Lecture 2 - Membrane Transport Flashcards
Describe osmotic forces
Two ways.
force/pressure of water entering a cell with semi-impermeable memb.
or force/pressure required to stop water from entering this cell with s.p memb.
aka measure of tendancy to take on water.
Describe the methods of molecular movement.
simple molecular movement, not movement across membrane comes from the normal Kinetic energy aka. kinetic motion of matter, this is also a measure of its temperature.
Describe mechanisms used by substances to cross cellular membranes
•Energy independent (except for kinetic energy)
Diffusion -
-simple diffusion - thru memb, which osmosis is.
-facilitated - uses protein
2 types of which each have 2 mechs.
(non gated: aquaporins, ion channels)
(gated: voltage and ligand/chemical gated)
•Energy dependent:
Active: Primary (atpase) and Secondary sym/antiporters)
3 Factors affecting rate of diffusion
- Proportional to concentration difference across membrane (aka. conc. grad.)
- Membrane electric potential (Nernst potential)
- Pressure difference
Facilitated diffusion differs from Simple in what important way?
Facilitated has a max rate, dependent on the carrier protein’s ability/rate of diffusion.
The most important things that used facilitated diffusion are?
Glucose and most A.A.
3 factor that determine the net rate of diffusion for a substance that can diffuse both directions
permeability
conc grad
elec. potential
Ligands are typically what type of molecule
Neurotransmitter like ACH or
a hormone
the rate of diffusion of a substance through a cell memb. is directly proportional to its what?
Lipid solubility
when facilitated diffusion plateaus, its called the
Vmax
All Cells have what Family/type of transport proteins?
GLUT Family
glucose transporters
Voltage is in reference to the inside or outside of the cell membrane?
inside
When can gated channels allow only partial flow of the substance through them?
Never!, they are all or none.
Challenging question
why do both Na and separate K ion channels (non gated) have such specificity?
B/c of their selectivity filters
and largely due to size
K - larger - the Carbonyl O’s on K ion channel are spaced further that they dehydrate K allowing it through 1000:1 K:Na
Na - smaller - So the strong Neg charges on Na ion channel are able to pull it in. then diffuses due to conc. grad.
Uniporter is what
a channel carrier protein that allows for Facilitated diffusion of 1 substance AT A TIME! and not necessarily always the same substance. Also there are binding sites that are alternately available on either side of the membrane. MEANING: the transport of substance can go BOTH ways B/C IT IS DIFFUSION (& based on conc. gradient)
Active Transport utilizes what energy source from what enzyme?
ATP
ATPase transporters
define multiporter
what type of transport does in take part in
2 examples and define them
carrier protein that carries 2 substances at once across a membrane.
its Secondary active Transport
Symporter (co transport) 2 same way & time
Antiporter - (counter transport) 2 opp way same time
Na/K pump creates a positive or negative charge inside the cell?
Net -1 charge INSIDE the cell for each round of pumping
the Na/K pump is important for controlling what?
The cell volume
where is there a higher concentration of the following ions
- Na
- Ca
- K
and why?
- extracellularly
- same
- intracellulary
Primary active transports through the Ca and Na/K pumps
What Ion is often involved in secondary active transport?
Na
for the Na/K pump…
how many binding sites are there for Na and K and where are they located?
Na 3 binding sites intracellularly
K 2 binding sites extracellularly
If sodium moves down its electrochemical
gradient, why is this referred to as secondary active
transport?
the conc grad for Na was originally created by primary active transport.
Sodium/calcium antiporters move three
sodium ions per calcium ion. Why does it take three
sodium ions to move one calcium ion?
bc it takes more E to move Ca
a conformational change in a membrane protein is caused by
Liberated or Freed energy from ATPase activity during active transport.
Say there is an excess of ADP. Whats unique about the Na/K pump?
It can run in reverse and used to generate ATP or pump the ions in opposite directions, depending on the relative
concentrations of ATP, ADP, phosphate, sodium, and potassium ions
in secondary active transport, at least one substance is moving which direction?
down its concentration. This is why its secondary. The Gradient that this substance is flowing down, was where the initial primary active transport took place.
Sodium glucose pump is what type of transport
Secondary active transport
and a symporter. aka co transport
What type of transport does Na/K pump provide?
Primary Active transport
Glucose Transporters (GLUT) employ which form of transport
Facilitated Diffusion
Na/H pump is what type of multiport
Antiport aka counter transport (active)
Na/Ca pump is what type of multiport
Antiport
aka counter transport (active)
Explain the role of the cell membrane in establishingintra- and extracellular environments.
We have no way to move water directly, ie. no proteins that move water. If we need to move water we can move ions so that osmosis occurs.
