Sources of Energy

What is the First Law of Thermodynamics?

energy cannot be created or destroyed, only transferred

Define 1 joule

1 joule is the energy used when 1 kg is moved 1 meter by a force of 1 Newton.

Define 1 calorie

Heat needed to raise the temperature of 1g of water by 1 degree Celsius

What is the conversion factor between kcal and kJ?

1 kcal = 4.184 kJ

Convert 175 kcal to kJ

732 kJ

Convert 285 kJ to kcal

68.12 kcal

What are the three main macronutrient energy sources?

Carbohydrates, Proteins, and Lipids

Name the three types of monosaccharides

glucose, fructose, galactose

Name the three types of disaccharides

Sucrose, Maltose, Lactose

Name three types of polysaccharides

Starch, Glycogen, Cellulose

Where is glycogen stored in the body

In liver and skeletal muscles

What is the chemical name for triglycerides?

Triacylglycerols

List four functions of fats/lipids

1. Unlimited energy storage

2. Insulation

3. Organ protection

4. Cell membrane component

How many essential amino acids are there?

9

How many total amino acids

20

Name the essential amino acids

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

What are the main functions of proteins?

Structural component of muscle, connective tissue and skin, also used in enzymes for growth, repair and maintenance

What is a bomb calorimeter used for?

To measure the gross energy (GE) content of food by burning it with oxygen at high pressure and measuring the heat release

How does a bomb calorimeter work?

Food is burned with oxygen and an electric element at high pressure. Energy is released and measured as a rise in heat in the water jacket surrounding the combustion chamber.

What is the formula for Metabolisable Energy (ME)?

ME = GE × Digestibility percentage - Urinary (or faecal) Loss

What energy is lost between Digested Energy and Metabolisable Energy?

Urinary energy and Surface energy

What is obligatory thermogenesis

Excess heat produced relative to glucose during ATP synthesis - unavoidable heat loss during metabolism

What causes non-obligatory dietary thermogenesis?

Effects of cold, drugs, hormones, bioactive compounds, or other stimulants

What 2 things do Atwater factors account for?

1. Incomplete digestion (not all nutrients are absorbed)

2. Urinary nitrogen losses (from protein metabolism)

What are the General Atwater Factors for the four energy sources

Carbohydrate = 4 kcal/g
Protein = 4 kcal/g
Fat = 9 kcal/g
Alcohol = 7 kcal/g

Why do Specific Atwater Factors exist?

Because general Atwater factors arent sufficient. Different proteins have different compositions and digestibility, fibre (a carb) cannot be fully digested, and food processing affects energy availability

How do you calculate kcal using Atwater factors?

kcal = weight (in grams) × Atwater factor

Why does food produce less energy when metabolized than when burned in a bomb calorimeter?

Because of losses in faeces (undigested nutrients/energy) and in urine (as urea)

What is energy density of food?

The amount of energy (kcal) per unit of weight/volume of food

What is the biggest contributing factor to energy density?

Water content - high water content means lower energy density

What disease are high fat diets associated with

Cardiovascular