Download Na+/K+ (Sodium/Potassium) Pump

3. Transport across the membrane
• Passive diffusion, facilitated diffusion, active transport
(primary and secondary).
• Structure, function and significance of Na+ / K+ ATPase
and Ca+ ATPase;
• Ion channels – leak channels, gated channels voltage
gated and ligand gated channels. Ionophores,
phosphotransferase system, transport antibiotics.
• Endocytosis and exocytosis , receptor mediated
endocytosis , clathrin coat, cholesterol transport and
familial hypercholesterolemia
MEMBRANE TRANSPORT
• Cytoplasm of each cell is bounded by delicate
plasma membrane/ plasmalemmma
• It perforforms variety of functions
• Transport of molecules & ions is imp. Function
Transport of molecules & ions
• Plasma membrane regulate traffic of molecules in to &
out of cells
• Also act as semi permeable barrier between cell and its
extracellular environment
• Allows passage of solvents but not solute called semi
permeable
• It is selectively semi permeable,
e.g. essential molecules Like glucose, f. acids easily enters in to the cell while
nitrogenous waste compound leave the cell
• Transport of molecules across the membrane
may be passive or active type
• Passive transport not requires energy while
active transport require energy- dependent on
ATP supply
Movement of Molecules
1.Diffusion: movement from high concentration to
lower concentration
2. Osmosis: movement of water across a semipermeable
membrane from low concentration to
high concentration
Yes, it is going against gravity!
Ex.; How the fluid part of blood is put back into your blood
vessels.
A.
Endosmosis: water molecules enter in to the cell
B.
Exosmosis: water molecules exit from the cell
Osmosis
• 2. Isotonic solution: solute concentration
inside and outside the cell are equal. No
loss no gain
1.Hypertonic solution: greater/ higher
concentration of solutes (ex. salts)
outside the cell than inside the cell
So
water moves out of the cell and the cell shrinks
• 3. Hypotonic solution: greater
concentration of solutes inside the cell
than outside the cell So water moves into the
cell and the cell expands/swells
Osmosis
• A) ISOTONIC SOLUTION:
• Is extra & intracellular conc, same, 0.9 percent NaOH solution,
no loss no gain
• B) hypertonic solution :Net water loss ,cell shrinks, higher than 0.9
percent NaOH solution, net water loss , cell shrink
• C) hypotonic solution :Net water gain, less than 0.9 percent NaOH
solution,
• A
B
C
Movement of Large Molecules in Cells
1. Exocytosis: movement out of a cell through the
formation of a vesicle
Ex. Proteins; digestive enzymes; mucus
• 2. Endocytosis: movement into a cell
Types of Endocytosis
• 1. Pinocytosis:
“cell-drinking” because its bringing into the
cell fluids with materials suspended in it
• Ex. Movement of blood
• 2. Receptor-mediated endocytosis:
specialized cell surface receptors bind
to molecules and pulls it into the cell
• Ex. Transport of iron
3. Phagocytosis:“cell-eating” because it
brings into the cell
large materials
• Ex. Bacteria; cell debris
Movement of Small Molecules in Cells
1.Passive transport
A. Simple diffusion: diffuses through
a membrane from high concentration to
low concentration
Ex.
How oxygen and
and out of our cells
carbon
dioxide
get
B.Facilitated
diffusion:
movement
from
high
concentration
to
low
concentration
through a membrane
with the help of a protein;
no
energy
required
Example of facilitated diffusion
Lower concentration
Molecules randomly
move through the
integral protein
Higher concentration
Molecules move from an
area of high
concentration to an area
of low concentration
Movement of Small Molecules in Cells
1.Passive transport
A. Simple diffusion
B. Facilitated diffusion
2. Active transport:
movement through a transport protein
movement against a concentration gradient
requires energy = ATP
Ex. Storage of glucose in the liver
Ex. Sodium-potassium pump
Types of Transport ATPases
Comparison of ion concentratration
inside and outside of typical mammalian cell
COMPONENTS
CATIONS
Na+
INTRACELLULAR
CONCENTRATION ,mm
(Million moles)
EXTRACELLULAR
CONCENTRATION ,mm
(Million moles)
K+
Mg+
Ca2+
5.15
140
80
1.2
145
05
1.2
3.5
ANION
CL-
04
110
Na+/K+ (Sodium/Potassium) Pump
(ACTIVE TRANSPORT)
• The Na+/K+ pump is found in the membranes of many
types of cells.
• In particular, it plays a very important role in nerve cell
membranes.
• Notice that 3 positive ions (Na+) are pumped out of the
cell for every 2 positive ions (K+) pumped into the cell
• This means that there is more positive charges leaving the
cell than entering it.
• As a result, positive charge builds up outside the cell
compared to inside the cell.
• The difference in charge between the outside and inside
of the cell allows nerve cells to generate electrical
impulses which lead to nerve impulses.
• The Na+/K+ pump illustrates "active transport" since it
moves Na+ and K+ against their concentration gradients.
• That is because there is already a high concentration of
Na+ outside the cell and a high concentration of K+ inside
the cell.
• In order to move the ions (Na+ and K+) againts
their gradients, energy is required.
• This energy is supplied by ATP (adenosine
triphosphate).
• An ATP molecule floating inside the cell, binds to
the pump transferring some energy to it.
• As the energy is used, the ATP falls off and having
lost its energy it is converted into ADP (adenosine
diphosphate).
Na+,k+ PUMP in Plasma Membrane
• The 3 Na+ ions on the inner surface of the
pump and the 2 K+ ions on the outer surface
of the pump.
• Since the pump requires an ATP every time it
works, ATP must be constantly supplied to the
cell.
• ATP is created during the processes called
"cellular respiration" which occur inside the
cell.
• Part of cellular respiration happens in the cytoplasm
and part happens in the mitochondrion.
• More ATP is made and the pump continues to do its
job. If something interferes with the production of ATP,
the pump will stop working and the nerve cell will also
stop working.
• This can cause serious loss of nerve function and even
death.
• Since cellular respiration requires oxygen, if you were
to stop breathing, ATP could not be produced and you
would die. Of course ATP is needed by many processes
in the body so it is not only the Na+/K+ pump that
would stop.
• There are poisons or toxins that also interfere
with the pump. One is called "oubain", an
arrow poison. Oubain works by attaching to
the pump and blocking its action.
• Pharmacologists have designed drugs that, if
administered fast enough, can travel to the
cells and attach to the oubain removing it
from the Na+/K+ pumps allowing them to
function properly
• Your body stores glucose in your liver and
muscles. In order to stockpile the glucose for
when you might need it, the glucose must be
pumped into cells building up a high
concentration there.
• Even though it uses up ATP to do this, every
glucose molecule can be broken down by
cellular respiration to produce 38 ATP's! So it's
a worthwhile process.
The Ca2+ ATPases
• A Ca2+ ATPase is located in the plasma membrane of
all eukaryotic cells.
• It uses the energy provided by one molecule of ATP
to pump one Ca2+ ion out of the cell.
•
• The activity of these pumps helps to maintain the
~20,000-fold concentration gradient of Ca2+ between
the cytosol and the ECF
• In resting skeletal muscle, there is a much higher
concentration of calcium ions (Ca2+) in the sarcoplasmic
reticulum than in the cytosol.
•
Activation of the muscle fiber allows some of this Ca2+ to pass
by facilitated diffusion into the cytosol where it triggers
contraction
• After contraction, this Ca2+ is pumped back into the
sarcoplasmic reticulum.
• This is done by another Ca2+ ATPase that uses the energy
from each molecule of ATP to pump 2 Ca2+ ions.
• Pumps 1. - 3. are designated P-type ion transporters
because they use the same basic mechanism: a
conformational change in the proteins as they are
reversibly phosphorylated by ATP.
• And all three pumps can be made to run backward.
• That is, if the pumped ions are allowed to diffuse
back through the membrane complex, ATP can be
synthesized from ADP and inorganic phosphate.
Functions of the Plasma Membrane
osmosis
Ion channels
• leak channels, gated channels voltage gated
and ligand gated channels. Ionophores,
phosphotransferase system, transport
antibiotics.
• ION CHANNELS:
• A single protein or protein complex that traverses the lipid bilayer
of cell membrane and form a channel to facilitate the movement of
ions through the membrane according to their electrochemical
gradient
• Ion channels may be open or gated. The potassium leak channel is
an example of open ion channel. Gated ion channels may be
voltage-gated, ligand-gated, or mechanically-gated channels.
• Ion channels are the common targets of pharmaceutical drugs,
directly or indirectly, since they are capable of regulating the flow of
ions to and from the cell. Many ions play in important physiological
role in the normal metabolism of cells.
•
Leak channels /potassium channels
• In the field of cell biology, potassium channels
are the most widely distributed type of ion
channel and are found in virtually all living
organisms.
• They form potassium-selective pores that
span cell membranes.
• Furthermore potassium channels are found in
most cell types and control a wide variety of
cell functions
• Function
• In excitable cells such as neurons, they shape
action potentials and set the resting membrane
potential.
• By contributing to the regulation of the action
potential duration in cardiac muscle, malfunction
of potassium channels may cause life-threatening
arrhythmias. Potassium channels may also be
involved in maintaining vascular tone.
• They also regulate cellular processes such as the
secretion of hormones (e.g., insulin release from
beta-cells in the pancreas) so their malfunction
can lead to diseases (such as diabetes).
• [edit] Types
Gated channel
• 1. Voltage-gated channel
• A class of ion channel's that open and close in response to change
in the electrical potential across the plasma membrane of the cell;
voltage-gated Na_ c.'s are important for conducting action potential
along nerve cell processes.
• 2. Ligand gated ion channel
• a transmembrane ion channel whose permeability is increased by
the binding of a specific ligand, typically a neurotransmitter at a
chemical synapse.
• The permeability change is often drastic, such channels let through
effectively no ions when shut, but allow passage at up to 10exp7
ions sexp 1 when a ligand is bound. Recently, the receptors for both
acetylcholine and gaba have been found to share considerable
sequence homology, implying that there may be a family of
structurally related ligand gated ion channels.
. Ligand gated ion channel:
A transmembrane ion channel whose permeability is increased
by the binding of a specific ligand, typically a neurotransmitter at
a chemical synapse.
The permeability change is often drastic, such channels let
through effectively no ions when shut, but allow passage at up
to 10exp7 ions sexp 1 when a ligand is bound. Recently, the
receptors for both acetylcholine and gaba have been found to
share considerable sequence homology, implying that there may
be a family of structurally related ligand gated ion channels.