Temperature 4: Mechanisms of Thermogenesis Flashcards
how can temperature affect enzyme kinetics (2)
- affects protein structure and function
- as a result, catalytic properties of enzyme are altered
how can the catalytic properties of enzymes be altered by temperature (3)
- changes in weak bonds affect 3D structure
- ionization state of critical amino acids can change within the active site
- ability of enzyme to undergo structural changes for catalysis can be altered
how are biochemical reactions affected by temperature (3)
- accelerated at higher temperatures
- reduced at lower temperatures
- due to Q10 effects
what are Km values (2)
- concentration of the substrate at which half of the active sites of the enzyme are occupied by the substrate
- determines binding capacity/affinity of an enzyme for a given substrate
conservation of Km
- Km values are relatively similar/conserved across animals in a variety of climates
how can ectotherm adapt to long-term changes in temperature
- ectotherms can remodel tissues in response to long-term changes in temperature
ectotherm tissue remodeling: quantitative strategy (2)
- changing the amount of metabolic “machinery”
- eg. increase in the number of muscle mitochondria in low temperature
ectotherm tissue remodeling: qualitative strategy (2)
- alter the type of metabolic “machinery”
- eg. use different myosin isoforms in winter and summer
what happens to proteins at high temperatures (2)
- proteins denature
- accumulation of denatured proteins can kill the cell
heat shock proteins (3)
- molecular chaperones
- catalyze protein folding
- help refold denatured proteins
heat shock response
- increase in the levels of HSP in response to extreme temperatures
what is endothermy intertwined with
- high metabolic rate to maintain heat production
thermogenesis
- metabolic processes that generate heat
what are advantages of high body temperature (2)
- faster enzyme activity speeds up all processes/systems inside body
- organism can respond more quickly to the environment
what are disadvantages of high body temperature (2)
- metabolically expensive
- higher food requirement
what does endothermy require regulation of (2)
- thermogenesis
- heat exchange with the environment
how is heat produced
- as a by-product of metabolic processes
what metabolic processes produce heat (3)
- energy metabolism
- digestion
- muscle activity
both endotherms and ectotherms produce metabolic heat, why do endotherms have high body temperature (2)
- only endotherms have ability to retain enough heat to elevate body temperature above environmental temperature
- endotherms possess futile cycles
futile cycles
- metabolic reactions which sole purpose is to produce heat
shivering thermogenesis: organism (2)
- birds
- mammals
shivering thermogenesis (2)
- uncoordinated myofiber contraction
- results in no gross muscle contraction
shivering thermogenesis: effective time frame
- works for short periods of time
why does shivering thermogenesis only work for short periods of time
- muscles are rapidly depleted of nutrients and become exhausted
when is thermogenesis used in insects (2)
- heat production in insects prior to flight
- insects spend time contracting muscles to generate heat
mechanism of heat production in insects
- carbohydrate metabolism in flight muscles
heat production in insects: flight muscles
- antagonistic flight muscles contract simultaneously
- expend energy and produce heat without movement
heat production in insects: wing movement
- frequency and orientation of the wings are controlled to contract, without generating lift
what are ion gradients used for
- membrane proteins use electrochemical energy from ion gradients to drive transport and biosynthesis
what is done to maintain ion gradients
- ions must be continually pumped because ions leak across membranes
how does ion movement contribute to thermogenesis
- ion-pumping membrane proteins produce heat
how are the plasma membranes different between endotherms and ectotherms (2)
- endotherms have leaker plasma membranes than ectotherms
- endotherms have increased thermogenesis due to ion pumping
brown adipose tissue (2)
- used for shivering thermogenesis
- important for thermogenesis in small mammals and newborns that live in relatively cold environments
where is brown adipose tissue located
- near back and shoulder regions
how does brown adipose tissue differ from white adipocytes (2)
- higher levels of mitochondria (making it brown)
- produces thermogenin protein
what does thermogenin do (3)
- inserts into mitochondrial membranes
- uncouples mitochondrial proton pumping from ATP synthesis
- increases leakiness of membrane, making it harder to maintain proton gradients
what are the characteristics of mitochondria with thermogenin (2)
- high rate of fatty acid oxidation
- more energy is release as heat
internal thermostat: mammals (2)
- information from central and peripheral thermal sensors is integrated in the hypothalamus
- hypothalamus sends signals to the body to alter rates of heat production and dissipation
internal thermostat: birds
- thermostat located in the spinal cord
how can hair/feathers help control heat
- piloerection
piloerection (3)
- hair and feathers act as insulation and fluff up when it is cold
- hair and feathers are pulled perpendicular by smooth muscles (erector muscles) attached at their base
- reduces thermal conductivity
what is the efficiency of insulation by piloerection determined by
- the thickness of the hair/feathers
how can blood vessels help control heat
- vasomotor response
vasomotor response
- altering blood flow to the body surface can change the rate of heat exchange
vasomotor response: cold ambient temperature (2)
- skin arteriole constricts and AV shunt dilates
- blood is directed away from the skin to minimize heat loss from blood at the skin
vasomotor response: hot ambient temperature (2)
- skin arteriole dilates and AV shunt constricts
- blood is directly toward to skin surface to maximize heat loss from blood
vasomotor response: normal body temperature (2)
- maintains tonic constriction of arterioles
- reduces unnecessary loss of heat
vasomotor response: mechanism (2)
- sympathetic nervous system maintains constriction of arterioles
- mediated by α adrenergic signals
countercurrent heat exchangers (2)
- transfer thermal energy from warm arterial blood to cooler venous blood at surfaces where heat exchange can occur
- retains heat away from the heat exchanger surface
nasal countercurrent exchange (3)
- incoming air is humidifies and heated
- outgoing air is condensed and cooled
- recycles and conserves water while preventing heat loss
which animals use sweating
- large animals with low SA:V ratio
how does sweating decrease body temperature
- evaporative cooling
how does NaCl content in sweat help decrease body temperature (2)
- raises heat of evaporation
- greater heat loss than evaporation of pure water
what is sweating controlled by (2)
- hypothalamus
- sympathetic stimulation of sweat glands
how and why does NaCl content change in sweat (2)
- NaCl content decreases in sweat during long exposure to heat
- minimizes ionic and osmotic problems
why is the respiratory surface good at heat loss (4)
- properties that make a respiratory surface good at gas exchange also enhance heat loss
- high vascularity
- moist surface
- high airflow
how can respiration be used to enhance heat loss (3)
- rapid ventilation increases heat loss by convection and evaporation
respiration to enhance heat loss: mammals
- panting
how can respiration be used to enhance heat loss: birds
- gular fluttering
how does panting results in heat loss (2)
- mouth lacks nasal countercurrent exchange system for heat conservation
- mouth is intentionally used to dump body heat
how does panting avoid affecting gas transport over the ventilatory surface (3)
- increased breathing frequency results in small volume of air moving in and out of animal
- each breath ventilates dead space more than alveolar space
- high air flow occurs over nasal mucosa, tongue and other moist surfaces to increase evaporative heat loss without altering gas transport conditions
what is relaxed endothermy (2)
- temporarily lowering basal metabolic rate (BMR) to achieve a hypometabolic state
- relaxes and resets body temperature
relaxed endothermy types (2)
- torpor
- hibernation
relaxed endothermy: torpor
- decrease in body temperature by ~10C to decrease metabolic rate
relaxed endothermy: what animals practice torpor (2)
- small birds
- small mammals
relaxed endothermy: hibernation
- decrease in body temperature by ~20C to decrease metabolic rate
relaxed endothermy: what animals practice hiberation
- small and large mammals
what is the advantage of relaxed endothermy
- saves fuel when food supply becomes limited
