Modes of transport across the plasma membrane Flashcards
Define: active transport
the uptake of a substance across the phospholipid bilayer (through pump proteins) against its concentration gradient, requiring ATP.
HOw many moelcules per pump?
1-2
How do pumps undergo a shape change?
MOlecule binds to it, shape change, pushes to other side.
Enzyme function of pumps?
catalyse the breakdown reaction of ATP -> ADP + Pi + energy
Define: bulk transport
the movement of very large substances onto or out of the cell, requiring ATP.
Define: endocytosis
the process of bulk transport of material into a cell.
How does endocytosis work
The cell membrane flexes to entrap the particle, then engulfs/closes the particles within a vesicle.
Define: phagocytosis
when a solid food particle is transported into the cell (most cells cannot do)
Define: pinocytosis
when material in solution is transported into the cell
Define: exocytosis
the process of bulk transport of material outside of a cell.
how does exocytosis ork?
Vesicles fuse with the plasma membrane and contents are secreted (if valuable) or voided (if not) from the cell.
Define: osmosis
the net movement of water molecules through a selectively permeable membrane from a region of lower solute concentration to one of higher concentration.
Describe how water passes through the plasma membrane.
Though it is hydrophilic, it still can pass through the hydrophobic fatty acid tails but does so in limited amounts.
In larger amounts, it passes through proteins in the plb called aquaporins.
Define: hypotonic solution
when a solution has a lower solute concentration than the (cytosol of the) cell placed within it.
Animal cell and hypotonic solution.
Water molecules will move from hypotonic solution into the cell, causing it to lyse or burst (distilled water)
plant cell in hypotonic solution?
Water molecules will move from hypotonic solution into the cell, causing it to become turgid but soon the cell will stop water coming in (fully turgid)
Define: isotonic solution
when the solvent concentration of a solution is the same as the solute concentration of the cell (cytosol) placed in it.
what will happen to cell in isotonic solution?
The same number of water molecules will diffuse into and out of the cell, and its shape will remain the same.
Define: hypertonic solution
when a solution has a higher solute concentration than the cell (cytosol) placed in it.
Describe animal cell in hypertonic solution.
From cytosol to hypertonic solution. Cell will crenate (shrink), and might see spikes from the cytoskeleton
Describe plant cell in hypertonic solution
Cell will become plasmolysed (cell walls will cave in, membrane will shrink from wall, forming pockets.)
Define: diffusion
the net movement of a substance, from a region of higher concentration to one of lower concentration.
What does net mean?
Overall, as the particles are moving randomly.
Is diffusion passive?
Yes
When is the endpoint?
Equilibrium (equal conc on both sides however rare in bio as the products are usually being used up_
Factors affecting rate of diffusion?
Temp (molecules move quicker so rod will be quicker)
Concentration (stepper the conc gradient, the faster)
Size and type (polar/non polar)
Surface area to volume ratio: lower size, higher sa:v and quicker rate of diffusion
permeability of membrane
2 types of diffusion?
simple diffusion and faciliated diffusion
Define: simple diffusion
movement of substances directly across the phospholipid bilayer from a region of higher concentration to one of lower concentration.
Define: facilitated diffusion
the movement of substances through transporter proteins (channel/carrier) in the plasma membrane from a region of higher concentration to one of lower concentration
2 types of transporter proteins?
Channel proteins and carrier proteins
Define: channel protein
A transmembrane protein that contains an always open, water-filled pore. Bc water is hydrophilic other hydrophilic substances can pass through it.
Are there separate channel proteins for charged and polar molecules?
Yes
Define: carrier protein
a transmembrane protein to which a molecule binds to, and then it changes shape, enabling the molecule to pass through it.
Are carrier proteins specific to one type of molecule?
Yes
Describe rate of diffusion for simple diffusion
LInear. as concentration gradient increases, rate of diffusion increases
Describe rate of diffusion for facilitated diffusion.
Non linear. As concentration gradient increases, rate of diffusion increases to a point but then goes steady as there are limited transporter proteins.
movement of non polar molecules across the plb?
They can pass through the plb through simple diffusion, as they can dissolve in/aren’t repelled by the fatty acid tails.
Small molecules (Co2, O2, urea) can pass through pores in the plb. Large molecules still can.
movement of polar/charged molecules across plb?
Note: small polar molecules (water, urea, ethanol) can pass, despite being polar, as they can fit through pores.
Large polar/charged particles can’t cross as they will be repelled by the hydrophobic fatty acid tails.
Ions pass through channel proteins.
Large charged molecules (amino acids and ATP?) pass through carrier proteins
Large polar molecules don’t move (glucose goes through carrier protein
Describe how active transport maintains concentration gradients using an example.
Water needs to flow inside of a cactus. Salt is actively transported into the cactus, so that water flows from low concentration (outside of cactus cells) to high concentration (inside)
