Toby, can I ask you a question? Yes, go ahead. Do you have any plans after school? Yes, I am going to play football. Cindy, can I ask you a question? Yes, go ahead. Do you know the answer to this Math problem? Sorry, I don’t know the answer.

Toby: Welcome to my home, Timmy! Please come in. Timmy: Thank you. I am very happy to be here. Toby: Do you want me to show you around first? Timmy: Sure, let me take off my shoes. Toby: This is our living room. We can watch TV here. Timmy: I like your sofa. It’s very comfortable. Toby: This is our dining room. We can eat dinner here. Timmy: Your apartment is very nice, Toby. Toby: Thank you, Timmy.

LARGE CARBON MOLECULES Many carbon compounds are built up from smaller, simpler molecules known as monomers (MAH-ne-mers), such as the ones shown in Figure 3-3. As you can also see in Figure 3-3, monomers can bond to one another to form polymers (PAWL-eh-mer). A polymer is a molecule that consists of repeated, linked units. The units may be identical or structurally related to each other. Large polymers are called macromolecules. There are many types of macromolecules, such as carbohydrates, lipids, proteins and nucleic acids. Monomers link to form polymers through a chemical reaction called a condensation reaction. Each time a monomer is added to a polymer, a water molecule is released. In the condensation reac- tion shown in Figure 3-4, two sugar molecules, glucose and fruc- tose, combine to form the sugar sucrose, which is common table sugar. The two sugar monomers become linked by a C—O—C bridge. In the formation of that bridge, the glucose molecule releases a hydrogen ion, H, and the fructose molecule releases a hydroxide ion, OH. The OH and H ions that are released then combine to produce a water molecule, H2O. In addition to building polymers through condensation reac- tions, living organisms also have to break them down. The break- down of some complex molecules, such as polymers, occurs through a process known as hydrolysis (hie-DRAHL-i-sis). In a hydrolysis reaction, water is used to break down a polymer. The water molecule breaks the bond linking each monomer. Hydrolysis is the reverse of a condensation reaction. The addition of water to some complex molecules, including polymers, under certain con- ditions can break the bonds that hold them together. For example, in Figure 3-4 reversing the reaction will result in sucrose breaking down into fructose and glucose. 2H2O Monomers Polymer C C O H OH C OH H CH2OH C H CH2OH C HO H C O H C OH H C CH2OH H C H OH O Sucrose C C O H OH C OH H CH2OH C H CH2OH C HO H C OH OH H C OH H C CH2OH H C H OH O Glucose Fructose H2O The condensation reaction below shows how glucose links with fructose to form sucrose. One water molecule is produced each time two monomers form a covalent bond. FIGURE 3-4 monomer from the Greek mono, meaning “single or alone,” and meros, meaning “a part” Word Roots and Origins A polymer is the result of bonding between monomers. In this example, each monomer is a six-sided carbon ring. The starch in potatoes is an example of a molecule that is a polymer. FIGURE 3-3 Copyright © by Holt, Rinehart and Winston. All rights reserved. 54 CHAPTER 3 ENERGY CURRENCY Life processes require a constant supply of energy. This energy is available to cells in the form of certain compounds that store a large amount of energy in their overall structure. One of these com- pounds is adenosine (uh-DEN-uh-SEEN) triphosphate, more commonly referred to by its abbreviation, ATP. The left side of Figure 3-5 shows a simplified ATP molecule struc- ture. The 5-carbon sugar, ribose, is represented by the blue carbon ring. The nitrogen-containing compound, adenine, is represented by the 2 orange rings. The three linked phosphate groups, —PO4 , are represented by the blue circles with a “P.” The phospate groups are attached to each other by covalent bonds. The covalent bonds between the phosphate groups are more unstable than the other bonds in the ATP molecule because the phosphate groups are close together and have negative charges. Thus, the negative charges make the bonds easier to break. When a bond between the phosphate groups is broken, energy is released. This hydrolysis of ATP is used by the cell to provide the energy needed to drive the chemical reactions that enable an organism to function.

Cinco de Mayo is a celebration that takes place on ________________ of May each year. Cinco de Mayo commemorates an important ____________________ that happened in Mexico. The battle that is celebrated on Cinco de Mayo took place in the city of ________________. In what year did the battle celebrated on Cinco de Mayo occur? ___________________________. What is the name of the Mexican general who led the army in the battle of Cinco de Mayo? ___________________________. Cinco de Mayo is not Mexico's Independence Day, but rather a celebration ofn _____________________. Which country attempted to invade Mexico in the battle celebrated on Cinco de Mayo? _______________________. What types of food can be enjoyed during Cinco de Mayo celebrations? ___________. What does Cinco de Mayo mean in English _____________________.

Toby: Do you have many neighbors, Timmy? Timmy: No, not really. I live in a house. I only have two neighbors. Toby: Do you usually say “hi” to your neighbors? Timmy: Yes! We are good friends. Timmy: Do you have many neighbors? Toby: Yes, I live in an apartment. There are many neighbors on my floor. Timmy: Do you usually say “hi” to your neighbors? Toby: No, not really. I don’t know them.

Laura y Toby

Delivery man: Delivery for Mr. Toby. Toby: Yes, come up to my apartment. I live on the 16th floor. Please use the elevator. Dad: What did you buy, Toby? Toby: I bought a new lamp for the dining room. Dad: We already have many lamps in the dining room. Toby: How about we put it in the living room next to the sofa? Dad: Of course! Good idea, Toby. Toby: Thanks, Dad. I hope that Mom likes the lamp too.

Timmy: Where do you live, Toby? Toby: I live in an apartment building. It’s not far from here. Timmy: Is your apartment in a tall building? Toby: Yes, it is. My building has 18 floors. Timmy: Wow! That’s very tall. Which floor is your apartment on? Toby: It’s on the 16th floor. Timmy: Does your building have an elevator? Toby: Yes, it does. I ride it every day.

Sam, what do you like to do? I like to read books. What does Toby like to do? He likes to climb trees. Anna, what do you like to do? I like to jump rope. What does Cindy like to do? She likes to sing songs.

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