Mar. 3rd - Mechanical Stress Flashcards
Why can ice cause mechanical stress
1.it is less dense than water
(is in closed spaces)
2. is crystal (hard & sharp)
3. can cause cell vol. changes
Ice being more dense than water is bad because
in closed spaces (ex. blood vessels) it can expand and cause damage to the boundaries of these spaces
ice being crystal is bad…
hard and sharp!
can pierce things, ex. membranes
ice can cause changes to cell volume …
that cause membranes to be stretched/ compressed
steps of the freezing process
- supercooling
- ice nucleation
- ice propagation
step 1 : supercooling
body/ cells fluids remain liquid below the melting point of these fluids
step 2 : ice nucleation
a few water molecules arrange into a crystalline structure (small ice crystals)
- homogenous: ice crystals form from just water itself
-heterogenous: ice crystals form on/around another molecules (e.g. ice nucleating agent)
step 3 : ice propagation
growth of ice crystals
Supercooling point (SCP)
temp at which nucleation and propagation begin
Amount of mechanical damage depends on …
- ice nucleation
-outside cells = safer - ice propagation
-slower=safer
Strategies for Freeze tolerance
- prevent ice formation
- controlling ice (rare)
strat 1 : Preventing ice formation
ex. freeze-avoidant organisms
- compatible osmolytes : ^ [osmolyte] = decreased chance of ice formation or SCP
- often double as cryoprotectants (glycerol, trehalose, proline) - antifreeze proteins : prevent small ice crystals from growing
strat 2 : Controlling ice
ex. freeze-tolerant organisms
- ice nucleating agents (can be proteins)
- can be used to Nucleate ice formation in extracellular spaces
or at higher temps
causes safer (slower) propagation - compatible osmolytes : [osmolytes] =decreased ice content (less ice = safer, often double as cryoprotectants)
