Functionality of carbohydrates

Function is always decided by structure. So the structure of the carbohydrate chain will determine what function would this carbohydrate be more suited for.

For example cellulose which has a structural role is composed of a linear chain of glucose "The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen molecules on the same or on a neighbor chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength." ( from wikipedia ) If you can imagine the chain, this structural characteristic would be lost to a certain extenct if cellulose was branched due to the decreased inermolecular interaction due to the presence of branches which would block the chains from interacting with each other.

Starch and glycogen are both energetic molecules which are highly branched, which also makes sense if you think about it, more glycosidic bonds in a smaller space ( breaking glycosidic bonds yields energy, so more bonds = more energy ).

Of course cellulose can also function as an energetic molecule but it won't have a good " functionality " as an energetic molecule as much as a structural molecule, and the opposite for starch and glycogen.

Hey Clukic,

in a nut-shell, the term carbohydrate describes any class of organic compound composed of carbon, hydrogen, and oxygen, including starches and sugars, produced in green plants by photosynthesis and are an important source of food for animals and people.

Take for instance a simple carbohydrate glucose. This monosaccharide has a central role as an energy source for cells. It is broken down to smaller molecules in a series of reactions, releasing energy that the cell can harness to do useful work. Cells use simple polysaccharides composed only of glucose units - principally glycogen in animals and starch in plants - as long-term stores of glucose, held in reserve for energy production.

Going back to your question, the functionality of a carbohydrate is dependent on the organism. For instance, in plants, the structural carbohydrate cellulose is used to create cell walls. In animal liver cells, carbohydrates are built into longer chains (glycogen) as a mode of storing energy. In insects, carbohydrates are made into chitin, a complex polymer which makes up the exoskeleton of the species. In epithelial cells, smaller carbohydrates can be covalently linked to proteins to form glycoproteins, or to lipids to form glycolipids. The surface of most cells are decorated with sugar polymers that belong to glycoproteins and glycolipids in the plasma membrane.

Moreover, the carbohydrate's chemical structure also has a lot to do with how the organism will use it! For instance, in order for an animal liver cell to create glycogen out of glucose molecules, it requires specific enzymes that allow glucose to specifically fit in into the enzyme and generate the condensation reaction. Not all animals have the same enzymes and thus this does not take place in every organism. Hence, the functionality of a carbohydrate is dependent on the organism itself.

Is that clear? Tell me if you need more assistance. This is somewhat of an elaboration of karim89  

Bio_man  8)

So, cellulose, chitin, glycogen are all made of glucose? And functionality of glucose is determined by a organism?
Is there a cellulose in humans and animals?

no there isn't

Yes, functionality is dependent on the organism. If the organism produces the right proteins, it will convert the carbohydrate into whatever compound it is prescribed to be. For instance, if the organism produces the enzyme Glycogen synthase (as in humans and mammals) the organism will have the ability to convert glucose into glycogen, and glycogen being a storage energy polymer found in the liver.

In other words, it all depends on the organism and its genome (genetic make-up).

Chitin is a linear polymer of a sugar derivative called N-acetylglucosamine. So at one point, glucose was the starting carbohydrate that was converted into this complex structural polymer. Moreover, like starch, cellulose is a polysaccharide with glucose as its monomer. And glycogen is totally made out of glucose as well.

Carbohydrates cannot be converted without proteins, specifically enzymes. Enzymes are produced according to the organisms genetic makeup.

Tell me if you still need clarification. 

Thanks bio_man you are being very nice! It's much clearer now, but is there something that determines how well will the carbohydrate (glycogen, cellulose, chitin etc.) perform assigned function?

Aha, that depends on the functionality of the organism itself. Take for instance a person who is diabetic. Although he/she may have the essential enzymes to create glycogen out of glucose, they cannot do so because their pancreas doesn't produce enough insulin to allow the cells of the liver to access the supply of glucose coming from the food. So, it's kind of difficult to respond to this CLukic, you see where I am getting at?

Another thing to consider is Chirality, but this is an advanced biochemical topic which I don't want to get into. For instance, the carbohydrate glucose can adopt several different structures, but all of these structures can be divided into two families of mirror-images (stereoisomers). Only one set of these isomers exists in nature, those derived from the "right-handed form" of glucose, denoted D-glucose. D-glucose is often referred to as dextrose, especially in the food industry. The mirror-image of the molecule, L-glucose. L-Glucose cannot be phosphorylated by enzymes, such as hexokinase, and so is not broken down by living organisms to release energy.

Oh okay bio_man. Thanks, I am just blown away by your knowledge!!! Thank you very much! 

you're welcome