Transport Mechanisms Flashcards
Two fonctions of cell membrane
- Support distinct compositions of ICF and ISF
- Be selectively permeable
Membrane is permeable to:
H20
Lipid-soluble substances
Dissolved gases
Small uncharged molecules
Membrane is a little permeable to:
Larger molecules
Charged particles
Membrane is impermeable to:
very large molecules
Membrane is amphipathic. What does that mean?
Polar and non-polar ends
Phospholipid bilayer has hydrophilic …
heads
Phospholipid bilayer has hydrophobic …
tails
Cholesterol in the membrane provides :
firmness and fluidity
Integral membrane proteins are :
transmembrane
Peripheral membrane are on the … side
inner (cytoplasmic)
Carbohydrates and glycoproteins constitue the
glycocalyx
Name of the current model for cell membrane
Fluid Mosaic Model
Functions of plasma membrane proteins (6)
Selective transport Enzyme Cell surface receptor Cell surface identity marker (glycoproteins) Cell-cell adhesion Attachment to cytoskeleton
Transmembrane transport pathways
- Via phospholipid bilayer
- Via interaction with protein cluster (channel or carrier/transporter)
What are the factors affecting movement across the cell membrane
- Lipid solubility
- Particle size
- Electrical charge
- Availability and number of carriers and ion channels
Passive (energy independant) and active (energy dependant) movements across the cell
Passive: 1. Diffusion
- Facilitated diffusion (carrier-mediated)
- Osmosis
Active: 1. Carrier-mediated active transport
- Primary
- Secondary
2. Pino/Phagocytosis
What is diffusion?
Movement of solute particles resulting from random thermal molecular motion
As they collide, they become dispersed
What is Net flux and equilibium?
Net flux : from a region of high concentration to one of lower concentration
At equilibrium, net flux = 0 (Diffusion fluxes in opposite directions are equal)
What are the factors that affect diffusion?
- Temperature
- Mass of the molecule
- Medium through which the molecule is diffusing
- Surface area between the two region
What is the relationship between the diffusion time and the distance?
Diffusion time increases in proportion to the square of the mean distance travelled by the solute
molecules = diffusion is only effective over short distances
What are the factors that affect diffusion across the cell membrane?
- Mass of the molecule
- Concentration gradient across the cell membrane
- Lipid solubility
- Electrical charge
- Availability of selective ion channels or membrane carriers
How the solute particule could penetrate the cell ?
- Dissolving in the lipid component (non-polar molecules —> O2, CO2, fatty acids)
- Diffusing through channels (ions)
Movement of the particule depends of what?
Movement depends of the concentration gradient
+ electrical gradient for ions (electrochemichal gradient)
What are ion channels?
Ion channels: clusters of proteins or single protein (sometimes)
Show selectivity by their diameter and distribution of charges
Exist in open or closed (gated) states (conformational changes)