Movement of substance a cross cell membrane

Movement of substance a cross cell membrane

1. Regents Biology
Movement of substance a cross
cell membrane
Asma Alilesh

2. Regents Biology
Semi-permeable membrane
Cell membrane controls what gets in or out
Need to allow somematerials —but not all
—to pass through the membrane
semi-permeable
only some material can get in or out
Substance move across membrane by:
1-passive transport ( diffusion).
2-Active transport ( energy coupled transport
process).

3. Regents Biology

4. Regents Biology
Passive transport (Diffusion)
no energy needed
Move from HIGHto LOWconcentration by
2 methods:
A-simple diffusion: directly through
membrane or nonspecific protein channel.
B-facilitated diffusion: help through a
protein carriers.

5. Regents Biology
Protein channel
Protein carrier

6. Regents Biology
1-simple diffusion
membranes are highly permeable to small inorganic
molecules, such as O2, CO2, NO, and H2O, which
are thought to slip between adjacent phospholipids.
In contrast, larger polar molecules, such as sugars,
amino acids.
solute can pass directly through the lipid bilayer, or
through an aqueous pore that spans the channel
protein in membrane.
-

7. Regents Biology
-The Diffusion of Ions through Membranes
chargedsubstances,includingsmallionssuchasNa,K,Ca,andCl
needchanneltopassmembranecalledionchannels.
Most ion channels are highly selective in allowing only one particular
type of ion to pass through the pore.
they exist in either an open or a closed conformation; such channels
are said to be gated. There are 3 type :
1-Voltage-gated channels whose conformational state depends on the
difference in ionic charge on the two sides of the membrane.
2-Ligand-gated channels whose conformational state depends on the
binding of a specific molecule (the ligand), which is usually not the
solute that passes through the channel.
3-Mechano-gated channels whose conformational state depends on
mechanical forces (e.g., stretch tension) that are applied to the
membrane.

8. Regents Biology

9. Regents Biology

10. Regents Biology

11. Regents Biology
Facilitated Diffusion
In many cases, the diffusing substance first binds
selectively to a membrane spanning protein, called a
facilitative transporter, that facilitates the diffusion
process.
bindingofthesolutetothefacilitativetransporteron
onesideofthemembraneisthoughttotriggera
conformationalchangeintheprotein,exposingthe
solutetotheothersurfaceofthemembrane,from
whereitcandiffusedownitsconcentrationgradient.
forexample:glucosetransporter.

12. Regents Biology

13. Regents Biology
Active transport
Cells may need molecules to move
againstconcentration “hill”
need to pump “uphill”
from LOWto HIGHusing energy
protein pump
requires energy
ATP
ATP

14. Regents Biology
Na+/K+-ATPase,
or the sodium–potassium pump.
It is the Na+/K+-ATPase that is responsible for the large
excess of Na+ ions outside of the cell and thel arge excess of
K+ ions inside the cell.
TheNa+/K+-ATPaseisanexampleofaP-typeionpump.The
“P”standsforphosphorylation,indicatingthat,duringthe
pumpingcycle,thehydrolysisofATPleadstothetransferof
thereleasedphosphategrouptoanasparticacidresidueof
thetransportprotein,whichinturncausesanessential
conformationalchangewithintheprotein.
Conformational changes are necessary to change the affinity
of the protein for the two cations that are transported.

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Other Ion Transport Systems
Ca2+ATPase:The calcium pump is present in the membranes of
the endoplasmic reticulum, where it actively transports calcium
ions out of the cytosol into the lumen of this organelle.
Plant cells have a H+-transporting, P-type, plasma membrane
pump.
The epithelial lining of the stomach also contains a P type pump,
the H/K-ATPase, which secretes a solution of concentrated acid
(up to 0.16 N HCl) into the stomach chamber.

17. Regents Biology

18. Regents Biology
Osmosis
Water is very important, so we talk about
water separately
Osmosis
diffusion of water from HIGH concentration
of water to LOW concentration of water
across a semi-permeable membrane

19. Regents Biology
Keeping water balance
Cell survival depends on balancing
water uptake & water loss
freshwater balanced saltwater

20. Regents Biology
Keeping right amount of water in cell
Freshwater
a cell in fresh water
high concentration of water
around cell
cell gains water
example: Paramecium
problem: cells gain water,
swell & can burst
water continually enters
Parameciumcell
solution: contractile vacuole
pumps water out of cell
freshwater
No problem,
here
KABOOM!
1

21. Regents Biology
Controlling water
Contractile vacuole in Paramecium

22. Regents Biology
Keeping right amount of water in cell
Saltwater
a cell in salt water
low concentration of water
around cell
cell loses water
example: shellfish
problem: cell loses water
in plants: plasmolysis
in animals: shrinking cell
solution: take up water
saltwater
I will
survive!
I’m shrinking,
I’m shrinking!
2

23. Regents Biology
Keeping right amount of water in cell
Balanced conditions
no difference in
concentration of water
between cell & environment
cell in equilibrium
example:blood
problem: none
water flows across
membrane equally,
in both directions
volume of cell doesn’t
change
balanced
I could
be better…
That’s
better!
3

24. Regents Biology

25. Regents Biology