Carbohydrates play a large part in the lives of all living things; there are many different types of carbohydrates, all with their own individual structures and functions.

Carbohydrates play a large part in the lives of all living things; there are many different types of carbohydrates, all with their own individual structures and functions. I am going to look at three specific carbohydrates and compare their structures and functions. The three carbohydrates I am going to examine are cellulose, glycogen and starch.

Cellulose is the most common biological molecule, it is a structural polysaccharide, and consists of glucose molecules. Unlike starch cellulose cannot be digested by humans and most animals, but it has an important function as dietary fibre in our

diet. Cellulose has a structural function, it forms cellular walls in plants and is therefore present in all plant tissues, with out it plants would not have a stable structure, and would not be able to stand up right. In the structure of cellulose the CH OH groups are not always above the plane, instead the positions alternate, from above to below.

Glycogen has the most complicated structure out of the carbohydrates I am going to look at. The reason behind glycogen having such a complicated structure is that its structure has many branches. The branches are a very important aspect of glycogen, as they enable it to be broken down much quicker. The reason for this is that the more branches a molecule has, the more starting points for the enzymes to attack. Glycogen is an energy source for the body, this is why it needs to be

easily and quickly broken down, it is stored in the ...

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easily and quickly broken down, it is stored in the liver and the muscles, for easy access.

Starch is a polysaccharide, which consists of alpha-D-glucose molecules, it is used by plants to store energy, and is digested when the need for energy arises, e.g., when a seed germinates, it may also be digested by humans and most animals. The reason behind plants using starch, instead of glycogen as their energy source is simple, if glucose remained in the state that it is in immediately after

photosynthesis and is stored solely as glucose, it may result in the cells exploding. The reason for this is that glucose is highly soluble, therefore if stored in a cell osmosis would take place, causing the chloroplasts to take in water and explode. Due to this the plant makes the glucose into starch, which is less soluble, therefore preventing osmosis from taking place. Starch is composed of two different polymers, amylose and amylopectin; most starches consist of both forms. The amylose molecules are essentially linear (1-4) glucan chains, whereas amylopectin are highly branched, making them similar to glycogen, just with fewer branches.

After examining the structures of all three carbohydrates I feel confident in comparing them. Although similar, there are differences between the molecular structure of cellulose and starch. Starch consists of alpha-glucose and cellulose consists of beta-glucose. In the diagrams, you can see that the first oxygen atom in each segment is below the plane of the sugar ring and the hydrogen atom on the first carbon atom is above the plane, this continues for the starch molecule, but alternates for the cellulose molecule. The glycogen molecule has a much more complicated structure than that of both the cellulose and starch molecule; it is in no way similar to either molecule.

The functions of glycogen and starch are very similar; they both store energy, but are each suited to their specific organism. Both molecules are easily broken down, to gain a quick energy supply, although they don’t have similar structures. Cellulose is not related to the functions of either starch, nor glycogen, its main purpose does not involve energy, but instead it involves structure and support.

Although all different in many ways, all three of the carbohydrates I have examined have proved to be very important to the organism they are designed to work in. Without them life for the organism would be very different.