Membrane transport Part 1 Flashcards
Rate of diffusion is affected by
hydrophobicity and size
Hydrophobic molecules and synthetic lipid bilayer
moves fast
ATP O2 CO2 N2 steroid hormones
small uncharged polar molecules and synthetic lipid bilayer
at slower rate
H2O urea glycerol NH3
Large uncharged polar molecules and synthetic lipid bilayer
v slow rate
glucose sucrose
ions and synthetic lipid bilayer
hydration schell - impermiable to membrane
two main classes of transport proteins
Transporters and Channels
difference between enzymes/substrate and transport cycle (transporter and solute)
solute is not altered/changed
Transporters
carriers, permeases
possess solute binding sites: Solute binds to binding site
Conformational change is transporter after solute binds
same still apply from enzime substrate - Vmax max rate of transport, rate when fully saturated - Km, binding affinity, solute and solute binding
open and close randomly but concentration gradient makes solute more likely to bind and cause change
Channels
interact with solutes more weakly
no energy requirement
no binding site
all channels alow solutes to cross the membrane passivly downhill
formation of pores do not exibit solute binding sites
which has fater rate of tansport, chanel or transporters
chanel because does not have to change conformations
Passive transport
Movement of solutes “down” their concentration gradient (High concentration to Low concentration)
If solute is charged, movement also dependent on electrical gradient (membrane potential).
Concentration + charge=“electrochemical gradient”
no energy requirement
Active transport
Movement of solutes “against” their concentration gradient. Always mediated by transporters
Primary Active transport
Free energy of ATP hydrolysis used to drive “uphill” movement of solutes.
direct energy reqirement - from ATP hydrolosis
Secondary Active transport
Ion gradient generated by ATPase elsewhere (indirect requirement of ATP).
Secondary active transport harnesses energy released from ion gradient by one molecule going down its electrochemical gradient to drive a different molecule against its gradient
indirect energy requirement - stored energy in gradent - used in second active transport
Gradients across the membrane (with and without charge_
without charge difference - move across gradient
with charge opposite - move faster
Uniports
unidirectional
one solute movement
Symports
simultaneous movement of more than one solute in one direction
Antiports
simultaneous movement of more than one solute in opposite directions
GLUT
glucose transporter - passive, facilitated - when concentration gradients change - moves opposite ways
Glc fits into GLUT binding site.
Glc binding drives conformational change.
Dissociation driven by low [Glc].
GLUT bounces back to original conformation.
Classes of ATP-driven pumps
- P type pumps
- ABC (ATP binding cassette) transporters
- V type pumps
all use ATP - bind to transporter (hydrolized-> energy)
P-type pumps
Formation, maintenance of
Na+, H+, and Ca2+ gradients.
Self-phosphorylate during cycle.
Mantain order in body, maintaion ion gradents, mediate cellular processes
ABC (ATP-Binding Cassette) transporters
Transport variety of nutrients, toxins, ions.
most abundant
medical relevance - drug resistance - involve in removing drugs
V-type pumps
Acifigy vaculoar compartments
use engery from ATP hydroslos - move H across - more acific enviorment (ex/ use in digestion)
Ca2+ pump
in eukaryotic cells
(P-type ATPase)
Eurcharylotic cells - (invest a lot of energy to) maintain very low concentrations of Ca2+ in their cytosol and very high extracellular Ca2+
Steep gradient maintained (Ca2+pumped out by Ca2+ pump and Na+Ca2+ Exchanger) at plasma membrane
When action potential depolarizes the muscle cell plasma membrane __
Ca2+ is released into cytosol from the sarcoplasmic reticulum through Ca2+ release channels, which stimulates muscle to contract
Sarcoplasmic Reticulum
Specialized Endoplasmic reticulum in muscle cell cytoplasm, intracellular storage of Calcium ions
Ca2+ pump in the Sarcoplasmic Reticulum
moves Ca2+ from cytosol back to sarcoplasmic reticulum, end of muscle contraction
Structure of Ca2+ Pump
Ca2+ cycle
- ATP bound Ca2+ (two) can bind
- binding causes conformational change, passage way is closed
- ATP is hydrolyzed (ATP to ADT and P) Phosphate transfer reaction
- ADP excanged for ATP - conformational change - passage is opened to lumen
- proton (two) is picked up (also with water) to stabalize empty binding site - passage is closed to lumen
- hydrolosis of phosphate, pack to orional conformation, so Ca2+ can be transpoted again (and again)
Why are the maximum rates of transport by transporters and channels thought to be so different.
because transportors binding of solvent on specific site (with weak ineractions) - slower
The permeability of a protein-free lipid bilayer to various molecules depends on their properties. Sort the following in order of low to high permeability from left to right.
A. O2
B. ATP
C. Na+
D. Glucose
B
C
D
A
Na+K+ Pump, concentration of K+ ions and Na+ ions
Concentration of K+ ions higher inside cells than outside, reverse is true of Na+ ions
Na+ gradient (in Na+K+ pump) drives
transport of most nutrients into animal cells (1/3 animal cells energy devoted to this pump)
Na+K+ pump is ___
electrogenic- volated difference across membrane (membrane potental) - when charges do not balansse out.
also antiporter
Na+K+ pump cycle
- Na binds to pump
- pump phosporilates itself (ATP to ADP and P)
- phosporlation triggers conformational change, Na is ejected
- K binds
- pump is dephosporlated
- pump returned to orional conformation, K is ejected
ABC Transporter family
Largest family of Membrane Transport Proteins
ABC transporter bacterial vs eukaryotic
bacterial - import process - to inside cell
eukaryotic - export - to out of cell
ABC transporter steps
2 ATP added (each own domain), small soluble molecule binds
hydrolized (2ATP to 2ADP and phospate) - opens
Clinical importance of ABC transporters in Eukaryotic cells
Multi-drug resistance (MDR) protein, also called P-glycoprotein: high levels in cancer cells, makes cells resistant to cytotoxic drugs (chemo).
Plasmodium falciparum (causes Malaria): transporter pumps out Chloroquine (drug resistance)
V type Pump
Present in vacuolar compartments.
(Lysosomes, endosomes, Golgi.)
Uses deltaG of ATP hydrolysis to make H+ gradient.
F type ATPases
Structurally related to V type pumps (exact opposite, protein gradient to make ATP)
Instead of using ATP hydrolysis to drive H+ transport, they use the H+ gradient across the membrane to drive the synthesis of ATP
is still considered primary active transport
Uncouplers
collapse proton gradient by equalizing proton concentrations on both sides of the membrane
Dinitrophenol (DNP)
Caused ___
Diet pill in 1920s
Caused increased oxygen consumption and an increased metabolic rate, but a decline in ATP production
Can be fatal, liver failure
lipid soluble picked up proton and diffuse to other side.
UNCOUPLER - collapse protein gradient
why was DNP effective for weight loss
not generated from carbohydrate metabolism,
get from fat (energy)
How did DNP cause hyperthremia
(rapid increase in body temp)
energy was released as heat (what not used)
Symporter cooperative binding
because ion gradient, favorable for Na to bind, promoting glucose to bind (what drives glucose against gradient) - called cooperative binding
Symporter occluded
not open to either side
either completely empty or full
Symporter steps
secondary active transport
___ facilitates the uptake of nutrients (in intestinal epithelial cells)
Asymmetric distribution of Transporters in plasma membrane
Transcellular Transport in Intestinal Epithelial Cells
intestinal lumen (atypical domain) - Na driven glucose symport (Na in and glucose into cell)
extracellular fluid (basal domain) - facilitate diffusion (no energy requirement) - carrier protein mediating
Na out- keeps gradient going (Na+K+ pump)
structural polarity in Transcellular Transport in Intestinal Epithelial Cells
two sides are different - distribution of transporters
