Flashcards in Adapting to extreme temperatures Deck (27)
How are tolerance zones different?
Be narrow or broad
Differ both within and between populations
Change between seasons, life stages, condition, age etc.
What is tolerance?
Capacity to endure conditions without adverse reaction
What is the zone of tolerance?
Range in which at animal is most comfortable, is bounded by upper and lower zone of physiological stress.
What factors affects tolerance to temperature?
Seasonal changes in temperature
What are the primary functions of heat shock proteins>
To promote the proper folding or refolding of proteins
To prevent potentially damaging interactions with proteins
Aid in the disassembly of formations of protein aggregates
How to heat shock proteins behave as molecular chaperones?
Stabilise other proteins
Minimise probability of inappropriate interactions
Involved in successful folding, assembly, regulation and degradation of other proteins
Where do you find heat shock proteins?
Present in all major compartments of all cells of all animals, plants and prokaryotes
Why are heat shock proteins important in stress?
Limit the consequences of damage from stress, and facilitate cellular recovery
When are heat shock proteins produced?
In response to stress, increased levels occur
What does stress do to proteins?
Causes them to unfold/denature, means they don't function properly
Why do Heat shock proteins not denature?
Because they have better and stronger H bonds and secondary structure, so are harder to denature
What are the secondary functions of heat shock proteins?
Usually found intracellularly, so if found extracellularly
suggests that cell membranes have been damaged
Helps to present antigens from diseased cells to T cells, which destroy diseased cells
Serve as a warning signal to the body
What happened in the experiment on drosophila where they engineered heat shock proteins to always be expressed?
Is very costly to produce, so showed a higher mortality and slower development
What happens to cells at sub zero temperature?
Ice formation, external fluid freezes, solute concentration of external fluid increased so water leaves cells by osmosis. cells shrink and membrane structure is damaged
What are the two strategies to deal with freezing temperatures?
Freeze avoidance and freeze tolerance.
What is freeze avoidance and geographically where does it often occur?
Avoid freezing by keeping the bodily fluids liquid, occurs in northern hemisphere, where temperature is seasonal and for a long period of time
What is freeze tolerance and geographically where does it occur?
Can tolerate the formation of internal ice, occurs in the Southern Hemisphere where seasonal cold temperatures are not as long or extreme
What are the mechanisms of freeze avoidance?
Selection of a dry hibernation site in which no ice nucleation from an external source can occur
Physical barrier such as a wax-coated cuticle that provides protection against external ice across the cuticle
Depress the temperature at which bodily fluids will freeze
What is supercooling?
Water requires a particle such as dust in order to crystallize (nucleate)
If no source of nucleation is introduced, water can cool to −42°C without freezing, so ice-nucleating agents in the gut or intracellular compartments are removed or inactivated
and water cools below its freezing point without changing phase into a solid, due to the lack of a nucleation source
What is cryoprotectant synthesis?
An alteration of biochemistry, there is an increased solute concentration, which leads to a decreased freezing point
Most common with glycerol
What are the mechanisms of freeze tolerance?
Limit supercooling, initiate freezing of body fluids at relatively high temperature
Produce ice structuring proteins - antifreeze
proteins, which bind to small ice crystals to inhibit growth/recrystallization of ice.
Why is freeze tolerance beneficial?
Can control to what extent and where internal ice forms, means organisms can avoid a sudden total freeze, as can imitate freezing at higher temperatures and regulate it
how do ice nucleating protein work with antifreeze proteins?
Ice nucleation proteins induce growth of single ice crystal nuclei, whilst antifreeze proteins inhibit any further growth
Describe freeze tolerance in the Arctic woolly bear moth
Withstand -70oC during annual period of diapause
Accumulate cryoprotectants in late Arctic summer
Form hibernaculum to eliminate nucleators
Describe freeze avoidance in Goldenrod gall moth larvae
Supercooling points dropped from -14oC to -38oC during autumn. Water content is decreased glycerol content increased
How does the wood frog deal with freezing temperatures?
Supercools to -3oC. Survives weeks at -8oC in frozen state with 48% of total body water as ice – tolerates freezing of extracellular water. No anticipatory accumulation of cryoprotectants during autumn, this is triggered by initiation of ice formation in the body