Carbohydrates are composed mainly of carbon, hydrogen and oxygen in a CH2 O proportion. For each carbon and oxygen there are 2 hydrogen atoms. This means all carbohydrates contain C, H, and O, with carbon and hydrogen in a 2:1 ratio. Carbohydrates are important as short term energy storage molecules (simple sugars such as glucose and fructose), as long term energy storage molecules (starches and glycogen), as structural molecules (e.g. cellulose, which is found in all plant cell walls) and as important components of DNA and RNA.
Monosaccharides are simple sugars that include galactose and fructose. The most common monosaccharide is glucose. Glucose is extremely important because it provides energy when broken down by the process known as cellular respiration. Furthermore it is at the crossroad of many chemical reactions. Many other molecules such as amino acids and fatty acids can be made from glucose and many molecules can be broken down to form glucose. Our brains cannot store glucose and must be constantly supplied with it by our blood. If this supply stops for too long, the brain cells will begin to die.
A disaccharide is formed when two monosaccharides are joined together by a reaction known as a dehydration, or condensation, synthesis. In this type of reaction water is removed, thus the name "dehydration". A new molecule is formed or "synthesized" from the two previously separate ones. The animation shows a molecule of the disaccharide, maltose, formed from two glucose molecules. An enzyme is required to make the reaction occur.
Click the link below to view an animation demonstrating dehydration:
A very common disaccharide is made of a glucose molecule and a fructose molecule. It is called sucrose, but is better known as the table sugar we so love to eat.
Polysaccharides (poly = many, saccharide = sugar) are made of many sugar molecules joined together by dehydration synthesis reactions. When several monosaccharides are bonded together a polysaccharide, or complex sugar, is created. There are many polysaccharides that serve different purposes. Cellulose, found in plants and chitin, found in the exoskeleton of invertebrates serve as structural polymers. Cellulose is the most abundant organic molecule on earth. Unfortunately, humans are unable to digest and obtain energy from cellulose.
Polysaccharides like glycogen and starch are great energy storage macromolecules. All living cells store glucose for energy in the form of glycogen in animals and in plants glucose is stored as starch. Both are made of many repeating units of glucose molecules. They are, therefore, polymers of glucose. They differ from each other in the amount of branching of the molecules, the way in which the molecules are connected to each other and in the addition of amino groups to the glucose.
1. Starch. Starch is the long term energy storage form of glucose in plants. It is found in abundance in the grains we eat, (rice, wheat, barley and rye) and in many vegetables, such as potatoes and corn. There will be many more glucose molecules similarly connected to complete this polymer of glucose.
When we eat or consume this energy storage macromolecule it is broken down in the body into smaller sugars. In this case water is added and starch is broken down to maltose and then two glucose molecules. The splitting apart reaction is called hydrolysis.
Click the link below to see an animation demonstrating hydrolysis:
2. Glycogen. Glycogen is the energy storage form of glucose. This polymer has the glucose molecules linked in the same way as they are in the plant starch. Glycogen molecules tend to be larger and much more branched than are starch molecules and they are found in the liver and muscles of animals. Human beings send their digested food to the liver where it is carefully monitored. If the supply of glucose in the blood is sufficient, glucose will be polymerized into glycogen. After enough glycogen is synthesized to supply glucose for two hours, the excess glucose will be converted into fat and stored in this efficient, but often unsightly way.
Click on the link below to learn more about Carbohydrates:
Carbohydrates have different structures, depending on their function in the body. Simple carbohydrates can provide immediate energy, while complex carbohydrates provide a longer-term energy source. ', BELOW, LEFT, BORDER, 1, BGCOLOR, '#7E4EF2', FGCOLOR, '#ffffff', WIDTH, 200, TEXTSIZE, 2, TEXTCOLOR, '#000000');" onfocus="return overlib('Disease characterized by lack of or abnormal action of insulin.', CAPTIONBACKUP, '', CAPTIONSIZE, 2, CGCOLOR, '', PADX, 5, 5, PADY, 5, 5, CLOSECLICK, CLOSETEXT, '', BELOW, LEFT, BORDER, 1, BGCOLOR, '#7E4EF2', FGCOLOR, '#ffffff', WIDTH, 200, TEXTSIZE, 2, TEXTCOLOR, '#000000');" onmouseout="nd(0);" onblur="nd(0);">Diabetes mellitus is a disease in which the body has difficulty regulating the amount of sugar in the blood. Individuals with type 1 diabetes do not produce enough ', BELOW, LEFT, BORDER, 1, BGCOLOR, '#7E4EF2', FGCOLOR, '#ffffff', WIDTH, 200, TEXTSIZE, 2, TEXTCOLOR, '#000000');" onfocus="return overlib('Pancreatic hormone that decreases plasma glucose concentrations.', CAPTIONBACKUP, '', CAPTIONSIZE, 2, CGCOLOR, '', PADX, 5, 5, PADY, 5, 5, CLOSECLICK, CLOSETEXT, '', BELOW, LEFT, BORDER, 1, BGCOLOR, '#7E4EF2', FGCOLOR, '#ffffff', WIDTH, 200, TEXTSIZE, 2, TEXTCOLOR, '#000000');" onmouseout="nd(0);" onblur="nd(0);">insulin, the hormone that regulates blood sugar, and must take regular doses of additional insulin. However, if the body gets too much additional insulin, it can cause the individual's blood sugar level to be too low. Individuals with type 1 diabetes often carry food like juice or candy with them to get their blood sugar levels up quickly.