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Home , Chitin, Disaccharide, Empirical formula, Glucagon, Glycogen, Hexose

Review Questions

1. What is the difference between an inorganic and an organic molecule? Organic always have and .

2. List the four classes of organic compounds. Carbohydrates, , , and Nucleic

3. Explain the difference between a molecule and a . A molecule is simply two or more chemically bonded to one another. A macromolecule is two or more molecules chemically bonded to each other. Organic compounds include molecules and .

4. What are and ? In organic , a is a molecule by itself. Monomer means “a single part”. Some examples of organic monomers are a molecule, a , or an amino . Polymers are macromolecules built of two or more monomers. means “many parts”.

Polymers are often long chains of monomers. For example, is a polymer. It is a long chain of glucose molecules. Proteins are polymers composed of chains of amino acids. DNA is a super- long polymer of . Even small macromolecules like a (two amino acids joined together) are polymers.

5. Explain the for building a polymer from a set of monomers. The process for connecting two monomers together (forming a covalent bond) is called dehydration synthesis. Dehydration means “removal of ” and synthesis means “to join together”. So in this process, two monomers are covalently bonded by the removal of a water molecule. Each organic monomer has a hydroxyl group (-OH) on one side and a hydrogen (H) on the other. When two monomers line up side by side, they will have these two functional groups facing one another (H & OH). The H and the OH will break off of their respective monomers and bond forming a water molecule. This is the dehydration part of the process. Each monomer now has a carbon that needs to covalently bond with something, so they bind to each other forming a polymer. That is the synthesis part of the process. Dehydration synthesis is an -requiring process. Every time a needs to build a or a starch, it has to expend some energy to form those chemical bonds. Dehydration synthesis is universal for building all organic polymers.

6. Explain the chemical reaction for breaking down a polymer into individual monomers. The process of splitting the bond between monomers is called . Hydrolysis means “to break with water”. Since a water molecule was lost during dehydration synthesis, hydrolysis brings the water back. To separate the monomers, the functional groups H and OH that broke off in the bonding have to be reattached to their respective monomers. So first the covalent bond is broken between the two holding the two monomers to each other and then a water molecule is introduced. The water molecule splits into a H and an OH and these attach to their respective monomer. Hydrolysis is an energy- releasing process. Living harvest energy from chemical bonds through hydrolysis. Like dehydration synthesis, hydrolysis is universal for breaking down all organic polymers. 7. List the names of the monomers and polymers of the four classes of organic compounds.

Class Monomer Polymer Carbohydrates Lipids (neutral ) glycerol and Proteins polypeptide Nucleic Acids nucleotide polynucleotide

8. What is a ? Carbohydrates are the and . Every kind of carbohydrate has to have carbon, hydrogen, and . Plus, the ratio of C, H, O is always 1:2:1. CH2O is a common way to represent this ratio. The term “carbohydrate” comes from the observation that the molecule is a carbon linked to a water molecule (C – H2O), “hydrate” meaning water. You can often recognize a carbohydrate by its suffix – ose (e.g. glucose, , , etc.)

9. Describe the . Monosaccharides are the monomers of carbohydrates and are often referred to as “the simple sugars”. There are dozens of them but they are classified according the number of carbons they contain. For example, glucose has 6 carbons and belongs to a group of monosaccharides called the sugars: “hex” meaning 6. sugars, like , have 3 carbons. sugars, such as , have 5. Monosaccharides range from 3 to 7 carbons.

We are going to focus on 3 hexose sugars that organisms use for fuel: glucose, , and . Glucose, also known as dextrose, has the empirical C6H12O6. Glucose is the main energy source for . We often call it . Some organs in our body feed on nothing but glucose; our , for instance. Fructose has the exact same empirical formula as glucose: C6H12O6. Fructose is also known as levulose. Sweeter than the other 2 hexose sugars, fructose is commonly found in fruits and . Since fructose is sweeter, less is required, and so it is cheaper. High fructose corn is now the major sugar source for soft drinks. Galactose, just like glucose and fructose, is C6H12O6. Galactose is rarely found free. Bonded to glucose, it forms or sugar. Once ingested, both fructose and galactose are converted into glucose for an ’s energy needs.

10.What are ? You may have noticed that glucose, fructose, and galactose all have the same formula C6H12O6. Then why are they different? Well, it is because they have different structures. Molecules with the same empirical formula but different structures are known as isomers. Slight changes in structure give these molecules unique properties. There are a variety of different types of isomers: structural, geometric, and (optical), just to name a few.

11.Describe the . As the name implies, disaccharides are two monosaccharides covalently bonded together. This covalent bond is called a glycosidic linkage. Dehydration synthesis is how disaccharides are built. There are 3 disaccharides we will review: , sucrose, and lactose. Maltose is a polymer composed of two glucose molecules. Maltose is produced by germinating grains as they break down their starchy endosperm. We feed this to when we make and whiskey. Sucrose is glucose and fructose bonded together. Sucrose is table sugar or cane sugar. We also find it in honey and .

Lactose is milk sugar and is built from glucose and galactose. Most of the world’s population has some level of (70%). The lactose-intolerant lack the to break down the sugar in the small intestines. Lactose in the acts as a and water remains in the large intestine resulting in and abdominal cramping. Thanks to recent developments, - sensitive folks can now enjoy milk by taking a pill containing lactase.

12.Describe the . Oligo” means “few”. So oligosaccharides, like and , are small chains of monosaccharides. In the figure below, raffinose (sucrose + galactose) is on the left and stachyose (sucrose + 2 galactose) on the right. We lack the enzyme to break these down but the bacterial flora in our gut do. Certain are rich in these sugars and create extra flatus. The gaseous effects of foods, like and the cruciferous vegetables, can be reduced by taking a dose of the enzyme (Beano). 13.Describe the . Complex carbohydrates like starch, , cellulose, and are long polymers of monosaccharides. Starch comes from and is a long-term storage form of sugar. Starch is also the major source of for every culture. A relatively simple macromolecule, it is built of many repeating units of glucose held together by glycosidic linkages. If you examine the cells of a under a microscope, the starch molecules are compacted into oval bodies called starch granules. Adding a little iodine to the potato turns the starch blue-black and the granules will pop into view.

Animals also store starch but we call it glycogen. Glycogen literally means “agent that initiates sugar”. Just like starch, glycogen is a long polymer of glucose. Glycogen is stored in our and muscles. We have on hand about 24 hour supply of glycogen in our liver. If we skip a meal, our blood sugar will drop and the will release a called . Glucagon stimulates the liver to break down enough of its store of glycogen into glucose to return our blood sugar levels to normal. Like plant starch, glycogen is stored as concentrated granules in the cells of the liver. Cellulose is another long polymer of glucose. Plant cells make their cell walls out of cellulose. In fact, 100 billion tons of cellulose is made every year on earth. Cellulose is indigestible in most , including us. Ever eat a cardboard box? You get the picture. We simply lack , the enzyme that can break it down. Some , some single-celled protists, and fungi have the enzyme. Animals that feed on cellulose harbor these microbes that help them digest it. Even though, we cannot break down this molecule, we do need cellulose in our diet. We call it “fiber”. Cellulose stimulates the colon to produce regular bowel movements and helps make the stools large and soft. A diet rich in fiber can prevent a painful intestinal disorder called diverticulosis. Hard impacted stools can sometimes cause the walls of the colon to form blind outpockets called diverticula which can periodically inflame. So what makes cellulose different from starch? Isn’t it made of glucose? Well it is but the glucose monomers are organized in an interesting fashion. The orientation of the glucose molecules alternates. So if the first one is right side up, the next one is upside down and then the next is right side up and the next one is upside down. Apparently this is a tricky arrangement for an enzyme to break. Chitin is similar in structure to cellulose. The only difference is that is has some -containing side chains stuck to it. Chitin is strong, lightweight, and waterproof. build their out of chitin. The cell walls of fungi are made out of it too.

14.What are the major functions of carbohydrates? Carbohydrates supply quick and short-term energy. Carbohydrates are a structural material. Plants, fungi, bacteria, and arthropods build their bodies with it. Carbohydrates are the raw material to make proteins, lipids, and nucleic acids. For example, plants make glucose first and then all their other organic compounds are built from that.

Principal Carbohydrates Subtypes Examples Monosaccharides Glucose Fructose Galactose Disaccharides Maltose Sucrose Lactose Oligosaccharides Raffinose Stachyose Polysaccharides Starch () Glycogen Cellulose Chitin