Lecture 4- Transport across the cell membrane Flashcards
what is diffusion?
process of moving solute molecules away from an area of high concentration towards area of low concentration (down the concentration gradient)
what is passive diffusion?
no external energy, just kinetic energy of molecules
when does diffusion stop?
when equilibrium is reached
when is diffusion fast? (3)
over short distances
high temperature
faster for small molecules
when is diffusion slow? (2)
over long distances
across a membrane
how do you calculate the time taken to get from one point to another in the membrane?
distance squared (if its 2 miles to get there it will be 2^2 therefore 4 miles, this is because molecules move randomly)
what is simple diffusion?
no membrane
diffusion is fast
(ex. small gases like O2)
how does a semipermeable membrane work?
allows selected solutes to pass, but more slowly (does not allow some solutes to pass)
what does the cell membrane allow to pass through it?
hydrophobic
non- polar
small uncharged polar molecules
are fat soluble molecules able to pass through the cell membrane?
yes, as well as, steroids, lipids, oxygen and carbon dioxide
is water able to pass through cell membranes?
yes, because its so small it can slip through but there is also some resistance against water
there are also water channels in the cell membrane
what is unable to pass through the cell membrane?
large molecules
uncharged molecules
polar molecules
what are the 5 rules of diffusion of solute across cell membranes?
- permeability across cell membrane
- concentration gradient
- surface area
- temperature
- composition of membrane/ lipid layer
what does the rule mean about permeability across cell membrane?
size
lipid solubility
what does lipid solubility describe?
polar: wont go through
non- polar: goes through but not easily
VERY non- polar: goes through easily
what does the composition of membrane rule mean?
types of phospholipids and sphingolipids
presence of cholesterol
simple bilayer or bilayer filled with proteins
why would the presence of cholesterol affect diffusion across a cell membrane?
if theres lots of cholesterol, its harder for a solute to diffuse across because cholesterol plugs all the spaces between tails
what are ficks 5 laws of diffusion?
lipid solubility
molecular size
concentration gradient
membrane surface area
composition of lipid layer
what will happen to a small polar molecule?
it will diffuse
why might some drugs have low bioavaliability?
poor solubility
why might some drugs be toxic at useful doses?
because some drugs like the cancer drugs (kill cancer cells) direct one thing in the body, so you need to take a higher dosage. the higher dosage can be toxic. this only happens with drugs that are targeted to a specific cell type.
what is liposomal drug delivery and what does it do?
selectively deliver their payload to the diseased site through passive and/or active targeting. in doing this it makes the drug not toxic!
how does liposomal drug delivery work?
drug molecules are implanted into the aqueous core of the liposome and turn smaller into micro- crystals in there. Over time the bilayer deteriorates and the liposomes release their inner drug contents.
what is a lipid nanoparticle?
liposome that uses the inner phospholipid bilayer to surround the drug when inside the cell
what are mRNA-LNPs used for?
mRNA-LNPs are used as delivery agents encapsulating lipophilic and hydrophilic medication because of their high targeting qualities through ligand functionalization
how much of the body’s total water volume is in the intracellular and extracellular fluid?
intracellular: 2/3
extracellular: 1/3
what does the extracellular fluid consist of? (2)
interstitial fluid (makes up 75% of ECF)
plasma (makes up 25% of ECF)
what is chemical disequilibrium?
chemical disequilibrium- more solutes are concentrated in either one body compartment or another which creates chemical disequilibrium.
what is electrical disequilibrium?
electrical disequilibrium is due to ionic imbalance from cations and anions not being equally distributed throughout the body.
what is osmotic equilibrium?
osmotic equilibrium is when the concentrations are equal on both sides of the membrane. This results in zero osmotic pressure and non net movement of water