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Lecture 11

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BIOL 370
Dinu Nesan

Lecture 11: Adjusting Metabolism - Hypometabolism is a strategy for reducing energy expenditure in response to adverse environmental conditions o Torpor, hibernation, estivation - Examples can be found in almost all animal orders - Regulation of hypometabolism is multi-part o Hormonal input, reversible phosphorylation, selective transcription - Metabolism: Sum of all processes by which energy is acquired, transformed, and channeled into useful functions to sustain life (energy for growth, reproduction, structural maintenance, & responses to the environment) - Food energy  Metabolizable energy  Fuel metabolic processes (Heat is generated as a waste product) - Metabolic rate = Rate of energy consumption (Energy/unit time) o Determines how much food an animal needs, the total activity of all physiological mechanisms & the pressure on energy supplies in the ecosystem - Respirometry: Measures the animal’s rate of respiratory gas exchange (O c2nsumption & CO produ2tion) o Indirect measurement because it assumes that  Chemical reactions are aerobic (oxidative phosphorylation, not anaerobic glycolysis)  Heat produced with volume of O co2sumed is constant regardless of different types of energy substrate  Oxygen is NOT stored within the body  C6H 12+66O  2CO + 6H 2 + 2220kJ (CO /O = 120 f2r carb, 0.7 for lipids & 0.8 for protein) o Open respiratory: O 2eters @ both ends or with a mask, continuous monitoring o Closed respiratory: Injection of pure O to balance out the colored water movements of manometer 2 - Adjustment of metabolic rate due to environmental factors o Extreme environmental conditions  Disturbances in homeostasis  Decrease in T A Increase in thermogenesis & metabolism  Constant T B o Animals that enters hypometabolic states can alter T Bet point at thermostat center “pre-optic anterior hypothalamus” – Recalibration, defend low T iBstead of compensates  Decrease in T A Decrease in thermogenesis & metabolism  Decrease T B - Hypometabolism “Hypoxic Metabolic Suppression” o Reduce metabolic rate below basal metabolic rate “normal” o Establishment of a new, lower energy expenditure set point (Energy expenditure < Intake + Stores) o Allows the animal to survive adverse environmental conditions o MR depression varies in duration, magnitude (up to 95% decrease) & physiology - Types of Hypometabolism o Torpor (Daily heterothermy  switchers from poikilothermic & homeothermic)  Few hours, depresses metabolic rate due to temperature effects (Lower T atAnight)  E.g. Rufous hummingbird (heart rate drops from 1000bpm to 80bpm)  Torpor onset when temperature drops below 8⁰C, little energy needed to maintain T , B much less O 2onsumption than normothermal T B o Hibernation (over-winter)  Metabolic rate can be suppressed to 2-5% of basal metabolic rate  E.g. Underwater hibernating turtle (180days) uses the same amount of ATP to normoxic turtle at 20⁰C (1day)  E.g. Freezing frogs, up to 65% of body can be converted to ice, can allow the body temperature to drop below freezing, no evident metabolism o Estivation  Similar to hibernation, but in response to hot conditions  E.g. Kangaroo rat, lower MR at high temperature with low food availabili2y, O consumption reduced by 50-75% - Hypometabolic Phenotypes o Lowered body temperature o Reduced heart rate o ↓ respiration, O2consumption, blood flow, movement & cellular activity - Metabolic rate is reduced REGARDLESS of TB o Reversible protein phosphorylation o Neurotransmitters (Serotonin, histamines, opioids) o Selective transcription/translation of genes during hibernation in selected tissues o Fatty Acid utilization  During hypometabolism, FAs are the preferred fuels, oxidation yields maximum energy (555000kJ) & they have higher storage capacity (37g) than carbohydrates (16g) - Hibernation in Bears o TBdecrease by 1-5⁰C (33-75% decrease in VO2), heart rate drops (40bpm  8-10bpm), loss of 16-37% body mass (almost all are adipose tissues) o However metabolic rate is similar to other hibernatorB, T only decreases slightly, the thermal neutral zone is high (~30⁰C) due to higher body mass, and they are easily aroused Lecture 12: Metabolism - Metabolism is a critical function for animals, necessary for a variety of different tasks - Animals mobilize food differently depending on their lifestyle needs o Measured via different methods, can calculate RQ o Metabolic transitions are controlled by hormonal input - Cost of transportation is a large part of metabolic rate o Understand the differences and reasoning behind Metabolic rate vs. Mass-specific Metabolic rate - Catabolic: Molecules break down & Anabolic: Molecules builds up o Physiologically dynamic processes require energy from metabolism - Specific Dynamic Action (SDA): Increase in metabolic rate caused by ingestion of food o Larger meal or More protein = larger SDA (Short term phenomenon) o Diet-induced thermogenesis (Long term phenomone) - Measure Metabolic Rates o Basal Metabolic Rate: Homeotherms, within thermoneutral zone, while fasting/resting o Standard Metabolic Rate: Poikilotherms while fasting/resting (Differs depending Bn T ) o Routine Metabolic Rate: MR of routinely quiet animals with only small, spontaneous movements o Field metabolic rate: MR of animals in its free-living natural state o Metabolic scope: Range in metabolic rate from Basal to Maximum - Methods for measuring metabolic rates o Respirometry: Measures gas exchange (O 2ntake & CO 2xpiration)  Indirect o Calorimetry: Direct thermal measurement of heat production o Mass-balance Measurement: Measures food intake & waste output (energy intake/time) - Locomotion (Moving from 1 place to another) o Mode of locomotion is constrained by the environment “aquatic, aerial, terrestrial” o Sensory system receives information  CNS  Motor neurons  Muscle contraction o Cardiovascular & Respiratory & Digestive system  ↑ Blood flow (Metabolites & 2 ) - Muscle Energy Metabolism requires A LOT of ATP o Myosin head connected to actin filament without ATP o ATP binds to Myosin head, it loses affinity for actin & is removed from the actin filament o DNA hydrolysis (ATP  ADP + P) causes myosin to extend towards the +ve end of the actin filament o After the removal of P, myosin head binds to actin filament  power stroke towards the +ve end  Ac+in+myosin ATPase: Cross-bridge cycling  Na /K ATPase: Re-establishment of ion gradients  Ca ATPase: Required to transport Ca into the Sarcoplasmic Reticulum - Pathways for ATP production
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