Lecture 22 - Energy balances in cells and organisms

Question 1

Overall idea of metabolism

Answer 1

The set of life sustaining chemical reactions in organisms, these reactions provide energy for vital processes and for synthesising new organic material

Question 2

First law of thermodynamics

Answer 2

The body follows the laws of thermodynamics as well, it cannot make or destroy energy, we put energy into our bodies in the form of food which is converted into a form that our bodies can use

The total energy within a system is constant
Energy can neither be created nor destroyed
Energy can be converted
Biology relies on energy conversions

Question 3

Energy balances in cells and organisms

Answer 3

Energy gets converted (sunlight to usable energy in the cells and organisms)

Anabolism - the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy
Catabolism/respiration - the set of metabolic pathways that breaks down molecules into smaller units that are either oxidised to release energy or used in anabolic reaction

Question 4

Energy balances in the human body

Answer 4

Food (chemical energy - carbohydrates and fats and proteins as well as nutrients - vitamins, minerals etc) are ingested along with oxygen
Carbon dioxide and water and breathed in and out
Then digestion of the food material occurs which produces heat as a byproduct
These digestion produced either go into storage or are metabolised by a variety of pathways such as glycolysis, beta oxidation and the CAC in order to make ATP in order to do cellular work

Question 5

Energy metabolism and ATP

Answer 5

Two opposing reaction sequences

Anabolism - turns ATP into ADP and inorganic phosphate in order to release energy, it uses this energy to do cellular work
Catabolism - uses energy to break down, breaks down food material which allows us to extract energy to do cellular work

Question 6

Carbon compounds in food…

Answer 6

Are oxidised to form ATP

Question 7

Energy balances in the body

Answer 7

Eintake = Eexpended (perfect balance) 
Food = basal metabolism + activities 

But in reality:
Eintake = Eexpended + Estored
Estored is = to weight gain

Question 8

Weight loss is achieved through

Answer 8

Reducing energy intake (eat less and/or take certain drugs)
Increasing activities
Increasing basal metabolism (the energy required for maintenance of life)

Question 9

Leptin deficient mouse…

Answer 9

Eats too much
Evidence is showing that Leptin is a compound that is centrally involved in helping animals control their energy utilisation and energy storage

Question 10

Units of energy

Answer 10

Joule (J) = energy required to push against 1 Newton of force for 1 metre

1 cal = 4.184J
1Cal = 4.184kJ

Daily dietary energy intakes and energy expenditures usually measured as MJ I.e. 1000 kJ

Question 11

How is the energy content of food measured?

Answer 11

Measured by calorimetry

Measurement of the combustion process that is occurring - measuring the heat energy generated under defined conditions for a defined material

Question 12

Atwater factors

Answer 12

Fat = 38kJ/g
Carbohydrate = 17kJ/g
Protein = 17kJ/g
Ethanol = 29 kJ/g 

Atwater factors is how much energy you can get out of each food source (not all of the food can be used to make energy)

Question 13

Not all of the energy in food is available

Answer 13

Losses in faeces I.e. fibre (cellulose)
Nitrogen is not oxidised (excreted in the urine)
Have to adjust for these factors

Question 14

Heat combustion of foods

Answer 14

Need to appreciate that there is a range of energy and it depends on the material

Question 15

Direct calorimetry - whole body calorimeters

Answer 15

Relies on meauring heat output from an individual

Good for determining basal metabolic rate (BMR) i.e. an individual at rest

Question 16

Indirect calorimetry

Answer 16

Based on oxygen consumption and carbon dioxide production using a respirometer
A certain amount of energy is associated with every litre of oxygen consumed
Conversion of oxygen to carbon dioxide produces some heat as well

Question 17

Respiration exchange ratio

Answer 17

CO2 produced/O2 consumed = RER

Said to be a useful calculation in terms of considering catabolic and anabolic reactions going on in the body and how this ratio relates to the interconversion of various products

RER can determine the fuel that is being used
Carbohydrate have an RER of 1
Fatty acids have an RER of 0.7

Question 18

Basal metabolism

Answer 18

Energy required for the maintenance of live i.e. for muscle contractions, nerve conduction, ion transport, synthesis of macromolecules, maintenance of body heat

Usually defined as energy expenditure at rest
Basal metabolic rate

Question 19

Basal metabolic rate define

Answer 19

Basal Metabolic Rate is the number of calories required to keep your body functioning at rest.

Question 20

Basal metabolism is increased by

Answer 20

Athletic training 
Late stage of pregnancy 
Fever 
Drugs e.g. caffeine 
Hyperthyroidism

Question 21

Basal metabolism is decreased by

Answer 21

Malnutrition
Sleep
Drugs such as beta blockers
Hypothyroidism

Question 22

Basal metabolic rate differs between individuals

Answer 22

Factors affecting basal metabolism include…

Gender, age, body size and composition, genetics, hormonal status, stress levels, disease status, certain drugs

Question 23

Respirometers

Answer 23

Gives a good idea of a person’s activity and fitness status