Chapter 4: Movement of molecules Flashcards
1
Q
Purposes of membranes
A
- membranes serve as boundaries between the cell interior and extracellular fluid (plasma membrane) and between organelle interiors and the cytosol
- -> regulate what substances enter and leave cells/organelles, how much and how fast
2
Q
Passive mechanisms of membrane transport
A
- don’t require energy
- diffusion, osmosis, facilitated diffusion
3
Q
active mechanisms of membrane transport
A
- require energy
- active transport, exocytosis, endocytosis
- exo and endocytosis are both bulk transport
4
Q
Active transport and facilitated diffusion
A
- both require carrier molecules and are considered transport mechanisms
5
Q
Diffusion
A
- movement of molecules from one location to another as a result of random thermal motion; movement of molecules from higher to lower concentration (decrease the concentration gradient)
- used to move substances in and out of capillaries and blood and cells
- most common process most likely
- may or may not occur across a semi-permeable membrane
- uniform concentration is eventually reached
6
Q
Flux
A
- amount of material crossing a surface in a unit of time
- magnitude determined by concentration gradient
7
Q
net flux
A
- the difference between two one-way fluxes
- the net amount of material transferred from one location to another
- net flux always occurs from regions of higher concentration to regions of lower concentration
- concentration difference determines the magnitude of net flux
- at a given concentration gradient, also influenced by temperature, mass, surface area, and medium
8
Q
diffusion rate
A
affected by distance
9
Q
diffusion time
A
square of the distance over which molecules diffuse
10
Q
diffusion through lipid bilayer
A
- plasma membrane is semipermeable/differentially permeable
- some, not all, molecules can diffuse across the plasma membrane
- small, uncharged, lipid-soluble molecules diffuse easily across lipid bilayer (nonpolar)
- charged (polar) molecules have more difficulty diffusing across lipid bilayer…slowly or not at all
- macromolecules can’t freely cross membrane
11
Q
Polar molecules and membrane
A
- lower permeability and harder to cross membrane
12
Q
Protein Channels
A
- used by ions because harder for them to pass because charge
- made of integral membrane proteins, either a single one or usually a protein aggregate
- small diameters
- ion selectivity
13
Q
Electrochemical gradient
A
- intracellular fluid is usually negatively charged
- extracellular fluid usually positively charged
- influences ion movement
- direction and magnitude of ion fluxes across membranes depend on both the concentration difference and membrane potential (electrical difference)
14
Q
membrane potential
A
- separation of electrical charge across the plasma membrane
15
Q
regulation of diffusion through ion channels
A
channel gating
- ligand-gated channels
- voltage-gated channels
- mechanically-gated channels
16
Q
ligand-gated channels
A
- open and close in response to a certain binding chemical ligate to protein of channel
17
Q
voltage-gated channels
A
- open and close in response to membrane potential
18
Q
mechanically-gated channels
A
- open and close due to the stretching of the membrane
19
Q
Mediated transport mechanisms
A
- responsible for the transport of some ions, and for polar molecules such as amino acids and glucose that are too large to move through channels
- use transporters/carrier molecules (integral mem proteins, undergo conformational change, can move molecules in either direction across mem, chemical specificity)
20
Q
how mediated transport mechanisms work
A
- the solute binds to a specific site on the transporter protein
- the protein changes shape, and the solute is released on the other side of the membrane
21
Q
magnitude of solute flux determined by
A
- extent of saturation of transporter binding sites (solute concentration and affinity of transporters for the solute)
- number of transporters in membrane
- rate at which conformational change in the transport protein occurs
- finite number of tranporters in any mem for a given solute –> maximal flux (saturation)
22
Q
mediated transport vs simple diffusion
A
- in mediated transport, the # of available transporters places an upper limit on the flux magnitude
- in simple diffusion, flux magnitude is limited only by the concentration gradient
23
Q
2 types of mediated transport
A
- facilitated diffusion
- active transport (primary and secondary)
24
Q
Facilitated diffusion
A
- uses carrier molecules/transporters to transport substances from areas of higher to lower concentration
- doesn’t require ATP
25
active transport
- uses carrier molecules to transport substances from areas of low to high concentration (against gradient!)
- i.e. sodium/potassium pump
- primary active transport requires ATP
- secondary active transport uses an electrochemical gradient across a membrane to drive the process
26
NA/K pump
- maintain proper concentrations
- usually high sodium out and potassium in
- concentration moves sodium in and potassium out but need to work against gradient
- uses ATP
27
cotransport
- form of secondary active transport
| - sodium and second solute cross membrane in same direction (symport)
28
countertransport
- form of secondary active transport
| - sodium and second solute move in opposite directions across membrane (antiport)
29
Osmosis
- the diffusion of water through a semipermeable membrane (movement of water from high to low concentration)
- responsible for much of the movement of fluids
- as solute increases, the water decreases. Water concentration determines the direction of osmosis
30
aqua porins
- membrane proteins that create channels for water
31
osmolarity
- the total solute concentration of a solution
- 1 osmo = 1 mol of solute particles
- 1 M solution NaCl contains 2 osmol of solute per liter; osmolarity=2OSM
32
Osmotic pressure
- the pressure that must be applied to the solution to prevent the net flow of water into it
- attractive force to water
- the higher osmolarity, the higher the osmotic pressure, the more water will move into solution via osmosis
- a tendency of a solution to attract water to move into it via osmosis
33
extracellular osmolarity and cell volume
- non-penetrating solutes can't cross plasma membrane (Na+, Cl-, K+ behave as nonpenetrating solutes
- penetrating solutes cross plasma membrane
- at equilibrium, the intracellular and extracellular fluids have an osmolarity of ~300 mOsm
34
tonicity
- the concentration of nonpenetrating solutes in a solution relative to the concentration of those solutes within the cell
35
isotonic solution
- has same nonpenetrating solute concentration as the cell
| - perfect concentration, stays the same
36
hypotonic solution
- has a lower nonpenetrating solute concentration than the cell
- cell swells and bursts
37
hypertonic solution
- has a higher nonpenetrating solute concentration than the cell
- cell gets skinny and shriveled and shrinks
38
isoosmotic, hypoosmotic, hyperosmotic
- osmolarity of a solution relative to that of the cell in regard to all solutes
39
Exocytosis
- moves larger molecules or groups of molecules OUT of the cell (bulk transport)
- uses vesicles which fuse with plasma mem
- requires energy ATP
- secretions ~ cells release subs that they generate into extracellular fluid
40
endocytosis
- moves larger molecules, whole cells, or groups of molecules INTO the cell
- requires ATP
41
3 mechanisms endocytosis may occus
- pinocytosis
- receptor-mediated
- phagocytosis
42
pinocytosis
- cell drinking
- invagination of the plasma mem forms a vesicle that encases a portion of the extracellular fluid and substances suspended in it
- nonselective
43
receptor-mediated endocytosis
- requires specific receptors
| - specific and selective
44
phagocytosis
- cell eating
| - cells engulf whole cells, pathogens, parts of cells, or large organic molecules
45
transcytosis
- endocytosis and exocytosis move a molecule across a cell
| - capillary exchange of fatty acids, albumin, and hormones such as insulin
46
luminal/apical/mucosal membrane
lines the hollow organs
47
basolateral/serosal membranes
opposite the luminal mem, usually adjacent to blood
48
lateral membrances
face adjacent epithelial cells
49
epithelial transport pathways
- paracellular and transcellular
50
paracellular pathway
- diffusion between adjacent epithelial cells
51
transcellular pathway
- movement through an epithelial cell (involves movement of the substance across the luminal and basolateral mem)
52
epithelial cells
- form lining of hollow organs and tubes and therefore epithelial cells regulate absorption/secretion across those surfaces
