MOLECULES. reflect. You might not want to eat a grasshopper, but you could!

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1 reflect If you ever travel to another country, you are bound to encounter unfamiliar foods. For example, in Mexico you might be offered a plate of grasshoppers. In Japan, salamanders could be on the menu. In China, you might have a choice of snake or starfish. Even if you travel around the United States, you might be surprised at some foods offered to you: fi ddlehead ferns, crayfi sh, and beef tongue are only three examples of unique foods eaten in America. Although we might find some foods to be weird and unappealing, they still function as food sources. Your body would be nourished if you ate them. Why is that? What makes something food? You might not want to eat a grasshopper, but you could! A single cell contains many different structures and performs many functions necessary for life. Food is a source of nourishment for a living organism. Food is matter that an organism takes in from its environment and uses for nourishment. Food supplies two things that help nourish matter: anything that takes up space and has mass the organism: a source of energy and a source of raw materials for the organism. All food comes from living or once-living things, which are composed of organic compounds. Organic compounds contain mostly the elements carbon (C) and hydrogen (H), as well as smaller quantities of oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S). Organic compounds form the structures that make up all cells. In order to build new cells and to have energy for carrying out life processes, cells need a constant source of these organic compounds. For living things, the main sources of organic compounds are other living things. 1

2 Food is composed of large molecules that fall into three categories. Different organic compounds have different chemical structures. Scientists divide the organic compounds that make up food into three basic categories based on these structures. These categories are proteins, carbohydrates, and lipids. These molecules also tend to be found in the different foods we eat. Proteins: Proteins are very large molecules. They contain the elements carbon, hydrogen, oxygen, nitrogen, and sulfur. Good sources of protein include meat, milk, and eggs, which all come from animal sources. Proteins are also found in plants, although usually in smaller quantities. Carbohydrates: Carbohydrates are also large molecules. Starch and cellulose are names of specifi c carbohydrate molecules. (Plants store the energy from photosynthesis in the form of starch starchy foods such as potatoes are basically energy storage units for the plants that make them. Cellulose gives plants the support they need to grow straight it is the main component of plant stems, including tree trunks.) These molecules contain the elements carbon, hydrogen, and oxygen. Fruits, vegetables, and other plant materials are good sources of carbohydrates. Lipids: Lipids are also known as fats. These compounds are generally smaller in size than carbohydrates or proteins. Lipids are made up of mostly carbon and hydrogen with small amounts of oxygen. Some lipids also contain phosphorus. Lipids are derived from both animal and plant sources. For example, butter contains lipids that come from cow s milk. Olive oil contains lipids derived from the fruits of olive trees. The following table summarizes the three main categories of food molecules. Molecule Main Components Common Sources Protein carbon, hydrogen, oxygen, nitrogen, sulfur animal products such as meat, milk, eggs; some plants such as beans Carbohydrate carbon, hydrogen, oxygen fruits, vegetables, and other plant materials such as grains Lipid (fat) mostly carbon and hydrogen; some oxygen animal products such as milk; oils from plants such as olives 2

3 what do you think? Take a look at the following photographs. Which foods represent common sources of proteins? Which represent common sources of carbohydrates? Which represent common sources of lipids? look out! A particular food item usually contains molecules belonging to all three categories of proteins, carbohydrates, and lipids. It is rare to find a food that contains molecules of only one type. For example, a taco is made from a tortilla (carbohydrates), beans (proteins), and cheese (lipids). 3

4 During digestion, large molecules are broken down into smaller, building-block molecules. The foods we eat contain large, complex molecules. However, the cells in our bodies cannot use these large molecules. Therefore, proteins, carbohydrates, and lipids must be broken down into much smaller molecules that cells can use. The breakdown of large molecules releases energy that cells also use. The process of breaking down large molecules from food is called digestion. During digestion, large food molecules are broken down into smaller molecules. This process releases energy that cells can use to stay healthy and function properly. Each larger molecule breaks down into different small molecules: Proteins break down into amino acids: A protein contains many amino acids bonded together in a long chain. A single protein contains anywhere from 2 to 2,000 amino acids. During digestion, this chain is broken apart into its amino acid components. The general structure of an amino acid is shown here. There are 20 different amino acids. Each has a different set of atoms located at the position marked with the red R in the diagram. Amino acids all have the same general structure (left). An atom of carbon (C) is bonded to various combinations of other atoms, particularly hydrogen (H), nitrogen (N), and oxygen (O). The letter R represents an additional group of atoms. Each type of amino acid has a different R group. For example, in the amino acid glycine (center), another hydrogen atom bonds to the central carbon atom. In the amino acid alanine (right), another carbon atom bonds to three more hydrogen atoms. 4

5 Carbohydrates break down into sugars: Like proteins, carbohydrates are made of long chains of smaller molecules bonded to one another. Unlike proteins, the chains can join together to form complex, branched molecules. Starch is one example of a branched molecule. One starch molecule may contain 500 or more smaller molecules, called glucose. Glucose, a simple sugar, contains six atoms of carbon, six atoms of oxygen, and 12 atoms of hydrogen. During digestion, starch molecules are broken apart into glucose molecules. In a glucose molecule, five carbon atoms (C) and one oxygen atom (O) form a hexagon. In the diagram above, a carbon atom is located at each corner of the hexagon except the one occupied by the oxygen atom. Each of these carbon atoms is bonded to various combinations of carbon, oxygen, and hydrogen (H) atoms. Lipids break down into fatty acids: Lipids are generally smaller in size than either proteins or carbohydrates. When they are broken down during digestion, lipids release smaller molecules called fatty acids. Fatty acids have long carbon chains. Bonded to the fi nal carbon atom at the end of the chain are two oxygen atoms. Fatty acids can vary in length, but they all have the basic structure of this example. A long chain of carbon atoms (C) is bonded to hydrogen atoms (H), with two oxygen atoms (O) at one end. 5

6 Everyday Life: Everyone needs to eat a healthy diet. Just about everyone has a favorite type of candy. Yet, it would be disastrous if people ate candy as their only source of food; just as it would also be disastrous if they ate broccoli as their only source of food. The reason is that any one food does not provide all of the nutrients a person needs to maintain good health. A healthy diet is varied. It is important to eat enough different types of foods so that you get the quantities of proteins, carbohydrates, and lipids that your body needs to function well. What do you know? Think about all of the ingredients that go into making a pizza with all the toppings. Then identify the primary category of organic compound protein, carbohydrate, or lipid each ingredient is made up of. State the organic molecule in the middle column. Finally, in the third column, write the names of the small molecules formed from each ingredient as your body digests it. Ingredient Pepperoni Primarily protein, carbohydrate, or lipid? Molecules produced by your body during digestion? Mushrooms Red and green peppers Cheese Pizza dough Olive oil 6

7 connecting with your child Planning Nutritious Meals With your child, keep a list of the foods you both eat for one day. Try to identify the source of each food. Did it come from a plant or an animal? Is it made of multiple ingredients that each came from different sources? For many of the foods you evaluate, you may fi nd it helpful to look at the packaging labels to determine where the food or the ingredients making up the food came from. Try to fi gure out how much of each kind of organic compound you ingested that day. Analyzing the foods you eat for one day is a good way to review the various organic compounds in your diet. For a longer-term project to learn more about the molecules in food and how they affect human health, work with your child to plan a week s worth of meals and snacks for your family. Try to collect recipes of unfamiliar dishes, and look through cookbooks and food websites to find recipes for dishes your child has never tried but might enjoy. Instruct your child to build a meal plan around the recipes you select. Be sure to consider how to incorporate the main categories of proteins, carbohydrates, and lipids into the plan to achieve a balanced diet for the week. Remind your child that a varied diet is also important. Bread is made from flour and eggs. Flour is made from wheat, a plant source. Eggs come from hens, an animal source. Once the meals have been planned, set aside a week to carry out the plan. Have your child work with you to prepare the meals and serve them. Here are some questions to discuss with your child: What types of foods should we plan in order to include the three main groups of organic compounds? What types of foods should we leave out or eat minimally? How can we analyze the recipe for a dish to determine whether it meets our criteria for nutrition? How can we plan meals that will be tasty, satisfying, and also nutritious? 7