Download Major molecule of food

UNIT 2. MAJOR MOLECULES IN FOOD
Learning objectives
After completing this chapter learner should be able to:
1.
understand the type of major molecules that make up
food
2.
become familiar about the sources that supply these
macromolecules
3.
understand the important functions of each
macromolecule.
1.MAJOR MOLECULES IN FOOD
1. Introduction
The four major classes of molecules in food are carbohydrates,
protein, fat and nucleic acids.
They are made up of relatively small micromolecules called
monomers that are linked together to create large
macromolecules, which are known as polymers.
When monomers are linked together to synthesize a biological
polymer, they undergo a process called synthesis.
2. Functions of macromolecules
•
To provide materials for growth and repair of tissues in
order to provide and maintain the basic structure of our
bodies.
•
To supply the body with energy in the form of ATP
required to perform external and internal activities
•
To provide materials which regulate the functions of the
body
•
To store and decode genetic information
•
To perform structural and catalytic roles in cells
3. Nature of Major molecules
• The main classes of molecules in food are are called
macromolecules or polymers.
• The small micromolecules that are linked together to
create these polymers are called monomers.
• Monomers are linked together to synthesize a
biological polymer by enzyme catalysed reactions.
3.1 Carbohydrates
• Carbohydrates are the most widely distributed and abundant organic
compound on earth.
• The dry substance of plant is composed of 50-80% of carbohydrates. The
structural material in plants is mainly cellulose and hemicellulose. Starch is
the major storage polysaccharide in plants.
• Pectins and sugars such as sucrose ang glucose are also plant
components.
• Glycogen is the storage form of carbohydrates in liver and muscle cells of
animls.
• The blood group substances, mucins and mucopolysaccharides of ground
substanes between cells are other important types of carbohydrates in
animals.
• Chitin is an important compound present in the exoskeleton of
invertebrates.
• Carbohydrate biosynthesis in plants starting from carbon dioxide and
water with the help of light energy (Photosynthesis) is the basis for the
existence of all other organisms which depend on the intake of organic
substances with food.
Functions
1.
2.
3.
4.
5.
They are the major source of biological energy through their
oxidation in the tissues.
They play an important role in the energy metabolism of
animals and plant.
The energy needed for mechanical work and chemical
reactions in all living forms are derived from carbohydrates.
The carbon skeletons of almost all carbohydrates are derived
from carbohydrates.
They provide the basic raw materials for the synthesis of
many industrially important compounds.
Sources of carbohydrates
• Carbohydrate rich foods are abundant and cheap
compared with fats and protein.
• Food carbohydrates : Starches and sugars found in cereal
grains, tubers, vegetables, legumes, fruits, milk and milk
products.
• Fructose is present in Honey.
• Fiber, consisting largely of cellulose and other non
digestible cell-wall polymers of plant origin that are non
digestible and plays no metabolic role but helps to
maintain proper motility in the intestinal tract.
Sources of Carbohydrate
3.2. Lipids
• Lipids refer to substances such as fats and oils and fat like
substances.
• They are another group of major molecules found in food.
• Lipids exhibit greater structural variety than the other
classes of biological molecules.
Functions of lipids
1.
2.
3.
4.
5.
6.
7.
Lipids containing hydrocarbon chains serve as energy
stores.Fats supply over twice as much energy per unit weight
as proteins or carbohydrates.
The presence of lipids in diet contributes considerably to
palatability.
Many enzymes need lipid molecoles for maximal activity.
Lipids supply the essential fatty acids which are not
synthesised in humen beings but are essential for growth..
They are essential for the absorption of fat soluble vitamins A,
D, E and K. In the form of lipid bilayers they are essential
components of biological membranes.
Many intra-and intercellular signaling events involve lipid
molecules. In addition to triglycerides, cholesterol and
phospholipids provide structure to the body cells.
The subcutaneous lipid deposits act as insulation against
excessive heat loss to the environment and insulate vital
organs against mechanical trauma.
Sources
• Important animal sources are meat, milk , eggs and fish
and important plant sources are all oils and vanaspathy.
• Fats from animal sources are relatively rich in saturated
fatty acids but contain a low content of polyunsaturated
acids.
• Fats from plant and fish are rich in polyunsaturated fatty
acids.
• Cholesterol is present in significant amounts in animal
products, such as egg yolk, butterfat, and meat.
• It is absent in plant foods.
3. 3 Proteins
• Proteins are the most abundant substances in all cells
forming about 50% of a cell's over all mass.
• A protein is a unbranched polymer of amino acids.
Functions
1.
Proteins supply the required building blocks for protein
biosynthesis.
2.
Amino acids are precursors of other nitrogen containing
substances such as enzymes, hormones, porphyrins,
and many other biomolecules.
3.
They also contribute to the flavour of food and are
precursors of aroma compounds and colours formed
during thermal or enzymatic reactions in production,
processing and storage of food.
4.
Oxidation of the carbon skeletons of amino acids also
furnishes significant fraction of the total daily energy
requirement.
Important sources of protein.
Animal Sources: Meat, fish, milk, egg,
Plant sources: Cereals, pulses, beans and peas
Sources of protein.
Meat, fish, milk, egg, pulses, beans and peas
3.4 Nucleic acids
• Nucleic acids are polymers composed of nucleotide monomers.
• The Nucleotide monomers are made up of a five-carbon sugar, a
heterocyclic nitrogenous base and phosphate group(s).
• They are joined to one another by covalent bonds between the
phosphate of one and the sugar of another by phosphodiester
linkages.
• Types of nucleic acids
• Deoxyribonucleic acid (DNA) and
• Ribonucleic acid (RNA).
• Nearly all the DNA is found within the cell nucleus.
• RNA occurs in all parts of a cell.
• DNA is repository of hereditary character.
• RNA is essentially required for protein biosynthesis.
Types of nucleic acids
• Deoxyribonucleic acid (DNA) and
• Ribonucleic acid (RNA).
•
•
•
•
Nearly all the DNA is found within the cell nucleus.
RNA occurs in all parts of a cell.
DNA is repository of hereditary character.
RNA is essentially required for protein biosynthesis.
Functions of nucleic acids
1.
Primary function of DNA is the storage and transfer of
genetic information.
2.
Information is used (indirectly) to control many functions of
a living cell.
3.
DNA is passed from existing cells to new cells during cell
division.
4.
RNA functions primarily in synthesis of proteins, the
molecules that carry out essential cellular functions.