Week 01 Transport Flashcards
What are the 3 main types of plasma membrane transport processes?
- Simple Diffusion
- Protein-mediated Membrane Transport
- Vesicular Transport
What are 4 major types of protein-mediated membrane transport?
- Solute Carriers - facilitated diffusion
- ATP-Dependent Carriers - AKA pumps, active transport
- Ion Channels - forms a “pore” for ions
- Water Channels - aquaporins
How do carriers and channels differ in their…
energy usage?
transport mode?
speed?
kinetics?
- Energy Usage:
- carriers: active/passive
- channels: passive
- Transport Mode:
- carriers: transport cycle
- channels: gated
- Speed:
- carriers: slow
- channels: fast
- Kinetics:
- carriers: saturatable
- channels: unsaturable (at physio. concentrations)
What is Fick’s 1st Law of Diffusion?
More important than just the memorizing the equation… what are some important factors that affect direction and speed of diffusion?
- Concentration Gradient (effects speed + direction, Δc)
- Thickness of the Membrane (effects speed, Δx)
- Solute Hydrophobicity (effects ability to diffuse/speed)
- Solute Size (effects ability to diffuse/speed)

- hydrophobicity + size are incorporated into the “diffusion coefficient”
What are some examples of molecules which diffuse easily through cell membranes?
O2
CO2
CO
NO
Urea
Hydrophobic Hormones
What are some examples of molecules which have more specialized modes of diffusion into cells?
And what kinds of molecules do not diffuse?
Specialized diffusion: water, ions, larger molecules such as glucose
Undiffusable molecules: peptides, proteins, disaccharides
In the case of glucose transport…
what kind of transport is it?
does it use energy?
does it effect electrical charge?
- facilitated transport with uniporter
- passive, no ATP use
- electroneutral (glucose is a neutral molecule)
Describe the general kinetics of GLUT transporters.
How is it affected by concentration?
- speeds up with increased concentration
- has a saturation point at which rate maxes out
Between GLUT-1 and GLUT-2, which one is at vmax in the physiological range of glucose concentration?
What is the consequence of this?
GLUT-1 has Vmax across whole range of physiological glucose concentrationand
- leads to the cell always having glucose available
- GLUT-2 has Vmax higher than any physiological glucose levels
- leads to different transportation rates across all possible glucose concentrations
What are some places that you find GLUT-1?
GLUT-2?
GLUT-4?
1: Red blood cells
2: Beta cells of pancreas
4: skeletal muscle, adipocytes
What are the properties of the Cl-/HCO3- exchanger?
Energy usage?
Electrogenicity?
Location/function?
- Cotransporter, anti-porter
- passive
- electroneutral (no change in charge)
- in RBCs, transports CO2
- goes in both directions
What are the propeties of Na/K-ATPase?
Transporter type?
Energy requirements?
Function?
Electrogenicity?
Inhibitors?
- is a pump
- active transport requiring ATP
- carries 3 Na+ out of and 2 K+ in to cell
- electrogenic, net transport of +1 charge out
- inhibited by Ouabain
What are the properties of the Ca2+-ATPase?
Transport type?
Electrogenicity?
Function/Location?
- Active Uniporter
- Electrogenic (due to calcium ion charge)
- present in both plasma membrane and ER membrane (carries calcium into ER lumen)
What are the ABC transporters?
What are the two types?
- a transporter superfamily standing for ATP-Binding Cassette
types: primer pump and channel
What is the function of the primer pump type of ABC transporter?
Examples of this?
- Active transport of mainly hydrophobic molecules
Examples:
- cholesterol transport
- bile secretion
- drug removal (multi-drug resistance pumps)
What is an example of the channel type of ABC transporter?
CFTR - Cystic Fibrosis Transmembrane Regulator
- works as a Cl- channel
- mutations in its gene can result in cystic fibrosis
How is water transported across the plasma membrane?
What drives this?
- passively via aquaporin proteins
- driven by osmosis
What is van’t Hoff’s law for osmotic pressure?

What is the reflection coefficient that is added to the van’t Hoff equation in physiological calculations?
What do its values represent?
- a coefficient that indicates the diffusability of the solute in consideration
- 0 means diffusable (ex: urea), 1 means undiffusable (ex: NaCl, sucrose)
How would a 290 mOsm/l solution of urea affect a cell’s volume?
- depsite the urea solution being at physiological osmolarity, the concentration gradient due to the lack of urea in the cell drives urea into the cell
- water follows the urea due to osmosis
- cell volume increases
What is oncotic pressure?
the osmotic pressure of large molecules (usually proteins)
What is the total fluid volume in a 70 kg adult?
Intracellular?
Interstitial?
Plasma?
Transcellular?
Total: 42 L
Intracellular: 25 L
Interstitial: 13 L
Plasma: 3 L
Transcellular: 1 L
How does receptor mediated endocytosis occur?
Give examples of proteins involved.
- via receptor-coated pits in the cell membrane
- clathrin, adaptin, and B-arrestin II
What are the two types of exocytosis?
An example of one type?
Constitutive
Regulated - histmaine release from mast cells
What are the 4 main compartments/spaces in relation to trans-epithelial transport?
- Luminal - within the epithelium-lined cavity
- Interstitial - beyond the basal membrane
- Paracellular - between epithelial cells
- Intracellular
What is transport from the lumen to the interstitium called?
From the interstitium to the lumen?
- resorption
- secretion/excretion
What are the 2 main types of transepithelial transport?
transcellular - thru cells from apical/basal or vice versa, passive/active
paracellular - thru tight junctions and then between cells, always passive
What is ENaC?
Where can it be found?
What controls it?
Epithelial Sodium Channel
- found in sweat glands + distal tubules of the kidney
- controlled by aldosterone (can change # of ENaCs in a cell membrane)