ANP1111 Lecture 11 Membrane Transport & Excitable Cells Part 1 PDF

https://www.pfizer.com/news/articles/little- ms-excitable-and-mr-na%C3%AFve-meet -some-varied-%E2%80%98cell-states%E 2%80%99  Membrane transport (pp. 63-79) Briefly describe the structure of the plasma membrane Basic structure according to the fluid mosaic model: phospholipid bilayer - what...

https://www.pfizer.com/news/articles/little- ms-excitable-and-mr-na%C3%AFve-meet -some-varied-%E2%80%98cell-states%E 2%80%99  Membrane transport (pp. 63-79) Briefly describe the structure of the plasma membrane Basic structure according to the fluid mosaic model: phospholipid bilayer - what is a phospholipid?? what do we mean when we say the hydrophilic and hydrophobic ends of phospholipids?? Phospholipid bilayer http://www.biology.arizona.edu/chh/problem_sets/kidneysmetals/07t.html But there is more to plasma membrane structure than just a phospholipid bilayer. 1. Integral membrane proteins - span PM (transmembrane); hydrophilic & hydrophobic regions; channels, carriers 2. Peripheral proteins: attached to integral proteins (often internal face of PM); can be enzymes, involved in attachment functions, shape changes.. or receptors if on the cell surface From Focus Fig. 3.1 3. Cytoskeleton: anchors to PM; 4. Glycocalyx: mix of carbohydrates attached to lipids & proteins on outer face; “sugar coating” on PM; allows cells to recognize one another NB: the glycocalyx changes when cell becomes cancerous - can even change repeatedly making it hard for immune system to keep up 5. Cholesterol: reduces general membrane fluidity & stabilizes its structure – ~20% of membrane lipid – but too much causes membranes to lose flexibility From Focus Fig. 3.1 Junctions are modifications of the plasma membrane that perform important functions – there are 3 types tight junctions desmosomes gap junctions Fig. 3.4  1. Tight Junctions: Fig. 3.4a Fusion of adjacent plasma membranes to prevent passage of molecules in between cells Why would these structures be http://www.nastech.com/nastech/junctions_biology important in the lining of the digestive tract? J. Carnegie, Uof  2. Desmosomes: Anchoring junctions: molecular linking of cells to resist mechanical stress Plaque + linker proteins (cadherins) & keratin filaments Where are desmosomes found? 3. Gap Junctions: Molecular channels between cells to allow passage of cytoplasmic molecules connexons electrically-excitable tissues Fig. 3.4b & c Some Functions of Plasma Membrane Proteins transport intercellular joining enzymatic activity cell-cell recognition receptors for attachment signal to ECM transduction Fig. 3.3 Plasma membranes also provide a selectively permeable, hydrophobic barrier between the interstitial fluid and the cytoplasm interstitial fluid is a filtrate of blood - contains salts, sugars, amino acids, vitamins, hormones, metabolites, gases such as O2 and CO2, etc. to maintain homeostasis and function normally, a cell must extract needed items, keep valuable materials inside & discard wastes How do water-soluble substances get across the plasma membrane? Transport across the PM can be active or passive  There are 3 types of passive simple diffusion transport mechanisms facilitated diffusion osmosis  Diffusion: “tendency of molecules or ions to scatter evenly throughout the environment”  molecules have kinetic energy: how does this facilitate diffusion?  How is diffusion rate influenced by? 1. Concentration gradient slope 2. Molecule size 3. Temperature  PM is hydrophobic barrier: to traverse PM a molecule must be lipid-soluble or have access to channels or transporters Fig. 3.5 J. Carnegie, Uof O Diffusion options are different depending on whether a molecule is water-soluble or lipid-soluble UREA NH2 - C - NH2 O Simple Diffusion – no carriers needed if lipid-soluble! nonpolar, lipid-soluble: O2, CO2, fats, urea, alcohol O2 & CO2 follow gradients into and out of cells, respectively molecule is moving down its concentration gradient!! Fig. 3.6a J. Carnegie, Uof O Facilitated diffusion: water soluble substances need help to traverse the PM: 1) specific 2) not ATP-requiring 3) limited by carrier/channel saturation 4) movement down concentration gradient A. Carrier-Mediated Facilitated Diffusion lipid-insoluble molecules too large to pass through membrane pores/channels What is the most well- known substance that is transported by carrier-mediated facilitated diffusion? Fig. 3.6b: Carrier mediated facilitated diffusion J. Carnegie,  B. Channel-Mediated Facilitated Diffusion selective due to pore size and the charges of the amino acids that line the channels some are always open (leaky channels) opening of others is regulated (gated channels) but movement is still always down the concentration gradient can be inhibited, can show saturation & are usually specific Fig. 3.6c: Channel- mediated facilitated diffusion Describe osmosis and explain its role in fluid homeostasis unassisted diffusion of water from area of more water to one of less water across a semipermeable membrane Water is polar, but small enough have a level of movement across the plasma membrane directly plus there are water channels called aquaporins on many cells What happens with plant vs animal cells if there is a lot of water entry? J. Carnegie, Uof O Fig. 3.6d More water in a solution means less solute (osmolarity) osmolarity and tonicity are not the same!!! Osmolarity: total concentration of solute particles in a solution (type doesn’t matter – additive; mOsmol/L) Tonicity: ability of solution to change the shape of a cell bathed by that solution by altering its water content – what are important are the nonpenetrating solute particles Usually described in relative terms: hypertonic, hypotonic, isotonic Fig. 3.7 Influence of membrane permeability on diffusion and osmosis Distinguish between pairs of solutions that are: isotonic, hypertonic or hypotonic bio.winona.msus.edu/.../ images/tonicity.gif  Molecules that are ionically bonded have greater osmotic power than those that are covalently bonded 8 + 4 12 Cl- Cl - Na+ Cl- Cl- Na Ca++ - Ca ++ Cl Cl- Cl- Cl - Na+ Cl- Ca++ Na+ Cl- Ca ++ Cl- Cl- 1 mM NaCl = 2mOsm 1 mM glucose = 1 mOsm 1 mM CaCl2 = 3 mOsm Q#1: What do we mean when we say that 0.9% NaCl is isotonic saline?? Q#2: What happens to a RBC when it is put into a hypertonic solution?? Into a hypotonic solution?? What does the term lysis mean?? J. Carnegie,  RBC in: isotonic hypertonic hypotonic solutions Applications: 1. Hypertonic solutions can be used carefully and with monitoring for edema: pull water out of swollen tissues. 2. Hypotonic solutions used carefully and with monitoring to rehydrate severely dehydrated patients. J. Carnegie, Uof O Active Transport requires ATP because the substance is: (1) too large for pores and is lipid insoluble AND/OR (2) moving against its concentration gradient 1. Active Transport (AT): like FD, requires a carrier: combines specifically & reversibly with substance unlike FD, solute pumps move substances (amino acids, glucose, Na+, K+, Ca+) AGAINST THEIR CONCENTRATION GRADIENTS many active transport systems are coupled systems: (a) symport: eg: Na+ & amino acids or glucose, Na+,K+,2Cl- cotransporter (b) antiport: eg: Na+/K+ ATPase  primary AT (Na+/K+ ATPase) vs secondary AT ( Na+ & amino acids ) J. Carnegie, Uof O Primary Active Transport – the Na+/K+ pump:  [K+] 10-20X higher inside cell than out; [Na+] higher outside cell than in  gradients essential to maintain normal cell function/responsiveness/volume  maintenance of this gradient challenged by: (1) slow leakage of K+ and Na+ along their concentration gradients (2) stimulation of muscle & nerve cells  Na+/K+ ATPase functions continuously to maintain Na+ & K+ gradients 3 Na+ ions are pumped OUT for every 2 K+ ions pumped IN - moving AGAINST their concentration gradients to maintain cell responsiveness Na+/K+ ATPase (example of an antiport) J. Carnegie, Uof Focus Fig. 3.2: The Na+/K+ ATPase, an antiport active transport pump  Secondary active transport: cotransport of amino acids, ions:  transport of a solute is NOT coupled directly to energy-yielding reactions  eg: transport of an ion or amino acid as Na+ leaks back into cell along its concentration gradient (gradient drives transport but gradient would not exist except for Na+/K+ ATPase) Is this a symport or an antiport?? Fig. 3.9 J. Carnegie, Uof O What is the ATP driving in this model of secondary active transport?? 2. Vesicular transport: define: exocytosis, endocytosis as active transport mechanisms · also ATP-requiring – but for vesicle movement · exocytosis (out) and endocytosis (in) Exocytosis:  secretion of hormones, neurotransmitters, mucus, ejection of wastes  substance is enclosed in a vesicle, vesicle moves to PM, fuses with PM, ruptures, releasing contents outside of cell Vesicle docking: What does this involve?? What is a v-SNARE? What is a t-SNARE? Fig. 3.12 Endocytosis  means by which large particles can enter cell  vesicle encloses substance; pinches off & moves into cytoplasm where contents may be digested; may also traverse cell to exit at other side Phagocytosis – e.g. for bacteria, cell debris Pinocytosis – fluid plus dissolved substances Receptor-mediated endocytosis – allows hormones, enzymes, other important macromolecules to be concentrated within a cell J. Carnegie, UofO Chapter 3 – A&P Flix: Membrane Transport – this 4.5-minute video that you can access in Mastering A&P (Study area → Animations and Videos → A&P Flix → 3D Animations → Membrane Transport) gives you a nice summary of what we have talked about – animating the processes so that you can really visualize them – Check it out!  Neurons – Chapter 11 Identify the different regions of the neuron and associate each region with the functions of reception, propagation and transmission of nerve impulses (pp. 394-396) Explain the phenomena (diffusion of ions, types of ion channels) that are responsible for the electrical activity of neurons (resting membrane potential, action potential) (pp. 400-409) Describe the factors that influence propagation of the action potential along an axon (pp. 409-412) Explain the mechanisms of synaptic transmission (synapse, post- synaptic potentials, synaptic integration (pp. 412-420) Neurotransmitters and neural circuits (pp. 420-427) J. Carnegie, Uof O Neurons conduct electrical impulses from one body part to another Special features: 1. Extreme longevity: if adequately nourished  can last 100 yr+ 2. Amitotic: why? what does this mean if neurons are damaged? 3. High metabolic rate: O2/glucose requirements? large, complex cells: all have a cell body + one or more processes "There are perhaps about one hundred billion neurons, or nerve cells, in the brain, and in a single human brain the number of possible inter-connections between these cells is greater than the number of atoms in the universe." (Robert Ornstein and Richard Thompson, The Amazing Brain. Boston: Houghton Mifflin Company. 1984, 21) J. Carnegie, UofO http://www.holisticeducator.com/neuron.htm 3 functional regions: (plasma membrane very important in all regions!) 1. Receptive region 2. Conducting region 3. Secretory region http://www.ualberta.ca/~neuro/OnlineIntro/NeuronStructure.htm A. Neuron Cell Body  large, spherical nucleus + granular cytoplasm = biosynthetic centre  extensive RER + ribosome clusters (Nissl bodies); also elaborate Golgi & lots of mitochondria Why??  In the CNS/ PNS as a whole: What is a nucleus? What is a ganglion? B. Neuron Processes dendrites axons axonal terminals 2 more terms: tract: bundle of nerve processes in CNS nerve: bundle of nerve processes in PNS Fig. 11.5 J. Carnegie, Uof O  B1. Dendrites: (receptive region)  short, tapering, branched extensions; usually hundreds/cell body  enormous SA for reception from other neurons  conduct impulses toward cell body  short distance, graded potentials B2. Axon + axon terminals  arises from axon hillock; variable length (can be > 1 metre)  rate of conduction increases with axon diameter J. Carnegie, Uof O  usu. 1 axon/neuron; branches at end (~10,000 terminal branches) which end in knob-like axonal terminals B2. Axons + axon terminals (cont.): Neurotransmitters convey information from one axon to the next Axon has same organelles as cell body, but no Nissl bodies; axons quickly degenerate if cut Elaborate cytoskeleton in axon moves material to & fro in one of 2 directions: anterograde (mitochondria, cytoskeletal elements, NTs) retrograde (primarily organelles to be degraded/recycled) Clinical Note: Viruses such as polio, rabies, herpes simplex & tetanus toxin reach neuron cell bodies by retrograde transport https://www.semanticscholar.org/paper/Rabies-and-other-lyssavirus-diseases-Warrell- J. Carnegie, Uof O Warrell/1ee238e5b1dd09991268a279822954acc2782e46