Living in extreme environments

What happens to the body when it gets too cold?

denature proteins- disrupt metabolism. Ice formation and tissue death.

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What happens to the body when it gets too hot?

denature proteins- disrupt metabolism. Dehydration and death.

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What are the 2 strategies to minimise damage at extreme temperatures?

Tolerance and Avoidance.

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What are Heat shock proteins?

In all major compartments of all cells. Limits consequences of damage from stress. Molecular chaperones

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What are their functions?

to promote the proper folding or refolding of protein. to prevent potentially damaging interactions with proteins. to aid in the disassembly of formations of protein aggregates.

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What can cause proteins to become stressed and denature?

High ad low temp. extremes. pH shift. Toxic substances/ pollution. Physical stress. Hypoxia (low O2 levels)..

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How can HsP be expressed?

Constitutively expressed (always present). Increased during/after stress. Exclusively induced by stress.

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How do HsPs work?

Protein come under stress and unfold/denature > these denatured proteins are detected > heat shock proteins are produced > they refold the denatured proteins.

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HsPs are proteins themselves, so why don't they denature during stress?

Better, more H bonds. Better secondary structure. So, harder for denaturing to occur.

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What is the secondary function of Heat shock proteins?

immune function- helps present antigens from diseased cells to T cells. Serve as warning signal to body.

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Costs of HsPs?

Drosophila genetically engineered to have more copies of HsP genes- compared to wild type, they were found to have greater mortality and slower development.

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What happens to cells under sub-zero temperatures?

external fluid freezes and solute conc. of external fluid increases so water leaves cells and they shrink. Also, ice crystals are pointy, damaging cells.

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Strategies to cope include Freeze avoidance and Freeze tolerance- where do both tend to occur?

Avoidance- Northern hemisphere and Tolerance- Southern Hemisphere (Arctic)

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How does freeze avoidance occur: keeping body fluids liquid.

selection of a dry hibernation site, where no ice nucleation from external source can occur. Physical barriers like wax-coated cuticle for protection.

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What is a nucleate?

water requires a particle like dust in order to crystallise- this is called a nucleate.

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Insects can reduce the temperature at which bodily fluids will freeze. What is this process called and describe it?

Supercooling. Nucleating sources like dust or food particles are removed or inactivated in gut or intracellular compartments. Water can then cool to -42 without freezing due to lack of nucleating source.

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What is another freeze avoidance strategy to lower the freezing point of water?

Cryoprotectant synthesis- alteration of biochemistry. Increased solute concentration so decreased freezing point. Eg. glycerol- attracts water molecules to be held inside cells, reducing amount of ice formed outside cells, reduces cellular dehydratio

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What do freeze tolerant organism do to cope?

Produce ice structuring proteins (antifreeze proteins)- change structure of ice crystals.

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Freeze tolerant species can also produce ice nucleating proteins. What are they?

regulated production of these can allow insects to control formation of ice crystals within their bodies- avoid a sudden, total freeze. Insect can moderate rate of ice growth.

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Give example of freeze tolerant insect

arctic woolly bear moth. accumulate cryoprotectants (glycerol and betaine) in late Arctic summer. Form hibernaculum to eliminate nucleators.

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Give example of freeze avoidance insect

Goldenrod gall moth larvae- supercooling dropped to -38C, water won't freeze at this temp.

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Snow fleas can synthesise antifreeze (ice structuring) proteins. What can they be used for?

can be made synthetically for use in extending storage life of donor organs for transplants.

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Living in extreme environments

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