membrane Transport Flashcards
methods of membrane transport ?
SIMPLE DIFFUSION
A. Through Lipid Bilayer
B. Osmosis
CARRIER-MEDIATED TRANSPORT
A. Facilitated Diffusion
B. Primary Active Transport
C. Secondary Active Transport
VESICULAR TRANSPORT
A. Endocytosis
B. Exocytosis
Cellular processes driven by energy stored in ion gradients across membranes ?
chemiosmotic - uptake/efflux of metabolites, nutrients and salts
osmotic volume regulation- h2o follows ions
chemical - H(Na) driven ATP synthesis
cell homeostasis- pH regulation/efflux .. removal and storage of toxic solutes
signal transduction - Ca entry and action potentials
mechanical- H+ Driven ,, flagellar rotation
simple diffusion ?
non polar and lipid soluble
diffuse directly through lipid bilayer
frick’s first law of diffusion
J=-DA * [(change in C)/(change in X)] J=flux/rate of diffusion per time unit D=diffusion coefficient A = area across which the diffusion is occurring C= con. gradient X=distance along which diffusion occurs
diffusion coefficient
D= -kT/6πrn k- boltzmann's coefficent T- Temp in K r=radius n=viscosity of medium
6 factors that affect the rate of diffusion through a cell’s membrane
lipid solubility con gradient cell membrane thickness molecule size mem surface area comp of lipid bilayer
Passive Processes: Facilitated Diffusion has certain lipophobic molecules that use
use carrier proteins or channel proteins,
what are characteristics of carrier proteins or channel proteins Facilitated Diffusion
Exhibit specificity
- Are saturable; rate is determined by number of carriers or channels
- Can be regulated in terms of activity and quantity
2 types of channel proteins
leakage ; always open
gated : controlled by chemical/electrical signaling
osmolarity
The measure of total concentration of solute particles
Osmolarity = Concentration x Number of dissociable particles
osmosis can occur when
Osmosis can occur when a membrane separates unequal solutions of a non-penetrating OR penetrating solute.
Osmosis can occur when a membrane separates pure water from a solution of a non-penetrating solute.
osmotic pressure equation
π=nCRT
n = number of dissociable particles per molecule
C = total solute concentration (in molarity, i.e., mol/L)
R = gas constant
T = temperature in degrees Kelvin.
Facilitated diffusion is the same as simple diffusion except
the diffusing substance is attached to a lipid soluble membrane carrier protein or moves through a channel
symport vs antiport examples
both Na dependent
sym: Na with glucose , aa, Bile salts, choline uptake (in nerves)and NT
anti- Na with H+ or Ca2+
exocytosis
i. Usually seen with hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes.
ii. TRANS face -side where the vesicle comes in.
iii. CIS face - side where the vesicle leaves.
endocytosis
i. Transcytosis – transport into, across, then out of cell
ii. Involve formation of protein-coated vesicles
iii. Usually receptor mediated, so it’s very selective.
phagocytosis
– pseudopods engulf solids in pods (aka phagosomes) and bring them into cell’s interior.
i. Usually done to macrophages and some WBCs.
ii. Combine them with a lysosome for digestion.
iii. Undigested contents remain in the vesicle or are ejected by exocytosis.
pinocytosis
– fluid-phase endocytosis where the plasma membrane infolds, bringing extracellular fluid and solutes into interior of the cell.
i. Done for nutrient absorption into the small intestine.
ii. No receptors are used, so process is non-specific.
receptor mediated endocytosis
i. Uptake of enzymes low-density lipoproteins, iron and insulin.
ii. Extracellular substances bind to specific receptor proteins in regions of coated pits.
iii. Contents can either be released inside the cell or bound to a lysosome for digestion.
