Lecture 4 - Thermal Biology & Ectothermy 2023 PDF

Biology 2601: Organismal Physiology Lecture 4: Principles of Thermal Biology & Ectothermy 2 Temperature • Temperature sets limits on where organisms can live and function • Some key questions in physiology and biology are related to temperature • Temperature is a key theme in this course infrare...

Biology 2601: Organismal Physiology Lecture 4: Principles of Thermal Biology & Ectothermy 2 Temperature • Temperature sets limits on where organisms can live and function • Some key questions in physiology and biology are related to temperature • Temperature is a key theme in this course infraredimagingservices.com But what is Temperature? Temperature A measure of the speed or intensity of the incessant random motions that all the atoms and molecules of any substance undergo on an atomic-molecular scale. More exactly, the temperature of a substance is proportional to the product of the mean square speed of the random molecular motions and the molecular mass. 3 Temperature Heat • Temperature ▫ Intensity of motion by the atoms in an object • Heat ▫ Amount of energy in the object • Temperature determines the direction of heat transfer ▫ Warm -> cool 4 5 Heat exchange with the environment 6 Plants can affect their leaf temperature • Latent heat of vaporisation of water: 2270 kJ/kg Low transpiration High transpiration James Morison, Essex • Transpiration is a very effective way to cool if you have water 7 Definitions: (animal) thermal biology • Endotherms • Ectotherms • Homeotherms • Poikilotherms • Heterotherms • Regional endothermy/ heterothermy • Rely mostly on external temperatures to determine Tb • Different Tb in different parts of the body • Defend a constant body temperature • Allow body temperature to vary • Generate internal (metabolic) heat • Have more than one temperature set point, or switch between homeo- and poikilothermy 8 Keep body temperature the same? yes no Alternative view of HWA Fig 10.1 Generate internal heat? yes no Ectotherms Endotherms Poikilotherms Homeotherms These are not always mutually exclusive, and some organisms (heterotherms) can switch between them 9 Relationship between temperature and metabolism in an ectotherm Tiger moth caterpillar M=a10nTb 10 Metabolic Rate nT M=a10 b a & n are constants Tb is Body Temperature 11 logM=log(a) + nTb Intercept = log(a) M Slope = n Tb 12 Q10- The Temperature Coefficient • The ratio of the rate of a process at one temperature over the rate of the same process at a temperature 10°C lower Q10 = RT R(T-10) HWA Eqn 10.7 13 Q10 Because the temperature-metabolic rate relationship is not exactly exponential, the impact of a change of temperature varies with temperature 14 Q10 The same relationship with Q10 holds true for plant functions like respiration Way and Sage, 2008 Q10 15 • ≈1 for many physical/chemical processes for.gov.bc.ca • ≈2-3 (or higher) for most biological processes 16 How does temperature cause metabolic change to occur? • Temperature determines motion of molecules, and therefore the rate at which they encounter one another ▫ More interactions = more reactions • Temperature also determines the conformation and efficiency of enzymes (Q10≈2-3 in biological systems) ▫ Most enzymes have a temperature optimum 17 mind42.com Basic enzyme function • Enzymes bind substrates and facilitate chemical reactions • Binding is determined by 3D structure of enzyme 18 Reaction Rate Vmax = maximum rate of reaction Vmax 50% Vmax Km Km = Amount of substrate required to reach 50% of Vmax. [substrate] mM Kcat = no. molecules of substrate processed per unit time at saturation 19 Protein (enzyme) structure depends on temperature E.g., Frataxin The enzyme’s active site can change shape with temperature, leading to a change in binding affinity for substrate, and therefore rate of reaction Camilloni, C., Bonetti, D., Morrone, A., Giri, R., Dobson, C.M., Brunori, M., Gianni, S., Vendruscolo, M.: Towards a structural biology of the hydrophobic effect in protein folding. Sci. Rep. 6 (2016) 20 HCA use “Enzyme-substrate affinity” (≈1/Km) High Km = low affinity Low Km = high affinity 21 How does enzyme –substrate affinity change with temperature? e.g., Lactate Dehydrogenase in the Goby Fish Normal ‘operating’ temperature HCA Fig. 10.20a 22 How does enzyme –substrate affinity change with temperature? Affinity too high: enzyme binds too tightly to substrate = slow reactions Affinity too low: enzyme binds substrate too loosely = reactions less likely to happen HWA Fig. 10.20a Adaptation vs Acclimatization (HCA – Glossary) Adaptation ‐ In evolution, a genetically controlled trait that, through the process of natural selection, has come to be present at high frequency in a population because it confers a greater probability of survival and successful reproduction in the prevailing environment than available alternative states. Altered genome Acclimitization ‐ A chronic response of an individual to a changed environment in cases in which the new and old environments are natural environments that can differ in numerous ways, such as winter and summer environments, or low and high altitudes. A form of phenotypic plasticity. Altered expression of genome 23 Adaptation across species: LDH from the tropics to the poles ‘Physiologically relevant’ substrate affinity Blue line denotes normal range of body temperature for each species 24 Adaptation among closely-related species 25 Acclimatization: In the field https://besidethefrontdoor.com/ Sun vs Shade https://www.pbase.com/ Summer vs Winter 26 Acclimation: Acclimatization In the lab Organism‐level measure: Respiration rate Sub‐cellular level: Organelle and/or enzyme abundance 27 Acclimation: Acclimatization In the lab e.g. cool- versus warm-grown plants Warm-grown Cool-grown Cool-grown Warm-grown Way and Sage, 2008 28 Compensation Maintain performance in the face of varying conditions • Requires a shift away from the acute response • Plasticity on the order of hours to days to weeks 29 Lake Erie Water Temperatures Temperature (°C) Temperature (°C) 25 20 15 10 5 0 Jan Jan feb Feb Mar Mar Apr Apr MayJun May Jun Jul Jul AugSep Aug Sep Oct Oct NovDec Nov Dec Month Month 30 Without compensation, metabolic rate changes with the environment High metabolic rate Temperature (°C) Temperature (°C) 25 20 15 10 5 0 Low metabolic rate Jan Jan feb Feb Mar Mar Apr Apr MayJun May Jun Jul Jul AugSep Aug Sep Oct Oct NovDec Nov Dec Month Month 31 After compensation: shape of response curves are modified High metabolic rate 20 15 10 MR Temperature Temperature (°C)(°C) 25 5 0 Low metabolic rate Jan feb Mar AugSep Jan Feb Mar Apr Apr MayJun May Jun Jul Jul Aug Sep Oct Oct NovDec Nov Dec Month Temperature Month 32 How can compensation work? Change enzymes in a pathway • • • • Amount of enzyme Version of enzyme (Isozyme) Covalent modification – e.g. phosphorylation Change the enzyme’s environment (pH, substrate availability, membrane lipids) 33 How compensation works: Changing the abundance of an enzyme will alter the rate at which a pathway can function Higher amount of enzyme to compensate for reduced efficiency at lower temperature 34 How compensation works: Matching enzyme isoform expression to environmental conditions. According to Wikipedia… “isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. different KM values), or are regulated differently. They permit the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage.” 35 Acetylcholinesterase Acetylcholine -----------------> Acetate + Choline Antarctic icefish (-2 °C to 6 °C) No compensation Km (1/affinity) 10 8 6 Km increases, affinity decreases Less able to bind substrate Reaction slows, then stops 4 2 0 0 10 20 30 40 Temperature, °C 36 Rainbow Trout (2°C to 24°C) Km (1/affinity) 10 8 2°C 6 4 2 0 0 10 20 30 40 Temperature, °C 37 Rainbow Trout (2°C to 24°C) Full compensation Km (1/affinity) 10 8 2°C 6 18°C 4 2 0 0 10 20 Temperature, °C 30 40 Preservation of function by preservation of Km 38 How compensation works: Changes in an enzyme’s microenvironment can change its activity and will alter the rate of the reaction • pH • substrate availability • lipid environment 39 Phospholipid membrane changes contribute to compensation • Homeoviscous adaptation • Maintain the same viscosity across temperatures • Short chain lengths increase fluidity • Incorporating double bonds increases fluidity • Changing head groups changes fluidity (e.g. phospoethanolamine increases, while phosphocholine decreases) Butter Olive Oil Sunflower Oil 4:0‐12:0 14.1 ‐ ‐ 14:0 11.0 ‐ ‐ 16:0 30.0 18:0 11.3 18:1 25.0 18:2 11.0 ‐ ‐ ‐ 75.5 21.2 8.5 67.0 40 Phospholipid membrane changes contribute to compensation 41 Going with the flow is better in some places than others Are ectotherms passive victims of their thermal environments? 42 Behavioural thermoregulation • Microhabitat choice (sun exposed, shaded, burrows etc) allows lizards to maintain more stable body temperature 43 Behavioural thermoregulation Drought‐stressed corn • Rolling leaves and pointing them vertically reduces sun interception, saving water 44