CBIO 3400 Week 2 Study Questions 1 List the 3 classes types of membrane transport proteins the basic characteristics of each and an example of each The 3 types of membrane transport proteins are 1 transporters 2 pumps and 3 channels Characteristics of transporters include bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across the membrane transport occurs at a moderate rate Mechanism of Carrier Mediated Transport Examples of carrier mediated transport include glucose transport in red blood cells and amino acid transport in bacteria transport occurs at a very slow rate often require ATP as an energy source to function Characteristics of pumps include Mechanism of P Type Active Transport Pumps Active Transport Movement Of Molecules Examples of pumps include the P type Na K and Ca2 active transport pumps Against a Concentration Gradient P type pump is phosphorylated during transport Binding of nucleotide to protein induces a conformational change Nucleotide state of enzyme controls conformation and affinity for ion high or low Sodium Potassium ATPase Maintains high K inside Maintains low Na inside Transports Na and K against gradient Electrogenic Requires ATP Strict ordering of steps Similar pumps for H and Ca No ATP hydrolysis without transport Domains of Pump Glucose transport in red blood cell Amino acid transport in bacteria Structure conserved 12 transmembrane domains Active Transport 1 Transport Cycle Calcium Active Transport Pump Characteristics of channels include Transmembrane Region Nucleotide Domain Phosphorylation Domain Activator Domain interact with the solute to be transported much more weakly than in transporters form aqueous pores that extend across the lipid bilayer when open these pores allow Coupled Transport Changes in nucleotide ligand induce conformational change from E1 to E2 States E1 inward facing and high affinity for calcium E2 outward facing and low affinity for calcium specific solutes usually inorganic ions of appropriate size and charge to pass through them and thereby cross the membrane transport occurs at a very fast rate can occur via symport antiport or uniport Electrochemical gradient drives transport integral membrane proteins with a hydrophilic pore that provides a path for ion movement Symport Na glucose most channels exist in open and closed states so that ion movement can be regulated Antiport Na H An example of a symport channel is the Na glucose channel and an example of an antiport Sodium gradient drives transport of other solutes channel is the Na H channel Another example of a channel is the K leak channel Energy supplied indirectly by Na K ATPase 2 structures 2 Use an intestinal epithelial cell as an example to explain how glucose sodium and potassium are transported Glucose is transported via coupled transport with Na this occurs through a symport mechanism The Na gradient drives the transport of glucose The energy for this process is indirectly supplied by the Na K ATPase Lac permease 2 Three Conformations of Voltage Gated Channel Na is transported through voltage gated Na channels Closed channels are depolarized causing them to open for a short time Open channels then inactivate themselves After the refractory period of inactivation inactivated channels revert back to the closed state The inactivated state ensures that signals are unidirectional There are 24 transmembrane spans composing 1 peptide in a single voltage gated Na channel The IFM isoleucine phenylalanine methionine complex is the only way to shut off a voltage gated Na channel Open Closed Refractory Lodish 5th 7 33 Structure Function of Voltage Gated Channels Pore 24 Transmembrane Spans Na channel 24 in 1 peptide K channel 4 peptides Quaternary structure Voltage Sensor charges M4 NH2 terminus on K channel IFM motif in Na channel Loop between M5 M6 is inserted in the bilayer and lines the pore Computer did NOT predict correctly Selectivity Filter Loop Bacterial Channel 3 Channel Closing Structure Function of Voltage Gated Channels K is transported through voltage gated K channels as well as K leak channels 24 TM spans compose 1 peptide in a voltage gated K channel and a single voltage gated K channel is composed of 4 of these peptides A voltage gated K channel can be turned off at any of its 4 NH2 terminuses 1 present in each of the 4 peptides Pore 24 Transmembrane Spans Na channel 24 in 1 peptide K channel 4 peptides Quaternary structure Voltage Sensor charges M4 NH2 terminus on K channel 3 If you were to place an electrode in the middle of an axon and artificially depolarize IFM motif in Na channel the cell in which direction i e toward the cell body toward the axon terminal in both directions or in neither direction will the action potential travel and why In such a situation the action potential would travel in both directions because all of the cells to both the right and the left of the electrode depolarization would be closed Normally cells to one side of a depolarization would be in an inactivated state ensuring that the signal is unidirectional By depolarizing an area in the middle of an axon the protective value of the inactivated state that is the inactivated state s ability to ensure a unidirectional signal is lost generating an action potential that travels in both directions toward the axon terminal and toward the cell body Loop between M5 M6 is inserted in the bilayer and lines the pore Computer did NOT predict correctly Selectivity Filter Loop 4 Briefly describe why Na is not able to pass through a K channel Na is too small to pass through a K channel A selectivity filter is able to strip water from K ions and replace that water with carbonyl groups in the pore Due to the smaller diameter of Na water cannot be stripped away from Na ions K channels thus do not allow Na ions to pass through because the K selectivity filter cannot strip water away from Na ions Na ions are thus effectively selected against by K channels Channel Closing 5 How are nerve impulses translated to cause the contraction of skeletal muscles Describe the mechanism in order STEP 1 The process is initiated when the nerve impulse reaches the nerve terminal and depolarizes the plasma membrane of the terminal The depolarization transiently opens voltage gated Ca2 channels in this membrane Since the Ca2 concentration outside cells is more than 1 000 times greater than the free Ca2 concentration inside Ca2 flows into the