cell membrane transport Flashcards
what type of transport is passive
-simple diffusion and facilitated diffusion
what are the two types of active transport
-primary (direct)
-secondary (indirect)
what does the electrochemical gradient do
-drives passive processes
-involves and based on both the electrical and chemical properties
-no additional energy input
-always depends on the concentration gradient of the solute
-for charged molecules also depends on any difference in voltage between the ECF and ICF
-if Na+ was trying to move past a +ve membrane, more force would be needed as the charges repel
what are hydrophobic solutes
-solutes that can move through the membrane, in other words, they like fatty acids
-can move through the membrane by simple diffusion
what’s the equation for Jx
Jx= Px ([X]o-[X]i)
Jx= flux
Px= permeability coefficient
difference in [X] between ECF and ICF
what are transmembrane proteins
-classed as integral membranes (embedded within membrane)
-composed of membrane-spanning alpha-helical domains (protein structure)
-can be single or multi pass
what is a protein’s membrane topology
how proteins move in and out of the membrane
what are the different types of transmembrane proteins
-pore (non-gated channel)
-channel (gated pore)
-carrier
-pump
why are there different types of transmembrane proteins
-solutes require specific types of transmembrane proteins
-all transmembrane proteins have multiple transmembrane segments surrounding a solute pathway
why do transmembrane proteins create hydrophilic permeation pathways through the membrane
-amino acids have different properties which determine whether the protein is hydrophobic or hydrophilic
-amphipathic helices- alternating hydrophobic and hydrophilic amino acids
-hydrophobic surfaces face lipid molecules
-hydrophilic surfaces create a central pore
*if confused look at slide, page 10
how do pores allow facilitated diffusion
-driving force for movement is electrochemical gradient
-always open as pores are conduits
-multiple subunits
-e.g. aquaporins
how do channels allow facilitated diffusion
-driving force for movement is the electrochemical gradient
-gated ion channels
-multiple subunits
-e.g. potassium channel
what are the different types of channels
-voltage gated
-ligand gated (ECF and ICF ligands)
-mechanical-gated
what do each type of channel have
-a moveable gate (determined by Amino Acids)
-a sensor : voltage (charge) , ligand (molecules which bind) or mechanical (stretch physically)
-a selectivity filter
-an open channel pore
how do carriers allow facilitated diffusion
-driving force for movement is the electrochemical gradient
-never had continuous transmembrane path
-e.g. GLUT
is carrier mediated facilitated diffusion faster or slow than a channel and a pore
slower
process of carrier mediated facilitated diffusion
-carrier is open to outside
-X enters from outside and binds at a binding site
-the outer gate closes and X becomes occluded, still attached to its binding site
-the inner gate opens with X still bound
-X exits and enters the inside of cell
-the inner gate closes occluding an empty binding site
-cycle can also follow in reversed order
how can carriers mediate active transport
-through pumps, co-transporters and exchangers
which way does active transport move a solute to
-against the electrochemical gradient
-AT needs metabolic energy (ATP)
what does primary active transport use
-pumps
-a chemical reaction e.g. ATP hydrolysis
-pumps depends on the hydrolysis of ATP to turn ATP-> ADP +Pi which releases energy
-primary AT needed for secondary AT
what does secondary AT use
-co-transporters and exchangers
-use the chemical gradient from the primary reaction to drive the movement of ions
what does saturation of pumps mean
-when all the pumps are fully saturated, this means there is a finite amount that they can transport
how can co-transporters move both solutes in the same direction
-when things move in the same directions (in or out)
-requires a driving force whose electrochemical gradient provides the ender - often inward Na+ electrochemical gradient
-e.g. Na+/glucose transporter
-also called symporters
exchangers can move solutes in opposite directions
-requires a driving solutes whose electrochemical gradient provides the energy
-often the inward Na+ electrochemical gradient
-e.g. Na+/Ca2+ exchanger
-called antiporters
