Carbohydrates Unit
Introduction to Carbohydrates: What is a carbohydrate and where do they come from?
Carbohydrates are compounds comprised of carbon and water (hydrogen and oxygen). Literally, the name means "hydrate of carbon," or carbon mixed with water. Carbohydrates are monosaccharides (single sugars) such as glucose, fructose, and galactose, disaccharides (double sugars) such as sucrose, lactose and maltose, and polysaccharides (complex sugars) such as starch. Monosaccharides are rings of carbon and oxygen atoms with hydrogen atoms and hydroxyl (OH) groups branching off, as well as ketone and aldehyde groups. Disaccharides are two monosaccharides linked by the loss of a hydrogen atom from one and a hydroxyl group from the other (the two are combined to form a water molecule as the two monosaccharides are combined to form a disaccharide). Polysaccharides are comprised of multiple monosaccharides linked in the same way; starch can be comprised of hundreds of glucose molecules. Sugars and starches are all carbohydrates, found in many foods, including fruits and vegetables, nuts, legumes, breads, and Big Macs. Essentially, anything sweet, starchy, or processed has carbohydrates in it.
When carbohydrates enter our bodies, they are broken down into their monosaccharide components if they are not already monosaccharides. Any monosaccharide but glucose is removed from the body, and glucose is either absorbed directly into the bloodstream or turned into fat for storage by the hormone insulin. Our bodies are essentially powered by glucose; however, two much power at once will, as in an electrical circuit, cause components to break or go haywire. In the case of the human body, the haywire component will be the pancreas; it will become insulin deficient, resulting in a medical condition such as diabetes. Eating glucose is already broken down, and can flood the bloodstream all at once, and sucrose is easy to break down, so the same effect can happen. Starch can also create too much glucose, but it takes time to be broken down, and so glucose enters the bloodstream in a slower, more drawn-out effect. Thus, starch is more likely to cause weight gain through fat than diabetes through high insulin spikes. So know what kinds of carbs you are eating, and generally watch your carbs!
When carbohydrates enter our bodies, they are broken down into their monosaccharide components if they are not already monosaccharides. Any monosaccharide but glucose is removed from the body, and glucose is either absorbed directly into the bloodstream or turned into fat for storage by the hormone insulin. Our bodies are essentially powered by glucose; however, two much power at once will, as in an electrical circuit, cause components to break or go haywire. In the case of the human body, the haywire component will be the pancreas; it will become insulin deficient, resulting in a medical condition such as diabetes. Eating glucose is already broken down, and can flood the bloodstream all at once, and sucrose is easy to break down, so the same effect can happen. Starch can also create too much glucose, but it takes time to be broken down, and so glucose enters the bloodstream in a slower, more drawn-out effect. Thus, starch is more likely to cause weight gain through fat than diabetes through high insulin spikes. So know what kinds of carbs you are eating, and generally watch your carbs!
Carbohydrate Structural Models (to the Right)
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Carbohydrate Lab Results
The carbohydrate lab involved four different tests: an iodine test, which tells polysaccharides from mono- and disaccharides; Benedict's test, which tells reducing sugars from non-reducing sugars; Barfoed's test, which tells reducing disaccharides from reducing monosaccharides; and the Seliwanoff test, which tells ketones from aldehydes. We used these four tests to initially determine which of five unknown carbohydrate samples - A through E - was starch, glucose, fructose, lactose, and sucrose. Only starch, the only polysaccharide, could pass the iodine test; sample D was starch. Only sucrose, the only non-reducing sugar remaining, could fail Benedict's test; sample C was sucrose. Only lactose, the only remaining disaccharide, could fail Barfoed's test; sample A was lactose. Finally, between the remaining compounds, fructose and glucose, only fructose had a ketone group and could pass the Seliwanoff test; sample B was fructose, and sample E was glucose.
We then used these tests on four known food samples: milk, bread crumbs, honey, and chocolate, in an effort to determine the carbohydrates they contained. Only bread crumbs passed the iodine test; milk, bread, and honey passed Benedict's test; honey and chocolate passed Barfoed's test; and honey and chocolate also passed the Seliwanoff test. Since only starch can pass the iodine test, bread has starch in it and no other sample does; this is not surprising. I was unsurprised as well that milk and honey have reducing sugars in them; lactose and fructose are both reducing sugars. Evidently bread has reducing sugars – and starch is not a reducing sugar. Since bread failed the Barfoed's test, it must have a reducing disaccharide, and since sucrose does not reduce, lactose is the most likely culprit; it is unsurprising that bread would contain milk. Honey and chocolate, having passed Barfoed's test, must contain reducing monosaccharides. However, chocolate failed Benedict's test, which would normally mean that it does not contain reducing sugars. The most likely cause of this conundrum is a recording error; chocolate most likely passed Benedict's test. I am surprised that chocolate would have passed either test, though; I would expect that the most common sugar in chocolate is sucrose, which is neither a reducing sugar not a monosaccharide. Finally, since both honey and chocolate passed the Seliwanoff test, they both most likely contain fructose, which is a surprise in chocolate but would explain its success in the two previous tests. This is completely unsurprising in honey.
We then used these tests on four known food samples: milk, bread crumbs, honey, and chocolate, in an effort to determine the carbohydrates they contained. Only bread crumbs passed the iodine test; milk, bread, and honey passed Benedict's test; honey and chocolate passed Barfoed's test; and honey and chocolate also passed the Seliwanoff test. Since only starch can pass the iodine test, bread has starch in it and no other sample does; this is not surprising. I was unsurprised as well that milk and honey have reducing sugars in them; lactose and fructose are both reducing sugars. Evidently bread has reducing sugars – and starch is not a reducing sugar. Since bread failed the Barfoed's test, it must have a reducing disaccharide, and since sucrose does not reduce, lactose is the most likely culprit; it is unsurprising that bread would contain milk. Honey and chocolate, having passed Barfoed's test, must contain reducing monosaccharides. However, chocolate failed Benedict's test, which would normally mean that it does not contain reducing sugars. The most likely cause of this conundrum is a recording error; chocolate most likely passed Benedict's test. I am surprised that chocolate would have passed either test, though; I would expect that the most common sugar in chocolate is sucrose, which is neither a reducing sugar not a monosaccharide. Finally, since both honey and chocolate passed the Seliwanoff test, they both most likely contain fructose, which is a surprise in chocolate but would explain its success in the two previous tests. This is completely unsurprising in honey.
Carbohydrate Reflection
Before this unit, I knew none of what I just explained above, so this has been a very educational past week for me in Chemistry class. This new knowledge may cause me to gravitate towards more starchy foods rather than sweet foods when I'm feeling like a snack, since if I had to choose the effects of starch or the effects of high glucose concentrations, I would prefer starch. I may also end up with a tendency to read nutrition labels more than I used to, since I now have some idea of how much sugar I should be eating with respect to the amounts of other carbohydrates, fiber, fat, and etc. that I consume.