L4: energetics & metabolism

what is energetics?

the study of energy transfer and use within biological systems

what is the significance of energy?

common currency of all life

what is metabolism?

sum of all biological transformations of energy & matter; overall use of chemical energy

what is the significance of ATP in regards to energy?

mediates energy transfers for all processes in living organisms; common currency of energy metabolism

ATP is generated through:

1. anaerobic metabolism

2. aerobic metabolism

when are anaerobic metabolic pathways used? why?

during short bursts of intense activity -> ATP generation speed

what are the downfalls of using anaerobic metabolism?

toxic - rapid buildup of end products

inefficient ATP production

what is glycolysis?

breakdown of glucose

the primary fuel source for glycolysis is:

glucose (other sugars can be used too but this is the main)

how is glucose stored?

stored as glycogen -> glycogen present in the cytoplasm as granules that also contain enzymes for synthesis/degradation

what is glycogenesis?

glycogen synthesis

what is glycogenolysis?

glycogen breakdown

what is gluconeogenesis?

Synthesis of glucose from non-carbohydrate precursors

(when glycogen stores compromised/glucose inadequate)

fuels for aerobic metabolism include:

1. carbohydrates (about 38ATP)

2. lipids ( 403 mol ATP)

3. amino acids (low ATP yield)

how much ATP is produced from glucose?

38 ATP

why are lipids considered highly concentrated fuels?

they can be stored in anhydrous state

lipolysis

breakdown of fat; stores accessed when stressed

most of animals accumulate fat as reserves, irrespective of food composition, why?

weight and energy; fat acts as highly concentrated energy stores

why does storage of glycogen involve more weight?

glycogen is deposited in cells with a lot of water

even though glycogen has lower energy content compared to fat, why is it used?

provides fuel very quickly & under anoxic conditions

what is metabolic rate?

metabolism/time

what does metabolic rate tell us?

1. rate of all physiological activities

2. resource needs

3. index of energetic demands from the environment

what are the 3 ways metabolic rates can be described?

1. basal metabolic rate (BMR)

2. resting metabolic rate (RMR)

3. field metabolic rate (FMR)

4. maximum metabolic rate (MMR)

define basal metabolic rate

rate of energy metabolism free of physical/thermal/psychological stressors; in animal not breeding/growing

define resting metabolic rate

metabolic rate associated with minimal unrestrained activity

define field metabolic rate

rate of energy metabolism during normal activity; includes digestion/exposure to temps outside thermoneutral zone

list the 4 types of metabolic rates from most oxygen consumption (top) to least oxygen consumption (bottom)

1. maximum metabolic rate

2. field metabolic rate

3. resting metabolic rate

4. basal metabolic rate

what are ways in which we can measure metabolism?

1. direct measure of heat production (direct calorimetry)

2. indirect measure: difference b/w energy value of all food taken in and energy value of the excreta

3. indirect method: amount of oxygen used in oxidation processes

how is heat a direct measure of metabolism?

heat produced by an animal is proportional to O2 consumed and CO2 produced

why would the amount of oxygen used in oxidation processes be used to measure metabolism?

the amount of heat produced for each liter of O2 remains nearly constant; obtain energy via oxidation of food

what can the respiratory exchange ratio reveal to us? what are the common ration seen and what do they indicate?

can suggest what the animal is consuming and what conversion factor can be used to calc metabolic rate

Ex: RER of 1.0 = carbohydrates

RER of 0.71 = Lipids

RER of 0.83 = Proteins

what are two methods to measure the amount of oxygen used in oxidation processes?

1. closed system respirometry (small animals)

2. open system respirometry

how does energy use compare between lab and field?

values of metabolic rate are 3x higher than in lab

how can we measure daily energy expenditure (DEE) or FMR?

Doubly-labeled water or 2H2 18O

what is the procedure for measuring DEE with doubly-labeled water?

1. inject a known quantity

2. take blood sampl3

3. release animal

4. recapture, take 2nd blood sample

what are some potential drawbacks of using doubly-labeled water to measure DEE?

- stress from capture can skew MR results

- recapture of the same animal within time constraint is difficult

- expensive

once we measure metabolism, what can we do with it?

1. find overall rate of all physiological activities

2. resource needs - conservation issues

3. index of energetic demands from the env

define sustained metabolic rate (SusMR)

time averaged metabolic rates that are measured in free-ranging animals maintaining constant body mass over period long enough that metabolism is fueled by food intake rather than depletion of energy reserves

what are the proximate physiological causes of metabolic ceilings?

1. central limitation hypothesis

2. peripheral limitation hypothesis

central limitation hypothesis

limitation in central system/digestive tract; max rate of energy assimilation

peripheral limitation hypothesis

an organism's maximum metabolic rate or energy budget is constrained by the capacity of peripheral effector organs and tissues (e.g., muscles, mammary glands) to process or utilize energy, rather than by the central supply rate

what are the ultimate evolutionary causes of metabolic ceilings?

1. metabolic capacities

* evolved to limits that food supply is able to fuel

2. design limitation

* higher SusMR needs more metabolic machinery thus

higher MR

what factors affect an animals metabolic rate?

1. temperature

2. food habits

3. activity

4. digestion

5. reproductive state

6. time of day

7. energy saving strategies

why does basal metabolic rate increase in lower/higher temperatures?

lower/higher temps require the body to use more ATP to fuel processes that help the organisms cope with temperature outside of it thermoneutral zone

how does digestion affect metabolic rate?

increases O2 consumption

give an example of an energy saving strategy

torpor

* state of slowed body functions used to conserve energy & heat

hibernation

* state of inactivity & metabolic depression in endotherms

what are energy budgets?

the partitioning of the ingested energy into various components

E in = E out + E p

*Ein = energy ingested as food

* E out = sum of energy losses

* E p = energy associated with production

principle of allocation

each animal has a finite amount of energy so there are tradeoffs in allocation among the components of its energy budget; competing demands

constraints on energy budgets include:

1. inputs: limits on rate of resource acquisition (central limit)

2. outputs: limits on expenditures (peripheral limitation)

energy maximizer

potential reproductive success increases with net energy intake; maximizes energy & time foraging

time minimizer

reproductive success is not limited by energy intake; when minimal E achieved, spend time in non-foraging activities

the rufous hummingbird is a energy maximizer while the Costa's Hummingbird is a time minimizer. Relative to a time minimizer, an energy maximizer like the Rufous Hummingbird should:

1. spend more time foraging

2. spend less time sitting

3. gain mass rapidly