Membrane Transport Flashcards
what living cells need to do for survival
maintain an internal ion composition
simple diffusion
-small polar and lipid soluble substances eg water, alcohol, fatty acid
-difuse directly thru the lipid bilayer
-high to low concentration
facilitated diffusion
-larger and polar molecules eg glucose amino acid
-transported substances bind to carrier protein or pass thru channel
osmosis
movement of water
carrier mediated facilitated diffusion
via protein carrier, binding of substrate cause shape change in transport protein
channel mediated facilitated diffusion
thru a channel, nostly ions selected based on size and charge
osmosis
diffusion thru aquaporin or lipid bilayer
factors that influence molecules moving across a cell membrane
-size
-lipid solubility
-temperature
-gradient
-distance to diffuse
osmosis definition
net diffusion of water across membrane
osmosis occurs when
-solutes cannot cross the membrane (no diffusion) so the solvent (water) crosses the membrane
-water molecules diffuse across membrane towards solution w more solute
-volume infreases on the side w more solute
animal cell is best in an __ environment
isotonic
plant cells are turgid and healthies in ___ environment
hypotonic
direction of transport depends on
the relative concentration of the solute
passive transport
solute at higher concentration outside the cell will move spontaneously across the membrane down its concentration gradient eithout energy by its membrane transport protein
active transport
-solute move against its concentration graduent with the help of transport protein (transporter) with energy . because they drive the transport of solutes against concentration gradient, transporters are called pumps
two types of membrane transport protein
transporter and channel
difference btw transporter and channel
the way they descriminate solutes than can pass thru
transporter (carriers)
-provide private passageway across tge membrane
-highly specific and selective
-eg transport protein only allow passage for na+ but not k+
-allows passage only to those molecules or ions that fit into a binding site of the protein, it transfers across the membrane at the same time changing its confirmation
-they are multipass transmembrane protein. by crisscrossing back and forth, the polypeptide chain forms a continuous protein-lined pathway that allows selected small hydrophilic molecules to cross the membrane without coming into contact with hydrophobic interior
channel discriminate based
-mainly based on size and electric charge
-if channel open. ion or molecules that is small enough and carries the appropriate charge can slip thru
function of transporter
to guide and propel the complex traffic of small molecules into and out of the cell, vtween cytosol, diff membrane enclosd organelles
example of transporter
glucose transporter-plasma membrane of most anima cells-none energy source-fx passive import of glucose
ca2+ pump-plasma membrane of eukaryotic cell-atp hydrolysis-fx active export of ca2+
H+ pump-plasma membrane of plant cells, fungi and bacteria-atp hydrolysis-active export or h+
transport of glucose (glucose transporter)
when sugar in plentiful outside the liver after a meal, glucose molecule bind to externally displayed binding sites, switches conformation , carries and release the glucose into the cytosol where glucose is low.
for uncharged molecule like glucose, the direction of passive movement determined solely by concentration gradient
glucose transport is passive but highly___
specific . the glucose transporter only bind to D-glucose and not L-glucose
for electrically charged molecule
additional force is needed
what is membrane potential
most cell membranes have voltage across each side of the membrane, a difference in electrical potential in each side is called membrane potential
how membrane potential help in transport of molecules
the difference in potential exerts a force on any molecule that carry charge
the net force driving charged solute across the membrane consists of 2 forces
- concentration gradient
- the voltage across the membrane
(electrochemical gradient)
voltage and concentration gradient work in the same direction creating
steep electrochemical gradient
eg na+ is positively charged and at a higher concentration outside cells than inside. Na+ tends to enter cells
active transport moves solute ___ electrochemical gradient
against
three main wagd in maintaining ionic composition
- coupled transporter
- atp driven pump
- light driven pump
types of active transport
- primary active transport : require atp at the same time substrate is moved
- secondary active transport: requires energy later
atp driven pumps
- P type pumps : structurally and functionally related to multipass transmembrane protein. named p type because they phosphorylate themselves during pumping cycle. maintaning NA+ K+ Ca2+ H+ across the cell membrane
- ABC transporter: differ structurally from p type atpase and primarily pump small molecules across the membrane
- V type pumps: transfers H+ into the organelle to acidify the interior of these organelles
- F type pumps: structurally same with v type but work in reverse where they use H+ to synthesize atp
what is coupled transporter
the downhill movement of molecules down its gradient provides energy to drive the uphill of the second solute
