1.4 Membrane Transport Flashcards
Active transport
movement of substances across membranes using energy in the form of ATP
Concentration gradient
a gradient resulting from an unequal distribution of ions across the cell membrane
Diffusion
passive movement of particles from a region o higher concentration to a region of lower concentration.
Endocytosis
the process in which the cell takes in materials from the outside by infolding of the membrane to form a vesicle
Exocytosis
the process in which the cell releases materials to the outside by discharging them as membrane-bounded vesicles that pass through the cell membrane.
Facilitated diffusion
diffusion through a membrane that requires protein
Hypertonic
a more concentrated solution relative to another fluid
Hypotonic
a less concentrated solution relative to another fluid
Osmoregulation
control of the water balance of a living organism
Osmosis
passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration
Secretion
when material is released from the cell
Semi-permeable membrane
membrane that allows some substances to diffuse but not others
Transport pumps
proteins in the plasma membrane that use ATP to move substances across the membrane
Vesicles
a bubble-like membranous structure that stores and transports cellular products
Passive transport
movement of substances down the concentration without energy
What factor can affect the rate of diffusion?
Temperature- an increase in temperature gives an increase gives an increase in kinetic energy which increases the rate of diffusion.
When does simple diffusion occur? e.g….
when substances are able to move between the phospholipid molecules of the bilayer e.g carbon dioxide,
oxygen, steroid hormones
why is facilitated diffusion different than simple diffusion?
Two examples
It involves the the channel proteins which let the solute pass through e.g larger particles which can not move through the hydrophobic layer can travel through it, ions
Specific carrier proteins that combine with solute molecules and change shape to let them through the membrane. Does not require energy. e.g Glucose, amino acids.
How do potassium channels work?
Potassium channels are voltage gated. Voltages across the membranes are due to an unequal distribution of + and - ions inside and outside of the cell.
During a nerve impulse there are more positive charges inside the cell. This causes the potassium channels to change shape and open. Potassium ions diffuse rapidly out of the cell down their concentration gradient
An extra globular sub unit moves into the open channel returns to it’s normal shape.
What makes this channel specific for potassium ions?
The width of the pore is 0.3 mm and the amino acids which line it are specific for potassium. ?
what does the term osmolarity mean?
The total concentration of the cell or solutes in the cell
What happens in active transport
a particle collides with a specific protein pump in the cell membrane.
the protein pump is activated by ATP, uses the energy released to change shape
the particle being transported is released on the other side of the membrane.
ADP and P are released from the protein pump and this causes it to revert back to it’s original shape, ready to receive another particle.
The sodium-potassium pump
restores and maintains unequal distributions of Na+ and K+ inside and outside of the axon.
How are sodium and potassium actively transported using the carrier protein?
- The interior of the pump is open to the inside of the axon; three sodium ions enter the pump and attach to their binding sites
- ATP transfers a phosphate group from from itself to the pump, this causes the pump to change shape and the interior is then closed.
- The exterior of the pump opens to the outside of the axon and the three sodium ions are released.
- Two potassium ions from outside can then enter and attach to their binding sites
- Binding of potassium causes release of the phosphate group; this causes the pump to change shape again so that it is again only open to the inside of the axon
- the interior of the pump opens to the inside of the axon and the potassium ions are released.
How is the rate of active transport affected by temperature?
As the temperature increases the rate of active transport increases as the particles have more kinetic energy, however once the proteins have reached a certain temperature they will begin to denature. Therefore the rate of active transport will then decrease.
what types of molecules are transported using endocytosis and exocytosis?
macromolecules(very large molecules) that are too big to cross the plasma membrane directly
How does the fluidity of membranes allow materials to be exchanged through endocytosis and exocytosis?
The phospholipids are able to move around each other, this means that when two membranes come close together the phospholipids can move between and around each other, allowing the membranes to fuse.
