Chapter 3: Food

Functions of Food

• Energy
  - Main source: Carbs
  - Comes from protein (deamination) and fats (ketosis) too.

• Growth of new cells (continuity) and repair existing cells, tissues, organs, etc.

• Needed for movement, active transport

• Supplies materials for metabolism.
  - Sum of all chemical reactions occuring in the body.

Elements in Food

Food also supplies the materials and energy for the process of:

Metabolism:
Sum of all chemical reactions occurring in the body.

Continuity:
Reproduction, growth.

Chemical Elements

Six Main Elements

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

(Most common, make up 96% of an organism’s weight in carb, lipids, and proteins)

• Phosphorous (P)

• Sulfur (S)

(Amino Acids)

Five Elements Dissolved in Salts

• Sodium (Na)

• Magnesium (Mg)

• Chlorine (Cl)

• Potassium (K)

• Calcium (Ca)

(Need 100mg or more of these every day, also known as mineral salts)

Three Trace Elements

• Iron (Fe)

• Copper (Cu)

• Zinc (Zn)

(Need less than 100mg of these every day)

Biomolecules

Molecules in living things (found or created in)

Contain carbon and are also known as biochemicals.

Four main types are:

• Carbohydrates

• Lipids (fats and oils)

• Proteins

• Minerals

The 14 elements combine in different ratios to form different food components (biomolecular units).

e.g plants use carbon dioxide and water to combine carbon (C), hydrogen (H) and oxygen (O) to make biomolecules of glucose - C6H12O6

Carbohydrates

Main source of energy in the diet

Contains the elements carbon, hydrogen, and oxygen in the ration of 1C:2H:1O.

e.g glucose

3 Types of Carbohydrates:

Monosaccharides → Glucose, Fructose

Disaccharides → Sucrose

Polysaccharides → Starch (storage), Cellulose (structural), Chitin (cell wall of fungi)

Monosaccharides

• Single sugar molecules

• Simple sugars

• Soluble in water

• Sweet to taste

• Smallest carbohydrate unit

• Found in: Fruit

Disaccharides

• Two monosaccharide sugar units joined together - known as double sugar molecule.

• Soluble in water

• Sweet to taste

• e.g Sucrose, Lactose, Maltose

• Found in: Table Sugar, Milk

Polysaccharide

• Many monosaccharide molecules joined together

• Not soluble in water

• Do not taste sweet

• e.g Starch, Cellulose

• Found in: Bread, Pasta, Cereals

Cellulose

• Form the cell wall in plants - structural carbohydrate

• Provides strength and support to plants

• Role: Called ‘Fibre’ or ‘Roughage’

• Found in: Vegetables, Bran

Lipids

Contain the elements carbon, hydrogen and oxygen - but in a different ratio to cabrohydrates.

Diverse group of substance which include fats and oils.

Fats: Solid at room temperature

Oils: Liquid at room temperature

Basic unit of a lipid is triglyceride which is made of three fatty acids and one glycerol.

Phospholipids are fat-like substances in which a fatty acid is removed and is replaced by a phosphate.

Lipid Function

• Long term store of energy

• Lipids under the skin used for insulation (subcutaneous).

• Provide protection to certain organs e.g. kidneys.

• Phospholipids have a structural role in cell membranes.

Proteins

• Sources of protein: Fish, eggs, chicken, meat, legumes, vegetables.

• Contains the elements carbon, hydrogen, oxygen, nitrogen.

• Composed of 20 amino acids.

• Peptide bonds hold amino acids together.

• Protease enzymes break these bonds.

• Protein synthesis: Ribosome makes these bonds

Peptide → less than 20 amino acids

Polypeptide → greater than 20 amino acids

Protein → chain of more than 200 amino acids

Protein Types

Globular Proteins → Alburen (egg whites) → Metabolic

Fibrous Proteins → Keratin and Collagen → Structural

Globular Proteins

Amino acid chains are folded into a 3-dimensional shape

e.g. Enzymes → They carry out biological reactions

Fibrous Proteins

Amino acid chains are folded into a-helixes or B-pleated sheets.

e.g. muscle fibres and hair

Role of Protein

• Structural
  Fibrous proteins form keratin which makes hair, skin, and nails. Myosin forms muscles

• Enzymes
  Globular proteins control reactions in cells.
  - Catabolic → Breaks complex molecules into simpler molecules.
  - Anabolic → Build simple molecules into complex molecules.

• Hormones
  Folded proteins regulate metabolism

Vitamins

Vitamins are organic carbon based compounds that are required in small amounts.

Vitamnis cannot be produced in the body (except vitamin D3).

e.g. Vitamin A, B, C, D, E, and K.

Water Soluble Vitamin

Vitamin C

• Needed to form connective tissue (skin, gums, blood).

• Deficiency of vitamin C causes scurvy.
  - Bleeding from the gums and slow healing of wounds, also bruising.

• Sources of Vitamin C: Citrus, Fruits, Potatoes, Green Vegetables

Fat Soluble Vitamin

Vitamin D

• Needed for the absorption of calcium for healthy bones and teeth.

• Deficiency of Vitamin D in children causes rickets (soft bones). In adults it causes oseomalacia (bones lose calcium and become weak and fracture).

• Sources of Vitamin D: Fish Liver Oil, Eggs, Dairy, Sunlight.