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

Describe the molecular structure of starch (amylase), glycogen and cellulose, and relate these structures to their functions in living organisms.

Extracts from this document...


Describe the molecular structure of starch (amylase), glycogen and cellulose, and relate these structures to their functions in living organisms. Carbohydrates are the main energy source for the human body. Chemically, carbohydrates are organic molecules in which carbon, hydrogen and oxygen bond together in the ratio: Cx(H2O)y where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring. Animals (including humans) break down carbohydrates during the process of metabolism to release energy. For example, the chemical metabolism of the sugar glucose is shown below: C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy Animals obtain carbohydrates by eating foods that contain them, for example potatoes, rice, breads, etc. These carbohydrates are manufactured by plants during the process of photosynthesis. Plants harvest energy from sunlight to run the reaction described above in reverse: 6 CO2 + 6 H2O + energy (from sunlight) C6H12O6 + 6 O2 A potato, for example, is primarily a chemical storage system containing glucose molecules manufactured during photosynthesis. In a potato, however, those glucose molecules are bound together in a long chain. As it turns out, there are two types of carbohydrates, the simple sugars and those carbohydrates that are made of long chains of sugars - the complex carbohydrates. In this essay I am going to attempt to describe the structure of starch, glycogen and cellulose and relate these structures to their functions in living organisms. Carbohydrates contain 3 elements which are Carbon, Hydrogen and Oxygen. The group includes monomers, dimers and polymers, as shown in this diagram: The Isomerism which rotates the plane of polarized light to the right is called the Dextro (D or +) form. The one which rotates the plane of polarized light to the left is called the Laevo (L or -) form. The chemical and physical properties of the two isomerism are the same. ...read more.


Non-reducing sugars can also be tested for using Benedict's reagent but first require addition of an acid and heating to hydrolyze (break apart) the sugar. The acid must then be neutralized using an alkali like sodium hydroxide before carrying out the test as described above. Polysaccharides are long chains of many monosaccharides joined together by glycosidic bonds and through a condensation reaction. Each successive monosaccharide is added by means of a glycosydic bond, as in disaccharides. The final molecule may be several thousand monosaccharideunits long, forming a macromolecule. The most important polysaccharides are starch, glycogen and cellulose, all of which are polymers of glucose. Polysaccharides are not sugars. Since glucose is the main source of energy for cells, it is important for living organisms to store it in an appropriate form. If glucose itself accumulated in cells, it would dissolve and make the contents of the cell to concentrated, which would seriously affect its osmotic properties. It is also a reactive molecule and would interfere with normal cell chemistry. These problems are avoided by converting it, by condensation reactions, to a storage polysaccharide, which is a convenient, compact, inert and insoluble molecule. This is in the form of starch in plants and glycogen in animals. Glucose can be made available again quickly by an enzyme- controlled reaction. Starch is the principal polysaccharide used by plants to store glucose for later use as energy. Plants often store starch in seeds or other specialized organs, for example, common sources of starch include rice, beans, wheat, corn, potatoes, etc. When humans eat starch, an enzyme that occurs in saliva and in the intestines called amylase breaks the bonds between the repeating glucose units thus allowing the sugar to be absorbed into the bloodstream. Once absorbed into the bloodstream, the human body distributes glucose to the areas where it is needed for energy or stores it as its own special polymer - glycogen. ...read more.


Together the cellulose and pectins give exceptional mechanical strength. The cell wall is also permeable to a wide range of substances. Here are some other polysaccharides that I find interesting. * Chitin (poly glucose amine), found in fungal cell walls and the exoskeletons of insects. * Pectin (poly galactose uronate), found in plant cell walls. * Agar (poly galactose sulphate), found in algae and used to make agar plates. * Murein (a sugar-peptide polymer), found in bacterial cell walls. * Lignin (a complex polymer), found in the walls of xylem cells, is the main component of wood. Functions of carbohydrates 1. Substrate for respiration (glucose is essential for cardiac tissues). 2. Intermediate in respiration (e.g. glyceraldehydes). 3. Energy stores (e.g. starch, glycogen). 4. Structural (e.g. cellulose, chitin in arthropod exoskeletons and fungal walls). 5. Transport (e.g. sucrose is transported in the phloem of a plant). 6. Recognition of molecules outside a cell (e.g. attached to proteins or lipids on cell surface membrane). The following table classifies carbohydrates. Monosaccharides (one sugar unit) Disaccharides (two sugar units) Polysaccharides (many sugar units) Glucose Maltose Starch Fructose Sucrose Glycogen Galactose Lactose Cellulose Pectins Both starches and cellulose are carbohydrates which are classified as polysaccharides since they are composed of chains of glucose molecules. While they are similar, starches can be used as energy sources by the human body while cellulose cannot. Enzymes are important in the metabolism of foods, and these enzymes are very specific. They are somewhat like keys which will fit the geometry of the starch bonds, but not those of the cellulose bonds. The carbohydrates are the compounds which provide energy to living cells. They are compounds of carbon, hydrogen and oxygen with a ratio of two hydrogens for every oxygen atom. The carbohydrates we use as foods have their origin in the photosynthesis of plants. The name carbohydrate means "watered carbon" or carbon with attached water molecules. Many carbohydrates have empirical formuli which would imply about equal numbers of carbon and water molecules. For example, the glucose formula C6H12O6 suggest six carbon atoms and six water molecules. Rhodri Arnall 5/6/2007 - 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

Here's what a teacher thought of this essay

4 star(s)

A good account of the structure and functions of starch, glycogen and cellulose. However it is very text heavy and would benefit from labelled diagrams when explaining harder concepts. 4 stars.

Marked by teacher Louise Star 09/04/2013

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. Marked by a teacher

    Reducing and non-reducing sugars tests.

    3 star(s)

    or ketone group of the reducing sugar to form cuprous oxide, a red-brown precipitate. The final colour of the solution depends on how much of this precipitate was formed and therefore the colour gives an indication of how much reducing sugar was present.

  2. Peer reviewed

    The Importance and Biological Functions of Carbohydrates.

    4 star(s)

    ? is in the down position and ? is in the up position. Maltose is a disaccharide formed by two ? glucose's which form a glycosidic bond by giving off water. Other disaccharides are formed in a similar way. Lactose is formed from ? glucose and galactose. Starch is a very important carbohydrate and is the main storage in plants.

  1. Give an account of the biological significance of polysaccharides

    Cellulose forms the bulk of the fibre in a human diet that is necessary to maintain a healthy colon and bowel. Like starch, cellulose is a polysaccharide with glucose as its monomer.

  2. Osmosis in Living Tissue.

    The results are shown below. 0.0 mol/dm� 0.5 mol/dm� 1.0 mol/dm� % change in mass % change in Length % change in mass % change in Length % change in mass % change in Length 12.9 0.0 -0.3 -3.3 -7.4 -6.6 10.2 3.3 -3.4 -3.3 -17.6 -6.6 6.3 0.0 -6.2

  1. Rate of Respiration

    In the end of this reaction we have a net gain of 2 ATP molecules and further a reduced NAD molecule as well, the reduced NAD goes onto the electron transport chain where it is finally converted into ATP. Enzymes Enzymes are globular proteins, and with a tertiary structure.

  2. An investigation to see whether the concentration of Sucrose effects the amount of Carbon ...

    More respiration-taking place can be identified on the graph as when the line levels out this means that the respiration has stopped because no mass is being lost i.e. no carbon dioxide is being released. On the graph it can be observed that as the concentration increases it takes longer for the line to level out.

  1. heart essay

    When the heart is systolic (relaxed) all four valves are closed and blood is drawn into the atria's. When the atria's reach a certain pressure the two valves between the atria's and ventricles are pushed open and they let blood flow through into the ventricles.

  2. The Process of Osmosis and its Importance to Living Organisms.

    If a marine osmotic conformer were put in fresh water, osmosis would cause water to enter its cells to form equilibrium, eventually causing the cells to pop. If a marine osmotic conformer were put in super salty water then osmosis would cause the water inside the cells to move out, eventually causing the cells to dehydrate.

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