Alpha Glucose as shown here above on both the left and the right join together with water being produced from the H group on the left hand glucose and the HO group from the right glucose. A glycosidic bond then forms between the two with the oxygen that is left; this final product is shown below.
As more glucose molecules join on to the end of the maltose a polysaccharide is made, they join in the same way with H2O being lost at each join.
Many many more glucose molecules would join on to the end of this polysaccharide molecule, and this is what the anabolic metabolism of carbohydrate is.
Lipids include fats and oils, they are important as another form of energy supply if there is not enough glucose, also as an insulator against the cold, protects organs against physical damage whist contributing to the overall shape of the body, that is just the triglycerides. Lipids come in many different forms, triglycerides, phospholipids, cholesterol and steroid hormones; which all play a different part in the body.
Triglycerides are made up of glycerol and three fatty acids as shown below; they are joined together, in a metabolic reaction, with ester bonds and water is lost from each fatty acid that attaches to the glycerol, so therefore 3 H2O are produced.
Above is the glycerol molecule on the left, and on the right is one fatty acid, although this is a very short chain, an average chain would be about 14 carbons long. On the next page you can see how the fatty acids join to the glycerol to form a triglyceride with the release of 3 water molecules.
This is one triglyceride; many animals store triglycerides as energy, because gram for gram they yield more than twice as much energy as proteins or carbohydrates. Due to the large amounts of C – H bonds, they can break down in respiration to form energy. Lipids are not as large as polysaccharides, proteins and nucleic acids, and so when they need to be transported around the body they can easily diffuse through the barriers, they need to move with the concentration gradient, from an area of high concentration to an area of relative lower concentration. When lipids first enter the body through food they must move through the digestive system, they are broken down and converted to micelles (microscopic droplets) these dissolve in water and pass through into the epithelial cells of the small intestine. Once inside the cells the fatty acids and glycerol can regroup and form triglycerides, but added to this is a protein coat which stops them sticking together, they are now ready to leave the cell in the form of chylomicrons. These molecules do not go into the blood stream, but into the lacteal, a branch of the lymphatic system. The chylomicrons remain suspended in the lymph fluid giving it a milky white colour until they move into a larger lymphatic vessel and eventually drained into a large duct, which empties into the blood. In the blood the chylomicrons are broken down into the primary substances of fatty acids and glycerol, where they can be synthesised into more complex lipids.
Ketosis is when the body’s carbohydrate level is reduced so much that the body is forced to use ketone bodies as fuel. Acetoacetate and D-3-hydroxybutyrate are the only two freely soluble lipids the body can use as ketone bodies in this situation. The major role of ketone bodies is to supply an alternative (to glucose) fuel for the brain in situations where there are little or no carbohydrates available with food. They are also used as building blocks for brain tissue. Ketone bodies are precursors for the essential substance (acetyl-CoA) required in the synthesis of myelin in the nerve cells as well as in the Krebs cycle in respiration. The normal rate of ketones in the body is a concentration of total ketone bodies in blood below 0.2 mmol/l. Ketosis is any amount over 0.2 mmol/l, but below 0.7 mmol/l (because at this level it becomes Ketoacidosis). Dieticians and nutritionists will continue to warn against getting your carbohydrates so low you need to live off of ketones, it can be dangerous not to have the correct levels of carbohydrates in the body.
Amino acids are required for the growth and repair of cells in the body, but the body cannot store proteins (of which amino acids are the building blocks), so appropriate amounts of proteins must be eaten everyday. The body only needs about 40 – 60 grams of protein per day, most people eat more than this, and so the excess amino acids are broken down in the liver, this can be done by deamination. If, however the correct amount of protein is not taken in, in the diet, some amino acids can be synthesised in the process that is transamination.
Deamination is the catabolic metabolism process, which breaks down the amino acids by removing the amino group (NH2) converting the amino acid to ammonia (NH3). The resulting products are: - an organic acid, which is respired, and ammonia, which is toxic to the body. The ammonia is quickly further broken down to form a less harmful product, urea in the ornithine cycle, shown below, and is removed by the kidneys.
Transamination is the metabolic process of synthesising amino acids by converting other substances. There are 20 amino acids that we use in the body, eight of these are essential and must be eaten in the diet, as they cannot be synthesised by the human body. The other twelve amino acids are classed as ‘non-essential’, as they can be synthesised by the metabolic process transamination, which takes place in the liver. An amino group is removed from an amino acid and transferred to an acid, making a new amino acid.
This shows that both metabolic reactions are important, if there are too many amino acids in the body, they must be broken down by deamination, if there are not enough of the ‘non-essential’ amino acids they must be synthesised by transamination.
All metabolic reactions are important in the body, they produce things that we need and remove the substances that are no longer required, and this helps to keep the body functioning properly.
