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Metabolism
Nitrogen metabolism: Conversion of Nitrogen
from food into proteins and waste products (urea)
Energy metabolism: How energy is acquired, used, and transformed in the body
Two types of metabolic reacEons: Chapter 6 Metabolism
1. Energy and its use in the body 2. Metabolic rate 3. Factors that affect metabolic rate
Energy metabolism • Chemical energy (food) consumed generates energy
• Used to perform physiological work – Synthesizing proteins, nutrients
– TransporEng solutes – Muscle movements – CirculaEon, digesEon, etc.
Energy metabolism 4 forms of energy:
1. Chemical energy: released when molecular structure changes • Food broken down (digested )
2. Electrical energy: created due to charge difference • Across cell membranes
3. Mechanical energy: produced when molecules move • Any body movement, circulaEng blood
4. Heat: Random molecular movement • Movement of water molecules in liquid form
Energy metabolism 4 forms of energy:
1. Chemical energy 2. Electrical energy 3. Mechanical energy 4. Heat
High-‐grade energy
Low-‐grade energy
Energy metabolism 4 forms of energy:
1. Chemical energy 2. Electrical energy 3. Mechanical energy 4. Heat
• Heat CANNOT be used for physiological work! – Low-‐grade energy
• Energy is degraded and loses heat – Inefficient process
High-‐grade energy
Low-‐grade energy
HEAT
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Energy metabolism 4 forms of energy:
1. Chemical energy 2. Electrical energy 3. Mechanical energy 4. Heat
• Heat CANNOT be used for physiological work! – Low-‐grade energy
• Energy is degraded and loses heat – Inefficient process
100 units Glucose
70 units ATP
30 units HEAT
Energy use by animals • Undigested food à fecal energy
• Digested food à absorbed 1. Biosynthesis 2. Maintenance 3. Create external
work
• All three uses generate HEAT
INEFFICIENT!!
Energy use by animals: Biosynthesis
• Chemical energy made by body and used for: 1. Growth
(compounds remain in body)
2. Exported (gametes, skin, hair, milk, etc.)
1. 2.
Energy use by animals: Maintenance
• Processes or parts that sustain life – All energy
becomes heat – Internal work
Energy use by animals: External work
• Use of energy to perform mechanical work outside body – Exercise
Energy use by animals • When energy is lost as heat, it CANNOT be
re-‐cycled
This is why we must eat
constantly!
INEFFICIENT!!
ENERGY HEAT
HEAT ENERGY
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Chapter 6 Metabolism
1. Energy and its use in the body 2. Metabolic rate 3. Factors that affect metabolic rate
Recap: Energy metabolism What we do
EAT
LIVE
What happens in our bodies Ingest and convert chemical energy
• DigesEon, absorpEon
Release chemical energy, heat, and external work
• Energy is consumed, never recycled!
Metabolic rate (MR): Rate that we consume energy
Metabolic Rate: What and why • Consuming energy generates lots of heat – MR ≈ rate of heat producEon
• ImplicaEons 1. Determines amount of
food required 2. Provides quanEtaEve
measure of work done 3. Measures “drain” on
ecosystem • Because ecosystem is
ulEmate source of energy (FOOD)
Metabolic Rate: How • MR ≈ rate of heat producEon – Measured in calories/unit Eme
• Basal metabolic rate (BMR): measurement used for homeotherms
• Standard metabolic rate (SMR): measurement used for poikilotherms
1. Direct calorimetry 2. Indirect calorimetry via respirometer 3. Indirect calorimetry via material-‐balance
Direct calorimetry • Measures rate of heat loss
• Lavoisier measured rate by collecEng melted ice
• Only 100% accurate when animal measured at rest – No external work
Indirect calorimetry via respirometer
• Respiratory gas exchange rate based on glucose oxidaEon reacEon
1. Measure either O2consumed or H2O produced 2. Calculate heat produced using conversion factor
(2820 KJ heat produced per 6 mol of O2 USED or for every 6 mol of H2O PRODUCED)
C6H12O6 + 6O2 è 6CO2 + 6H2O + 2820 KJ (HEAT)
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Indirect calorimetry via respirometer • Problems??? – Not all food created equal • Energy contained within different food types varies
– Without exact diet composiEon, MR sEll just esEmate
– Bokom line: O2consumpEon is proporEonal to heat generated
Indirect calorimetry via material-‐balance
– FOOD = organic material in – WASTE = organic material out
• Measurement of chemical energy of organic materials in and out of body
• Problems?? • Some chemical energy used to fuel growth • Material-‐balance only
looks at maintenance use of energy
• hkp://northlandphys.wordpress.com/2014/01/26/cool-‐research-‐on-‐gut-‐bacteria-‐and-‐diet/
Chapter 6 Metabolism
1. Energy and its use in the body 2. Metabolic rate 3. Factors that affect metabolic rate
Factors that affect metabolic rate • EaEng • Age • Gender • Stress • Hormones • Salinity • Temperature • Physical acEvity
EaEng: Specific dynamic acEon • Temporary increase in metabolic rate following eaEng aner a fast – Increase in SDA is proporEonal to size of meal
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Body size • Bigger bodies require more food • But it isn’t proporEonal to body size! – Calculate weight-‐specific BMR
Body size: Weight-‐specific BMR • Small mammals have a higher weight-‐specific BMR
WHY???
Body size: Weight-‐specific BMR • Heart size is proporEonal to body size (all mammals)
• Small mammals have a higher resEng HR – require more O2/g body weight
Ecological implicaEons • Small mammals require more food per gram of body Essue – Accumulate more toxins and pesEcides – Metabolic rate measures “drain” on ecosystem
1 SINGLE deer = 440 mice!!!
