Mechanisms of Thermal Tolerance

Mechanisms of Thermal Tolerance

1. Avoiding Protein denaturation at high temperatures

   • the Heat Shock Response
     • Through heat shock proteins
       • either constitutive or inducible
         • Work normally folding proteins
       • when heat shock occurs HSPs act to refold damaged proteins (ATP dependent)
     • Dutton and Hoffman (2009) HsPs in field collected Mytilus galloprovincialis
       • Found a greater response in different populations
       • southern population were used to higher temps so difdnt suffer as much damage
         • Lower HSP expression

2. Avoiding Blood Freezing at low temperatures

   • Freeze avoidance
     • Using Antifreeze proteins
       • Proteins bind to ice surface preventing more water molecules joining
         • proteins then melt the ice
     • Notothenoid fish
   • Cold Tolerance
     • Ice Nucleating Proteins (INPs)
     • Murphy (1977) looked at blood Ca level and freezing in Ribbed Mussel
       • Found that Ca binds to membrane reducing cell damage during freezing
         • Calcium stabilizes the membrane, preventing denaturation

3. Maintaining reactions over a range of temperatures

   • Short Term
     • Alterations of enzyme effective concentration
     • Alterations to concentration on the subtrate
     • Increased energy supply for enzyme being catalysed
     • Alterations to intracellular environment
   • Mid Term
     • Alterations to isoform
       • e.g. myosin in slow muscle fibres of Common Carp
   • Evolutionary enzyme adaptions
     • Somero (2010) Looked at Enzyme bindng to NADH in limet
       • Found enzyme activity stopped at 42 Degrees
       • Each form could tolerate a different temp
         • Only differed in one amino acid

4. Maintaining membrane stability over a range of temperatures

   • Short Term
     • have to maintain cell structure in order to maintain Membrane structure
       • Done through variation of lipid structure
         • using short, unsaturated fatty acids (more fluid)