 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 signal o Signals travel to target by diffusion o Plants plasmodesmata allow long distance transport o 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 shape o 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 executed o Responder activates deactivates other cellular effectors o Cell activity is altered Chunk 2 Receptors sense signals o Binding is reversible o Ligand is not changed by binding o The receptor alternates between active and inactive conformations o Many behavior altering drugs work by binding ligand binding site of receptor proteins in brain cells 1 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 neurotransmitters o Electric charge differences o Sensory stimuli such as light sound pressure 2 Protein Kinase Receptors Transmembrane proteins that also have a cytoplasmic kinase domain that catalyzes phosphorylation of themselves and or other proteins o A phosphate is transferred from ATP to the protein shape change to active state Example o Mammalian insulin receptor Phosphorylates itself and other insulin response substrates Initiates insertion of glucose transporters into the plasma membrane 3 G protein linked Receptors Seven transmembrane domain proteins with a cytoplasmic domain that binds a G protein o When extracellular domain binds ligand the shape of the cytoplasmic region changes and exposes a binding site for a G protein o 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 effector o Heart muscle cells Epinephrine adrenalin binds to G protein linked receptor and activates an enzyme to produce cylic AMP cAMP o 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 expression o The receptor is responder and effector