What is food and what happens to it?

You need to understand that food consists largely of parts of other organisms. This could be plant, animal, fungal etc. These organisms are made from the same types of molecules as are humans hence, all life has the same biochemical molecules.
Humans are "Heterotrophs" – they need to have a ready-made, organic carbon source for their food needs. Unlike plants, we cannot use inorganic carbon to ‘make’ our own food.
The 3 main molecules are sometimes called “Macromolecules” because they are large polymers that have been made by joining smaller molecules together in condensation reactions.
These macromolecules are: Lipids, Carbohydrates and Proteins – Learn the basic structure of what makes a protein, a carbohydrate and a lipid. See below for more information.
These large macromolecules need to be hydrolysed to smaller molecules or monomers to be absorbed in the gut. This is usually where ENZYMES come in.

Question: Do you know what Hydrolised means and what a condensation reaction is?

Carbohydrates

Monosaccharides make disaccharides and polysaccharides.
Glucose molecules may link together to form maltose, starch, glycogen and cellulose.
A glycosidic bond links one glucose molecule to the next Glucose is a monosaccharide, maltose is a disaccharide, starch, glycogen & cellulose are polysaccharides.
Polysaccharides are known as “complex carbohydrates”.
Excess carbohydrate can be stored by the body in the form of fats.
Carbohydrates are broken down by various enzymes such as amylases. These separate the polymers into their constituent monomers.
Carbohydrates are the first macromolecule type to be used for energy release in the respiratory chain.

Proteins

Proteins are made of amino acids that are linked by Peptide bonds. The overall shape of a protein molecule occurs when it has achieved the tertiary structure.
This structure is held together by hydrogen and ionic bonds, as well as disulphide bridges.
A protein becomes denatured when some or all of these bonds are compromised such as when excessive heat, acid, alkali or other substance affects the protein.
Excess protein taken in the diet cannot be stored. The amino acids are broken down in the liver by deamination and excreted in the urine.
Proteins are broken down by proteases into the individual amino acids.
Proteins are the last of the macromolecules in humans to be used as an energy source.

Fats

Fats are made of glycerol and fatty acids.
Glycerol and fatty acids are linked by ester bonds.
Fats are usually called lipids.
Lipids contain the highest energy level of all the macromolecules. They are long term energy storage molecules.
Excess fat in the diet is not usually stored.
Lipids are broken down by lipases after being emulsified by bile secreted from the liver. Bile is stored in the gall bladder.

The Digestive Enzymes

Digestive enzymes allow hydrolysis reactions to take place rapidly under the physiological conditions found in the gut.
Remember, all enzymes are themselves proteins.
Digestive enzymes break down large molecules so that they can be diffused through the lining of the small intestine and into the blood stream.
The blood stream carries all these nutrients to the liver where they are dispersed to where ever the body needs them.
The monomers of the macromolecules are then reassembled into the various proteins, carbohydrates and lipids that are found in the body’s tissues.

How can you calculate the quantity of various macromolecules?

Chromatography with the calculation of R_f values is a technique by which the components of a mixture can be identified. Thus the relative value of a certain type of amino acid in a mixture can be quantitatively worked out.

Chromatography uses the principle that a solvent will be able to carry certain molecules to a given distance along a medium. The larger the molecule, the less distance it can be carried.

What is food and what happens to it?

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