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H H H H H H H O H H H H H O H C OH C C C C C C H H C O C C...

H H H H H H H O H H H H H O H C OH C C C C C C H H C O C C C C C C H HO H H H H H H H H H H H H O H H H H H H O H C OH + C C C C C C C H H C O C C C C C C C H + 3 H2 O HO H H H H H H H H H H H H H H H H O H H H H O H C OH C C C C C H H C O C C C C C H HO H H H H H H H H H H glycerol 3 fatty acids fat 3 water molecules Figure 1.12 Notice that in each fatty acid chain of a triglyceride molecule only the carbon atom at the glycerol end has oxygen attached to it. All the rest of the carbon atoms on the fatty acid have only hydrogen atoms attached to them. All fat molecules have the same basic three- Glycerol always has the same composition; branched structure. Figure 1.13 shows how this not so for the three fatty acids, which may be structure forms in a chemical reaction involving identical or nonidentical, short or long, saturated one molecule of an alcohol called glycerol and or unsaturated. In the hydrocarbon chain of a three molecules of fatty acid. Another name for saturated fatty acid, each of the carbon atoms this structure is a triglyceride. beyond the one bonded to oxygen is bonded to four other atoms. An unsaturated fatty acid has bonding sites (double bonds) where additional hydrogen Fatty acid 1 atoms could be attached. Figure 1.14 shows the difference between a saturated and an unsaturated glycerol Fatty acid 2 fatty acid. If unsaturated fatty acids dominate, the resulting Fatty acid 3 fat will likely be liquid at room temperature. If saturated fatty acids dominate, the resulting fat will likely be solid at room temperature. Figure 1.13 On this simple model of a triglyceride (fat) macromolecule, the triangles represent glycerol’s three FAST FORWARD reaction sites. To learn about double bonds, turn to Appendix 2. A fatty acid is a hydrocarbon chain with a difference: at one end, the carbon has an acidic H H H H H H O — COOH group instead of hydrogen attached to it. A C C C C C C C H It is this acidic group of a fatty acid that attaches to HO H H H H H H one of the three main reaction sites on a glycerol molecule, as shown in Figures 1.13 and 1.14. The H H H H H O triglyceride produced is nonpolar. This means that B C C C C C C H it will not be attracted to (polar) water molecules, HO H H H which is why fats are insoluble in water. Figure 1.14 (A) This fatty acid is saturated with hydrogen. (B) This fatty acid has room for two more hydrogen atoms, PAUSE RECORD one on each of the highlighted carbon atoms. Such a fatty Compare Figure 1.12 (lipid formation) with Figure 1.9 acid is called unsaturated. (carbohydrate formation). What do the two reactions have in common? (Hint: Look at the blue highlighting on each figure.) How do they differ? Exploring the Micro-universe of the Cell MHR 13  BIO FACT Steroids (and cholesterol) are lipids too, although the structure of these molecules differs markedly from the structure of fats. News reports from the sports world may have led you to think of steroids as harmful to health. In fact, your body makes several different kinds of steroids from the fats you eat. You need all of these steroids for normal health and development. Your body manufactures all the steroids it needs, so injecting or ingesting steroids can lead to abnormal development of sex organs and even early death. The Structure and Biological Function of Proteins Most cellular structures are made of various types of protein. Proteins also serve many other functions in cells. In fact, they display greater Figure 1.15 Feathers, spider webs, wool, and silk are made structural complexity and functional diversity than up of proteins. In fact, feathers consist mostly of the same either lipids or carbohydrates. protein, keratin, that makes up human nails and hair. Your hair and fingernails are both made of the same type of protein, keratin, yet each has its own act as chemical messengers (some hormones are distinctive properties. The bones and muscles proteins rather than lipids, such as the insulin inside your hand and the ligaments and tendons that helps to regulate the amount of glucose connecting them also contain distinctly different available to cells) proteins. Without these proteins, you would not be Like other macromolecules, proteins are able to move your hand. assembled from small units. In proteins, the In addition to their structural functions, building blocks are amino acid molecules. proteins also Figure 1.16 shows the chemical structure of five function as enzymes to facilitate chemical representative amino acids. Note the unhighlighted reactions (the enzyme amylase in your saliva part of each amino acid. It contains two carbon begins the breakdown of starches into simple atoms, two oxygen atoms, four hydrogen atoms, sugars while you chew) and one nitrogen atom per molecule. The number help transport substances across cell membranes and arrangement of these atoms is identical for or to different parts of an organism (the all but one amino acid (proline). What differs hemoglobin in your blood transports oxygen substantially from one amino acid to another is the from your lungs to each cell in your body) highlighted remainder group (or R group). alanine valine cysteine phenylalanine H H O H H O H H O H H O H N C C H N C C H N C C H N C C OH OH OH OH H C H CH H C H H C H Remainder group, or R group H H C H H C H SH C H H H C C H H C C H C H Figure 1.16 Note that these five representative amino acids differ from one another by their R groups. 14 MHR Cellular Functions  peptide bond H H H R H H O R O OH OH H N C C + N C C H N C C N C C + H2 O OH H O O R H R H H amino acid amino acid dipeptide water Figure 1.17 In the first stage of the formation of a polypeptide, two amino acids are linked together. The R groups appear only as “R” because they do not take part in the reaction that produces or breaks a peptide bond. A chemical linkage called a peptide bond joins individual amino acids together. Figure 1.17 shows how a peptide bond between two amino acids is formed or broken. Regardless of which R group is present, amino acids always bond to each other in the manner shown in Figure 1.17. However, a chain of amino acids is not yet a protein, only a polypeptide. Figure 1.19 on the next page shows the steps between a peptide bond and a finished protein molecule. The final shape of the protein’s three- dimensional structure determines what properties it will have and therefore what functions it can perform. If a protein molecule is exposed to extreme temperatures, extreme pH conditions (very acidic or very basic), or harsh chemicals, it will unfold or change shape. When this happens, the protein is Figure 1.18 This computer-generated image of a protein said to have been denatured. The protein loses its molecule makes the protein’s complex, three-dimensional ability to perform its normal function. structure easier to visualize. Why can some proteins such as enzymes or hemoglobin function in a water solution while Humans need 20 amino acids — known as others (such as the keratin in your fingernails) are the common amino acids — to make the protein usually insoluble in water? This depends on how macromolecules required for healthy body the polypeptide(s) making up a protein are twisted structures and functions. Your body can and folded. When the parts of the R groups that can manufacture 12 of these amino acids from non- interact with water end up on the outside of the protein food sources. The other eight must be final protein structure, the protein is soluble in present in your food because your body cannot water. When the parts of the R groups that do not manufacture them for itself. These eight are interact with water or react only slightly with it referred to as essential amino acids. end up on the outside, the protein will not dissolve With 20 different amino acids to combine, in water. proteins exist in thousands of distinctly different forms. Each kind of organism manufactures its PLAY own characteristic proteins or variations on To enhance your learning about macromolecules, go to your proteins common to a number of species, such as Electronic Learning Partner. hemoglobin. Indeed, it is our proteins that make us different from ants, amoebas, or ash trees. Exploring the Micro-universe of the Cell MHR 15  + amino acid H3N peptide bond Many amino acids are COO− joined together to form a polypeptide chain. O O C CH C O C O C C O N R CH N H N H C N H C α (alpha) helix R C O C O C H H CH R O R C O When a polypeptide grows H N H C O H R C R C O H H beyond 30 amino acids, it O N H N N CH begins to either coil up into a C H pleated sheet C O N H C O C R helix or bend into a pleated CH R O C H N O C R H O sheet. The dotted lines N H R C N H N H C R represent the weak attraction O H O R C O C H O C CH H between the O and H O C R C “sidearms” that holds the O N C O N H CH R R C H H molecule in a helical or C N H N N pleated shape. R CH C O C O H N The helix then folds into a three-dimensional Many proteins contain two or more structure, the exact shape of which depends folded polypeptides joined together. on which R groups are present and in what order. Figure 1.19 The formation of a protein molecule from a polypeptide 16 MHR Cellular Functions  make up much of the structure of a cell and control how it functions. phosphate Like proteins and carbohydrates, nucleic acids P consist of long chains of linked subunits. These O N N subunits are called nucleotides, which are depicted in Figure 1.20. DNA is made up of just four S nitrogen- containing different nucleotides. So is RNA. Each DNA base nucleotide has an RNA nucleotide counterpart. pentose sugar RNA consists of a single, long chain of nucleotides. In DNA, two enormous nucleotide Figure 1.20 Generalized nucleotide. Nucleotides consist chains are attached in a ladder-like structure, of a five-carbon simple sugar (ribose in the case of RNA and which then coils into a double helix shape. deoxyribose in DNA), a nitrogen base, and a phosphate group, symbolized here by P. Figure 1.22 illustrates this DNA structure. Nucleic Acids Nucleic acids direct the growth and development of every living thing by means of a chemical code. They determine how the cell functions and what characteristics it has. The cell contains two types of nucleic acid: RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). You may already have learned that DNA is the main component of the genes, or hereditary material, in all cells. Each gene contains Figure 1.21 This image shows the shape of individual instructions for making RNA. RNA, contains the atoms on a section of a DNA molecule. It was mapped using instructions for making proteins. These proteins a probe through which a tiny electric current flows. P P T A S S P P C G S S C G A P P T T one A C G nucleotide S S T A P P C G S S P P T A S S Figure 1.22 DNA’s structure. Each DNA strand contains carbon rings (sugar) and phosphate molecules, while the ladder “rungs” between the strands consist of nitrogen bases. Exploring the Micro-universe of the Cell MHR 17  Investigation 1 A SKILL FOCUS Conducting research What’s Here? Testing for Macromolecules Performing and recording Biochemists have developed standard tests to determine the presence Analyzing and interpreting of the most abundant macromolecules made by cells: carbohydrates, lipids, and proteins. In this investigation, you will conduct standard Communicating results tests to determine the presence of glucose, starch, lipid, and protein in known samples. Each test involves an indicator, which is a chemical that changes colour when it reacts with a specific substance. Pre-lab Questions Use the same graduated cylinder to measure Glucose is a monosaccharide. What does this samples of the same substance for all four mean? parts of this investigation. For example, use the same graduated cylinder to measure out Proteins are made of amino acids. What atom vegetable oil each time. is present in an amino acid that is not present in a sugar molecule? Perform parts B, C, and D of this investigation while you heat samples for part A. Identify two health hazards related to using a copper sulfate solution. Carefully clean your work area after you finish each test. Problem Wash glassware throughly with soap and water. How can you determine the presence of glucose, starch, lipid, and protein in various samples? Part A 1. Set up the hot water bath as shown below. CAUTION: Be careful when handling iodine, Use a medium setting for the hot plate. Benedict’s solution, Sudan IV, and Biuret reagent as they are toxic. Avoid allowing the hot water bath to boil vigorously because this can cause test tubes to break. Clean up spills immediately, and notify your teacher if a spill occurs. Materials safety goggles 40 mL sucrose solution disposable gloves 40 mL starch solution apron 40 mL distilled water marker Benedict’s solution in a 6 graduated cylinders dropper bottle 12 test tubes iodine solution in a test tube rack dropper bottle 2. Mark the six graduated cylinders with the hot water bath Sudan IV solution numbers 1 to 6. test tube clamp (0.5% alcohol solution) 3. Mark six test tubes with the numbers 1 to 6. test tube brush in a dropper bottle 40 mL protein solution Biuret reagent in a 4. Measure out 10 mL of protein solution into (2% gelatin solution) dropper bottle graduated cylinder 1, 10 mL of vegetable oil 40 mL vegetable oil glassware soap into graduated cylinder 2, 10 mL of glucose 40 mL glucose solution solution into graduated cylinder 3, 10 mL of sucrose solution into graduated cylinder 4, Procedure 10 mL of starch solution into graduated Follow your teacher’s instructions for the cylinder 5, and 10 mL of distilled water into disposal of the test solutions and samples. graduated cylinder 6. 18 MHR Cellular Functions  5. Add 10 mL of each sample to the test tube Part D with the same number. 1. Repeat steps 3, 4, and 5 from Part A. 6. Add 5 drops of Benedict’s solution to each 2. Add 5 drops of Biuret reagent to each test test tube. Safely mix the contents of each test tube. Safely mix the contents of each test tube by swirling the test tube as shown below. tube. 3. Record your observations for each test tube. Then wash the test tubes and graduated cylinders. A. B. C. D. Benedict’s Iodine Sudan IV Biuret solution + solution solution reagent Sample heat 1. protein solution 2. vegetable oil 7. Heat each test tube in the hot water bath Post-lab Questions for 5 min. If your hot water bath is large enough, heat two test tubes at a time. After 1. Describe a positive test for starch. Explain 5 min, use a test tube clamp to move each how you know. test tube to the test tube rack. 2. Describe a positive test for glucose. Explain 8. When all the test tubes have been heated how you know. and removed, turn off the source of heat and 3. Describe a positive test for lipids. Explain let the water bath cool. how you know. 9. Record your observations for each test tube. 4. Describe a positive test for protein. Explain 10. When the test tubes have cooled, wash how you know. them. When the hot water bath has cooled, pour out the water and wash the glassware. Conclude and Apply 5. What was the purpose of testing distilled Part B water for each part of the investigation? 1. Repeat steps 3, 4, and 5 from Part A. 6. Suppose you have a sample of breakfast 2. Add 5 drops of iodine solution to each test cereal that may contain one, two, three, or tube. Carefully mix the contents of each test all four of the macromolecules you tested tube. for in this investigation. Write a procedure describing how you would test the sample 3. Record your observations for each test tube. to determine which macromolecules Then wash the test tubes. it contains. Part C Exploring Further 1. Repeat steps 3, 4, and 5 from Part A. 7. Physicians often want to know the glucose 2. Add 5 drops of Sudan IV solution to each and lipid levels in a patient’s blood and test tube. Safely mix the contents of each whether proteins are present in a patient’s test tube. urine. Research to find out what this information might show about an 3. Record your observations for each test tube. individual’s health. Then wash the test tubes thoroughly. Exploring the Micro-universe of the Cell MHR 19  MINI LAB Manipulating Macromolecules Analyze The study of biological molecules has been revolutionized 1. Describe each type of model the site(s) allowed you to by the use of computers. Today, sophisticated software view, for example, a bail-and-stick model, space-filling programs allow biochemists to explore, build, and model, and so on. manipulate three-dimensional models of macromolecules. 2. How does rotating a molecule change what you can In this lab, you will use the Internet to view and manipulate see about it? similar models. (You may need to download free software to run the simulations, such as Chime. Check with your 3. Draw structural formulas for two of the three- teacher before you download anything onto a school dimensional models that you viewed. computer.) Your teacher will give you a list of sites that 4. What did the computer simulations of molecules show contain three-dimensional models of proteins and other you that would be more difficult to see using molecular macromolecules. Go to each site, and use the simulations model kits? to view and manipulate the molecular models. SECTION REVIEW 1. K/U List the key life processes of cells. milk change its chemical make-up? Predict any changes, and design a lab that would test your 2. K/U Identify three inorganic molecules important prediction. for cells. 8. K/U Some oils, such as olive oil, are liquid at room 3. K/U Describe the unique properties of water. Explain temperature. How can the structure of the oil how each property is important to cells. molecules be changed so that they are almost solid 4. K/U Copy and complete this chart: at room temperature? Macromolecule Sample Function in 9. MC Find a Materials Safety Data Sheet, and identify type Diagram Molecule the cell health hazards related to Biuret’s reagent. monosaccharide 10. MC Explain how computer molecular-model simulations could benefit biomedical research. carbohydrate lipid (2 examples) UNIT INVESTIGATION PREP protein (2 examples) How is whole milk different from skim milk? nucleic acid Design a series of tests to identify the macromolecules in whole milk. Which indicators would you use? 5. K/U What is a peptide bond? Predict which macromolecules you would find if you 6. K/U Why are some amino acids described as performed the tests you designed above. Would you essential amino acids? expect different results with skim milk? Explain. 7. I Some people add cold milk to hot coffee. Others heat milk so that it is hot and steamy. Does heating 20 MHR Cellular Functions S E C T I O N 1.2 Cell Membrane Structure E X P E C TAT I O N S Identify the structure and function of phospholipids. Describe the fluid-mosaic structure of the cell membrane. Figure 1.23 From an altitude of 10 000 m, a city may look quiet and still. From 1000 m, it becomes clear that buses, trucks, and cars are moving. Airplanes fly into its airport. Ships and boats come and go from its harbour. How does this city resemble a cell? When viewed with even the most powerful The efficient operation of a city such as the one light microscope, the cell membrane looks like pictured in Figure 1.23 would soon grind to a halt nothing more than a thin, dark line. Yet if the cell without adequate routes for the flow of people and membrane functioned only as a barrier separating things in and out. Similarly, the activities of a the inside of the cell from its external environment, living cell depend on the ability of its membrane to how could the cell survive? How would the cell get transport raw materials into the cell the raw materials it needs to build macromolecules? transport manufactured products and wastes out The cell membrane must also regulate the movement of the cell of materials from one environment to the other. prevent the entry of unwanted matter into the cell prevent the escape of the matter needed to perform the cellular functions Getting the Cell Membrane in Focus The development of the electron microscope gave scientists the information they needed to begin exploring how the cell membrane performs its regulatory functions. An electron microscope uses beams of electrons instead of light to produce images. Electron microscopes and other devices separate electrons from their atoms and focus them into a beam. For example, the image on a TV set is formed by electron beams that cause the inner coating on the screen to glow. Compared to light, an electron beam has a very short wavelength — so short that it can pass between two cell features less than 0.2 µm apart and form an image of them that shows two distinct Figure 1.24 What was the original purpose of this wall around the old part of Québec City? How did its original and separate points. function resemble that of a cell membrane? Exploring the Micro-universe of the Cell MHR 21  analysis revealed that this bilayer is composed mainly of phospholipid molecules, a type of lipid. Phospholipids have two fatty acids bonded to a glycerol “backbone.” The third glycerol reaction site is bonded to a chain containing phosphorus, and in some cases nitrogen as well. This makes the shape and properties of a phospholipid quite different from those of a triglyceride. The phosphate chain forms a “head,” while the two fatty acids form two “tails.” The electric charge in the molecule is unevenly distributed, as shown in Figure 1.27: the molecule has a polar head and nonpolar tails. The polar head of a phospholipid molecule is attracted to water molecules, which are also polar. This makes the phosphorus end of a phospholipid water soluble. The hydrocarbon chains in the fatty- acid tails of the phospholipid are not attracted to water molecules. They are, however, compatible Figure 1.25 James Hillier was in his early twenties when with other lipids. his professor asked him to help build a practical electron microscope. The microscope that Hiller and Albert Prebus Wo rd built is now on display at the Ontario Science Centre in LINK Toronto. It has 7000x magnification. Earlier in this chapter, you learned that hydro means water. Many textbooks use the terms hydrophobic and hydrophilic to The first really usable electron microscope was describe the way that molecules interact with water. Write a built in 1938 at the University of Toronto by two definition for each of these words, including the word soluble graduate students, James Hillier (1915–) and Albert in one definition and insoluble in the other. Which end of a Prebus (1913–1997). Their microscope revealed phospholipid is hydrophobic and which is hydrophilic? that what look like “grains” under the light microscope are complex cellular structures. In Figure 1.28 shows what can happen when a film Chapter 2, you will learn more about these of phospholipid molecules is spread in a water structures. This section continues the story of sample. Through a combination of attraction and research into the cell membrane. repulsion, the phospholipids spontaneously When electron microscopy finally yielded a arrange themselves into a spherical, cage-like more detailed view, microscopists saw that the bilayer. Their water-attracting polar heads face both cell membrane is in fact a bilayer, or a structure the inside and the outside of the sphere, while consisting of two layers of molecules. Chemical plant cell membrane animal cell membrane Figure 1.26 Electron microscopy showed that the cell membranes of both plant and animal cells have a two-layered structure. This gave scientists the clue they needed to begin unravelling the mystery of how the cell membrane works. 22 MHR Cellular Functions  CH3 + nitrogen CH2 N CH3 group CH2 CH3 O polar head phosphate group O P O− group O water CH2 CH CH2 glycerol O O C O C O CH2 CH2 head CH2 CH2 CH2 CH2 tail CH2 CH2 B CH2 CH2 Figure 1.28 The molecular structure of a phospholipid CH2 CH2 bilayer. Unlike the cell membrane of a living cell, this bilayer fatty acids nonpolar CH2 CH2 contains only water inside it. tail group CH2 CH CH Based on intensive research by biochemists CH2 CH2 and electron microscopists, biologists have inferred CH2 CH2 that the cell membrane also contains a mosaic of CH2 CH2 different components scattered throughout it, much CH2 CH2 like raisins in a slice of raisin bread. For example, CH2 numerous protein molecules stud the phospholipid CH2 CH2 CH2 bilayer. The phospholipid molecules and some of CH2 these proteins can drift sideways in the bilayer, a CH2 CH3 phenomenon which supports the idea that the CH2 phospholipid bilayer has a fluid consistency. Thus, A CH3 this description of the cell membrane is called the fluid-mosaic membrane model. Figure 1.27 Constructed much like a triglyceride (fat), Figure 1.29 on the next page shows how proteins phospholipids contain a phosphate group and sometimes and phospholipids fit together in the continuous also a nitrogen group. mosaic of an animal cell membrane. Note that this cell membrane also contains another type of lipid: their water-averse, nonpolar lipid tails face each cholesterol molecules. Cholesterol allows animal other. This sandwich-like phospholipid structure, cell membranes to function in a wide range of called a phospholipid bilayer, forms the basis of temperatures. At high temperatures, it helps the cell membrane. maintain rigidity in the oily membrane bilayer. At low temperatures, its keeps the membrane fluid, BIO FACT flexible, and functional — preventing cell death The ability of phospholipids to spontaneously form a from a frozen membrane. Cholesterol also makes spherical bilayer in water likely played a key role in the the membrane less permeable to most biological formation of the first cells about 3.8 billion years ago. molecules. Plants have a different lipid that serves a similar function in their cell membranes. The shapes of the membrane proteins vary The Fluid-Mosaic Membrane Model according to their function, and each type of cell has a characteristic arrangement of proteins in its The fact that lipids do not dissolve in water creates membrane. For example, the membrane of a human a border around the cell. The phosphate edges of red blood cell includes 50 different protein types this border help to define and contain the more arranged in a pattern that only other cells from fluid lipid centre. However, there is much more to humans with the same blood type can “recognize.” a cell membrane than its phospholipid bilayer. Exploring the Micro-universe of the Cell MHR 23  Outside cell carbohydrate glycolipid glycoprotein chain phospholipid integral bilayer protein cholesterol Inside cell peripheral filaments of protein the cytoskeleton Figure 1.29 Fluid-mosaic model of membrane structure. its cytoskeleton) support the membrane. Each type of cell Notice that many lipids and proteins facing the exterior of has its own unique “fingerprint” of carbohydrate chains that the cell have carbohydrate chains attached to them, while distinguish it from other kinds of cells. on the interior of the cell, parts of the cell’s skeleton (called SECTION REVIEW 1. K/U List the functions of the cell membrane. 7. K/U Why does your body manufacture cholesterol even if you do not eat any foods that contain 2. C Compare the structures of a phospholipid and a cholesterol? fatty acid using a simple diagram of each type of molecule. Label any differences in polarity. 8. K/U Explain why the electron microscope is better than the light microscope for looking at the cell 3. C Make a model cell membrane that shows the membrane. different components. Include a legend that makes your model easy to understand. 9. K/U What other cellular structures might the electron microscope provide useful information about that a 4. C Cells are organized differently from the world light microscope could not? outside the cell membrane. Draw a diagram of a predator cell, showing how this organization inside 10. MC Oil acts as an organic solvent. What kinds of the cell is different from the material outside the cell. problems would organisms coming into contact with Then make a second diagram to show the impact an oil spill have? that opening a hole in the cell membrane would have on the cell. 5. K/U Identify the component(s) of the cell membrane that give it a fluid consistency. 6. K/U Why does the cell membrane require a fluid consistency? 24 MHR Cellular Functions