Biochemistry of Freeze Tolerance

Question 1

Freezing point (=melting point)

Answer 1

The freezing point (FP) (synonymous with melting point, MP, with the notable exception of when antifreeze proteins are present) is the temperature at which a small ice crystal in a larger volume of liquid water is stable, but a slight elevation in temperature causes the crystal to melt completely, whereas a slight decrease in temperature results in noticeable crystal growth

Question 2

What is the super cooling point (=nucleation temperature)?

Answer 2

When the temperature of a volume of water is lowered through the freezing point in the absence of a “seed” crystal, the water typically does not freeze at the FP, but supercools (undercools) below the FP to some lower temperature where spontaneous nucleation (freezing in the absence of a seed crystal) occurs. This lower temperature is termed the super=cooling point (SCP) or nucleation temperature (NT).

Supercooling point = temperature at which spontaneous freezing occurs

Question 3

Thermal hystersis

Answer 3

The difference between the freezing point and melting point caused by Antifreeze proteins. AFPs depress the freezing point, but NOT the melting point

Question 4

How do AFPs inhibit freezing?

Answer 4

Adsorption inhibition theory based on the demonstrated ability of AFPs to bind to ice (Duman and DeVries, 1972; Raymond and DeVries, 1977). by this theory, the AFPs hydrogen-bond to the crystal at sites of preferred growth (probably step sites) and thus inhibit growth until the temperature is lowered (Raymond et al., 1989; Knight et al., 1991)

Question 5

Diapause

Answer 5

A period of suspended development in an insect, other invertebrate, or mammal embryo, especially during unfavorable environmental conditions

Question 6

Aestivation

Answer 6

Prolonged torpor or dormancy of an animal during a hot or dry period. (i.e. summer hibernation/dormancy)

Question 7

Hibernation

Answer 7

Hibernation is a type of dormancy. Three very specific requirements for an animal to be considered a true hibernator: reduced metabolism, slower heart rate, and lowered body temperature

Question 8

Dormancy

Answer 8

Bears enter dormancy, not hibernation, because they don’t drop their body temperatures

Question 9

Brumation

Answer 9

Common in snakes and other reptiles. Triggered by colder temps and less daylight, no eating but still drink water throughout winter