2. Transport across cell membranes, Transepithelial transports Flashcards
6 functions of plasma membrane protein
- Selective transport of molecules
- Cell recognition via surface antigens
- Cell communication (plasma membrane receptors)
- Tissue organization through adhesion molecules
- Enzymatic activity
- Determination of cell shape by linking the cytoskeletal to the membrane
3 functions of plasma membrane lipids
- Transport of molecules
- Source of second messengers
- Surface
Classification of transport processes through the plasma membrane
- Simple diffusion
- Protein-mediated membrane transport
- Vesicular transports
4 subtypes of protein-mediated membrane transport
- Solute carriers (facilitated diffusion)
- ATP-dependent carriers (pumps)
- ion channels
- water channels
2 subtypes of vesicular transports
- Endocytosis
- exocytosis
3 modes of endocytosis
pinocytosis, phagocytosis, receptor-mediated endocytosis
Simple diffusion is ___ (active/passive) transport
passive
What is the driving force of simple diffusion?
Chemical gradient (concentration difference)
What is the mechanism of diffusion?
Random movement of solute due to the Brownian motion
What does Fick’s First Law of Diffusion state?
Fick’s First Law of Diffusion states that substances will diffuse from areas of high concentration to lower concentration.
→ a system will reach a steady state, where the concentrations, or particles per unit volume of the substances, will be the same throughout, given enough time
Formula for Fick’s First Law of Diffusion
Fick’s First Law of Diffusion states that substances will diffuse from areas of high concentration to lower concentration.
→ a system will reach a steady state, where the concentrations, or particles per unit volume of the substances, will be the same throughout, given enough time
Interpret the formula of Fick’s first law of diffusion in case of membrane
- Through the lipid bilayer
- Driving force: concentration difference between the 2 sides of the membrane (∆c)
- Thickness of the membrane (∆x)
- rate depends on the hydrophobic city and the size of solute (incorporated into D)
What can pass through lipid bilayer of membrane in case of simple diffusion?
- O2, CO, CO2, NO, urea, hydrophobic hormones
- (H2O, ions, glucose)
- no peptides, no proteins, no disaccharide
Carrier is also an ___
enzyme
Channel is also a ___
gate
4 properties of carrier are
- Energetically:
- Transport mode:
- Speed:
- Kinetic:
- Passive/active
- Cycle
- Slow (4 orders of magnitude)
- Saturation
4 properties of channel are
- Energetically:
- Transport mode:
- Speed:
- Kinetic:
- passive
- gated
- fast (4 orders of magnitude)
- can not be saturated
What is Facilitated transport (facilitated diffusion)? ( a type of Protein-mediated membrane transport (carriers) )
passive transport not linked to metabolic energy
What is active transport? ( a type of Protein-mediated membrane transport (carriers) )
Transport linked to energy metabolism in some way
2 types of active transport
- direct/primary active transport - pump
- indirect/secondary active transport (works together with a pump)
What is uniporter?
a membrane transport protein that transports 1 substance in 1 direction
What are 2 types of cotransport?
- Symtransport
- Antitranpsort
What is symtransport?
a membrane transport protein that transports 2 substances in 1 direction
What is antitransport?
a membrane transport protein that transports 2 different substances in opposite directions
What is electroneutral?
having no net electric charge
What is electrogenic?
producing a change in the electrical potential of a cell.
Basic structure of the GLUT family of glucose transporters
Properties of facilitated diffusion
- integral plasma membrane protein mediated
- rapid transport compared to free diffusion through the lipid layer
- passive transport, no energy required
- driving force: concentration difference (solutes without charges)
- saturation kinetics
- chemical specificity
- competition between structurally related molecules
- specific inhibition
The water permeability of lipid bilayer is high or low?
Low
Which type of transport do water channels have?
Protein-mediated transport
How many isoforms do aquaporins have?
11 isoforms
Is water transport through the membrane passive or active?
→ What is the driving force?
Osmosis
What is osmosis?
Water flows to where osmotic concentration is higher
When the hydrostatic pressure applied to the solution in chamber A
→ this pressure is equal to ___
the osmotic pressure of that solution
When the hydrostatic pressure applied to the solution in chamber A
→ this pressure is equal to the osmotic pressure of that solution
→ What can you conclude from this?
there is no net water flow across the membrane.
Formula for van’t Hoff’s Law on Osmotic Pressure
π = RTnc
- π = osmotic pressure
- n = number of dissociable particles per molecule
- c = total solute concentration
- R = gas constant
- T = temperature in degrees Kelvin
What is osmolarity?
Osmolarity
= concentration x number of dissociable particles (mOsm/L)
