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MEMBRANE TRANSPORT - Coggle Diagram

- - - - MEMORIZE SLIDE 11
    - - MEMORIZE SLIDE 10
    - - MEMORIZE EQN
    - - work is required to move ions across a membrane
      - 1 joule is required to move 1 coulomb to yield a potential difference of 1 volt
      - electrochemical potential difference includes both concentraion and electrical potentials
      - source of change in electrical charge across membranes:
        
        diffusion down preexisting gradient
        
        electrogenic pumps against gradient
      - membrane potential: sun of all ion gradients, with about 60% of this due to H+ gradient alone
        
        resting membrane potential = -125 mV
        
        cyanide depolarizes membranes, inhibits ATP synthesis
        
        cyanide removal restores membrane potential; ATP synthesis resumes and PM ATPase restores H+ gradient
      - ion movement in/out of cell:
        
        homeostasis determined by transporters
        
        transport in/out PM--passive = K+, active = other ions
        
        sequestration of ions in vacuoles
        
        internal store of ions
        
        regulates cytoplasmic concentrations
        
        transport is regulated at each membrane via the PM and tonoplasts
  - - - symplast: 80-95% of root volume
      - apoplast: 5-15% of root volume
    - - ring of cells around stele whole walls contain the Casparian Strip, regulating ion entry into vascular tissues and preventing escape of solutes from stele
    - - passive process, with ions moving from high to low electrochemical potential
      - actively regulated
      - responds to hormones
      - sensitive to metabolic inhibitors
      - carriers in xylem parenchyma PM identified by electrophysiology and genetics and include H+ pumps, aquaporins, and ion efflux carriers
    - - excised root sealed in two-compartment chamber
        
        addition of radiolabeled ion to apical compartment (A) to measure ion uptake by root and determine root free-space
        
        radiolabel in distal compartment (B) due to xylem transport
        
        may add regulatory compounds to apical compartment (A) including hormones and inhibitors
        
        buffer composition
- - - - depends on membrane composition
      - permeability constant based on size and shape
      - transport rate: movement of solute from one side of membrane to other side
        
        MEMORIZE P20 TRANSPORT RATE DIFFUSION VS CARRIER
    - - Ion Channels
        
        voltage-gated channels are pores in membrane that permit ions to flow with a gate that opens or closes according to membrane potential
        
        ions flow with concentration gradient as passive transport
        
        channels are specific for a particular ion
        
        channels open/close in response to intracellular signals via regulatory subunit, depending on electrochemical gradients
        
        K+ shaker channels strongly regulated
        
        cyclic-nucelotide dependent channels weakly regulated by cGMP binding and functions to transport K+, Ca2+, and Na+; associated with disease resistance and bacterial pathogens
        
        K+ ion channel consists of 6 membrane-spanning regions with voltage sensing occurring on S4 and the pore-forming region occurring between S5 and S6
        
        MEMORIZE STRUCTURE
        
        channel kinetics:
        
        hypothetical = channel function not being controlled by voltage
        
        actual = channel function being controlled by membrane potential (voltage)
        
        MEMORIZE HYPOTETICAL VS ACTUAL DIAGRAMS P35
        
        Cation Channels
        
        50 cation channels in arabidopsis
        
        some highly selective for K+
        
        some allow passage of variety of cations including Na+
        
        Types:"
        
        Types:
        
        shaker channels
        
        highly K+ selective
        
        may be inward or outward rectifying
        
        includes K+ uptake by guard cells, K+ uptake from soil. K+ release into xylem vessels from living stelar cells, K+ uptake by pollen
        
        two-pore domain K+ channels
        
        Kir-like K+ channel
        
        cyclic nucleotide gated channels
        
        glutamate receptors
        
        homologous to glutamate receptors in mammalian nervous system
        
        glutamate induces Ca2+ uptake, so glutamate receptors act as Ca2+ permeable cation channels
        
        vacuoles
        
        TPK/K are highly selective K+ channels activated by Ca2+
        
        TCPC1/SV are non-selective Ca2+ channels
        
        Anion Channels
        
        operate in direction of passive eflux
        
        inorganic ions: NO3-. Cl-, SO4 2-, PO4 3-
        
        major organic ion: malate2-
        
        many permeable to a variety of anions
        
        Aquaporins
        
        common plants and highly expressed in epidermis, endodermis, and xylem parenchyma
        
        regulated via phosphorylation, pH, Ca2+, heterodimerization, ROS
  - - - high affinity carrier: low Km
      - low affinity carrier: high Km
      - FAMILIARIZE W/ P22 CONCENTRATION DIAGRAM
    - - high affinity carrier exhibits saturable kinetics and described by Km and Vmax
      - non-saturable carrier follows linear transport kinetics and may be a very low affinity transporter
    - - MEMORIZE EX P25
    - - Na+ sequestered in vacuole
      - Salt Overly Sensitive (SOS) gene
        
        mutant very sensitive to external NA+
        
        excludes Na+ from roots
        
        dilutes Na+ in roots via extrusion into transpiration stream for sequestration in vacuole in leaves
    - - N in soil" NH3, NH4+, NO3-
      - NH4 transporter follows free energy gradient
      - NO3- transport
        
        FAMILIARIZE W/ PROCESS P27
    - - abundance: seed germination, carnivorous plants, arabidopsis
      - families:
        
        Di- and tri- peptides and tetrapeptides participate in H+ cotransport
        
        ATP-binding Cassette (ABC) superfamily
        
        very large family
        
        direct ATP hydrolysis during transport
        
        wide range of substrates
    - - five superfamilies, three of which involve H+ transport; include high and low affintiy carriers and tissue-specific patterns
      - functions:
        
        distribution of N-resources
        
        distribution of hormones conjugated to AA and peptides
    - - selective for particular ions, with energetically uphill transport into the cell
      - examples: NO3- transporters, Malate transporters, citrate transporters, phosphate transporters, and phosphate translocators
    - - ZIP transporters include 25 related transporters that move substances like Fe, Mn, and Zn, with other transport families addressing Cu, Mo, and Cd; high affinity transporters due to low soil abundance of metals
      - In plants, metals chelated to other molecules for xylem transport
        
        free Fe and Cu lead to toxic ROS production
        
        Vacuole sequestration keeps metals below toxic levels in cytosol
- - - - ions are pumped against concentration gradient
      - Unequal distribution of ions generates electrical gradient
      - ATP hydrolysis provides energy for ion movement
      - used to establish/ restore ion homeostasis of cell
      - MEMORIZE PROCESS DIAGRAM P42
  - - - H+ Glucose Symport
        
        FAMILIARIZE WITH P52 DIAGRAMS
        
        Evidence in duckweed:
        
        glucose uptake into cell measured
        
        as glucose moves in, H+ moves in, increasing hP of external medium
        
        as H+ moves in, transient membrane depolarization occurs
        
        H+ pumps to re-establish resting membrane potential, increasing membrane potential and decreasing pH of external medium
- - - - proton channel takes place in membrane spanning regions 1-6
      - Catalytic domain includes intertransmembrane loops at 2/3 and 4/5; site of ATP hydrolysis and phosphorylated during ATP hydrolysis
      - Autoinhibitory domain: regulates enzyme activity via physical and biological signals; active when phosphorylated
  - - - multi-subunit structure
      - ATP binding sites on cytoplasmic face
      - H+ channel
      - utilizes a molecular motor
- - - - plasmodesmata connect most cells
        
        structure penetrates cell wall, with PM continuous between cells and ER appressed through PD
        
        globular protein anchors ER in PD
        
        Frequency: up to 15 per mm
        
        PD type based on formation
        
        primary: form during cell plate
        
        secondary: form later by PM invagination
        
        PD type based on macrostructure: simple or branched
        
        plasmodesmatal transport can be passive or selective and regulated
        
        passive PD transport uses size exclusion limit (SEL)
        
        Selected and regulated PD transport
        
        endogenous proteins target the proteins or RNAs to be transported to PD
        
        viral movement proteins interact with endogenous proteins to PD for transport
- - - - lipid bilayers composed of phospholipids with polar head groups exposed to aqueous solution on both surfaces and non-polar fatty acids in the interior
        
        polar head group is charged and hydrophyllic
        
        non polar fatty acid tails are hydrophobic, 14-24 carbons long, with one saturated and one unsaturated
      - unit membrane proteins:
        
        integral proteins maintained by hydrophobic interactions and act as transporters or receptors
        
        peripheral proteins located at surface of membrane and maintained by ionic or h-bonds and act as helper proteins or cytoskeleton attachment sites
      - MEMORIZE AND CREATE DIAGRAM