metabolism Flashcards
Metabolism
the sum total of all the chemical
reactions occurring in an organism
Remember the 2nd law of thermodynamics
– In a closed system the direction of change is
toward disorder
– Animals are an open system
* They require energy to maintain order in
their bodies
Two Metabolic pathways
anabolic and catabolic
Anabolic
– Assembling of substances into complex
molecules
– Requires energy
– Net incorporation of N-containing molecules by
protein synthesis
Catabolic
– Breakdown of complex energy-rich materials
into simpler molecules
– Releases chemical energy
– Some energy stored as ATP or glucose
Three forms of energy
– Chemical
* Freed/needed for atom reconfiguration
– Electrical
* Charge separation of molecules
– Motional
* Mechanical
– Energy of organized motion
* Heat
– Formed by random motion of all molecules
Work and Physiological work
- Work- the transfer of energy from one source
to another - Physiological work- any process carried out by
an animal (or plant) that increases order in the
environment (internal and external)
– Breakdown of molecules
– Bodily movements - Heat generation is NOT physiological work
Heat
- Can only convert heat to work if there is a temperature
discrepancy within the system- Internal combustion engine propels a car
- Heat is important to organisms and MR
- Energy forms and heat
– High-grade energy- can perform phys. work
* Chemical, electrical, mechanical
– Low-grade energy- cannot perform phys. work
* Heat
* Degrade energy when convert from high to low
Animal energy use
- Ingested energy- chemical bonds of food
– Food unable to be digested- Fecal energy
– Food assimilated into body- Absorbed energy - Absorbed energy has 3 routes
– Biosynthesis
– Maintenance
– External work
note to self, study what is happening on the uses of energy by an animal image
page 2 slide 3 on page
Biosynthesis
- Synthesis of body proteins and lipids
– Accumulation of chemical energy in body
tissues- during growth
– Also during fat storage
– Eventually eaten or die (decompose) - Some synthesized chemicals are exported
– Gametes, milk, excreted mucus, skin, hair, etc. - Some energy lost as heat
Maintenance
- Maintain integrity of the organism as a whole
– Internal work- Circulation, respiration, gut motility, etc.
- Very costly to the organism
– Almost all of the high-grade energy is degraded
to heat
– Every step of ATP use causes additional
degradation
External work
- Mechanical work performed outside the body
– Necessary events to be biologically successful- Food, sex, and practicing for both!
- Some of this energy is degraded to heat (ATP)
- Some is transferred outside of the body where
it ultimately finds the same fate
– Resistance to motion (heat)
– Potential energy followed by resistance (heat)
All animals create heat
- Think about the diagram
– Most of the absorbed energy becomes heat
– Are endothermic organisms unique? - The pathway is one-way
– Not possible to convert heat into high-grade
energy
– Energy is not recycled
* Explains why animals require continued
consumption throughout their lives - Collective heat from all organisms radiates into space
Metabolic rate
– Conversion of chemical energy into heat
– Expressed as heat energy released per unit
time, rate of heat production
– Determines how much food is needed
– Representative of an animal’s lifestyle/intensity
– Measures an organism’s drain on the
ecosystem by degradation of chemical energy
Measurement of metabolism
- Direct calorimetry
– Measurement of energy released as heat over a given
period - Indirect calorimetry
– Measures metabolism from food intake and waste excretion- Respirometry
– Rate of gas exchange with the environment - Material balance
– Measure chemical energy of organics that enter
and leave the body
- Respirometry
- Radioisotopes (in vivo)
– Inject radioisotopes of O2 and H, then measure loss of body water with respect to loss of O2
not all food is equal
The heat produced from catabolism differs with the
food item. Carbs are the cheapest, proteins are the middle, and lipids are the most expensive.
Respiratory ratios
- Respiratory exchange ratio (R) and respiratory
quotient (RQ) are often used interchangeably
– Not always correct, but often is
RQ= O2 consumed per unit time/ CO2 produced per unit time
Factors affecting metabolic rate
Note: look at the slide and study what the effects are.
– Age/gender
– Amount of lean muscle
– Physical activity level
– Diet
– Hormones
Absorptive (fed) state
– Ingested nutrient molecules enter the blood
– Some are used to supply various needs of the
body
– Net synthesis of proteins, glycogen, and fat
Post-absorptive (fasted) state
– Digestive tract is empty of nutrients
– Available pool of nutrients in blood decreases
– Net degradation of proteins, glycogen and fat
Homeotherm vs. poikilotherm
- Basal Metabolic Rate (Homeotherms)
– In Thermal Neutral Zone
– Fasting (postabsorptive)
– Resting - Standard Metabolic Rate (Poikilotherms)
– Fasting
– Resting - BMR/SMR- Stable rate of energy metabolism
under conditions of minimum environmental and
physiological stress and after fasting
Temperature and hormones involved
Q10 = R2/R1^(10/(T2-T1) enzymatic activity by time
10 degree increase causes a 2-3 times increase of enzymatic activity.
– Insulin
– Glucagon
– Epinephrine
– Glucocorticoids
– Growth hormone
– Thyroid hormone
Body size: Does metabolic rate increase
proportionally
meadow vale consumes 175 grams of food and weighs 30 grams, and a white rhino consumes 650 kg of food and weighs 1900 kg. vale has a higher metabolic rate than rhino
Factors influencing
metabolic rate
Body size-
smaller animals
respire at higher
metabolic rates
per unit body
mass than larger
animals
MMR
- Maximum Metabolic Rate
– Exercise induced metabolic rate
– Approximately ten times BMR or SMR - Exponent difference between BMR and MMR
– M (metabolic rate) = a Wb
– 0.7 for BMR
– 0.85 for MMR
Locomotion
- The amount of energy required (beyond BMR)
to move a unit of mass of an animal a unit
distance (kcal/kg/km) - Small animals use more energy to achieve a
given velocity of locomotion than larger animals
Who cares?
- These relationships are allometric
- Relationship between two characters
- Nonlinear relationship between metabolism
and body mass - Ventilatory rate and heart rate allometric
- Ecological: pop biomass/sq km func of size
- Size and pollutants: sm size accum more
Heart rate proportions
Heart size in mammals is roughly proportional to body size, but heart rate is not the same.
Explanation for allometry
- Surface area to volume theory
– As a sphere increases in volume by 1, surface
area increases by 2/3
– Applies to animals- Big animals have proportionally smaller surface
area per volume - Small animals have more surface area and lose
more heat
- Big animals have proportionally smaller surface
- Data don’t always support the theory- SA/V is still
important - Does not apply to poikilotherms
Energetics of Food and Growth
- One organisms growth is another’s food
- Energy value/unit weight
– Fat has at least twice as much energy (per unit)
more than proteins and carbohydrates
– Fat is the most energy dense substrate- Important in all migrating species
- Must consider the absorption efficiency of the
food item
Energetics of Food and Growth Cont
Energy abs. efficiency =
Absorbed energy
Ingested energy
Gross growth efficiency =
Chem. bond energy growth
ingested energy
Net growth efficiency =
Chem. bond energy added
absorbed energy
Is growth efficiency always constant?
- Declines with age
- Consideration in agriculture/aquaculture
