Carbohydrates!

Energy, Energy storage, and Structural materials Carbohydrates Carbohydrates are the most plentiful biological molecule in the biosphere! Carbohydrates serve a variety of purposes, but the most common are Energy, Energy storage, and Structural materials

H O H2OH O H OH HO H HO H H OH H OH H OH H OH H2OH H2OH CH2OH CH2OH O Carbohydrates H O H2OH O H OH HO H Glucose and Fructose Which is an Aldehyde? Which is a Ketone? HO H H OH H OH H OH H OH H2OH H2OH CH2OH CH2OH Two monosaccharides: Glucose (on the left) and fructose (on the right). Notice the functional groups circled in red. Both are carbonyl groups, but one is an aldehyde while the other is a ketone. Can you identify which one is which? O OH H O H H OH H OH H H CH2OH HO OH H OH OH H

Glucose, a monosaccharide Carbohydrates H O H OH Glucose, a monosaccharide “Saccharide” is a greek root that means sugar HO H H OH H OH H2OH CH2OH Carbohydrates are biomolecules with a ratio of 1 carbon: 2 hydrogen: 1 oxygen. For example, the molecular formula of glucose is C6H12O6. Glucose is an example of a monosaccharide. (Mono=1). Monosaccharides are the building blocks of larger carbohydrates (for example, disaccharides and polysaccharides). The pictures on the left show glucose in its linear and ring form. The image on the right shows glucose in an abbreviated form. H O H H OH H HO OH H OH

Some vocabulary: Monosaccharide Disaccharide “two sugars” “one sugar” Disaccharide “two sugars” Oligosaccharide “a few (3 or more) sugars” Polysaccharide “many sugars”

Lets pause a second…. C6H12O6 CH2O Cm(H2O)n What is the chemical formula for Glucose? C6H12O6 What is the simplest ratio we can express those atoms in? CH2O In general, we can write carbohydrates in the form of Cm(H2O)n So why do we call them Carbohydrates?

b Structure of fructose H O H2OH O H OH Condensation (dehydration synthesis) Reaction between the monosaccharides glucose and fructose to form the disaccharide Sucrose HO H HO H H OH H OH H OH H2OH H2OH CH2OH CH2OH H O OH H O H H OH OH H OH CH2OH OH H H OH OH H a Structure of glucose b Structure of fructose A condensation reaction (also called dehydration synthesis reaction) between glucose and fructose. The resulting molecule is a disaccharide called sucrose. Have you noticed that most carbohydrates end in “ose”? O O OH HO glucose fructose O O sucrose + H2O O

Condensation (dehydration synthesis) Reaction between the monosaccharides glucose and fructose to form the disaccharide Sucrose Once again, glucose and fructose bonding together to form sucrose. Sucrose is table sugar.

Lactose

Maltose

Ok! Time to test your disaccharides!

Draw a glucose!

What kind of reaction joins two monosaccharides together? A Condensation reaction

What is maltose? A disaccharide made from two glucose monomers

What is lactose? A disaccharide made from glucose and galactose

What is sucrose? A disaccharide made from glucose and fructose

Bonus: What is sucralose? Sucralose was discovered by accident in 1976 when researchers were trying to develop a new pesticide.

Complex Carbohydrates (Polysaccharides) Poly= many. Polysaccharides form from multiple monosaccharides bonded together. Three polysaccharides are shown in the images above. A= amylose (also called starch), B= cellulose, C= glycogen. Can you notice any structural differences between these polysaccharides? Now can you think of why the chemical evolution of hydroxyl groups was a huge step toward the evolution of life?

Complex Carbohydrates (Polysaccharides) Another view of A= cellulose, B= starch, C= glycogen. Notice the dotted lines between hydroxyl groups of glucose molecules in the cellulose molecules? These are hydrogen bonds. In addition to the covalent bonds that form between glucose molecules, the hydroxyl groups between glucose molecules also hydrogen bond together, which causes cellulose to be an extremely strong structure. Plants use cellulose as part of their cell walls. When we eat plants, the indigestible material (also called fiber) is cellulose.

Amylose has primarily α(1-4) bonds Starch is a combination of amylose and amylopectin - how plants efficiently store glucose Amylose has primarily α(1-4) bonds Plants store energy in the form of amylose (starch). The image on the bottom left shows potato cells stained with iodine, which causes starch to turn blue/black in color. Each small clump in these cells is called an amyloplast (a storage structure for starch). Starch can be easily broken down into its glucose components and used for energy.

Amylopectin has α(1-4) bonds, and α(1-6) branches Starch is a combination of amylose and amylopectin - how plants efficiently store glucose Amylopectin has α(1-4) bonds, and α(1-6) branches Plants store energy in the form of amylose (starch). The image on the bottom left shows potato cells stained with iodine, which causes starch to turn blue/black in color. Each small clump in these cells is called an amyloplast (a storage structure for starch). Starch can be easily broken down into its glucose components and used for energy.

- how animals efficiently store glucose Glycogen - how animals efficiently store glucose Glycogen is similar to amylopectin, But glycogen has more α(1-6) branches. This makes it easier to breakdown for energy quickly Animals store carbohydrates in the form of glycogen. Glycogen can be found in our liver and muscle cells. Glucose molecules can be cut from the larger structure when blood sugar is low and our body needs energy quickly. Only a small amount of energy is stored in the form of glycogen. Most energy storage in animals occurs in the form of trigylcerides (fats), which we will discuss in one of the next slides.

Which is Amylopectin, which is Amylose, and which is Glycogen?

Cellulose - how plants use glucose to provide themselves structure Cellulose’s unique structure is what makes it so strong, but it is only glucose molecules. It is only sugar. When you look at a piece of dried wood (such as in the picture on the top right), you are seeing what remains of the cell walls of plant cells, containing mostly cellulose. It would not taste sweet to eat it, but it is made from the same sugars that taste sweet when they are monosaccharides or disaccharides. Hydrogen bonding holds cellulose chains together.

Keto-glucose amine (Chitin) - a polysaccharide modified for high strength and low mass Similar to cellulose, chitin is also a structural carbohydrate. It is used in the shells of insects and crustaceans. It is also part of the cell walls of fungi cells. Chitin is a polysaccharide made from repeating monomers. One of these monomers is shown in the bottom image. It is also called keto-glucose amine. Can you figure out why? (hint: find the functional groups) Why is the monomer of chitin called “keto”-glucose “amine”?