Protein-Mediated Transport Flashcards
What family do water channels belong to?
aquaporins
channels are only capable of facilitating what kind of transport
downhill
describe water channels
pores/channels with diameter greater than water but less than solute molecules so it only lets water through
where are you likely to find nonselective pores
epithelia, brain, smooth muscle, cardiac muscle
what weight do gap junctions allow molecules to pass through
up to 1200-1500
you will find what kind of junction being used for nonselective pores
gap junction
what kind of molecules can pass through gap junction
water soluble
up to 1200-1500 weight
lower km = ?
higher affinity
generates faster rate of solute entry
carriers are only capable of facilitating
downhill transport
where are active sites accessible in channels
both sides
where are active sites accessible in carriers
one side at a time
pumps are only capable of faciliating
trick question!
pumps can oppose the equilibrium
what cells are you likely to find water channels
RBC
epithelium of lung, kidney, intestines
channels (non-selective pores) allow for synchronization of
electrical activity of heart and gut
the only significant transport of charged ions is through
protein ion channels
in ion channel where is active site
on both sides
channels and carriers want to do what
equilibriate
pumps do what to equilibrium
oppose it
rate of entry for protein mediated transport is much faster than what
if there is no aid from protein
describe reaction rate with protein mediated transport
reaction rate is much faster with protein mediated transport
saturation
solute entry rate in protein mediated transport is always maximized
why is it always maximized
active sites are full
Tm and Vmax are another way of describint
saturation - when all the binding sites are full
Specificity
things with similar structure can compete for same binding site
competitive inhibition
common property of protein mediated transport
just glucose - certain rate of entry for glucose
glucose + galactose - transport for glucose goes down b/c galactose competes for same site
d-galactose d-arabinose d-xylose d-mannose describe in relation to protein mediated transport
sugar structure that can bind to binding site
d isomer will bind to the binding site
L won’t bind (specificity!)
Km is defined as
half max (half of Vmax)
what are three main categories of PMT
channels
carriers
pumps
what determines what direction an ion will flow
chemical & electircal gradient
what has to happen in any PMT for it to work
conformational change
carrier mediated transport is a form of
PMT
carrier mediated transport is also called
facilitated diffusion
can water normally go into a cell
yes - they are so small they can go through
what is the name of the pores in nonselective pores
connexon channels
what is the normal state of non-gated ion channels
open
how do we generate our resting membrane potential
non-gated ion channels
what is another name for non-gated ion channgels
leak ion channels
what is RMP of cell
-70 millivolts
what does RMP stand for
resting membrane potential
there are a lot of what kind of leak ion channels and not as much
lots of potassium
not as much sodium
(ICF)
describe how RMP is numbered
inside relative to outside, so -70 means negative 70 milivolts relative to positive outside
gated ion channels at resting are
closed
do gated ion channels contribute to RMP
no
when do gated ion channels change conformation
from stimulus
the probability that gated ion channels is open is dependent on
membrane potential, specific ligands or chemicals, and mechanical distortion.
describe gated ion channels that are controlled by membrane potential
Some channels only open when the membrane potential changes beyond a certain threshold value, and are called voltage-gated ion channels.
describe voltage-gated ion channels
closed at resting membrane potential
open when depolarized, then they will have conformational change and open
they are specific to a certain ion, so there are potassium voltage-gated ion channels, etc
describe gated ion channels that are controlled by specific ligands
Ligand-gated ion channels cannot open unless they first bind to a specific stimulus or agonist.
nicotinic receptor at nuromuscular junction
protein receptor ion channel that is on the skeletal muscle and have alpha motor neuron innervating skeletal muscle
what are an examples of ligand-gated ion channels
ACh-gated nicotinic receptor
describe gated ion channels controlled by mechanical distortion
Mechanosensitive ion channels only open when the membrane is mechanically stretched
membrane potential inside the cell is neg. or pos.
negative
membrane potential outside cell is neg. or pos
positive
what are some examples of cells that use mechanical distortion
mechanosensitive sodium channels in hair cells of the auditory-vestibular system
stretch-sensitive channels in muscle spindles.
in the acetylcholine-gated nicotinic receptor describe the amount of Na+ and K+ going into cell
more Na+ going into cell than K+
what is another name for carrier-mediated diffusion
facilitated diffusion
describe how carriers work
something binds to carrier’s active site, only one at a time (on one side of membrane at a time) and is then moved to lower concentration gradient
do glucose transporters need sodium
no
what is example of glucose transporter
GLUT1-5
what are categories of aa transporters (carriers)
neutral AAs
Basic AAs
Acidic AAs
what do pumps do to quilibrating system
oppose to maintain asymetric distribution of all solutes
describe diffusion potential in regards to potassium
there is electrical driving force because insid ethe cell it is negatively charged
what is net driving force for potassium in regards to cell and why
to leave cell
b/c the chemical driving force for potassium is a little stronger than the electrical driving force
why do we need potassium pumps
b/c of the stronger chemical driving force, need to keep potassium levels higher in cell. pump trying ot maintian concentration of potassium inside and have it be low outside
what are two types of active transport for pumps
primary active transport
secondary active transport
what is primary active transport
uses ATP directly to drive solute back
what is secondary active transport
uses energy derived secondarily from energy stored in form of ionic concentration differences b/w two sides of membrane
what is example of secondary active transport
sodium glucose transport
SGLT1 transport
in secondary active transport what is the driver solute
sodium
what are two kinds of secondary transport
co-transport
or countertransport
what is SGLT1
co-transporter
in primary active transport the active site is accessible
one side at a time
what is main way digestive system spew out hyrogen for Hydrochloric acid
primary active transport
what is level of calcium inside cell
.0001 mM
list levels of ions inside and outside of cell
pg 5 of homeostasis power point
what is the most abundant pump in higher organisms
Na+K+ ATPase
describe the makeup of sodium potassium pump
Heterodimer of an alpha subunit of 100,000 MW and
a beta subunit of 55,000 MW
What does the sodium potassium pump out exactly
3 Na+ out of cell for every 2 K+ pumped into cell
what is the function of the sodium potassium pump
maintains low Na+ and high K+ inside cell
controls cell volume
helps keep RMP
Where is the Ca2+ ATPase pump located
in cell membrane & organelles
what organelles is Ca2+ ATpase pump located
Sarcoplasmic reticulum
mitochondria
what is the function of Ca2+ ATPase
keep a very low level of Ca2+ inside cell
In the SR what is calcium bound by
calreticulin & calsequestrin
Where is H+K+ATPase pump located
gastric glands of GI tract
epithelial cells of renal system
What is the purpose of H+K+ATPase pump
acidify urine, controls acid-base balance
basis for secreting hydrochloric acid in the stomach for digestive secretions
Ion pumps are a form of what kind of transport
primary active transport
describe the basis of secondary active transport
the cell keeps higher concentrations of some things inside vs. outside the cell which ultimately creates stored energy. when an ion moves down its electrochemical gradient it releases energy
what do most secondary active transports use as the driver solute
sodium
describe how sodium works as driver solute
the energy released from sodium going down its gradient allows uphill transport of another solute
draw out primary and secondary for symporter, antiporter, and channel
pg 22
whats another word for cotransport
symport
what are different mechanisms for secondary active transport
cotransporter
countertransporter
describe what happens with a cotransporter
solute being transported moves in same direction as driver solute (sodium!) and almost always inside cell
cotransporter almost always moves solute in what direction
inside cell
What are examples of solutes being moved with a cotransporter
Na-glucose Na-AA NaK2Cl NaCl KCl
what are other names for countertransporter
antiports
exchangers
what do countertransporters do
exchange one type of anion for another anion
or one cation for another cation
name examples of countertransporters
Na+ Ca+ exchanger
Cl- HCO3-
Na+ H+ exchanger
What does HCO3- stand for
bicarbonate
What is purpose/function of Na+ Ca+ exchanger
maintains low calcium levels in cell
3 sodium in cell for one calcium out
What is purpose/function of Cl- HCO3- exchanger
RBC!
helps carry carbon dioxide from tissues to lungs
what is purpose/function of Na+ H+ exchanger
controls intracellular pH
what are the similarities b/w carrier-mediated and secondary active transport
conformational change once solute binds
Both mechanisms uses specific carrier proteins*
Both are saturable
Affinity plays a role in both mechanisms *
what are the differences b/w carrier-mediated & secondary active transport
For carrier-mediated transport - downhill transport of solute occurs, while secondary active transport - uphill transport of solute occurs
*Secondary active transport needs the driver solute to expend energy for the uphill transport of solute to occur, while carrier-mediate transport does not require energy to be expended for downhill transport of solute.
if you just had leak non/gated channels for K+ and Na+ what would happen
would equilibriate
for every phosphorylation/dephosphorylation cycle what does sodium potasium pump do
3 sodiums pumepd out for every 2 potassiums pumped in
what is purppose of Na+K+ATPase do
making sure concentration of potassium and sodium in ICF and ECF maintaing number they need to be
what happens if there is not functioning NA+K+ATPase?
cell would move towards equilibrium
how many sodium binding sites on Na+K+ATPase
3
how many potassium binding sites on Na+K+ATPase
2
why is Na+K+ATPase called an electrogenic pump
generates electrical potential difference across cell membrane. losing a positive charge inside cell each time. makes the cell a little bit more negative inside each time
how does Na+K+ATPase control cell volume
water follows solute, it puts an extra ion outside the cell
does Na+K+ATPase trigger RVI or RVD
RVI - it is trying put more water back into cell b/c water leaves cell due to Na+K+ATPase pump
for RVI do you want Na+K+ATPase activity increased or decreased
decreased - want to slow loss of solute to gain osmotic pressure in cell
if there is hypotonic solution what would happen in regards to Na+K+ATPase
RVD mechanism, Na+K+ATPase would increase activity
miliequivalent =
valence x concentration
chemical gradient for Ca2+ to go into cell is
HUGE!
Ca2+ ATPase primary function
opposing system to bring calcium back down in cell by pumping it out of cell
H+K+ATPase function
pumps hydrogen against electrochemical gradient into lumen of stomach
the reason we can have hydrochloric acid
what direction is K+ pumped in H+K+ATPase function
into cell
what is an example of antiporter
H+K+ exchanger
a cell on one side is lumen other side is blood which is apical and basolateral side
lumen is apical side
blood is basolateral side
in KCL which is driver solute
potassium
some drugs block sodium potassium ATPase, so what would that do to calcium (CHF)
the gradient went down so not as much sodium will go into cell, which means not as much calcium will leave cell. when there is more calcium in cell it will result in longer strong contraction of muscle (and cardiac muscle?)
pancreas has specialized epithelial cells that have
Cl-HCO3 exchangers
