hi this is Mr W from sciencemusicvideos and this video is about carbohydrates. Carbohydrates include foods like sugars and starches and also plant fiber like cotton. All carbohydrates contain carbon, hydrogen, and oxygen. This formula says that the ratio of hydrogen to oxygen is 2 to 1 like water that makes carbohydrates "hydrates of carbon:" water attached to some number of carbon atoms. the monomers of carbohydrates their building blocks or monosaccharides and the monosaccharide that you learn most about is glucose that's because glucose is the fuel of life it's the input for cellular respiration and it's the product of photosynthesis glucose is chemical formula is c6h12o6 here's its full structural formula an abbreviated structural formula you have to imagine the carbon and hydrogen atoms at each angle vertex and a chain form in solution which means in cells in life glucose is almost always in a ring fructose is another monosaccharides should know it's a structural isomer of glucose which means it has the same empirical formula but a different structure fructose is naturally found in fruit where it attracts fruit eating animals which eat the fruit swallow the seeds and then defecate those seeds far away from the parent plant that's an important adaptation for plant dispersal we humans love fructose and other sugars that's because our distant ancestors were tree living primates who ate fruit and passed that preference on to us today most of our fructose comes from corn and up to 10 percent of the calories in a North Americans diet can come from this monosaccharides monosaccharides are the monomers of carbohydrates in my video about monomers and polymers I compared monomers to Legos that can be put together to create larger structures let's see what happens when we start combining monosaccharides when enzymes linked to glucose monomers together through a dehydration synthesis we get maltose a disaccharide let's focus on the bond between the two glucose monomers to do that we're going to use a system that biochemists have devised where they sign a number to each of the carbons in a monosaccharide here you can see the numbers for each carbon in glucose when enzymes link the two glucose monomers together to form maltose they connect the number one carbon of one glucose with the number four carbon of the second glucose that's called an alpha 1-4 glycosidic linkage and the prefix glyco is widely connected with the carbohydrates and we'll see it again throughout this unit what do you need to know about that bond well the main thing is that it's covalent gand and it has a specific shape and we have enzymes that can break that bond changing maltose into two glucose monomers that we can absorb into ourselves for energy here's the disaccharide sucrose it's table sugar and it's what we put into our coffee and tea sucrose consists of a glucose connected to a fructose and the bond between them is an alpha one two glycosidic linkage what do you need to know about that it's another covalent bond it has a different shape we have enzymes that can break it apart releasing glucose and fructose but our cells can absorb and use for energy sucrose in other words is a digestible sugar the last disaccharide that we'll meet is lactose it's the sugar in milk and it consists of a glucose linked to another mountain saccharide galactose all mammals drink milk is infants that's what makes us mammals in order to digest the lactose in milk we need to be able to break this beta 1-4 glycosidic linkage between the glucose and the galactose and all mammals are born with an enzyme that enables them to do that it's called lactase and it takes lactose and breaks it apart into glucose and galactose now a lot of adult humans including me are lactose intolerant that means that as adults we don't synthesize the lactase enzyme and therefore we can't digest lactose and ingestion of lactose leads to all kinds of indigestion cramping flatulence diarrhea nasty stuff lactose intolerance might seem like some unfortunate disease but when you think about it lactose intolerance is the norm for mammals you only need to digest lactose when you're a suckling infant those adult humans who can digest lactose are the inheritors of a genetic mutation that arose thousands of years ago in a certain population and that mutation keeps the lactase enzyme active throughout adulthood and those populations where that mutation arose and spread a whole wide array of dairy food sources was opened up and that became quite a beneficial adaptation for those of us who haven't inherited that mutation don't despair there's an entire industry producing lactose free dairy products and also lactase supplements so that you can eat lactose and digest it without a problem if you want to learn more about lactose intolerance and the evolution of lactose tolerance there's more about that at my website now let's turn our attention to carbohydrate polymers which are known as polysaccharides we'll start with starch starch is a polymer of glucose and it's used by plants for long term energy storage that's why you find starch in plant parts like potatoes and also in seeds like beans and corn the simplest form of starts his amylose it's just a straight chain of glucose monomers held together by an alpha 1-4 glycosidic linkage the same one that we saw when we were discussing maltose another form of starch is analog pectin in addition to chains there are also branches between the number one carbon of one glucose and the number six carbon of another glucose that bond is called a beta 1-6 glycosidic linkage to digest amylose or analog pectin we have enzymes that can break that alpha 1-4 beta one six bond releasing the glucose monomers that's why starchy foods like potatoes are loaded with food energy and that's why potatoes were the key to astronaut Mark Watney survival in the science fiction novel and movie the Martian here on earth starchy foods from plants like wheat rice beans and corn along with potatoes are the staple foods that power human civilization glycogen is an energy storage molecule that's made by animals that's structurally very similar to have a low pectin in fact it's sometimes called animal starch that subscript indicates the number of glucose monomers that are chained together in that part of the molecule glycogen gets huge molecular complexes like this in our liver tissue and our muscles when our blood sugar level gets low our bodies will convert stored glycogen into glucose on the other hand after a carbohydrate rich meal our bodies will take excess blood glucose and converted into glycogen this inter conversion is controlled by hormones like insulin and glucagon and breakdown of blood sugar homeostasis can cause diseases like diabetes there's a lot more information about this on my website cellulose is another polysaccharide that's built from glucose monomers it's the primary component of plant cell walls and because of that cellulose is the most common biological polymer on earth cellulose is incredibly useful cotton fiber wood paper they're all composed to varying degrees of cellulose like starch cellulose it's a polymer of glucose but the glucose monomers are held together by a beta one four linkage unlike starch we and many other animals don't have enzymes that can break that bond that explains why a cup of potatoes mostly starch has about ten times the food energy as a cup of celery which is mostly cellulose we just don't have the enzymes that can break these glucose monomers off the cellulose chain and feed them into cellular respiration you know that cellulose is strong that's because the cellulose strands form hydrogen bonds with one another and the collective effect of those hydrogen bonds creates a strength that we see in things like rope and wooden boards mammals like this deer have evolved mutualistic relationships with bacteria that have enzymes that can break the glucose monomers off of cellulose making its chemical energy available other mammals like goats and sheep and cows have these say mutualistic bacteria and they live in a digestive chamber that's called a rumen collectively these animals are called luminance among the insects termites have evolved a mutualistic relationship with a protozoan that enables them to digest the cellulose in wood that's for the termites but it's disastrous for the billions of dollars of damaged structures in the United States alone each year that's it for carbohydrates it's a lot of detail so right now head on over to science music videos dot-com where I've got an interactive tutorial waiting for you so that you can get on top of all this material if you're part of a class that's not using science music videos please have your teacher contact me about setting up a site license so thanks a lot for joining me I'll see you at the next video and I'll see you over at science music videos dot-com thank you