Membrane transport mechanism Flashcards
What is plasma membrane transport?
Movement across membrane needed for cell to get substances it needs in and wastes out.
Movement either a passive or active process.
Passive processes rely on kinetic/movement energy of
molecules moving down concentration or electrical
gradient.
Active processes require cell energy (ATP ); can move
substances against concentration or electrical gradient.
Passive transport
NO cell energy is needed.
Movement is down a concentration or electrical gradient
e.g. from high to low solute concentration
e.g. from positive to negative charges
Passive processes:
simple diffusion and facilitated diffusion
Diffusion
Random mixing of particles in a solution due to kinetic energy.
If high solute concentration in one area and low in another,
solute molecules diffuse to the lower concentration region
DOWN the concentration gradient.
Movement down the concentration gradient until equilibrium occurs
Solution
Solutes (substances ) dissolved in a solvent
liquid doing the dissolving
5 factors affecting diffusion rate across a membranes
1.Concentration gradient, the greater the concentration
difference between the two sides, the faster the diffusion
rate.
2.Temperature, the higher the temperature, the faster the
diffusion rate.
3.Size of diffusing molecules, smaller particles diffuse faster than larger particles.
4.Surface area, the larger the membrane SA, the faster the
diffusion rate.
5.Diffusion distance, the shorter the diffusion distance the
faster the diffusion rate.
Simple diffusion
Passive process relying on kinetic energy and concentration of solutes in different areas.
Non polar , hydrophobic molecules diffuse directly through the phospholipid bilayer e.g. O 2 , CO 2 , fatty acids, steroid
hormones, fat soluble vitamins.
Small, uncharged polar molecules also diffuse directly
across phospholipid bilayer e.g. water.
Facilitated diffusion and 2 types
Highly polar or charged molecules/solutes need an integral
membrane protein to move across the membrane.
Two types: channel mediated facilitated diffusion and carrier
mediated facilitated diffusion
Channel mediated facilitated diffusion
allows movement of small, inorganic, hydrophilic ions. Ions cross at selective points e.g. lots of integral protein channels for potassium and chloride ions but fewer for
sodium and calcium ions.
They are gated
Gated channels
Either open or closed; part of protein acts like a plug or gate; protein shape change needed to move molecules across.
Carrier mediated facilitated diffusion
A carrier/transporter protein changes shape when a solute binds which moves the molecule across the membrane.
Passive process via concentration gradient.
Maximum transport rate when all transporters for that
molecule are active/occupied i.e. maximum saturation
Molecules moved this way include glucose, fructose,
galactose and some vitamins.
Osmosis
Passive diffusion of a solvent across a selectively permeable membrane. In our body the solvent is water. Water moves from an area of high to low water concentration OR from an area of low to high solute concentration.
What are the 2 ways water moves in osmosis?
1.Diffusion via wiggling past adjacent phospholipids in the
bilayer.
2.Moving through integral channel proteins (aquaporins).
What are the 2 forces in osmosis?
Hydrostatic pressure : pressure exerted by liquid which
forces water to move from higher to lower water region
across the membrane.
Osmotic pressure : pressure exerted on a fluid by dissolved
solutes too large to cross the membrane; prevents water
movement across the membrane.
What is tonicity and how does it happen?
The ability of a solution to change cell volume by changing water content (via solutes that can’t cross the membrane).
It happen by body cells in a solution with a different osmotic pressure than the cytosol change size and shape due to osmosis.
What are the 3 types of solutions?
Isotonic solution : concentration (of solutes than can’t cross
the membrane) is the same in both solutions.
Hypotonic solution : concentration of solutes higher inside
the cell than in outside solution; net water movement into
cell causes it to swells and eventually bursts.
Hypertonic solution : concentration of solutes higher in the
solution outside the cell than in the cytosol; net water
movement out of cytosol causing to cell to shrink.
