Important Concepts
Carbohydrates are some of the most common organic materials on Earth. Plants and Algae produce carbohydrates through the process of photosynthesis. Most organisms use carbohydrates as a source of energy, as building materials, and as cell surface markers for cell-to-cell identification and communication. Typically carbohydrates contain carbon, hydrogen, and oxygen atoms in a 1:2:1 ration respectively. The simplest carbohydrates are known as monosaccharides or simple sugars. These monosaccharides are listed below. Simple sugars contain a single chain of carbon atoms to which hydroxyl groups are attached. These monosaccharides can be distinguished between each other through whether they contain an aldehyde of ketone carboxyl group, or by the number of carbons present in their backbone. Simple sugars with a 5-carbon backbone are known as pentose (fructose) and sugars with a 6-carbon backbone are known as hexose (glucose and galactose). All 3 simple sugars listed below (glucose, fructose, and galactose) are isomers of each other because they have the same number and types of atoms, but a different arrangement of those atoms.
Disaccharides are the combination of 2 monosaccharides though a glycosidic linkage. The 3 possible disaccharides are listed below. Oligosaccharides are sugars containing several simple sugars attached to one another. Polysaccharides are known as complex carbohydrates because they are monosaccharide polymers composed of several hundred to several thousand monosaccharide subunits held together by glycosidic linkages. The 3 different polysaccharides are listed below. Plants store energy in the form of glucose and other carbohydrates through photosynthesis. These storage molecules are two different polysaccharides, amylose and amylopectin.
Monosaccharides are simple sugar molecules (all isomers of each other):
Disaccharides are two sugar molecules linked
Polysaccharides are three or more monosaccharides lined together.
Disaccharides are the combination of 2 monosaccharides though a glycosidic linkage. The 3 possible disaccharides are listed below. Oligosaccharides are sugars containing several simple sugars attached to one another. Polysaccharides are known as complex carbohydrates because they are monosaccharide polymers composed of several hundred to several thousand monosaccharide subunits held together by glycosidic linkages. The 3 different polysaccharides are listed below. Plants store energy in the form of glucose and other carbohydrates through photosynthesis. These storage molecules are two different polysaccharides, amylose and amylopectin.
Monosaccharides are simple sugar molecules (all isomers of each other):
- Glucose (source of energy in all cells)
- Fructose (fruit sugar)
- Galactose (component of lactose milk sugar)
Disaccharides are two sugar molecules linked
Polysaccharides are three or more monosaccharides lined together.
- Starch (amylopectin) and glycogen are energy storage polysaccharides: They have alpha-1–4 glycosidic linkages between –glucose monomers in the main chain and a-1–6 linkages at the branch points
- Cellulose is a structural polysaccharide: They have Beta-1–4 glycosidic linkages between monomers in the main chain
Curriculum Links
B2.3 construct and draw three-dimensional molecular models of important biochemical compounds, including carbohydrates, proteins, lipids, and nucleic acids [PR, C]
B3.2 describe the structure of important biochemical compounds, including carbohydrates, proteins, lipids, and nucleic acids, and explain their function within cells
B3.3 identify common functional groups within biological molecules (e.g., hydroxyl, carbonyl, carboxyl, amino, phosphate), and explain how they contribute to the function of each molecule
B3.2 describe the structure of important biochemical compounds, including carbohydrates, proteins, lipids, and nucleic acids, and explain their function within cells
B3.3 identify common functional groups within biological molecules (e.g., hydroxyl, carbonyl, carboxyl, amino, phosphate), and explain how they contribute to the function of each molecule
Misconceptions
- Students think there is only one type of glucose molecule (the general structure they learn in grades leading up to 12). This general structure of glucose is usually in the form of alpha-glucose, where the hydroxyl group on carbon #1 is facing down. However, there is another form of glucose, which is known as beta-glucose, where the hydroxy group on carbon #1 is facing up.
- Students think that only food such as bread and pasta (which are carbohydrates) contain starch. However there are also some vegetables, such as corn, that also contain starch, which most students are unaware of. The food lab below where students are identifying foods that contain starch is a great lab to address this misconception.
Activities and Teaching Strategies
Showing students the difference between alpaha- and beta-glucose. This is shown in the image to the right ->
It is important to show the students the structure of starch, glycogen, and cellulose, and how they are different from each other. Point out the 1-4 linkage points and the 1-6 branch points and how to count the carbons to locate the points of interest. Here is a great activity for students to build disaccharides and polysaccharide:
Here is a great lab to do with the students that involves identifying starch in different types of foods. First, show students the structure of starch, and then lead into the lab.
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Assessment #2
Macromolecule Quiz
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