Energy metabolism Chris Elliott [email protected]. Learning Objectives: nTo understand how oxygen consumption is used as an index of metabolic rate nTo.

Energy metabolism

Chris [email protected]

Learning Objectives: To understand how oxygen consumption is

used as an index of metabolic rate

To be familiar with the variation in energy expenditure between species (related to life strategies)

To appreciate the extent to which energy expenditure is elevated by animal movement in the laboratory and field

Reading … http://biolpc22.york.ac.uk/303/

Schmidt-Nielsen, K (1997) Animal Physiology CUP

So what is the cost of living?

Living organisms need energy just to exist

Basal metabolic rate

First estimated by Lavoisier ~1790.

At equilibrium: rate of ATP hydrolysis = rate of ATP synthesis(but ATP hydrolysis levels difficult to measure!)

1 mole glucose

+

6 moles O2

36 moles ATP

Energy as ATP…

Although Lavoisier measured heat production, the possibilities include measuring:

heat

Metabolic rate Metabolic rate: rate at which an organism

uses energy

determine from heat produced work done food ingested oxygen consumed CO2 production ?

And CO2

Respiratory quotient

RQ = CO2 produced / O2 consumed

1 for carbohydrate 0.7 for fat

O2 consumption = energy consumption

1ml O2 = 5 cals = 20 Joules

For a 70 kg human:• 65 kg ATP/day• 350l O2/day • 70 W (one light bulb)• 7 million joules of energy/day

Cost of doing nothing??

Physiological food value

How long live on a Kitkat?

20 g so 2105/100*20 = 421 kJ 421*1000/70 /60 ≈ 100 min

Warning!

food is often labelled in cal when they mean kcal

12% for a Mars bar!

In terms of energy cost (O2 required/kg/h), what is the most expensive tissue in the human body?

[ and why ? ]

Oxygen consumption by pigeon tissue slices maintainedin saline

Tissue ml O2 consumed kg-1h-1

Kidney 41Liver 34Brain 23Heart 13Muscle 10

(metabolic rate of tissue slices = 70% of basal metabolic rateof intact animal)

Spending: 20% ion pumping; 20% protein synthesis and turnover

Summary so far oxygen consumption as proxy for energy

consumption

Getting bigger…

mass

met

abol

ic r

ate BMR = K * mass0.75

and bigger… 0.75 law is called Kleiber’s law

Homeotherms need more energy

Getting bigger requires more metabolism become more efficient

for a 10% increase in size, metabolic rate increase is 5.6%

Evolutionary drive to get bigger

why 0.75 ? If directly proportional

big animals overheat small animals need several cm of fur

if index were 2/3 would agree with

surface / volume ratio

Pumping matters… West suggested 0.75 was due to

fractal branching pulsatile blood flow

Summary so far oxygen consumption as proxy for energy

consumption basal metabolic rate increases with size

Now onto: effect of activity on metabolic rate

Another day at the office……

Cost of running

body mass, kg, log scale

speed of running, km/hr

total costnet cost

0.01 1000

10 0

Classic study by Dick Taylor on ponies, three gaits: walking,Trotting, galloping on a treadmill:Same gait: different speeds

Black boxes: preferred speed at each gait = minimal metabolic cost

In general:

Animals use uniform amounts of energy/distance coveredat all speeds.

i.e. walk or run from here to Heslington Hall, uses the same amount of energy, but running takes you there faster

Metabolic costs of running (kJ kg-1 km-1):

Larger animals more efficient than small; think evolution!Number of legs does not matter

Swimming flying graph

maximum MR when running is 10 x BMR

Flying v swimming v running

European Eel (Anguilla anguilla)

Migrates 6000miles from W. Europe to Sargasso sea to spawn

Swimming eels consume 23mg fat/kg/h

2kg eel (20% fat) swims at 43.2 km/day for 139 days

consumes 153g fat = 38% of stored fat

…….leaving 413g fat for egg production

Sprinting… Some species can ‘sprint’: running faster than

O2 can be supplied to the muscles How possible?

Red Fibres: ATP production by aerobic respiration, fuelled by O2 delivery via blood during exertion of moderate force for extended periods

White Fibres: ATP production independent of O2 (little blood supply) during exertion of strong force for short periods – build up lactate during exercise.

All muscles have mixture, but some have high ratios of white to red.

Red and white muscle fibres

Limits to power output <1sec 4500 W muscle output <2 min 1500 W anaerobic energy store

kettle

<2 hours 350 W oxygen transport All day 150W need to eat/sleep

2 light bulbs

Mars bars again… How far can you run on a Mars bar ?

Summary so far oxygen consumption as proxy for energy

consumption basal metabolic rate increases with size cost of movement

independent of speed up to 60x BMR transiently, 5x BMR for several hours

Now onto: Life in the field

How do you study metabolic rate in the field?

Back to the originalquestion:

What is the cost of livingand how do you measureit?

Double Labeled Water technique

Key Technique: Aim: to measure FMR (field metabolic rate)

over period of time Only works on air-dwelling animals

Inject animals with 2H218O (harmless heavy

isotopes) Later time point: blood sample and

quantify 2H and 18O

DLW - 2loss of water : carries away 2H and 18Oloss of CO2 : just carries 18O

How does 18O get from water to carbon dioxide ?carbonic anhydase (very high turnover)

CO2 + H2O H+ + H2CO3¯ [proton + bicarbonate]

difference between loss of 18O and 2H measures CO2 used in expirationSo how much extra energy does an

active bird use?

Using double labeled water technique:

Blue-tits breeding in evergreen oak woodlandsin south of France (new leaves in May) and Corsica (new leaves in June)

FMR---------BMR

Nagy, K. A. J Exp Biol 2005;208:1621-1625Index of 0.80

FMR ~3x BMR

Summary to end oxygen consumption as proxy for energy

consumption basal metabolic rate increases with size cost of movement

independent of speed up to 60x BMR transiently, 5x BMR for several hours

field studies FMR 3-6 x BMR