Lecture 6- Membrane transport Flashcards
Membrane Transport Importance: (5)
- ) Nutrients – move into cells
- ) Wastes – move out of cells
- ) Ionic balance
- ) Electrical balance (resting membrane potential)
- ) Regulatory molecules – certain hormones
~20% of all genes in E. coli are involved in
membrane transport
Types of membrane transport: (3)
- ) Simple Diffusion
- ) Facilitated Diffusion
- Carrier mediated
- Channel mediated - ) Active Transport
- Direct (1)
- Indirect (2)
- Simple Diffusion =
- Driven by? =
- Always proceeds towards…
- Diffusion across cell
- Membranes is limited to =
= Movement from region of high to low concentration
= concentration gradient
…a decrease in free energy of the system (delta G < 0)
= Small, Non-polar
(Example: O2 , CO2)
Factors that influence diffusion rates across membranes: (3)
- ) Solute size
- ) Polarity
- ) Solute charge
(1. Solute size)
- ______ molecules diffuse faster
- What can freely diffuse across membranes?
- Smaller
- Uncharged, non-polar molecules with MW up to ~100
(2. ) Polarity)
- _______ molecules diffuse faster
- The ______ the polarity the faster the diffusion
- Non-polar
- lower
(3. ) Solute charge)
- Lipid bilayer is highly impermeable to…
- Ions are charged, therefore…
- Requires energy to…
- …ions
- …associated with a shell of hydration (water molecules attracted to the charged ion)
- …remove the shell of hydration (break hydrogen bonds), which would be needed to allow the ion to enter into the hydrophobic layers of the membrane
Osmosis is…
- in a region of _____ to _____
…Simple diffusion of water across a semipermeable membrane
-Diffusion of H2O from region of low solute concentration to region of high solute concentration
2 Factors that effect rates of diffusion
Permeability and Concentration gradient (provides energy for movement)
Fick’s 1st law of diffusion..
…J =-D∆C/∆X
J = rate of diffusion
= flux/unit area = (amount of substance moving)(time−1)(area-1)
D = Diffusion coefficient (inherent property of the solute in a given solvent, related to particle size, solubility, & solvent viscosity)
∆C = concentration difference (C2 - C1) between positions X2 & X1
∆X = distance from X2 to X1
(note: ∆C will be a negative value)
Fick’s law and biological membranes
J =-D∆C/∆X
D is determined by the permeability coefficient (P)
∆X, membrane thickness is
Very thin (7 - 8nm)
Similar among all membranes
Essentially invariable for any 1 specific membrane
∆C can be expressed as difference in solute concentration (absolute value of ∆S) across the membrane
J can be expressed as a molar velocity per area (v)
v = P∆S Units = moles/(min.mm2)
Therefore, for diffusion across a biological membrane:
V is essentially determined by just 2 factors
P, permeability
∆S, difference in solute concentration
Membrane permeability is largely determined by these (2)
Partition Coefficient (solubility in lipid vs water) Size
Factors that influence diffusion rates across membranes (ions)
-Sphere of hydration
…Ordered water molecules that are attracted to dissolved solutes
…Prevent ionic molecules from crossing lipid bilayers (hydrophobic membranes)
For sphere of hydration, the ____ shell is attracted to the _____ shell through _____ bonding
…. it requires _____ energy to remove these hydration shells/ why would it be required?
-outer hydration
-inner hydration
-hydrogen
….. substantial/ (required for ion to enter lipid portion of membrane)
How do solutes that are not membrane permeable cross biological membranes?
Facilitated diffusion or Active transport
Facilitated Diffusion involves….
- the molecule still moves with concentration gradient
an integral membrane protein that facilitates the movement of the solute across the membrane barrier
Facilitated diffusion can be carried out by two different types of proteins…
… Carrier proteins and channel proteins
Carrier protein kinetics
- carrier proteins are _____
- specific (each transporter will only transport a specific compound or group of compounds)
Carrier protein types (2)
-______ transporter
-______ transporter
2 types for the second one
- Uniport transporter
- Coupled transport
- Symport and Antiport
Uniport transporter
– transports only a single solute
Coupled transport – transports 2 or more solutes
** 2 different types, Symport(?) and Antiport (?)
– transports 2 or more solutes
** solutes transported in the same direction
solutes transported in opposite direction
Look at slides #27-29 too many pics
LOOK AT THEM!!
Channel proteins form _______ channels through the membrane
hydrophilic
Channel proteins are highly…
… specific for a particular solute
Channel proteins do not undergo
Conformational change
Channel proteins types (3)
Ion channels, Porins, and aquaporins
(1) Ion channels are ____ specific and most are _____
- Highly specificity for particular ion
- Gated (open and closed states)
Gated ion channels (3)
- Ligand-gated (Ach receptor)
- Voltage-gated (Na+ channels in neurons and muscle)
- Mechanosensitive channels (K+ and Ca2+ channels in the heart)
(2) Porins have ____ pores and ____ specificity
… contain ____ barrels and allow what type of molecules to pass?
- large/low
….. beta/ Allow large molecules to pass, up to 5000 Da (include small proteins)
(3) Aquaporins contain pores for….
- and have high levels in?
…rapid conduction of water
-High levels in tissues that rapidly conduct water – kidney tubules
(3) Aquaporins contain pores for….
- and have high levels in?
…rapid conduction of water
-High levels in tissues that rapidly conduct water – kidney tubules
Active transport requires….
- they are ____ mediated
…ATP (moves against concentration gradient)
- protein
Active transport can be
Direct (1*) active transport, or
Indirect (2*) active transport
Active transport performes functions (3)
- Allow for the efficient uptake of nutrients
- Allow for the elimination of wastes
- Allow for the unequal distribution of ions across membranes
ATPase pumps (4)
- P-type
- V-type
- F-type
- ABC-type
P-type will pump…
- it is _____ phosphorylated
…Cations
- transiently/ inhibited by vanadate
V-type will pump…
… protons (H+) into various organelles
F-type…
Slides 41-44
- Also involved in transport of H+
- May function in reverse**
Example = FoF1 ATPase = ATP synthase in mitochondria
Direct (1*) Active Transport
- transport is directly linked to _____
(Slide 46)
-ATPase function
Examples:
Calcium Pump
Na+/K+ - ATPase Pump
Indirect (2*) Active Transport
- Transport is indirectly linked to _____
- ATPase pump (indirectly linked to ATP hydrolysis)
Indirect 2* Active transport involves (2)
** look at slide #48
- ATPase pump - that establishes a concentration gradient (actually an electrochemical gradient) for one solute (usually an ion, like H+, Na+)
- Coupled transporter protein - makes use of the solute gradient to move another substance (could be a sugar, amino acid or any other solute) against its concentration gradient.
- Symporter or antiporter
