Transport across the Plasma membrane
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Explain selective prermeability
the lipid pilayer portion of the membrane is premeable to non polar, uncharged molecules such as oxygen, carbon dioxide and steroids but is impermeable to ions and large, uncharged polar molecules such as glucose.
a substances moves down its concentration or electrical gradient to cross the membrane using only its own kinetic energy.
Cellular energy is used to drive the substance "uphill" against its electrical and concentration gradient. The cellular energy used is usually in the form of ATP.
Diffusion: Passive Process
a passive process in which the random mixxing of particles in a solution occurs because of particle kinetic energy.
Diffusion rates: What makes particles diffuse faster?
- -Steepness of the concentration gradient
- -Temperature: higher tempretures cause particles to move faster
- -Mass of the diffusing substance: the larger the mass the slower the diffusion
- -Surface area- the larger the surface area the faster the diffusion rate
- -Diffusion distance- greater the distance the longer the diffusion process
is a passive process in which substances move freely through the lipid bilayer without the help of membrane transport porteins. ex: non polar hydrophobic molecules move across the lipid bilayer through simple diffusion
Facilitated diffusion: passive process
- - solutes that are too highly charged or polar to move through the bilayer through simple diffusion.
- -an integral membrane protein assists a specific substance across the membrane. The integral protein can either be a channel or a carrier.
Channel mediated facilitated diffusion (ion channel): passive process
-a solute moves down its concentration gradient across the lipid bilayer through a membrane channel
- -integral transmembrane protein that allow passage of small inorganic ions that are too hydrophilic to penetrate the non polar interior of the lipid bilayer
Carrier-mediated facilitated diffusion: Passive process
- a transporter or carrier is used to move a solute down its concentration gradient across the plasma membrane
-the solute binds on one side of the membrane and is realeased on the other side after the carrier has undergone a change in shape
Osmosis: passive process
- -is a type of diffusion in which there is net movement of a solvent through a selectively permeable membrane.
- -water moves across the plasma membrane from an area of higher water concentration to an area of lower water concentration
integral membrane proteins that act as water channels.
- -the solution with the impermeable solute exerts a force called the osmotice pressure
- -the osmotic pressure of a solution is proportional to the concentration of the solute particles that cannot cross the selective membrane.
is a measure of the solution's ability to change the volume of cells by altering their water content.
Any solution in which the a cell- for example a red blood cell, maitains its normal shape and volume is an isotonic solution
- a solution that has a lower concentration of solutes than the cytosol inside the RBC's (red blood cell)
- - in this case water molecules enter the cell faster than they leave causing the RBC to swell and eventually to burst
the rupture of blood cells due to thier placment in hypotonic solutions.
the rupture of cells, other then RBC's, due to their placement in hypotonic solutions
- has a higher concentration of solutes then does the cytosol inside RBCs.
- - water molecules move out of the cells faster then they enter, causing the cell to shrink. such shrinking is called crenation
Active transport: Active processes
- is considered an active process because energy is required for carrier proteins to move solutes across the membrane against a concentration gradient.
Primary Active Transport
-energy derived from hydrolysis of ATP changes the shape of a carrier protein, which "pumps" a substance across a plasma membrane against its concentration gradient.
- -carrier proteins that mediate primary active transport are called Pumps
- -Pumps move specific ions
Sodium-potassium pump or NA+/K+ATPase
- so named after the specific ions that it moves.
- -because a part of the sodium-potassium pump acts as an ATPase, an enzyme that hydrolyzes ATP, it is also called NA+/K+ATPase.
- - how it works
- 1) the NA+ in the cytosol binds to the pump protein
- 2) this triggers the hydrolysis of ATP into ADP which attaches a phosphate group to the pump protein. This reaction changes the shape of the pump protein which releases the NA+ into the extracellular fluid. Now the pump is in a shape that favours K+ attachment.
- 3) the binding of K+ triggers the realease of the phosphate group from the pump protein.
- 4) as the pump protein changes shape it releases K+ into the cytosol and is now in the shape that favours NA+ attachment.
Secondary Active Transport
-the enrgy stored in NA+ and H+ concentration gradient is used to drive other substances across the membrane against their own concentration gradients. Because a NA+ or H+ gradient is established by promary active transport, secondary active trasnport indirectly uses energy obtained by the hydrolysis of ATP
Transport in Vesicles: Active process
Active process in which substances move into or out of the cells in vesicles (sacs) that bud from the plasma membrane; requires ATP energy
movement of substance into a cell in vesicles
ligand-receptor complexes trigger infolding of a clathrin-coated pit that forms a vesicle containing ligands
- "cell eating"; movement of a solid particle into a cell after pseudopods engulf it to form a phagosome
- -bacteria, viruses, or aged dead cells
bulk phase endocytosis
"cell drinking" ; movement of extracellular fluid into a cell by infolding of plasma membrane to form a vesicle.
movement of substances out of a cell in secretory vesicles that fuse with the plasma membrane and release their contents into the extracellular fluid
movement of a substance through a cell as a result of endocytosis on one side and exocytosis on the opposite side
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