Plasma Membrane Handouts PDF

Seifter, Fig 2-11 CARRIER-MEDIATED TRANSPORT  CARRIER-MEDIATED TRANSPORT Specificity and selectivity: – One carrier for one (or closely related) substance – Different cells may have different carriers – Dysfunction leads to diseases Saturation: – Finite number of carriers, affinity...

Seifter, Fig 2-11 CARRIER-MEDIATED TRANSPORT  CARRIER-MEDIATED TRANSPORT Specificity and selectivity: – One carrier for one (or closely related) substance – Different cells may have different carriers – Dysfunction leads to diseases Saturation: – Finite number of carriers, affinity/number can be regulated – Tm = transport maximum (rate-limiting factor in transport) Competition: – Occurs when carrier transfers closely related substances – Reduces the rate of transfer of each substance transported – Does not affect the total amount of transfer  Sherwood, Fig 3-14 FACILITATED DIFFUSION  Sherwood, Fig 3-15 FACILITATED DIFFUSION Example: transport of glucose into the cell Movement of a substance from high to low concentration Does not require energy  ACTIVE TRANSPORT Movement of a substance from low to high concentration – Example: uptake of iodine in thyroid gland cells Two types: – Primary active transport: ATP required directly; carrier splits ATP (has ATPase activity) Requires energy (ATP) to change the shape of the carrier AKA “pumps” (hydrogen ion pump, Na-K-ATPase pump) – Secondary active transport: ATP not required directly; carrier lacks ATPase activity  Sherwood, Fig 3-16 PRIMARY ACTIVE TRANSPORT  Na+ K+ ATPase PUMP Establishes Na+ and K+ concentration gradients: electrical signals Regulates cell volume by controlling tonicity Energy (ATP) used also serves for secondary active transport http://blogs.scientificamerican.com/urban- scientist/hotline-bling-sodium-potassium- pumps/ Movie to summarize  Sherwood, Fig 3-18 SECONDARY ACTIVE TRANSPORT  Sherwood, Fig 3-18 SECONDARY ACTIVE TRANSPORT  SECONDARY ACTIVE TRANSPORT Co-transport of glucose and amino acids Intestinal and kidney cells, against concentration gradients Energy not expended directly, mediated by co- transport carriers Contain two binding sites, one for Na other for nutrient molecule Na binding  affinity for glucose binding Transported out in blood by facilitated diffusion  VESICULAR TRANSPORT Large polar molecules (hormones) and multi- molecular materials (bacteria) Wrapped-up in a membrane-enclosed vesicle Requires energy Materials inside do not mix with cytosol, fuse with target membrane for transfer Two types: endocytosis and exocytosis  VESICULAR TRANSPORT Endocytosis: substances transported into the cell, can fuse with lysosome or released on the other side of cell – Pinocytosis (non-selective uptake of ECF) – Receptor-mediated endocytosis (selective uptake of large molecule) – Phagocytosis (selective uptake of multimolecular particle) Exocytosis: substances transported out of the cell, accomplishes two major purposes – Provides a mechanism for secreting hormones/enzymes (large polar molecules) – Enables cell to add specific membrane components: carriers, channels, receptors Rate of endocytosis = rate of exocytosis  Sherwood Fig 2-6 VESICULAR TRANSPORT  Sherwood Fig 2-9 TYPES OF ENDOCYTOSIS (c) Phagocytosis  Seifter, Fig 3-1 CELL-CELL COMMUNICATION Co-ordination of activity & homeostasis Achieved by: – Direct communication: Gap junctions Tunneling nanotubes Juxtacrine – Indirect communication: Paracrine Autocrine Via chemical Endocrine messengers Neuronal  Sherwood, Fig 4-19 COMMUNICATION VIA GAP JXNS Most intimate & rapid means of communication  Sherwood, Fig 4-19 JUXTACRINE COMMUNICATION Direct contact through plasma membranes Restricted to cells in contact (cannot diffuse) Ag-Ab reaction, phagocytosis, CAMs etc.  Sherwood, Fig 4-19 AUTO/PARACRINE COMMUNICATION Autocrine: Paracrine:  Sherwood, Fig 4-19 ENDOCRINE COMMUNICATION Hormones secreted in blood Travel to distant sites Acts on cells possessing receptors FSH, thyroid, insulin etc.  Sherwood, Fig 4-19 NEURONAL COMMUNICATION Short range, released by electrical signals Diffuse to act on target cells (gland/neuron/muscle) Local Neurotransmitter target cell  SIGNAL TRANSDUCTION Chemical messengers: lipid soluble or water soluble Signal transduction process: → message (signal) is “transduced” inside the cell by “transducers” (convert one form of energy to another e.g., radio/phone) Lipid soluble: cross membranes → affect gene transcription → affect activity of proteins Water soluble: do not cross membranes, bind to receptors → transduce signal inside the cell – 1st Messenger-receptor binding → intracellular events: By opening/closing ion channels allowing ions to move in/out By transferring the signal to intracellular 2nd messenger  Sherwood, Table 4-3, Fig 4-28 SIGNAL TRANSDUCTION  ION CHANNELS Leak channels Gated channels Always open, permit leakage Open/close in of ions into/out of cells response to stimuli Ligand-gated Voltage-gated ion channels ion channels Chemical messenger binds Changes in electrical to a receptor associated status of the plasma with ion channel membrane Ionic movement leads to physiological response  Sherwood, Fig 4-21, 4-25, 4-26 SECOND MESSENGER PATHWAYS  Sherwood, Fig 4-27 SECOND MESSENGER PATHWAYS Message is “relayed” inside the cell via 2nd messenger 2nd messengers relays it further to other IC proteins Signaling cascade amplifies the initial response Major ones: – Cyclic AMP – Ca2+/DAG Others exist! Disturbances lead to diseases  Sherwood, Fig 3-19 MEMBRANE POTENTIAL PM is polarized electrically = membrane potential – Separation of opposite charges across the membrane due to difference in relative number of cations/anions  MEMBRANE POTENTIAL “Potential” (capacity) to do work – Unlike charges attract, energy used to separate them – When allowed to come together, energy released – This energy is harnessed to perform work Membrane itself is not charged! Measured in millivolts (one-thousandth of a volt) – Depends on the “degree” of separation  Sherwood, Table 3-3 GENERATION OF RMP Constant membrane potential of tissues at rest: −70mV Unequal distribution of Na+, K+ & A- across membrane – Na-K-ATPase pump Pumps three Na+ outside and two K+ inside Outside becomes more positive than inside, membrane potential! – Leak channels for Na & K ions Always open, allow passive diffusion due to concentration gradient Ion Extracellular Intracellular Relative concentration concentration permeability Na+ 150 mM 15 mM 1 K+ 5 mM 150 mM 25-30 A- 0 mM 65 0  Sherwood, Fig 3-20 GENERATION OF RMP Equilibrium potential of K+ (EK+): Concentration gradient = electrical gradient Given by Nernst equation: E = 61 log Co/Ci EK+ = 61 log 5/150 EK+ = 61 (-1.477) EK+ = -90mV  Sherwood, Fig 3-21 GENERATION OF RMP Equilibrium potential of Na+ (ENa+): – Concentration gradient for Na+ pushes it in leaving Cl- outside – Concentration gradient = electrical gradient – Given by Nernst equation: E = 61 log Co/Ci ENa+ = 61 log ____/___ ENa+ = 61 (_______) ENa+ = _____mV – ENa+ lower than EK+: why?  Sherwood, Fig 3-22 GENERATION OF RMP Concurrent effect of Na+ & K+ movement: movie  Sherwood, Fig 4-1 CHANGES IN RMP Polarization: any state, positive or negative, other than 0 mV  MEMBRANE POTENTIAL: USE Nerve & muscle cells are excitable tissues Undergo transient, rapid changes in their RMP Triggering event Membrane permeability changes Membrane potential changes Ions move across cell membranes Electrical signals Graded potentials: Initiate contraction Travel short distances Types Functions Action potentials: Receive,process, initiate Travel long distances & transmit messages