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The three main food groups and their structures

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The three main food groups and their structures Carbohydrates: Carbohydrates contain the elements carbon, hydrogen and oxygen as their name suggests. Carbohydrates are comprised of monosaccharides, disaccharides and polysaccharides. Each monosaccharide is structural and/or optical isomer of glucose (C6H12O6) Monosaccharides are single sugar units and have between three and ten carbon atoms per molecule monosaccharides include alpha glucose, beta glucose and fructose. Alpha glucose Beta glucose Fructose Disaccharides are two monosaccharides which formed in a condensation reaction to produce glycosidic bonds joining the two monosaccharides together and water being produced as a by product. This is also a reversible reaction and the process of hydrolysis can form two monosaccharides. In a condensation reaction 2 hydrogen atoms and one oxygen atom (per molecule!) react to produce water, leaving the other monosaccharide with one oxygen atom which is free to bond with the other monosaccharide producing either a 1,4, a 1,2 or a 1,6 glycosidic bond allowing for polymerisation to produce complex carbohydrates (polysaccharides). Alpha 1,2 glycosidic linkage Sucrose is made from this reaction as seen here. Disaccharides are used as an energy source and are found in most foods i.e. natural cane sugar (sucrose) ...read more.


Proteins therefore have these elements present in them. In order to form long chains which in turn form proteins they undergo condensation reactions to form peptide bonds (which is also reversible in the process of hydrolysis). Individual molecules containing this atomic arrangement are called amino acids, which when joined to another by a peptide bond produces a dipeptide. This can go on to produce long complex chains called polypeptides producing proteins. With amino acids being the constituents of protein the protein contains composites of the amino acids. There are only 20 amino acids but they go on to make up thousands of different proteins. The primary structure of a protein refers to the number of sequencing of amino acids in a polypeptide chain joined by peptide bonds. This determines the 3D shape of the protein. The secondary structure refers to the folding of a polypeptide chain either in an alpha helix or a beta pleated sheet. Which is the type of structure found in fibrous protein such as keratin present in nails, hair and wool or collagen (the main protein present in connective tissue). The beta pleated sheet is a different form of a secondary structure where the polypeptide chains are folded and attached by weak hydrogen bonds this type of structure is present in the protein fibroin which is the main composite of silk. ...read more.


The formation of mono, di or triglycerides happens in a condensation reaction when the OH groups on the end of glycerol (an alcohol) forms a single bond with an oxygen which then to for fill its valence, bonds with the other carbon atom, the result of which is a triglyceride and three molecules of water. These oxygen linkages are called ester bonds. A triglyceride Fats are stored in adipose tissue and work to provide energy when needed which provide approximately 30Kj of energy per gram whilst carbohydrates provide 17Kj per gram. Fats also provide insulation, which in amphibious mammals is specialised as blubber. They also provide protection for delicate organs like the kidneys. Another attributable function is that they provide the materials for cell membranes composed of phospholipids glycerol and 2 fatty acids. This diagram shows the phospholipids arranged as they would be in the cell membrane. The hydrophilic heads point outwards and forms hydrogen bonds with water molecule whereas the hydrophobic tails point outwards. Cholesterol is used to make certain types of lipids called sterols used to make steroid sex hormones like oestrogen and testosterone. Waxes are fats which have an alcohol other than glycerol, these provide weather protection of some animals. ...read more.

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