Osmotic Stress Flashcards
What is osmosis
The spontaneous diffusion of water molecules across a semipermeable membrane from a solution of lower solute concentration to one of higher solute concentration
What is the hydrostatic pressure
Osmotic pressure between solutions use van Hoff equation to determine the solution B to prevent water flow pie = RT (Cb-Ca)
What does osmotic pressure depend on
The total number of all solute moelcules not just concentration which can be ions or non ison
Does 1 mol of glucose have the same osmotic pressure as 0.5 NaCl
Yes because NaCl dissasociates into 0.5 Na and 0.5 Cl
What determines the volume of an individual cell
The movement of water across the plasma membrane
What is istonic
Solution causes neither shrinking nor swelling of cells
What is hypertonic vs hypotonic
Hypertonic is the concentration of solute is higher than in the cyrosl as water moves out
Hypoton the concentration of solutres is lower thatn cytsol as water moves in
What is the concentration of Na Cl and K
Na Cl are higher outside than inside the cell and K is higher inside
What do the low concentrations of Na Cl
Balance the high intracellular concentration of organic compounds equalizing the osmotic pressure and preventing the net influx of water
How is water mediated
Transmembrane protiens called aquaportins
What was the frog oocyte experiment
Resistant to pont water impermable to water
Control oocyte remained unchanged under hypotonic conditions
If injected with aquaporins they become sensitive to hypotonic solution
Aquaporins specifically increase the permability of biomembranes to water
How many transmebranes are there
Each subunit contaisn six transmembrane alpha helicas connected by 2 hyrdophillic loops (Asp)
Why is it specefic to water binding
0.28nm in diameter so only slightly larger than the diameter of a water molecule forms hydrogen bonds with channel-lining hydrophilic amino acids so block passage of ions
How many genes in human express protiens for aquaporin
11
What happens if you inactivting mutations in the aquaporin 2 gene
Causes diabetes insipidus a kidney diease marked by excretion of large volumes of dilute urine due to inability of certain kidney cells to resorb water form the urine
What is the osmotic concertation measured in
Osmoles that corresponds to the total molar concentration of solute particles both molecules and ions
What is osmolality
The solution is the number of osmoles per kg solvent usually expressed in millosmoles
Is hypersomotic conditions in animal tissues unusual
NO lymphoid and hepatic tissues are hyperosmolar and kidney so animal cells have systems that allow them to be adapted to hypertonic conditions
What is osmotic shock or osmotic stress
Sudden change in the solute concentration around a cell causing a rapid change in the movement of water across its cell membrane in cel lvolume
What is an immediate cellular response
Takes place within seconds and involves changes in the intracellular concentrations of ions such as K NA and CL
What are some other immediate responses
Cytoskelton reorganization
activation of integrinis
Receptro tyrosine kinases
various channles and transporters
What is the most common osmotic stress
Hypertonic conditions
What is TonEBP
Specefic transcrption factors that are releated to signal transduction networks leading to synthesis of organic molecules
What is one of the immediate responses to hyperosmotic stress
Do with the skelton
Remodling actin cytoskelton induces hyperoniciinty and accumulation of F-actin and reduces stress fibers in the cytoplasm that helps cells to resist increased osmotic pressure
What does the activation of TonEBP require
Nuclear redistribution, dimerization and phosphorylation
What is the TonEBP pathway
Binds to the TonE enhancer elements and stimulate transcrption of osmoprotective genes (SMIT) (AR) (BGT1) allowing cells to adapt to the high osmolaity by accumulating intracellular non-ionic organic osmolytes or compatible solutes
What compounds are induced
Inositol
Sorbitol
Betaine
Taurine
Glycerphosphocloine
Glycerol
non tocix and allow cells to adapt to high osmolality reducing intracellular ionic strength which would be more dangerous as ions
What else TOnEBP stimulate
Transcrption of genes encoding HSP70 and AqB2 and UTA which help to cope and prevent cell death
What are the domains of TonEBP
Consists of at least 7 domains two transactivation domains DNA binding domain RHD dimerization domain and three doamine to nuclear transport (NES, AED, NLS)
Why is NFAT5 different from other NFATS
Lacks docking sites for calcineurin and thus the calcimum calcineurin signaling cascade is dispensable for its activating
What is NFATS5
Transcrpition regulator of the cellular response to hypertonic stress since its sevelral domains are senestive to hypertonian leading to TonEVP activation adn translocation to the nucleus
How TonEBP activated
First pos-translational modifications of TonEVP including phosphorylation possibly sumolyation (nuclear localization)
Second interaction with other regulatory molecules such as RNA helicase A, Pls and ROS
How does TonEBP dimerize
Inhibiton of RHA binding to RHD which unblocks dimerization domain and allows TonEBP dimerization
When is TonEBP active
Isotonic conditions based on expression of its target genes
What is bidriectional regulation
TonEBP activity and nuclear localzation increase with ambient toncitis is lowered whereas it increases when ambient tonicity is elevated
Where is TonEBP is different condtions
Cytoplasma-Hypotonic
Both_ Isotonic
Nucleus- Hypertonic
How does the dimer work with TonEBP
Complete circle around DNA interacating RHD-C and two RHR-N domains
One binds to the consensus tonicity-responsive enhancer wile the other binds the nonconsensus seqeunce
What are the two different modes of TonEBP
- Nuclear redistribution of available TonEBP
- Increase in the abudncae of TonEBP in mRNA
What happens if long term to hypertonic stress
Takes more time they express the sufficient basal elvels to mediate response to hypertonic stress
What does the TonEBP expression in other tissues that are normally not exposed to hypertonic environment
A general safety system that protects agains pathologic hypertonicity
