Physiology 8: Extreme temp

Question 1

What happens when regulatory strategies are not enough…

Answer 1

Too cold:
Proteins denature → disrupt metabolism
Ice formation = tissue death (hypothermia)

Too hot:
Proteins denature → disrupt metabolism
Dehydration and death (hyperthermia)

Question 2

What 2 strategies are there to minimise damage at extreme temps?

Answer 2

Tolerance

Avoidance

Question 3

Define tolerance in relation to extreme temp

Answer 3

capacity to endure environment conditions without adverse reaction

Question 4

Define avoidance in relation to extreme temp

Answer 4

prevent damage from occurring

Question 5

What is the zone of tolerance?

Answer 5

The central range at which an animal is comfortable:
Bounded by zones of physiological stress, within which they can survive for a limited period of time

Question 6

What affects tolerance range?

Answer 6

• Ability to tolerate varies between taxa, life stages, pop.s, individuals
• Ability to tolerate varies within an individual’s thermal exposure (builds on idea of
  acclimatisation)

Question 7

What are heat shock proteins (HsPs)

Answer 7

Found in all major compartments of all cells (animals, prokaryotes, plants) → highly conserved
Limit consequences of damage from heat stress
Molecular chaperones

= better name would be stress proteins (as they operate in response to all kinds to stressors, not just heat!)

Question 8

What are the primary functions of heat shock proteins?

Answer 8

• To promote the proper folding/ refolding of a protein
• To prevent potentially damaging interactions with proteins
• Aid in the disassembly of protein aggregates

Question 9

Describe the expression of heat shock proteins

Answer 9

Some are constitutively expressed (present at all times)
Others are increased during/after stress
Or others are exclusively induced by stress

Question 10

Describe how HsPs work

Answer 10

1. Under stress conditions proteins start to denature = malformation
2. Detected by other molecules
3. In organisms where HsPs are not constitutively expressed, these molecules induce the expression, transcription & translation of HsPs
4. HsPs bind to malformed proteins and refold into correct formation

Question 11

Why don’t heat shock proteins dennature?

Answer 11

Better H bonds
More stable secondary structure
= hard to denature, but in extreme conditions even HsPs would denature

Question 12

What are the secondary function of HsPs?

Answer 12

Immune function:
Usually found intracellularly, so if found extracellularly it suggests cell membranes have been damaged
Helps to present antigens from diseased cells to T cells, which destroy diseased cells

Question 13

What is the cost of having too many HsPS?

Answer 13

Drosophila larvae were genetically engineered to have more copies of HsP genes
Compared to the wild type they had:
Greater Mortality
Slower development

Question 14

Describe what happens inside organisms at sub-zero temps

Answer 14

• Ice formation
• Internal fluid freezes so solute conc. of internal fluid increases = water leaves cells by osmosis and cells shrink
  = Cell membrane structure degrades because vol shrinks too much

Question 15

Name and define 2 strategies organisms use to deal with sub-zero temps.

Answer 15

Freeze avoidance → avoid freezing by keeping the bodily fluids liquid (Northern hemi)

Freeze tolerance → can tolerate the formation of internal ice crystals and the effects of dehydration (Southern hemi arctic)

Question 16

Describe freeze avoidance

Answer 16

1. Selection of a dry hibernation site where no ice nucleation (crystallisation) from an external source can occur
2. Physical barrier e.g wax-coated cuticle that provides protection against external ice across the cuticle
3. Depress the temps at which bodily fluids will freeze (supercooling)

Question 17

What is supercooling?

Answer 17

Where water is cooled below freezing without ice forming

Question 18

Describe how organisms use supercooling to stop ice formation

Answer 18

• Water requires a particle e.g dust inorder to crystallise (nucleate)
• Ice-nucleating agents (dust, food particles, bacteria) in the gut or intracellular compartments are removed / inactivated
• If no source of nucleation is introduced, water can cool to -42oCwithout freezing
• Physical process

Question 19

Describe cryoprotectant synthesis

Answer 19

• Alteration of an organism’s biochemistry
• Increased solute conc. so decreased freezing point
• Most common is glycerol

Question 20

Describe how glycerol is commonly used in cryoprotectant synthesis

Answer 20

• Attracts water molecules
• Some water is held inside cells (increases osmolarity inside cells)
• Reduces amount of ice formed outside cells
• Reduced cellular dehydration

Question 21

Describe how organisms are freeze tolerant

Answer 21

They avoid a sudden, total freeze:
1. Limit supercooling, initiate freezing of body fluids at relatively high temps
2. Produce ice structuring proteins (antifreeze proteins)
3. Produce ice nucleating proteins

Question 22

What are antifreeze proteins?

Answer 22

actually help ice to form in a controlled way by
binding to small ice crystals to inhibit growth/recrystallisation of ice

Question 23

Describe ice nucleating proteins.

Answer 23

Used by freeze tolerant organisms:
- Regulated production of ice nucleating proteins allows control of the formation of ice crystals within their bodies
- Allows organisms to moderate the rate of ice growth, adjust more slowly to the mechanical and osmotic pressures imposed by ice formation

Question 24

Give an example of a freeze tolerant organism

Answer 24

Arctic wooly bear moth:
- Withstand -70°C during annual period of diapause (hibernation)
- Accumulate cryoprotectants (glycerol and betaine) in late Arctic summer
- Form hibernation to eliminate nucleators

Question 25

Give an example of a freeze avoidant organism

Answer 25

Goldenrod gall moth larvae
Supercooling points dropped from -14°C to -38°C during autumn
Water content decreased Glycerol content increased

Question 26

Describe how the Wood frog combines freeze tolerance and avoidance

Answer 26

Supercools to -3°C
Survived weeks at -8°C at frozen state with 48% of total body water as ice - tolerates freezing of extracellular water
No anticipatory accumulation of cryoprotectants during autumn - triggered by initiation of ice formation in the body