• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Carbohydrates are substances with the general formula Cx(H2O)y, where x and y are variable numbers; their name carbohydrates (hydrates of carbon) comes from the fact that hydrogen and oxygen are present in the same amounts as in water.

Extracts from this document...

Introduction

pCARBOHYDRATES0 Carbohydrates are substances with the general formula Cx(H2O)y, where x and y are variable numbers; their name carbohydrates (hydrates of carbon) comes from the fact that hydrogen and oxygen are present in the same amounts as in water. Carbohydrates are divided into three main classes: Monosaccharides, Di-Saccharides and Polysaccharides. Monosaccharides * Monosaccharides are single sugar units. * Their general formula is (CH2O)n (where n is between 3-9). * They are classified according to the number of carbon atoms as trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C). Of these, pentoses and hexoses are the most common. * Monosaccharides are important as energy sources and as building blocks for larger molecules, they are suitable for this because they are chemically reactive molecules and show a wide variety of structures, including the variation in the number of carbon atoms. Aldoses and Ketoses * In Monosaccharides, all the carbon atoms except one have a hydroxyl group attached. * The remaining carbon atom is either part of an aldehyde group, in which case the Monosaccharides is called an aldose or aldo sugar, or is part of a keto group, when it is called a ketose or keto sugar. ...read more.

Middle

Open chain and ring forms Fig 1.3 shows glucose as both its 'open chain' and ring structures. The open chain form can be straight, but because of the bond angles between carbon atoms it is possible for sugars with 5 or 6 carbon atoms to bend round and form stable ring structures. In hexoses like glucose, the first carbon atom combines with the oxygen atom on carbon atom number 5 to give a six-membered ring. Note that oxygen is part of the ring and that one carbon, carbon atom number 6, sticks up out of the ring. In pentoses, the first carbon atom joins with the oxygen atom on the fourth carbon atom to give a five-membered ring. (As shown in fig 1.4) The ring structures of pentoses and hexoses are the usual forms, with only a small proportion of the molecules existing in the open chain form at any one time. The ring structure is the form used to make disaccharides and polysaccharides. Alpha and beta isomers Fig 1.3 shows that glucose can exist in two possible ring forms, known as the alpha and beta forms. ...read more.

Conclusion

Lactose * Also known as milk sugar. * Found exclusively in milk. * Is an important energy source for young mammals. * Can only be digested slowly, and so provides a slow release of energy. Sucrose * Also known as cane sugar. * It is the most abundant disaccharide in nature. * Most commonly found in plants, where is it transported in large amounts by phloem tissue. * It is a good transport sugar as it is very soluble and so can be moved efficiently in high concentrations. * It is relatively unreactive. * It can be obtained commercially as sugar cane or the sugar we buy in shops. Reducing Sugars * All monosaccharides and some disaccharides, including maltose and lactose, are reducing sugars. * This means that they can carry out a type of chemical reaction known as reduction. * Sucrose is the only common non-reducing sugar. * Two common tests for reducing sugars are Benedict's test and Fehling's test, which make use of the ability of these sugars to reduce copper from a valency of 2 to a valency of 1. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Exchange, Transport & Reproduction section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Exchange, Transport & Reproduction essays

  1. Peer reviewed

    "An investigation into the Respiration of Carbohydrate Substrates by Yeast."

    5 star(s)

    It only has one glycosidic bond to break, which is not very significant and therefore it is broken almost immediately and sucrose begins to produce carbon dioxide, just a short time after glucose. The big difference between starch and sucrose can be related to the fact that starch is a

  2. Biochemical Tests for Carbohydrates

    Two monosaccharides may join together to form a disaccharide, and they do this through dehydration, forming a covalent, glycosidic linkage. During this reaction, aided by enzymes in the cytoplasm of cells, one glucose molecule, for example, donates a hydroxyl group from its carbon skeleton, and another glucose donates a hydrogen atom.

  1. Compare and contrast the digestion and absorption of carbohydrates and lipids.

    However, fibre is important in maintaining the health and functioning of the digestive tract. Most of the carbohydrates ingested in the body, is converted to energy. Glucose, from our diet in the form of sugar or carbohydrates, is the preferred fuel molecule for the brain.

  2. Carbohydrates are made up of carbon, hydrogen and oxygen.

    Glucose, fructose and galactose make up the principal monosaccharides. They are all hexoses. Glucose is mildly sweet and is the important carbohydrate in the blood. There are two types of glucose, ?-glucose and �-glucose. These are isomers i.e. they have the same chemical formula but different structural formula.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work