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Ch12 Transport Across Cell Membranes, Charge quantity must be balanced…

- - - - O2
      - CO2
    - - Water, ethanol readily diffuse across
      - glycerol cross less rapidly
      - glucose hardly cross
- - - - pyruvate import
      - ATP export
    - - monomers
    - - H+ transporters
  - - - gap juntions
      - porins
      - NOT simple holes bc not always open
    - - ion selectitve
        
        diameter and shape of ion channel
        
        distribution of charged AA lining it
      - most are gated
        
        need spec stimulus to trigger a conform change (closed to open)
        
        voltage-gated
        
        voltage sensor domains
        
        Na+ and K+ channels propagate APs
        
        Ca2+ channels of nerve terminal participate in converting electrical to chemical signal
        
        ligand-gated
        
        transmitter-gated ion channels
        
        convert chem back to electrical signal
        
        "ion-channel-couple receptors"
        
        mechanically-gated
        
        auditory hair cells
        
        light-gated channels
        
        inactivate/activate neurons of live animals
  - - - Na+ K+ ATPase
        
        conformational changes drives exchange of Na+ and K+
        
        antiport (?)
        
        generates steep conc gradient across membrane
      - Ca2+ ATPase
        
        unlike Na+/K+ pump, don't need another ion to return to orig conformation
        
        remove Ca2+ from cytosol
        
        ER
        
        plasma membrane
        
        symport (?)
      - H+ pump
        
        lysosome of animal cells
        
        central vacuole of plant and fungal cells
    - - downhill solute movem used to power uphill transport of second solute
      - direction
        
        symport
        
        glucose-Na+ symport
        
        anitport
        
        Na+-H+ exhanger
        
        pH regulation: cytosol ~7;
        organelle interior acidic
  - - - uncharged
        
        direction determined solely by its concentration gradient
        
        osmosis
        
        aquaporin channels
        
        glucose
        
        glucose transporters (uniports)
      - all channels are passive
      - many pumps can also be for passive
      - charged
        
        concentration gradient
        
        membrane potential
        
        pull + in and drive - out
      - electrochem gradient
        
        concentration gradient of solute
        
        force from membrane potential (change in V)
    - - help cell achieve appropriate intracellular ionic composition
      - need pumps
- - - - proteins
      - cell metabolites
      - nucleic acids
      - So inside of cell is more neg than out
        
        resting mem pot is between -20 adn -200 mV