lecture 22 - transport across cell membranes Flashcards
(42 cards)
non-mediated transport
doesn’t use transport protein, substances move directly through the lipid bilayer.
mediated transport
requires transport proteins (membrane is otherwise a barrier to this material)
passive transport
moves substances down concentration gradient using only their kinetic energy
active transport
uses energy to drive substances against concentration gradient or electrochemical gradient
vesicular transport
move materials across membrane in small lipid vesicles by either exocytosis or endocytosis
transport involved with absorption of nutrients and excretion of waste
non-mediated transport
What is transported via “non-mediated transport”?
- non-polar hydrophobic molecules
- e.g. O2, N2, small alcohols, fatty acids, steroids, fat soluble vitamins AEDK
fat soluble vitamins are…
A, E, D, and K
ion channels are _______ filled pores
ion channels are water filled pores
which type of amino acids line the inside and the outside of the ion channels
hydrophobic amino acids coiled into alpha helices on the outside. hydrophilic amino acids on the inside of the channel
do the ions interact and bind with the ion channel? what does this allow?
NO, this allows for rapid transport (1million per second)
in ion channels what determines direction of the ion flow?
down electrochemical gradient
ion selectivity filter = ?
selectivity of the channel to specific ions, achieved using various amino acids. Allows only specific ion gradient’s energy to be harnessed.
why do ion channels have gates
if they were always open you would not be able to store energy in ion gradients - they would always equilibriate
5 stimuli for opening/closing gates
- voltage
- ligand binding
- cell volume
- pH
- phosphorylation
patch clamp technique
measures the current travelling through an individual channel. measures ion channel function.
diffusion of over 1 _______ ions per second generates current of ____A
diffusion of over 1 million ions per second generates current of _10^-12_A
what do current fluctuations indicate
opening and closing of gates
main way carrier-mediated transport differs to ion channels. implications?
the substrate being transported binds directly to the channel, inducing a conformational change, meaning the rates of transfer are much slower
how are carrier transport proteins like enzymes?
- specificity
- inhibition (covalent bonds form)
- competition (glucose/glactose compete for same site)
- saturation (transport maximum)
carrier-mediated can be ______ or _______
carrier-mediated can be Passive or Active
passive mediated transport called…
facilitated difsussion
3 steps to facilitated diffusion of glucose
- glucose binds to GLUT
- Glut changes shape. Glucose moves across cell membrane DOWN concentration gradient
- Kinase reduces glucose concentration (tranforms to glucose-6-phosphate) otherwise you reach an equilibrium g
primary active transport
energy comes straight from the hydrolysis of ATP.
