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Chemistry Carbohydrates 52,654 views

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Carbohydrates are macromolecules composed of carbon, hydrogen and oxygen. Biologists are interested in carbohydrates because they serve as energy storage and as structural frameworks within cells. Simple carbohydrates consist of only 1 or 2 monomers, or monosaccharide's, while complex carbohydrates, or polysaccharides, are chains of monomers. Some types of carbohydrates are sugars, starches and cellulose. Plants manufacture carbohydrates through photosynthesis.

Carbohydrates are one of the four basic kinds of organic molecules. They're used to store energy in the form of sugars or starches and many of them are also used to form complex structures such as the cellulose polysaccharide that is used to form the cell walls of plants. Now the basic monomer of carbohydrates is known as a monosaccharide which we can put together to form disaccharides and polysaccharides.

Let's take a closer look at the monosaccharides. A monosaccharide is a chain of anywhere from five to eight carbons with some hydrogens and some OH groups on them. Here we see a couple of monosaccharides in their chain form. Now you can take these chains and also circularize them as we see over here with this glucose ring. Now if you take a couple of monosaccharides and put them together, you get a disaccharide as we see here. Here is the monosaccharide known as glucose and another common monosaccharide called fructose. When we pull out some water we can join them together to form a very common disaccharide called sucrose. That's the table sugar that you know and love so much from cereal. Other disaccharides that you might encounter include, lactose which is that milk sugar that gives some people some problems.

Now, this is one, this is two mono and di, after that scientist got kind of of bored just kind of lumped them together into many, a real word that we use for the many is poly. So a polysaccharide is a whole group of these monosaccharides joined together just like we did with the disaccharides. I like drew four of them here but in reality a starch molecule like this would be made out of hundreds of thousands of these glucose molecules joined together.

Now you can see this and this look very similar. But some tiny structural changes like here you'll see that the CH2OH group is sticking up all the time, here it alternates. And those tiny changes can make some big structural and functional differences. This molecule here, this polysaccharide is starch. This substance is in French fries and you get so much yummy goodness out of. This is cellulose. If you ate this instead of getting hmm, you'll get ouch splendorous. So these tiny changes can make some big differences in the chemical and structural functions of these molecules.

Some other polysaccharides that you might encounter include, glycogen which is an animal version of starch that is stored in your liver and muscles for common and release. There's also some polysaccharides that are used on the surfaces of you membranes that are involved in cellular recognition. So there you go, that's carbohydrates.