biob34 Flashcards
What is animal physiology?
The study of how animals work (function)
Integrated function
The August Krogh principle
For every biological problem, there is an animal on which it can most conveniently be studied
Physiological processes governed by:
Laws of chemistry, governed by:
Laws of physics
Mechanical theory is useful (helps understand locomotion, cell motility muscle function, skeletal dynamics)
Laws of electricity apply (help understand excitable cells, membrane potential, neural circuits)
What makes a metazoan (an animal)?
Metazoans are eukaryotes
Distinguished from prokaryotes
metazoans are multicellular
But not all eukaryotes are multicellular
Multicellularity evolved several times independently
Exposure to a changing environment
Exposure to a changing environment
Food sources
pH
Temperature
Oxygen
toxins/waste products
single cell
Direct interaction with environment
Multi-celled animals
no/few cells directly exposed to environment
“Environment” of cells is the interstitial fluid
Defense (maintenance) of environment cells exists in = homeostasis
Defended by:
Behavior
Multiple tissue/organ systems
temperature, body size
More cells ≈ bigger size (a big cell or many cells)
More control over internal environment (simple organs will have fewer cell types so less tissues)
Digesting large meals
Control of metabolites, ions
Over temperature
microbiome/symbionts(?)
Size and temperature impact almost every physiological function
enzyme activity vs. temp
As the temperature goes up, the enzyme works faster. It reaches its peak performance at a specific temperature, known as the enzyme’s optimum temperature. If the temperature keeps rising after this point, the enzyme starts to lose its effectiveness quickly because its active site, where the reaction happens, gets damaged.
Scaling relationships
Some things are function of volume
Total metabolic rate
Total heat production
Some things are function of surface area (across the surface)
Respiration
Absorption, expulsion
Balance heat production (internal) and heat loss/gain (to/from external environment)
If resting animal cells (regardless of animal size) had a similar metabolic (i.e. heat production) rate, larger animals would have relatively less and less surface area for dissipating extra heat
complexity and specialization
Multicellularity permits divisions/distinctions
Of cell types
Of tissues
Into organs and organ systems
`Physiological phenotype is product of genotype and environment
Phenotype may change
Phenotypic plasticity (daphnia in clean water vs. in chemical water that smells like predator (formed a spike to help protect from predator))
Ontogenetic changes (tadpoles)
Reversible: acclimation (in response to controlled variable)/acclimatization (acclimatization)
What makes a metazoan (an animal)?
All animal species can utilize sexual reproduction
Some animals can utilize asexual reproduction
Sexual vs. asexual reproduction
Sexual reproduction enables greater genetic variation across generations
This greater variation might make some individuals better suited if climate/ecosystem changes
I.e. could enhance chance of survival for species
If sexual reproduction is so great, why do some animals use asexual reproduction?
Genetic variability of sexually-produced offspring may mean some in a “litter” possess better “adapted” genes than others in that litter
Asexual reproduction makes(potentially many) clones of a individual
energy, work, power, metabolism, metabolic rate
Energy: the capacity to do work
Work: the transfer of energy by a force acting on an object as it is displaced
Power: the rate at which work is done
Metabolism: the set of processes by which cells and organisms acquire, rearrange, and void commodities (e.g. elements or energy) in ways that sustain life
Metabolic rate: an animal’s rate of energy consumption; the rate at which it converts chemical-bond energy to heat and..work
So metabolic rate is a measure of power
What is animal physiology?
Metabolism is cellular, biochemical… integrates up to whole animal metabolism/metabolic rate
Metabolic pathways
Series of reactions that convert substrates to products
Catalyzed by enzymes
Synthesis (anabolic) (construct large macromolecules)
Degradative (catabolic)
Metabolic pathways are linked by intermediates
Metabolism-sum of metabolic pathways for the synthesis and breakdown of molecules
Cells store energy in 2 main forms
Reducing energy
High energy bonds (covalent bonds, ATP)
Mostly happening in us is catabolism
High energy bonds
Energy can be “stored” in covalent bonds
Energy is released when bonds are broken
ATP is the most common “high energy” molecule
Carbohydrates
“Hydrates of carbon”
Many hydroxyl (-OH) groups
Glucose is the most common carbohydrate in animal diets
Energy metabolism
Biosynthesis-precursor to many other carbohydrates
Monosaccharides
Used for energy and biosynthesis
Small carbohydrates have three to seven carbons- six is most common
Complex carbohydrates
Polysaccharides
Long chain of monosaccharides
Energy storage
Example: glycogen, scratch (bread), insulin (diet bars: making you fuller since we dont have the enzymes to digest)
Structural moecles
Chitin, hyaluronate, cellulose (in plants)
Amylose +amylopectin = starch
Glycogen metabolism
Main carbohyrdtae storage form in animals (vertebrates)
Glycogen synthesis (glycogensis)
Glycogen breakdown (glycogenolysis)
Note reciprocal regulatory enzymes which act on glycogen synthase or glycogen phosphorylase
Glucose breakdown (glycolysis)
Produces reducing equivalents
Releases energy
Glucose + 2ADP + 2NAD -> 2ATP + 2 pyruvate + 2NADH + 2H
Takes place in cytoplasm
Does not require oxygen
Produces intermediates for synthesis of various molecules
Carbohydrates, nucleic acids, amino acids, and fatty acids
End product, pyruvate, can be used in further catabolic processes
First half is endergonic (the cell invests 2 ATP to provide activation energy by phosphorylating glucose)
Second half is exogenic cuz the energy is being released (4 ATP are produced and NAD+ is reduced to NADH by electrons released by the oxidation of glucose)
Oxidation of pyruvate in the presence of o2
Glycolysis
Converts carbohydrates to pyruvate within the cytoplasm
Lactate and amino acids can also be converted to pyruvate
Pyruvate is carried into the mitochondria
Pyruvate dehydrogenase (PDH)
Pyruvate is oxidized by PDH to form acetyl CoA + NADH
Oxidation of NADH in the presence of o2
Glycolysis can only continue if NADH is oxidized to NAD+
Two “redox shuttles” carry reducing equivalents from cytoplasm <-> mitochondria
Alpha-glycerophosphate shuttle (typically seen in invertebrate metazoans)
Malate-aspartate shuttle (in vertebrates)
Oxidation of NADH in the absence of o2
NADH cannot be used rapidly by mitochondria when oxygen is not present
NADH is oxidized in the cytoplasm
Buildup of NADH (in cyto) means drop in [NAD+]
This would inhibit glycolysis (since NAD+ is an important substrate)
Pyruvate + NADH + H <-> lactate +NAD+
Catalyzed by the enzyme lactate dehydrogenase (LDH)
Also reversible
Other anaerobic pathways form less toxic end products and more ATP than lactate (2 ATP)
Ex. succinate (4 ATP) and proprionatte (6 ATP)
More common in invertebrates (we can’t make these compounds)
Lipids
All are hydrophobic (don’t dissolve in water)
Carbon backbone
Linear-aliphatic
Ring-aromatic
Ex. fatty acids, triglycerides, phospholipids, steroids (ringed structure)
Lipids are used for energy metabolism, cell structure (e.g. membranes), and signaling
Fatty acids
Chain of carbon atoms ending with a carboxyl group
Usually an even number of carbons
Saturated: no double bonds between carbons (straight chain)
Unsaturated: one or more double bonds between carbons
Fatty acid oxidation (beta-oxidation)
Fatty acids are more dense form of energy storage than carbohydrates (not as many carboxyl groups)
Water associated with carbs, not with oils/fats
More reduced form of carbon
Take more o2 (more oxidation) to unlock energy
No significant anaerobic ATP production possible
Breakdown of fatty acids
Beta oxidation
Takes place in mitochondria
Results in formation of acetyl CoA
Acetyl CoA is then oxidized
Ketones
Made from acetyl CoA
Some tissues cannot metabolize fatty acids, but they can metabolize ketones
For example, vertebrate brain, shark muscle
Ketogenesis
Fatty acids converted to acetyl CoA
Acetyl coA converted to ketones
Ketone bodies can move through circulation
Ketolysis
Ketones are broken down to acetyl CoA
Which can then participate in oxidation phosphorylation
Ketogenesis: the production of ketone bodies from fatty acids, typically in the liver; generate energy when glucose is low or during fasting; fatty acids are converted into acetyl-CoA, which is then converted into ketone bodies(β-hydroxybutyrate)
Ketolysis: the breakdown or utilization of ketone bodies for energy; provides energy for the brain, heart, and other organs when glucose is low; ketone bodies are converted back into acetyl-CoA, which enters the TCA cycle to produce energy
Mitochondrial (oxidation) metabolism
Energy-yielding reactions that require oxygen
Enzymes convert nutrients into metabolites
Metabolites enter mitochondria
Many metabolites are converted to acetyl CoA
Acetyl CoA enters the tricarboxylic acid cycle (TCA or Krebs cycle)
Acetyl CoA is oxidized to form reducing equivalents
Reducing equivalents are oxidized to release energy
O2 is final electron acceptor
Oxidative metabolism
Cellular respiration: glucose and other energy sources enter the cell
Glycolysis: glucose is converted into pyruvate, producing a small amount of ATP and NADH
Krebs: pyruvate is converted into acetyl CoA which enters the Krebs cycle producing more ATP, NADH, and FADH2
Electron transport chain (ETC): electrons from NADH and FADH2 are passed through a series of protein complexes, generating a proton gradient
Oxidative phosphorylating: the proton gradient drives the production of ATP through the process of chemiosmosis
We are in mitochondria
Tricarboxylic acid (TCA) cycle
Generates reducing equivalents within the mitochondria
Acetyl coA + 3NAD+ + GDP + P + FAD -> 2CO2 +3NADH +FADH2 +GTP
GTP, NADH, CO2 and FADH2 are generated
Amphibolic pathway
Some intermediates are broken down (catabolic)
Some intermediates are used for syntheses (anabolic)
Oxidation: Isocitrate is oxidized to form α-ketoglutarate, producing NADH
Decarboxylation: α-Ketoglutarate is converted into succinyl-CoA, producing NADH and CO2.
Succinyl-CoA is converted: Into succinate, producing GTP (similar to ATP).
Succinate is oxidized: To form fumarate, producing FADH2
Electron transport system (ETS)
Electrons from NADH and FADH2 are transferred to the ETS
Found within the inner mitochondrial membrane
Composed of four multisubunit proteins (complexes 1,2,3,4) and 2 electron carries (ubiquinone and cytochrome c)
Oxidation: 4e +4h + o2 -> 2h2o
Generates a protein gradient, heat, water, and reactive oxygen species (ROS)
ATP synthesis
Phosphorylation: ADP + P = ATP
Proton motive force (Δp): pH gradient and the membrane potential
f1f0ATPase uses energy in Δp to produce ATP
There is no physical linkage between oxidation and phosphorylation
Two processes are functionally coupled through Δp
F1: the catalytic subunit, responsible for binding ADP and Pi (inorganic phosphate) and releasing ATP
Fo: the membrane-embedded subunit, responsible for proton transport and driving the rotation of the stalk that connects F1 and Fo
Proton flow: Protons flow through the Fo subunit, causing the stalk to rotate.
Conformational change: The rotation of the stalk induces a conformational change in the F1 subunit.
ADP binding: ADP binds to the F1 subunit.
Phosphorylation: Pi binds to the F1 subunit, and the energy from the conformational change drives the phosphorylation of ADP to ATP.
ATP release: The newly synthesized ATP is released from the F1 subunit.
Phosphocreatine
Alternative high-energy phosphate compound
Creatine + ATP <-> ADP + phosphocreatine (this reaction is catalyzed by the enzyme creatine kinase)
Creatine phosphokinase (CPK)
Reaction is reversible so relative rate of ATP vs phosphocreatine production depends on ratio of concentration of substrates/products
Phosphocreatine can also move throughout cell (like ATP)
Thus, it can enhance flux of high-energy phosphate molecules from site of synthesis (e.g. mitochondria) to site of hydrolysis (e.g. muscle sarcomeres)
Integration of metabolic pathways
Fluctuations in nutrient availability, energy demand, and environmental conditions (animals are going to have a period of time where there is a net influx of glucose cuz u just ate a big meal and you can take that glucose and fructose up into tissues and turn into glycogen in muscle cells, oxidize it into co2 in your nerve cells to sustain ongoing brain function or turn it into lipids in liver and saved for later)
Reciprocal regulation avoids simultaneous synthesis and degradation (futile cycles)
Use of appropriate metabolic “fuel”
Carbohydrate vs. lipid
Energetic intermediates regulate balance between anabolism and catabolism
Measuring metabolic rate: 31P-NMR spectroscopy
Measures ATP turnover
Detects change in NMR spectra as p groups shift between ATP and inorganic phosphate
Pros:
Measures cellular energy currency
Accounts for aerobic, anaerobic metabolism, etc
Accurate over extremely short time scales
E.g. a single muscle contraction
Cons:
Logistically difficult
Subject must be restrained, possibly anesthetized
Equipment not portable and complicated
Hess’s law
Total amount of energy released (eventually as heat) for breakdown of given amount of fuel always the same
Regardless of intermediate chemical steps (e.g. particular ATP synthesis pathways)
Measuring metabolic rate: direct calorimetry
Calorimetry: measurement of heat of chemical/physiological processes (unit can be ‘calorie’)
Pros:
Quite accurate under many conditions
Accounts for aerobic and anaerobic energy production
Cons:
Subject must be restrained
Equipment heavy and complicated
Makes assumptions about anabolic vs. catabolic activity
Animals held in central chamber surrounded by 2 concentric chambers filled with ice or ice water
Exterior of the 2 is to buffer influx of heat from outside
Melts ice, but inner edge stays ice cold
Interior of the 2 melts die to animal heat production only
Water collected, volume measured
If we know how much heat it takes to melt a given amount of ice:
Calculation of metabolic rate
Respiratory quotient
Type of fuel being used can be monitored by measuring the RQ (similar to respiratory exchange ratio-rer)
Respiratory quotient (RQ) = rate of co2 production/o2 consumption
What is actually used/produced by mitochondria?
RQ
=0.7 for lipids
=1.0 for carbohydrates
≈0.85 for proteins
Under many circumstances, catabolism of protein is negligible
RQ can directly reveal ratio of carb/fat oxidation in such cases
RER is measured at respiratory interface (actual breathing animal)- can be ‘uncoupled’ from what happening at mitochondria
Measuring metabolic rate: indirect calorimetry
Indirect calorimetry
Inferring metabolic heat production
E.g. through respiratory gas exchange-respirometry
pros:
Relatively user-friendly and easy
Equipment can be portable
Can be very accurate if assumptions met
Can be easily used on active animals
Cons
Dependent upon certain assumptions
Aerobic metabolism only
E.g. known relationship between o2 (or co2) and atp
Must sample gasses effectively
All revant gasses, limit leaks
Animal ‘tied’ to equipment, at least
RQ and ATP turnover
If the relative amounts of o2 and co2 consumed and produced, respectively, differ depending on which fuel is being oxidized
Does # of ATP produced per unit molecular o2 consumed vary as well? Yes
How does the ATP/O stoichiometric relationship vary with fuel type? The ATP/O stoichiometric relationship, also known as the P/O ratio, represents the number of ATP molecules generated per oxygen atom consumed during cellular respiration. This ratio varies depending on the fuel type (substrate) being metabolized.
Chamber respirometry: closed system
Animal enclosed in chamber
Pros (you know the air is from the inside)
Easiest approach
More sure that all expired gases accounted for
More accurate
Quality of air provided (environment) easier to control
Cons
Animal-constrained, less natural behavior
Risk of asphyxiation if o2 levels get too low, CO2 level gets too high
Can be messy
Animals may do all their functions in chamber
More accurate with longer time scales
Activity state must be known for consent
Switching between rest and activity complicates calculations
Mask respirometry
A variant of flow through chamber respirometry in which the chamber only covers the month/nose/head
Pros: small volume, faster flow rates mean even greater temporal resolution; animal can behave nearly naturally
Cons: poorer signal to noise raion; composition of gasses hardware to control; must assume gas concentrations in surrounding ambient air
Energy and changes in activity state
There is not necessarily instantaneous matching between ATP turnover rate and rate of fuel (carb, fat, o2) delivery to, or supply in, the cell
For example, in muscle cells, as we transition between rest and activity, the maintenance of [ATP] occurs via activation of three pathways, each with different kinetic
O2 consumption and metabolic rate
O2 consumption/co2 production measured at the respiratory interface with the environment (e.g. mouth/nose, gills, etc) does not reflect instantaneous 02 consumption/co2 production in tissues
Nor does it necessarily reflect totality of ATP turnover-even if, integrated through time, all ATP turnover is essentially aerobically powered
For example, during transition between exercise (high ATP turnover rate) and rest (low ATP turnover rate), there can be offset in tissue level o2 consumption or metabolic rate, and VO2
O2 consumption and metabolic rate
O2 consumption can remain high after returning to lower activity level as muscle glycogen stores are replenished and anaerobic end products (e.g.lactate and creatine) are dealt with, using aerobic metabolism
Lactate
Cori cycle: used in gluconeogenesis in liver (glucose returned to rise rebuild glycogen)
Lactate shuttle: used as substrate (via conversion -> pyruvate -> acetyl coA) in oxidative phosphorylation in aerobic tissue
Creatine
Rebuilding phosphocreatine at expense of ATP (now largely being generated aerobically)
O2 consumption, metabolic rate, and diving
O2 consumption (at ventilatory tissue) may not be possible
Diving animals must cease/dramatically reduce exchange of o2/co2 with environment
hypoxic/hypercapnic environment can pose similar challenges
There can be compensatory hyperventilation
Recover o2
“Blow off” stored co2
Uncoupling of RER from RQ
Metabolic rates: some definitions
Basal metabolic rate (BMR)
Metabolic rate of homeothermic animal at rest (typically quiescent phase), post-absorbive, at a temperature within thermal neutral zone
Homeotherms only
Standard metabolic rate (SMR)
Same as BMR, except for poikilothermic animals, at a defined environmental temperature
Poikilotherms, only
Resting metabolic rate (RMR)
Metabolic rate of animal at rest under defined conditions
Not necessarily during quiescent phase, or totally post-absorptive, or with TNZ
Maximum aerobic metabolic rate (VO2max)
Maximum sustainable VO2
Such as:
During intense aerobic exercise
When homeotherm is exposed to very cold temps
Supramaximal metabolic rate
Burst only
Field metabolic rate
The actual, recalIed metabolic rate of an animal behaving naturally in the wild
Daily energy expenditure
Total energetic cost of a day of life
Not a metabolic rate, and energy amount
Useful for considering ecological, survival, etc
Why scaling exponent <1 for BMR in mammals?
BMR is metabolic rate of maintenance function in homothermic animal
Perhaps maintenance of body temperature is paramount (match body heat production rate to rate of heat loss)
Rate of heat production should be a function of volume
The size of all the cells consuming energy and producing heat
Rate of heat loss should be a function of surface area
Scaling exponent for BMR in mammals
Actually, surface area scales with an exponent of 0.63
In some cases, BMR scales with similar exponent comparing within a species
Surface area to volume scaling relationship should affect a lot more than just heat balanced. E.g
Gas exchange
Across respiratory surface, but needed by a column of tissue
Nutrient absorption
Across gut surfaces, but used by all tissues in volume
But BMR scales interspecifcally with an exponent closer to 0.75
And, this scaling exponent seems to hold for more than just mammals
E.g. comparing BMR or SMR
Different groups have different scaling coefficients
Thermal energy
influences chemical interactions that affect macromolecular structure and biochemical reactions (physical process)
Thermal strategy
Behavioral, biochemical, and physiological responses that ensure temperature (TB) is within an acceptable limit
Ambient temperature (TA)
Temperature of the animal’s surroundings
Most important environmental influence on animals’ thermal strategy
Animals must be able to survive thermal extremes and thermal changes specific to their environment
Two major thermal strategies:
Tolerance: body temperature is allowed to vary with ambient temperature (save energy)
Regulation: body temperature does not vary with ambient temperature (higher cost to stay warm)
Both strategies have costs and benefits
Heat fluxes
Body temperature is a reflection of the thermal energy of the molecules in the body
Thermal energy can move from the animal to the environment or vice versa
Thermal energy moves “down” a temperature gradient
There are many sources and sinks of thermal energy
Total thermal energy
total = metab + conduct + convec + rad + evap
Convection
Transfer of thermal energy between an object and an external medium that is moving
Rate of heat exchange depends on:
The thermal gradient
The rate of flow of the fluid
The conductivity of the fluid
Radiation
Emission of electromagnetic radiation
The most important source of radiant heat is the sun
Basking: darker colors enhance heat absorption
Evaporation
Water molecules absorb thermal energy from a surface when making the transition from liquid to vapor
Evaporative cooling
Magnitude of heat loss depends on the volume of water and heat of vaporization
Salt increases the heat of vaporization (makes it an effective cooling method)
Conduction
Transfer of thermal energy from one object or fluid to another
Heat flux (Q)
Rate of heat transfer (from hotter to colder)
Conduction
Thermal conductivity varies with the type of material and is affected by geometry
water has very high thermal conductivity
Insulation
Layer of material that reduces thermal exchange
Internal insulation (under the skin)
Blubber
External insulation (on the body surface)
Hair, feathers, air, water
Effectiveness of insulation depends largely on its thickness
Surface area to volume ratio
Influences all aspects of heat exchange
Large animals exchange that more slowly than small animals
Bergmann’s rule
Animals living in cold environments tend to be larger (favor surface area for heat)
Allen’s rule
Animals in colder climates have smaller extremities (not really true)
Behavioral adjustments
Body posture can alter exposed surface area
Huddling behavior reduces effective surface area
Thermal strategies
Relative stability of body temperature
Poikilotherm (variable body temperature)
Homeotherm (stable body temperature)
Thermal strategies
Source of thermal energy
Ecotherm: environment determines body temperature
Endotherm: animal generates internal heat to maintain body temperature
Most animals best described by a combination of terms
Temporal and regional endothermy
Hypometabolic phase accompanied by a decrease in body temperature
E.g. hibernation, torpor (flexible)
Metabolic energy that would normally be used for thermoregulation is saved
Time course differs among animals and types of dormancy
Torpor: usually less than a day
hibernation/estivation: longer
Homeothermy is relative
Circadian rhythm evident in metabolic rate, body temperature
Animal breeding is big business: important to know when fertilization is possible
Can be tracked in hormones (costly)
Solution: easier way of tracking fertility
Metabolic rate and body temperature vary with reproductive cycle
Unsurprisingly, there is a general relationship between body size and the magnitude of these daily fluctuations
Thermal zones of homeotherms
Thermoneutral zone
Optimal range for physiological processes; metabolic rate is minimal
Upper critical temperature (UCT)
Metabolic rate increases as animal induces a physiological response to prevent overheating
Lower critical temperature (LCT)
Metabolic rate increases to increase heat production
Animals differ in the width of their thermoneutral zone, UCT, and LCT
Thermal tolerance of poikilotherms
Poikilotherms do not have a thermoneutral zone, UCT, or LCT
Preferred temperature
ambient/body temperature for optimal physiological function
Incipient lethal temperature
Ambient temperature at which 50% of animals die
Incipient upper lethal temperature (IULT)
Incipient lower lethal temperature (ILLT)
Thermal tolerance of animals
Eurytherm
Can tolerate a wide range of ambient temperature
Stenotherm
Can tolerate only a narrow range of ambient temperatures
Eurytherms can occupy a greater number of thermal niches than stenotherms
Temporal and regional endothermy
Regional heterotherms
Body temperature varies in regions of the body
Billfish heater organs near eyes
Thermogenesis by ion pumping
Ion gradients degrade for 2 main reasons
Membrane proteins use electrochemical energy to drive electrochemical energy to drive transport and biosynthesis
Ions leak across membranes
Ions must be continually pumped
Ion-pumping membrane proteins produce heat
E.g. billfish heater organs (modified muscles that don’t contract)
Plasma membranes of endotherms are leakier than those of ectotherms
Increased thermogenesis due to ion pumping
Leaker cells so higher rate of heat production
Regional heterotherms
Body temperature varies in regions of the body
Billfish heater organs near eyes
Tuna retains heat in red muscle (sustains activity)
The thorax of some flying insects
Heat production in insects prior to flight
Mechanisms:
Carbohydrate metabolism in flight muscles
Futile cycling: 2 opposing enzymes are activated simultaneously
Antagonistic flight muscles contract simultaneously
Energy is expended and heat is produced without movement
Not uncoordinated, like in shivering
Wing movement
Frequency and orientation of the wings are controlled to avoid generating life-wing buzzing
Temperature effects: biochemistry and physiology
Proteins and lipids are affected by temperature over the normal range encountered by animals
Hydrogen bonds and van der Walls forces are disrupted by high temperature
Hydrophobic interactions are stabilized at high temperatures
Macromolecule structure
Proteins and lipids are affected by temperature over the normal range encountered by animals
Hydrogen bonds and van der Walls forces are disrupted by high temperature
Hydrophobic interactions are stabilized at high temperatures
Membrane fluidity
Membrane fluidity is affected by temperature
Low temperatures cause membrane lipids to solidify
High temperatures increase membrane fluidity
Changes in membrane fluidity affect protein movement and membrane function
Increased protein movement with increased fluidity
Homeoviscous adaption
Homeoviscous adaptation: maintain membrane fluidity at different temperatures by changing membrane lipids, cholesterol content
Mechanisms of homeoviscous adaptation:
Fatty acid chain length
Shorter chains increase fluidity
Saturation
More double bonds increase fluidity
Mechanisms of homeoviscous adaption cont:
Phospholipid classes
Phosphatidylcholine (PC): decreases fluidity
Phosphatidylethanolamine (PE): increases fluidity
Cholesterol content
Prevents solidifying when the membrane is cooled
Thermal adaption, acclimation, acclimatization
Ectotherms remodel tissues in response to long-term changes in temperature
Quantitative strategy
More metabolic “machinery”
For example, increase the number of muscle mitochondria in low-temp
Qualitative strategy (seasonality)
Alter the type of metabolic “machinery”
For example, different myosin isoforms in winter and summer
Might be less stable
Cold adaptation
Psychrotrophs: animals that thrive at low temperatures
Protein “breathing”: changes in 3-D shape during the catalytic cycle
Enzymes do not breathe well at low temperatures because weak bonds are strengthened
Decreased enzyme efficiency
Psychrotrophs possess cold-adapted enzymes
Fewer weak bonds
Enzymes breathe (jiggle) more easily at low temperatures
But cold-adapted enzymes are more vulnerable to temperature-dependent unfolding
Strategies for surviving freezing temperatures
Freeze-tolerance: animals can allow their tissues to freeze in a controlled, safer way
Freeze-avoidance: animals use behavioral and physiological mechanisms to prevent ice crystal formation
Supercooling: in the absence of a nuclear, water can remain liquid below 0°C (lowest is -40°C)
Ice crystal formation needs a trigger: either a cluster of water molecules or a macromolecule that acts as a nucleator
Deleterious effects of ice crystal formation
Points and edges can pierce membranes, if crystals grow large enough
Crystal growth removes surrounding water
Osmolarity increases
Free-avoidance
Solutes depress the freezing point of a liquid (colligative property of water)
As osmolarity increases, freezing point decreases
Antifreeze macromolecules
Proteins or glycoproteins that depress the freezing point by non colligative actions
Disrupt ice formation by binding to small ice crystals and preventing growth
Freeze-tolerance
Two mechanisms of freeze-tolerance
Produce nucleators outside of the cell
Control the location and kinetics of ice crystal growth
Extracellular fluid freezes, but intracellular fluid remains liquid
Produce intracellular solutes to counter the movement of water
maintaining a constant body temperature
Endothermic intertwined with high metabolic rate
High metabolic rate causes increase heat production
Thermogenesis
Advantages of high body temperature
Increase growth, development, digestion, biosynthesis
Endothermy requires ability to regulate
Thermogenesis
Heat exchange with environment
Both endotherms and ectotherms produce metabolic heat
Only endotherms have the ability to retain enough heat to elevate body temperature above environmental temperature
Endotherms possess futile cycles
Metabolic reactions whose sole purpose is to produce heat
Regulation of body temperature
Coordination of multiple physiological systems
Internal thermostat
Mammals
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
Birds
Thermostat is located in the spinal cord
Shivering thermogenesis
Unique to birds and mammals
Uncoordinated myofiber contraction that results in no coordinated net muscle work
World for short periods of time
Muscles rapidly depleted of nutrients and become exhausted
Has costs
Prevents the animal from using locomotory muscle for foraging or predator avoidance
Patterns of fuel use during shivering (as function of intensity)
Mirror patterns of fuel use in muscle with exercise intensity
Muscle glycogen use dominates at high intensities
Brown adipose tissue (BAT)
Used for nonshivering thermogenesis
Found in small mammals and newborns that live in cold environments
Located near the back and shoulder region
Differs from white adipocytes
Higher levels of mitochondria
Produces the protein UCP1 (uncoupling protein 1)
UCP uncouples the mitochondrial electoral transport system and proton pumping from ATP synthesis (leads to futile cycling of protons)
High rate of fatty acid oxidation
Energy is released as heat
High density
darker brown tissue
Activated by sympathetic nervous input
Activates fatty acid beta-oxidation
And upregulates UCP translation/transcription
This, then, activates UCP activity
ETC received reducing energy
Pumps protons, building/maintaining proton motive force
UCP lets H+ move down gradient
So does ATP synthase
Unlike ATP synthase UCP’s moving of H+ does not power ATP synthesis
Futile cycle
Torpor: a spectrum of behaviors
Daily changes in body temperature in various animals
“Deep” torpor is identifiable
But what about lots of examples of “shallow” torpor?
Shallow torpor can still save energy: via reduced metabolic rate
A regulated, moderate temperature
Doesn’t strongly track ambient temp
Contrast with deep torpor, which does track ambient
Go as low as ambient allows.
A regulated state: still will defend min Tb
Duration of torpor, more than depth predicts energy savings
