active, bulk, and cotransport Flashcards
passive transport
No Energy
Diffusion, Osmosis, Facilitated Diffusion
Move down concentration gradient From HIGH to LOW
facilitated diffusion
Speeds up the transport, but does not change the direction
passive transport
active transport
moves substances AGAINST their concentration gradient
requires energy
what form is the energy in with active transport
ATP usually
how does active transport work
Transfers a terminal phosphate group to the transport protein
induce change in shape
translocates solute across
what proteins do active transport
carrier
active transport allows cells to maintain
concentration gradients that differ from their surroundings
2 common examples of active transport
sodium-potassium pump,
proton pump
6 stages of sodium potassium pump
- cytoplasmic Na binds to sodium-potassium pump
- Na binding stimulates phosphorylation by ATP
- phosphorylation causes the protein to change its shape, Na is expelled to the outside
- Potassium binds on the extracellular side and triggers release of the phosphate group
- loss of the phosphate restores the protein’s original shape
- potassium is released and the cycle repeats
membrane potential definition
voltage difference across a membrane
Electrical potential energy, acts like a battery
how is membrane potential created
by differences in the distribution of positive and negative ions
what is membrane potential maintained by
ion pumps
cell (inside and outside) voltages
Inside cell: NEGATIVE
Outside cell: POSITIVE
Membrane potential ranges from -50 to -200 millivolts (mV)
what does membrane potential affect
the traffic of all charged substances
Because the inside is NEGATIVE, the cell membrane potential favors
the passive transport of cations (+) INTO the cell and anions (-) OUT of the cell
electrochemical gradient
Force acting on an ion that drives the diffusion of ions across a membrane from chemical and electrical force
chemical force
the ion’s concentration gradient
electrical force
the effect of the membrane potential on the ion’s movement
In cases where electrical forces due to membrane potential oppose simple diffusion of an ion down its concentration gradient, what might be necessary?
active transport
electrogenic pump
transport protein that generates voltage across a membrane
sodium-potassium pump
major electrogenic pump of animal cells
With each “crank” of the pump, there is a net transfer of 1 + charge from cytoplasm to the extracellular fluid
sodium-potassium pump stores energy as
voltage
sodium-potassium pump ion exchange
Pumps 3 Na+ ions OUT of the cell for every 2 K+ ions INTO the cell
proton pump
The main electrogenic pump of plants, fungi, and bacteria
proton pump ion exchange
Actively transports H+ protons OUT of the cell
cotransport
active transport of a solute indirectly drives transport of another solute
A substance that has been pumped across a membrane can do work as it moves back across by diffusion
Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
bulk transport requires
energy
how do Large molecules, such as polysaccharides and proteins, cross the membrane in bulk?
vesicles
what do Small molecules and water enter or leave the cell through
lipid bilayer or transport proteins
exocytosis
transport vesicles migrate to the membrane, fuse with it, and release their contents
many secretory cells use _ to export their products
exocytosis
endocytosis
the cell takes in macromolecules by forming vesicles from the plasma membrane
relationship between endocytosis and exocytosis
Endocytosis is a reversal of exocytosis, involving different proteins
3 types of endocytosis
Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis
phagocytosis
cell engulfs a particle/food in a vacuole
The vacuole fuses with a lysosome to digest the particle
pinocytosis
molecules are taken up when extracellular fluid is “gulped” into tiny vesicles
receptor-mediated endocytosis
binding of ligands to receptors triggers vesicle formation
ligand
any molecule that binds specifically to a receptor site of another molecule
