Where is glucose found in organisms

Glucose was first isolated in from raisins by Andreas Marggraf. The name glucose was coined in by Jean Dumas, from the greek glycos , sugar or sweet , and the structure was discovered by Emil Fischer around the turn of the century. In fact, there are 2 forms of glucose, the L-form the left-handed form and the D-form the right-handed form.

One is the mirror image of the other, but otherwise they are structurally identical. But since most of the biological processes which make glucose involve complex enzymes, which are 'stereospecific' that is, they prefer to react with only one form of the 2 isomers , the result is that only the D-form of glucose is found in nature a fact which has given rise to the other commonly-used name for glucose, dextrose.

Glucose can be thought of as a derivative of hexane a 6-carbon chain with -OH groups attached to every carbon except the endmost one, which exists as an aldehyde carbonyl. However because the chain is flexible it can wrap around until the 2 ends react together to form a ring structure. Thus a solution of glucose can be thought of as a rapidly changing mixture of rings and chains, continually interconverting between the 2 forms.

Glucose is a ready source of energy, since its carbon atoms are easily oxidised burnt to form carbon dioxide, releasing energy in the process. However, unlike other hydrocarbon fuels, which are insoluble in water, the numerous OH groups in glucose allow it to readily hydrogen-bond with water molecules, so making it highly soluble in water. This allows the glucose fuel to be transported easily within biological systems, for example in the bloodstream of animals or the sap of plants. In fact the average adult has grams of glucose in the blood about 1 teaspoon , which will supply the body's energy needs for only about 15 minutes, thereafter the levels must be replenished from compounds stored in the liver.

Because glucose is found in ripe fruits, the nectar of flowers, leaves, sap and blood, over the years it has been given various common names, such as starch sugar , blood sugar , grape sugar and corn sugar.

Glucose is called a monosaccharide , since it is made up of only one unit, but it is possible to join individual sugar units together to form a chain, in much the same way as monomer units are linked up to form a long polymer. We start digesting it in our mouths. Salivary amylase, an enzyme found in saliva, starts the hydrolysis of starch and produces a mix of polysaccharides, maltose and glucose.

This is the reason why, after a few seconds of chewing, a piece of relatively tasteless bread develops a certain sweet taste. This hydrolysis by amylase continues all the way to the stomach, then the m altase present in the small intestine splits the maltose molecules into two glucose molecules and completes the hydrolysis. The glucose is then actively absorbed by the cells of the intestine and enters the bloodstream.

When it arrives in the liver, part of it is used to synthesise glycogen, an energy reserve in the form of a polysaccharide made up of tens of thousands of glucose units.

This glycogen can then be converted back into glucose released into the bloodstream as and when the body needs it.

This mechanism determines the level of glucose in the blood and is carefully controlled by two hormones, insulin and glucagon. These hormones inform the cells if they need to store or release glucose into the bloodstream to enable the body to function properly. The concentration of glucose in the blood plasma is called glycaemia.

In a healthy person, blood glucose concentration is between 0. Glucides Vevey. Home Glucose. Glucose Glucose is one of the fundamental molecules of life on Earth, the product of photosynthesis of solar energy stored in plants.

A cellulose-like material, called chitin, is used by insects and arthropods to stiffen and give form to their outer exoskeleton, and other complex polysaccharides are used in animals in places where tensile strength is needed. Starch is a polymer of the alternate anomer of glucose and is used by plants as a way of storing glucose. It is a major reserve of energy that can be quickly mobilized as necessary. Most plants cells have stored starch reserves in the form of tiny granules.

Within these granules are two kinds of starch; amylose and amylopectin , which differ from one another in the amount of branching taking place in the molecule. Many plants also have specialized regions of starch storage in which parenchymatous cells process and package starch molecules for long-term use.

Tubers, such as potatoes, and seeds with their valuable embryos, are both plant structures with high concentrations of stored starch. Mobile animals, such as humans, need energy reserves in much the same way. A small amount of these reserves is in the form of an amylopectin-like molecule called glycogen , which is found in the liver and some muscles.

However, carbohydrates like starch or glycogen only produce about 4 kilocalories of energy per gram of weight, about the same as that for protein.

While this kind of efficiency is fine for plants which don't have to move , it is not enough for animals with their higher metabolic needs. Lipids store about 9 kilocalories of energy per gram, almost twice that of carbohydrates, so they are the preferred fuel in the animal body. Glucose has one great advantage, however, it is soluble in water and blood and thus easy to distribute around the body.

Animals use this simple monosaccharide as a portable source of instant energy, adding and releasing it from the liver if and when it is required. Humans need about , kilocalories of energy per day 24 hours. When possible, humans try to eat and digest meals with high caloric value, such as meat and lipids. But food of this sort is rare and hard to find or catch!

Plants are a much more readily available and easy to catch! Interestingly, cellulose cannot be digested by most animals, including humans. Grass eating animals, such as cows, must therefore enter into a partnership with micro-organisms that can break the bonds between the glucose molecules in the cellulose.