chemistry of living things
classes of biochemical compounds
Biochemical compounds make up the cells and tissues of living things. They are also involved in all life processes. Given their diversity of functions, its not surprising that there are millions of different biochemical compounds. Even so, all biochemical compounds can be grouped into just four main classes: carbohydrates, proteins, lipids, and nucleic acids. The classes are summarized in Table 2.1. Class Elements Examples Functions Class Carbohydrates Elements carbon hydrogen oxygen Examples sugars starch glycogen cellulose Proteins carbon hydrogen oxygen nitrogen sulfur carbon hydrogen oxygen carbon hydrogen oxygen nitrogen phosphorus enzymes hormones Lipids Nucleic acids fats oils phospholipids DNA RNA Functions provide energy to cells stores energy in plants stores energy in animals makes up the cell walls of plants speed up biochemical re- actions regulate life processes store energy in animals store energy in plants make up cell membranes stores genetic information in cells helps cells make proteins
Besides water, most of the compounds in living things are biochemical compounds. A biochemical compound is a carbon-based compound that is found in living organisms. Carbon is an element that has a tremendous ability to form large compounds. Each atom of carbon can form four chemical bonds with other atoms. A chemical bond is the sharing of electrons between atoms. Bonds hold the atoms together in chemical compounds. A carbon atom can form bonds with other carbon atoms or with atoms of other elements.
Carbohydrates are biochemical compounds that include sugar, starch, glycogen, and cellulose. Sugars are simple carbohydrates with relatively small molecules. Glucose is the smallest of all the sugar molecules with its chemical formula of C6 H12 O6 . This means that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen. Plants and some other organisms make glucose in the process of photosynthesis. Living things that cannot make glucose can obtain it by consuming plants or organisms that consume plants. Starches are complex carbohydrates. They are polymers of glucose. Starches contain hundreds of glucose monomers. Plants make starches to store extra glucose. Consumers can get starches by eating plants. Common sources of starches in the human diet are pictured in the Figure 2.8. Our digestive system breaks down starches to sugar, which our cells use for energy. Like other animals, we store any extra glucose as the complex carbohydrate called glycogen. Glycogen is also a polymer of glucose. Cellulose is another complex carbohydrate found in plants that is a polymer of glucose. Cellulose molecules bundle together to form long, tough fibers. Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to stems and tree trunks.
characteristics of biochemical compounds
You can see from Table 2.1 that all biochemical compounds contain hydrogen and oxygen as well as carbon. They may also contain nitrogen, phosphorus, and/or sulfur. Almost all biochemical compounds are polymers. Polymers are large molecules that consist of many smaller, repeating molecules, called monomers. Most biochemical molecules are macromolecules. The prefix macro- means large, and many biochemical molecules are very large indeed. They may contain thousands of monomer molecules. The largest known biochemical molecule contains more than 34,000 monomers!
Lipids are biochemical compounds that living things use to store energy and make cell membranes. Types of lipids include fats, oils, and phospholipids. Fats are solid lipids that animals use to store energy. Examples of fats include butter and the fat in meat. Oils are liquid lipids that plants use to store energy. Examples of oils include olive oil and corn oil. Phospholipids contain the element phosphorus. They make up the cell membranes of living things. Lipids are made of long chains consisting almost solely of carbon and hydrogen. These long chains are called fatty acids. Fatty acids may be saturated or unsaturated. The Figure 2.10 shows an example of each type of fatty acid.
Proteins are biochemical compounds that consist of one or more chains of small molecules called amino acids. Amino acids are the monomers of proteins. There are only about 20 different amino acids. The sequence of amino acids in chains and the number of chains in a protein determine the proteins shape. Shapes may be very complex. You can learn more about the shapes of proteins at this link: MEDIA Click image to the left or use the URL below. URL: The shape of a protein determines its function. Proteins have many different functions. For example, proteins: make up muscle tissues. speed up chemical reactions in cells. regulate life processes. help defend against infections. 2.2. Chemistry of Living Things transport materials around the body in the blood. blood How hemoglobin transports oxygen in the
The student athlete in Figure 2.13 is practically flying down the track! Running takes a lot of energy. But you dont have to run a race to use energy. All living things need energy all the time just to stay alive. The energy is produced in chemical reactions. A chemical reaction is a process in which some substances, called reactants, change chemically into different substances, called products. Reactants and products may be elements or compounds. Chemical reactions that take place inside living things are called biochemical reactions. Living things depend on biochemical reactions for more than just energy. Every function and structure of a living organism depends on thousands of biochemical reactions taking place in each cell.
Nucleic acids are biochemical compounds that include RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). Nucleic acids consist of chains of small molecules called nucleotides. Nucleotides are the monomers of nucleic 40 acids. A nucleotide is shown in Figure 2.11. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen. 2. a sugar, which is deoxyribose in DNA and ribose in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form bonds with each other. The bonded bases are called base pairs. Bonds form only between adenine and thymine, and between guanine and cytosine. They hold together the two chains of DNA and give it its characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in Figure 2.12. Sugars and phosphate groups form the backbone of each chain of DNA. Determining the structure of DNA was a huge scientific breakthrough. You can read the interesting story of its discovery and why it was so important at this link: DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in DNAs nucleotide chains. RNA copies and interprets the genetic code in DNA. RNA is also involved in the synthesis of proteins based on the code. You can watch these events unfolding at this link: MEDIA Click image to the left or use the URL below. URL:
Each of the trillions of cells in your body is continuously performing thousands of anabolic and catabolic reactions. Thats an amazing number of biochemical reactionsfar more than the number of chemical reactions that might take place in a science lab or chemical plant. So many biochemical reactions can take place simultaneously in our cells because biochemical reactions occur very quickly. Thats because of enzymes. Enzymes are proteins that increase the rate of biochemical reactions. Enzymes arent changed or used up in the reactions, so they can be used to speed up the same reaction over and over again. Enzymes are highly specific for certain chemical reactions, so they are very effective. A reaction that would take years to occur without its enzyme might occur in a split second with the enzyme.
The sum of all of an organisms biochemical reactions is called metabolism. Biochemical reactions of metabolism can be divided into two general categories: catabolic reactions and anabolic reactions. You can watch an animation showing how the two categories of reactions are related at this link: Anabolic reactions involve forming bonds. Smaller molecules combine to form larger ones. These reactions require energy. For example, it takes energy to build starches from sugars. Catabolic reactions involve breaking bonds. Larger molecules break down to form smaller ones. These reactions release energy. For example, energy is released when starches break down to sugars.
photosynthesis and cellular respiration
Some of the most important biochemical reactions are the reactions involved in photosynthesis and cellular respira- tion. Photosynthesis is the process in which producers capture light energy from the sun and use it to make glucose. This involves anabolic reactions. Cellular respiration is the process in which energy is released from glucose and stored in smaller amounts in other molecules that cells can use for energy. This involves catabolic reactions. Photosynthesis and cellular respiration together provide energy to almost all living cells. Figure 2.14 shows how photosynthesis and cellular respiration are related. You can read more about both processes in the chapter Cell Functions.
elements and compounds
An element is pure substance that cannot be broken down into other substances. Each element has a particular set of properties that, taken together, distinguish it from all other elements. Table 2.1 lists the major elements in the human body. As you can see, you consist mainly of the elements oxygen, carbon, and hydrogen. Element Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Percent of Body Mass 65 18 10 3 1.5 1.0 0.35 0.25 In your body, most elements are combined with other elements to form chemical compounds. A compound is a unique type of matter in which two or more elements are combined chemically in a certain ratio. For example, much of the oxygen and hydrogen in your body are combined in the chemical compound water, or H2O.
atoms and molecules
The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7.
whats the matter
All known matter can be divided into a little more than 100 different substances called elements.
No diagram descriptions associated with this lesson
___smallest particle of an element that still has the properties of that element
a. enzyme b. protein c. molecule d. cellulose --> e. atom f. lipid g. nucleic acid
___carbohydrate that makes up the cell walls of plants
a. enzyme b. protein c. molecule --> d. cellulose e. atom f. lipid g. nucleic acid
___biochemical compound that consists of nucleotides
a. enzyme b. protein c. molecule d. cellulose e. atom f. lipid --> g. nucleic acid
___smallest particle of a compound that still has the properties of that compound
a. enzyme b. protein --> c. molecule d. cellulose e. atom f. lipid g. nucleic acid
___class of biochemical compound that consists of amino acids
a. enzyme --> b. protein c. molecule d. cellulose e. atom f. lipid g. nucleic acid
___class of biochemical compound that consists of fatty acids
a. enzyme b. protein c. molecule d. cellulose e. atom --> f. lipid g. nucleic acid
___protein that speeds up biochemical reactions
--> a. enzyme b. protein c. molecule d. cellulose e. atom f. lipid g. nucleic acid
___Atoms can be observed only with an electron microscope.
--> a. true b. false
___Glycogen is a complex carbohydrate found in animals.
--> a. true b. false
___Glucose is a polymer of starch.
a. true --> b. false
___Saturated fatty acids are found in oils
a. true --> b. false
___The genetic code tells cells how to make proteins.
--> a. true b. false
___The substances that start a chemical reaction are called products.
a. true --> b. false
___Cellular respiration involves catabolic reactions.
--> a. true b. false
Major elements in the human body include
--> a. hydrogen. b. carbon dioxide. c. water. d. all of the above
Which of the following is one of the four main classes of biochemical compounds?
--> a. carbohydrates b. sugars c. fats d. DNA.
Uses of lipids include
--> a. storing energy. b. making proteins. c. making up cell walls. d. regulating life processes.
Functions of proteins include
a. making up muscles. b. fighting infections. c. transporting materials. --> d. all of the above
How does RNA differ from DNA?
--> a. RNA consists of one chain of nucleotides rather than two chains. b. RNA has the nitrogen base thymine instead of uracil. c. RNA is a fatty acid rather than a nucleic acid. d. all of the above
Anabolic reactions are biochemical reactions in which
a. chemical bonds are broken. --> b. chemical bonds are formed. c. energy is released. d. two of the above
Which statement about enzymes is true?
a. Enzymes are products in biochemical reactions. --> b. Enzymes speed up biochemical reactions. c. Enzymes are used up in biochemical reactions. d. Enzymes are reactants in biochemical reactions.
No diagram questions associated with this lesson