1-Membrane Transport Flashcards
membrane
function
- create chemical compartments by acting as barrier
-uneven distribution of molecules across membrane - conduit for molecules
non-vesicular transmembrane transport
- passive: no energy
-diffusion thru lipid bilayer, channels, or facilitated (carriers) - active: energy required
-primary (ATPase), secondary (sym/antiporters)
vesicular transmembrane transport
aka endo/exocytosis forr bulk transport
mediated by lipid vesicles, energy required
simple diffusion
-straight thru bilayer
-only gases + small uncharged
simple diffusion factors
- lipid solubility
- molecular size
- cell membrane thickness
- concentration gradient
- membrane surface area
- composition of lipid bilayer
O2/CO2 inverse proportion to thickness and size, rest are direct
diffusion thru channels
types of molecules
- small, uncharged molecules
-affected by # of water channels, water selectivity, water down concentration gradient - ions
-affected by # of ion channels, ion selectivity, moves down electrochemical gradient
aquaporin
channel specific to water
mediates water permeability of cell membrane, regulate by insert or remove channel
4 subunites = functional channel = fast transport rate
osmosis
movement of water across water permeable membrane
water follows osmotic pressure (high > low)
nephrogenic diabetes insipidus
NDI
mutation in aquaporin-2 gene so reabsorption of water in kidney compromised
-normally vasopressin or ADH signals aquaporins to move to apical surface to absorp water
-excrete large amounts diluted urine + xs thirst
gating mechanisms
ion channels
- no gate
- voltage gating
- ligand gating (extra/intracellular)
- mechanically gated
uniporters
facilitated diffusion
-transport is substrate specific
-changes affinity for subtrate based on configuration
-higher rate than simple diffusion
-has maximum transport rate (Vmax)
-reversible
transport rate factors
- concentration gradient (equil @ Vmax)
- # transporters (direct prop to Vmax)
- binding affinity (inverse to Km)
small Km = high affinity = fast transport
diabetes mellitus type I
glucose transporters
insulin deficiency > inadequate transporters on cell membrane = hyperglycemia in blood/urine
normal: insulin inc glucose transporters on cell membrane for uptake from bloodstream
primary active transport
via carrier proteins and energy
-uncharged moles vs concentration gradient
-ions vs electrochemical gradient
carrier proteins are similar to diffusion ones
ATP powered pumps
primary active transport
ATPase driven by ATP hydrolysis
i.e. Na/K pump = 3 Na out + 2 K in against ion gradient
ouabain and digoxin poison
ABC Superfamily
Primary active transport
ATP binding cassette
all have common ATP binding domain
i.e. CFTR and MDR (multidrug resistance, normally good for remove toxins but if tumor and overexpress then resist cancer therapy)
secondary active transport
transport vs concentration gradient via downhill movement of another molecule (instead of metabolic ATP)
-energy lost by downhill movement captured for other gradient
usually Na+ ion gradient
glucose reabsorption @ kidney
secondary active transport
- secondary active of 2 Na/1 glucose symporter from lumen (low) to epithelial cells (high)
- facilitated diffusion of glucose out to blood stream (low)
+ primary active transport of Na/K to maintain gradient and keep intracellular low for Na
other types of cotransporters/symporters
- Na/K/Cl
- K/Cl
- Na/neurotransmitter (GABA, dopamine)
exchanges/antiporters types
- Na/Ca
- Na/H
types of endocytosis
- phagocytosis
- pinocytosis
- fluid phase
- receptor mediated
- caveolae
fluid phase endocytosis
uptake of materials into cell dissolved in extracell fluid
low specificity = ineffective
receptor mediated endocytosis
highly specific = effective
i.e. clathrin pathway
clathrin pathway
- ligand binds receptor
- adaptin and clathrin recruited intracell
- clathrin forms a net that pulls receptors on surface into coated pit
- coated vesicle forms
- pinched off by dynamin
- vesicle uncoats
- adaptin and clathrin recycled, uncoated vesicle fuses
