Carbohydrates are the most abundant organic compound. They play a number of roles in all form of life including:
- energy stores
- formation of DNA and RNA
- structural function in bacteria, plants and animals
- energy supply
A monosaccharide is the basic unit of a carbohydrate and represents the simplest form of sugar. In order for two monosaccharides to bond and form a disaccharide a condensation reaction occurs in which water is lost. The resulting bond is called a glycosidic bond: the -OH of one molecule of sugar joins with the -OH of another.
Polysaccharides, like cellulose, are formed when a number of monosaccharides bond together.
The basic structure of different carbohydrates affects their function as you can see from the table below.
| Name | Structure | Function |
| Starch
Glycogen Cellulose |
It’s composed of two polymer: amylose and amylopectin. Amylose is a polymer of glucose molecules joined together by ?-1, 4-glycosidic bonds. Amylopectin is also composed of ?-1, 4-glycosidic bonds but also consists of ?-1, 6-glycosidic bonds which branch out.It has a similar structure to amylopectin but consists of a lot more shorter, branches.
It’s composed of long, unbranched glucose polymers, joined by ?-1, 4-glycosidic bonds. |
This is used as an energy store in plants. Due to the fact that it folds up into a helix it allows for more storage space within cells. It’s also insolublein water which prevents it from dissolving in the plant. The branches mean that it can easily be hydrolysed and release glucose monomers.This is used as an energy store in animals. It’s a highly branched polymer which can be easily broken down into glucose, the primary source to making ATP. It can be stored internally as it’s unable to pass into the blood. It short branches make it very compact.
This is used as a structural building block in plants. It’s an unbranched polymer of glucose residues which are connected by ?-1,4 linkages. The result is long, straight chains which bond to each other via hydrogen bonds. This network of strong fibres ideal for a structural function. Cellulose is also insoluble in water. |
The Bohr Effect
Carbon dioxide has an effect on the dissociation graph known as the Bohr Effect. This explains why at a high concentration of carbon dioxide haemoglobin releases its oxygen molecules. When haemoglobin reaches a respiring cell the level of carbon dioxide is high. In a red blood cell, carbon dioxide is converted by an enzyme into carbonic anhydrase. This reaction leads to an excess in hydrogen ions which bind easily to haemoglobin creating haemoglobinic acid. When this occurs the oxygen molecules are released.
In terms of the graph, the Bohr effect causes the S-curve to move a little to the right. This simply shows that at a higher partial pressure of carbon dioxide the haemoglobin is less saturated than if there is a lower partial pressure.