BIOL 4010 Lecture Notes - Lecture 2: Mummichog, Gibbs Free Energy, Cytochrome C Oxidase
2 May 2018
School
Department
Course
Professor
Temperature Adaptation
Overview:
• Scope of problems
• Background - thermodynamics
• What is affected
• Solutions to problems - what can be modified?
• Relation to climate change
*see diagram illustrating temperature ranges for various organisms
Background:
• Extremes:
o Coldest: -89.2C in Antarctica in 1983
o Hottest: hydrothermal vent (400C); Desert in Libya (58C); hot springs (100C)
Complexity and Thermal Tolerance:
• *see slide
• There is a relationship between complexity and ability to adapt to heat (heat tolerance decreases
with increasing organizational complexity)
o Adding higher levels of function and coordination limits functional integrity --> limits set at
highest levels of functional integration
Changing Temperature
• Historically, average global temperatures have cycled (fluctuated) over time
o Overall, atmospheric CO2 has decreased significantly
• The global lows of temperature produced many adaptational changes for organisms, including the
production of antifreeze proteins
Temperature Change with Depth (thermocline):
• Rapid temperature change: e.g. vertical migration through thermocline
• Biomass, light and temperature all decrease with increasing depth in water
o Can be important for animals that vertically migrate (usually diurnally)
o There is little variation at higher depths in the water
• Deep sea animals are less affected
Temperate, Rates & Enzymes
• Temperature affects rates
o In the cold, reactions are slowed (chemical, biochemical, physical)
• Temperature affects equilibria
• Some animals (endotherms) control their body temperature within narrow limits and this gives them
an advantage over animals that don’t (ectotherms)
• Thermal compensation - conservation of rates of respiration
o Fish from different thermal environments (Antarctic - arctic - temperate winter - temperature
summer - tropical) contain similar rates of O2 consumption
• *evolutionary change
Protein Adaptation to Temperature: Roles of Enzymes
• Catalyze vast majority of chemical reactions in the body
• Can be linked to macroscopic processes such as respiration rate, movement..etc
• Easy to measure
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• Huge data base
• As proteins can serve for models for other processes, receptor transporters..etc
• Can relate structure to genome - protein sequence can be related to DNA sequence allowing us to
understand the evolutionary changes needed to adapt enzyme
Temperature Effects on Enzymes:
Protein Property
Sensitivity to Temperature
Primary Structure
Minimal
Secondary Structure
Sensitive
Tertiary Structure
Sensitive
Quaternary Structure
Very Sensitive
Membrane interactions, ligand binding,
catalytic function, regulation
Very Sensitive
Enzyme Function can be Summarized by Two Parameters:
• The rate at which they catalyze chemical reactions
o Frequently measured as Vmax
o Maximal activity of enzyme
o May not function at this rate in vivo
• The binding of substrates
o How strongly bound is substrate, measured as Km
o Km is inversely proportional to the strength of substrate binding
*see slide illustrating relationship between Vmax and Km
Compensation for Low Temperatures:
• Make more enzyme molecules (phenotypic adaptation) - higher enzyme activity in tissue
**energetically expensive
o Ex. Cytochrome oxidase activity: higher in 10 degree acclimated (vs. 30 degree acclimated)
• Activity of lower temperature acclimated group is higher than that of high temperature
group
• Tissue specific response
o Ex. Mitochondrial density in Fundulus heteroclitus
• Mitochondrial density is higher in northern populations --> more cytochrome oxidase
• Make different enzyme molecules
o This is an example of phenotypic adaptation
o Within the lifetime of the individual, different thermal isoforms of the protein can be made
o Ex. New isoforms of contractile proteins in the skeletal muscle are made in carp acclimated
to colder temperatures
• --> LC3 = myosin light chain 3
Constraint: changing the energy content (kinetic energy) affects the rate at which things happen
• *see Maxwell-Botzmann Distribution
o Higher temperatures have a larger fraction of molecules with energy needed to obtain
activational energy
• Therefore, reaction is slower in lower temperatures (harder to attain activational
energy)
• *see Arrhenius Effect
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o As temperature decreases, the rate decreases
o One can change the activational energy (adaptively) to increase the reaction rate at colder
temperatures
• First law of thermodynamics:
o Energy cannot be created nor destroyed (conservation of energy)
o *see slide for equation
• deltaG = Gibbs free energy (convention - negative if energetically favourable)
• deltaH = Enthalpy change (heat content change - heat released or taken up)
• deltaS = Entropy change *sensitive to temperature
o Entropy is important in many biological contexts and systems
• Boltzmann's definition: S = k lnW
▪ k = Boltzmann's constant
▪ W = number of possible arrangements of the particles which compromise the
system
• Therefore, S is large if there are a large number of possible arrangements
• Second law of thermodynamics:
o Entropy of the universe or a closed system cannot decrease (e.g. diffusion)
o Entropy is the degree of disorder of a system
• An ordered system has low entropy
• A disordered system has high entropy
• *important in the role of water
How do thermal isoforms work better at different temperatures?
• *see slide
• Gibbs free energy of activation:
o deltaG+ can be changed (lowered by enzymes to decrease activational energy needed)
o deltaGo cannot be changed
o *see equation
• Functional classes of proteins:
o Orthologous - proteins encoded by a common gene in different species
o Paralogous - proteins are variants on a common protein theme that are encoded by different
gene loci
• Orthologs of Enzymes:
o Enthalpy - how much heat is taken up or released by reaction
• Lower at lower temperatures
o Entropy - how much the order of the system is changed
• Lower (more negative) at lower temperatures
o The activation energy of homologous enzymatic reactions differs across species that have
adapted to different temperatures
• Activation energy is lower in species adapted to colder temperatures
• Enthalpy/Entropy Compensation:
o Enthalpy is lower and entropy is higher (but more negative) at low temperatures
• *see graph on slide
o Higher structural rigidity in warm adapted protein - required more energy (enthalpy) for
conformational change
o Higher negative entropy (more disordered) in cold adapted (enzyme more fluid)
• Due to role of water molecules in protein and function
• Mechanisms for adjusting net stabilization free energies (deltaG) of proteins:
Amino Acid Change
Mechanism of Effect
Adaptation to Cold
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Overview: scope of problems, background - thermodynamics, what is affected, solutions to problems - what can be modified, relation to climate change. *see diagram illustrating temperature ranges for various organisms. Background: extremes, coldest: -89. 2c in antarctica in 1983, hottest: hydrothermal vent (400c); desert in libya (58c); hot springs (100c) Changing temperature: historically, average global temperatures have cycled (fluctuated) over time, overall, atmospheric co2 has decreased significantly, the global lows of temperature produced many adaptational changes for organisms, including the production of antifreeze proteins. Temperate, rates & enzymes: temperature affects rates. *see slide illustrating relationship between vmax and km. Compensation for low temperatures: make more enzyme molecules (phenotypic adaptation) - higher enzyme activity in tissue. Cytochrome oxidase activity: higher in 10 degree acclimated (vs. 30 degree acclimated: activity of lower temperature acclimated group is higher than that of high temperature group, tissue specific response, ex.
