Lecture 2.2 - Membranes, Channels and Transport Flashcards
- diffusion of water across a selectively permeable embrane
- continues until the solutions are isotonic
osmosis
osmosis continues until the solution are __
isotonic
in osmosis, water moves from __ to __ water potential
higher to lower
the movement of water can produce a __ __, resulting in a pressure gradient across a semipermeable membrane
hydrostatic pressure
hydrostatic pressure is a __ __ pressure
fluid mechanical pressure
the difference in hydraulic pressure of a solution and water which must be overcome to prevent the entry of water into the solution across the membrane
osmotic pressure
osmotic pressure is described by __ equation
Van t’Hoff
when two aqueous solutions exert the same osmotic pressure through a membrne permeable only to water
isosmotic
if one solution exerts less osmotic pressure than the other
hypoosmotic
if one solution exerts greater osmotic pressure than the other
hyperosmotic
the concentration of a solution expressed as the total number of solute particles per liter
osmolarity
response of cells or tissues immersed in the solution
tonicity
osmotic pressure property of a solution
osmoticity
- no osmotic pressure difference between the cell and interior and the extracellular solution
- no net water gain
- cell/tissue neither shrinks nor swell
isotonic solution
solution causes swelling of tissue
hypotonic solution
solution causes shrinking of tissue
hypertonic solution
what happens to the cell in a very hypotonic solution
- lysis (animal cell)
- turgid (plant cell)
what happens to the cell in an isotonic solution
- normal (animal cell)
- flaccid (plant cell)
what happens to the cell in a very hypertonic solution
- shriveled (animal cell)
- plasmolyzed (plant cell)
hydrostatic pressure that puts cell walls in tension
turgor pressure
fatty acid tail in soap bubble
pointing out
fatty acid tail in lipid vesicle
pointing in
transport proteins tend to be __ for one molecule, so substances can only corss a membrane if it contains the appropriate protein
specific
Two kinds of transport proteins
- channel
- carrier
allows charged substances (usually ions) to diffuse across membranes
water-filled pore or channel
most channels can be __, allowing the cell to control the entry and exit of ions
gated
small organic compounds that specifically transport ions across the plasma membrane
ionophores
open or closes gated chanels
physical or chemical stimulus
transports a single solute from one side of the membrane to the other
uniporters
transfer one solute and simultaneously or sequentially transfer a second solute
coupled transporters
two types of coupled transporters
- symporters
- antiporters
transfer solutes in the same direction
symporters
transfer solutes in opposite directions
antiporters
show saturation kinetics
channel and carrier-mediated transport mechanisms
binding site for a specific solute and constantly flip between two states so that the site is alternately open to opposite sides of the membrane
diffusion through carrier
in diffusion through carrier, the substance will bind on the side with __ concentration and be released at __ concentration side
higher, lower
require metabolic energy and moves substances against their gradients
active transports
supplies the energy for most active transport
ATP
actively maintains the gradient of sodium (Na+) and potassium (K+) across the membrane
sodium-potassium pump
ratio of sodium to potassium
3 Na+ out of cell
2 K+ into cell
sodium is transported (interior to exterior) against a __ concentration gradient
10:1
net flux of charge in sodium-potassium pump
one positive charge
(3 Na+ - 2K+)
membrane protein couples the transport of two solutes
cotransport
cotransport with __ renders substrate transport against its concentration gradient energetically favorable
Na+
run on energy stores in ion gradients
symporters
- Na+/H+ in the proximal tubule of mammalian kidney
- for each H+ expelled, one Na+ is taken up into the cel
- avoids expenditure of energy to perform electrical work
antiporters
Summary of Membrane Transport:
Uses energy
- Lipid diffusion - N
- Osmosis - N
- Passive Transport - N
- Active Transport - Y
Summary of Membrane Transport:
Uses proteins
- Lipid diffusion - N
- Osmosis - N
- Passive Transport - Y
- Active Transport - Y
Summary of Membrane Transport:
Specific
- Lipid diffusion - N
- Osmosis - Y
- Passive Transport - Y
- Active Transport - Y
Summary of Membrane Transport:
Controllable
- Lipid diffusion - N
- Osmosis - N
- Passive Transport - Y
- Active Transport - Y
how do small molecules and water enter or leave the cell
through lipid bilayer or by transport proteins
how do large molecules, such as polysaccharides and proteins, cross the membrane
via vesicles
Two types of movement of large molecules across membranes
- endocytosis
- exocytosis
cell brings in macromolecules and particulate matter by forming new vesicles from the plasma membrane
endocytosis
Types of endocytosis
- pinocytosis
- phagocytosis
- receptor-mediated endocytosis
- cell creates a vesicle around a droplet of extracellular fluid
- cellular drinking
- non-specific process
pinocytosis
- cellular eating
- ingesting and eliminating particles larger than 0.5 μm in diameter
phagocytosis
- depends on the presence of receptor molecules embedded in the cell membrane
- triggered when extracellular substances bind to special receptors, ligands, on the membrane surface, especially near coated pits
receptor-mediated endocytosis
- molecules that bind to receptors and cause changes in cell signaling
- can be intracellular or extracellular
Ligands
transport proteins from organelle to organelle
clathrin- coated vesicles
when vesicle and plasma membrane come in contact, the bilayers fuse and spill the contents to the outside
exocytosis
Three main types of intercellular links
- tight junctions
- adhering junctions (zonula adherens, desmosomes)
- gap junctions
- membranes of adjacent cells are fused, forming continuous belts around cells
- prevent leakage of extracellular fluid across a layer of epithelial cells
tight junctions
- fasten cells together intro strong sheets, much like rivets
- reinforced by intermediate filaments of keratin
- attach muscle cells to each other in a muscle
desmosome (anchoring junctions)
- provide cytoplasmic channels between adjacent cells
- salt ions, sugar, amino acids, and other small molecules can pass
gap junction (communicating junctions)
every cell maintains concentrations of inorganic solutes inside the cell that are different from those outside the cell
ionic steady state
Two ways to prevent osmotic swelling in cells
- pump water out as fast as it leaks in
- pump out solutes that leak into the cell
major mechanism for regulation of cell volume
pump out solutes that leak into the cell
Where do membrane permeability to charged particles depend on
- membrane permeability constant
- electrical signal
Two forces that act on charged atoms and molecules to produce a net passive diffusion
- chemical gradient
- electric field
arising from differences in the concentration of the substance on the two sides of the membrane
chemical gradient
difference in electrical potential across the membrane
electric field
where will an ion move away from
regions of high concentration
where will an ion move toward
increasing negative potential (if it is a cation)
determined by the sum of the combined forces of the concentration gradient and electrical gradient
electrochemical gradient
potential at which an ion is in electrochemical equilibrium
equilibrium potential
how can an ion species passively diffuse AGAINST its chemical concentration gradient
if electrical gradient across the membrane is in the opposite direction and exceeds the concentration gradient
will not be affected by electrical forces but by the concentration gradient
uncharged molecules (sugar)
- results in an unequal distribution of diffusible ions across the membrane.
- Despite the unequal distribution, the solutions on both sides of the membrane remain electrically neutral.
Donnan equilibrium
