Nutrition
Functions of food:
 Energy
 Provides raw materials for growth and repair
 Makes chemicals needed for metabolic reactions
Chemical elements present in food:
There are six common elements:
Carbon (C)
Hydrogen (H)
99% of living organisms consist
Nitrogen (N)
of these four elements
Oxygen (O)
Phosphorous (P)
Sulphur (S)
Another five elements are found as dissolved salts:
Sodium (Na)
Magnesium (Mg)
Chlorine (Cl)
Potassium (K)
Calcium (Ca)
There are three trace elements (only found in small amounts):
Iron (Fe)
Copper (Cu)
Zinc (Zn)
Apart from carbon, hydrogen and oxygen the rest of these elements are often called minerals.
Biomolecular Structure:
The atoms of the above fourteen elements join together in different ratios to form most of the
molecules found in living things – called biochemicals/biomolecules. The four major types of
biomolecules are:
Carbohydrates
Lipids (fats and oils)
Protein
Vitamins
Carbohydrates
These contain the elements carbon, hydrogen and oxygen. Usually present in the ratio C (H O) where
x=y. So there is always twice as much hydrogen as oxygen e.g. glucose has the formula C H O.
The smallest unit of a carbohydrate is a monosaccharide.
Monosaccharides – sweet to taste and soluble in water
glucose and fructose
Disaccharides – sweet to taste and soluble in water, two monosaccharides joined
together
sucrose (table sugar) = glucose +fructose
maltose = glucose + glucose
Polysaccharide – insoluble in water, many polysaccharide joined together
starch – long chains of glucose molecules, storage of glucose in plants
cellulose – chains of glucose in plant cell walls
glycogen – glucose storage in animal muscles and liver
Sources: bread, potatoes, rice, cakes, sugar, fruit, sweets
Fats and Oils (Lipids)
These contain the elements carbon, hydrogen and oxygen but in different ratios to carbohydrates.
Fats are solid at room temperature.
The smallest unit of a fat is a triglyceride.
Triglyceride = glycerol + 3 fatty acids
Oils have same basic structure as fats but contain different types of fatty acids and remain a liquid at
room temperature.
Phospholipids are fats-like substances where one of the fatty acid groups in the triglyceride is
replaced with a phosphate group.
Sources: Animal fats – butter, lard, fat on meat
Plant fats – margarine, sunflowers, olives
Protein
These contain the elements carbon, hydrogen, oxygen and nitrogen. Some may contain sulphur,
phosphorus and other elements.
The smallest unit of a protein is an amino acid.
H
varies from R
C
COOH carboxylic group
are amino
acid to
NH amine group
another
There are twenty common and several rare amino acids found in proteins. Many more amino acids
are known to occur free in different cells and tissues but not in proteins. Amino acids join together by
peptide bonds.
A proteins function does not depend on the amino acid sequence alone but also on the way a protein
folds and takes up a three-dimensional shape.
Sources: meat, fish, eggs, nuts, milk, peas and beans.
Vitamins
These are complex organic substances that the body cannot make, they are only needed in tiny
amounts. They may be referred to by letters or by names based n their chemical structure.
Vitamin C (ascorbic acid)
Water soluble
Vegetables and fresh fruit especially citrus fruit e.g. oranges and lemons
Vitamin D (calciferol)
Fat soluble
Liver, fish oils, milk, egg yolks and sunlight
Energy Transfer Reactions
All the reactions taking place in an organism are referred to as it’s metabolism. Metabolic reactions
can be divided into:
1.
2.
Anabolic reactions - convert smaller molecules into larger ones using enzymes
and absorb energy e.g. photosynthesis
CO + H O + Energy  C H O + O
Catabolic reactions – a complex molecule is broken down to simpler ones using enzymes and
releases energy
e.g. aerobic respiration
C H O + O  CO + H O + Energy
Different pathways of enzymes are used for catabolism and anabolism and are not the opposite of one
another.
Structural Role of Biomolecules
1. Carbohydrates – the polysaccharide cellulose forms plant cell walls
2. Protein – fibrous protein such as keratin is found in skin and hair, myosin is
found in muscles, when linked with phosphorous forms
phosphoproteins which are found in the cell membranes
3. Lipids – these form important storage molecules in organisms, but they have a
secondary role as heat insulation (fat under skin) and a protective
function (fat surrounds heart and kidneys), when linked with
phosphorous they form phopholipids which are found in the cell
membranes
Metabolic Role of Biomolecules
1. Carbohydrate and Lipids – are broken down in respiration in a catabolic
reaction to produce energy. They are made during
photosynthesis using sunlight in an anabolic
reaction to produce food in plants.
2. Proteins – enzymes, which are proteins, are used to control reactions,
antibiotics to fight infections, hormones are used to regulate body
reactions.
3. Vitamin C – this is needed for the growth of connective tissue found in skin,
gums, cartilage, ligaments and blood vessels. It is also needed for
the growth of bones and teeth, it helps to heal wounds and keeps
the immune system functioning properly.
Deficiency of Vitamin C causes Scurvy – this causes poor healing of skin, bleeding that is often
seen under the skin as bruising and bleeding gums with loose teeth.
4. Vitamin D – helps to absorb calcium from the intestine, so it is indirectly
needed for healthy bones and teeth.
Deficiency of Vitamin D in children leads to Rickets, in adults it leads to Osteomalacia –
symptoms of both are weak deformed bones that break easily.
Minerals




Plants:
Minerals are needed in small amounts by organisms and are used in four ways:
To form part of the rigid body structure e.g. calcium in bones and cell walls
To form soft body tissues e.g. nitrogen and sulphur in muscles
They play a role in forming cell and body fluid e.g. sodium in saliva and liquid part of blood
To form biomolecules e.g. iron in haemoglobin, magnesium in chlorophyll
Symbol
Source
Calcium
Ca
Magnesiu
m
Mg
Salts absorbed from soil Forms calcium pectate in cell
walls
Salts absorbed from soil Part of structure of
chlorophyll
Mineral
Use
Animals:
Mineral
Calcium
Symbol
Source
Use
Ca
Milk, cheese, hard
drinking water
Forms bones and teeth
Iron
Fe
Liver, meat, green
vegetables
Forms part of haemoglobin
Water
Water is important as:
 A component of cytoplasm and body fluids (70 –95% of cell mass)
 A good solvent (dissolves things) and provides a medium in which chemical reactions take
place and transport occurs
 A participant in chemical reactions e.g. respiration and photosynthesis
 A participant in the movement of molecules in and out of cells and so controls cell shape
 Has a high specific heat capacity – the amount of energy needed to change the temperature of
water by 1 C is quite large and so it keeps it’s temperature despite temperature changes
around it which provides a stable environment for living organism and their reactions