Chapter 2: Chemistry Raw materials and fuel for our bodies Lectures by Mark Manteuffel, St. Louis Community College Learning Objectives Describe what atoms are, their structure, and how they bond. Understand water’s features that help it support all life. Describe carbohydrates—their structure and function. Learning Objectives Describe lipids—their structure and function. Describe proteins—their structure and function. Describe nucleic acids—their structure and function. 2.1 Everything is made of atoms. An element is a substance that cannot be broken down chemically into any other substances. An atom is a bit of matter that cannot be subdivided any further without losing its essential properties. Atomic Structure: The nucleus, protons, and neutrons Atomic Structure: Electrons Atomic Numbers 25 Elements Found in Your Body and the Big 4 Take-home message 2.1 Everything around us, living or not, is made from atoms, the smallest unit into which material can be divided. Atoms They all have the same general structure. are made up of protons and neutrons in the nucleus and electrons, which circle far around the nucleus. 2.2 An atom’s electrons determine how (and whether) the atom will bond with other atoms. Electron shells Electron Shells Ions Take-home message 2.2 The chemical characteristics of an atom depend upon number of electrons in their outermost shells. Atoms are most stable and least likely to bond with other atoms when their outermost electron shell is full. 2.3 Atoms can bond together to form molecules or compounds. Molecules Products of bonding! Covalent Bonds Ions and Ionic Bonds Hydrogen Bonds Take-home message 2.3 Atoms can be bound together in three different ways. Covalent bonds, in which atoms share electrons, are the strongest. Take-home message 2.3 In ionic bonds, the next strongest, one atom transfers its electrons to another and the two oppositely charged ions are attracted to each other, forming a compound. Take-home message 2.3 Hydrogen bonds, the weakest, involve the attraction between a hydrogen atom and another polar atom or molecule. 2.4 A molecule’s shape gives it unique characteristics. Molecular Shape Personalities determines function • Physical properties such as: »Taste »Smell Molecular Interactions and Insect Mating Behavior Take-home message 2.4 The properties of a molecule—such as how the molecule tastes or smells, or its likelihood of bonding with other molecules—depend upon the shape in which the atoms are linked together and the electrons in their outermost shells. 2.5 Hydrogen bonds make water cohesive. Take-home message 2.5 Water molecules easily form hydrogen bonds, giving water great cohesiveness. 2.6 Water has unusual properties that make it critical to life. Cohesion Large Low heat capacity density as a solid Good solvent Cohesion Heat Capacity Why do coastal areas have milder, less variable climates than inland areas? Low Density as a Solid Why don’t oceans freeze as easily as fresh water lakes? Take-home message 2.6 The hydrogen bonds between water molecules give water several of its most important characteristics: • • • • cohesiveness low density as a solid the ability to resist temperature changes broad effectiveness as a solvent 2.7 Living systems are highly sensitive to acidic and basic conditions. Hydrogen Ions and Hydroxide Ions OH - O H Ionized Hydroxide Molecule H2O O H H Non-Ionized Water Molecule pH Scale The amount of H+ in a solution is a measure of its acidity and is called pH. Acids Bases H+ Ions and Acids H+ very reactive Acids can donate H+ to other chemicals Stomach acids Bases Low H+ High OH Antacids Baking soda, seltzer, milk of magnesia Blood pH Buffers • can quickly absorb excess H+ ions to keep a solution from becoming too acidic, • and they can quickly release H+ ions to counteract any increases in OH concentration. Take-home message 2.7 The pH of a fluid is a measure of how acidic or basic a solution is and depends on the concentration of dissolved H+ ions present. Acids, such as vinegar, can donate protons to other chemicals while bases, including baking soda, bind with free protons. 2.8 Carbohydrates are macro-molecules that function as fuel. Health topics of the year Low-carb diet? Hi-carb diet? “Carbo-loading”? Fiber intake? What are carbohydrates? Four Types of Macromolecules Carbohydrates Lipids Proteins Nucleic acids Carbohydrates C, H, and O Primary fuel for organisms Cell structure Energy is in the chemical bonds! Take-home message 2.8 Carbohydrates are the primary fuel for running all cellular machinery and also form much of the structure of cells in all life forms. Take-home message 2.8 Carbohydrates contain carbon, hydrogen, and oxygen, and generally have the same number of carbon atoms as they do H2O units. Take-home message 2.8 The C-H bonds of carbohydrates store a great deal of energy and are easily broken by organisms. 2.9 Simple sugars are the most effective source of energy. Monosaccharides 37 carbon atoms Glucose and fructose Glucose Most carbohydrates — ultimately converted into glucose Blood sugar What is “carbo-loading”? Take-home message 2.9 The simplest carbohydrates are called monosaccharides or simple sugars. They contain from three to seven carbon molecules. The sugar glucose is the most important carbohydrate to living organisms. 2.10 Complex carbohydrates are time-released packets of energy. More than 1 sugar (monosaccharide) unit Disaccharides • • sucrose lactose Polysaccharides • • starch cellulose Chemical Fuel Preliminary Processing Starch > 100’s of glucose molecules joined together Barley, wheat, rye, corn, and rice Glycogen—“animal starch” Complex Carbohydrates “Time-release” fuel pellets Take-home message 2.10 Multiple simple carbohydrates sometimes link together into more complex carbohydrates. Types of complex carbohydrates include starch, the primary form of energy storage in plants, and glycogen, a primary form of energy storage in animals. 2.11 Not all carbohydrates are digestible. Chitin Cellulose Fiber “Roughage” Colon cancer prevention/reduction Termites ecological role Take-home message 2.11 Some complex carbohydrates, including chitin and cellulose, cannot be digested by most animals. Such indigestible carbohydrates in the diet, called fiber, aid in digestion and have numerous health benefits. 2.12 Lipids are macromolecules with several functions, including energy storage. Why does a salad dressing made with vinegar and oil separate into two layers shortly after you shake it? Hydrophobic Hydrophilic Take-home message 2.12 Lipids are non-soluble in water and greasy to the touch. They are valuable to organisms in longterm energy storage and insulation, membrane formation, and as hormones. 2.13 Fats are tasty molecules too plentiful in our diets. Glycerol: region Fatty “head” acid “tails” Triglycerides Fat molecules contain much more stored energy than carbohydrate molecules. Saturated and Unsaturated Fats # of bonds in the hydrocarbon chain in a fatty acid Health considerations Chocolate chip cookie recipes call for some lipids. How will the “chewy-ness” of the cookies differ depending on whether you use butter or vegetable oil as the lipid? Which cookies will be healthier? Many snack foods contain “partially hydrogenated” vegetable oils. Why might it be desirable to add hydrogen atoms to a vegetable oil? What are trans fats? Olestra is a recently developed “fake fat” chemical that gives foods the taste of fat, without adding the calories of fats. What chemical structure might make this possible? Take-home message 2.13 Fats, including the triglycerides common in the food we eat, are one type of lipid. Take-home message 2.13 Characterized by long hydrocarbon tails, fats effectively store energy in the bonds connecting the molecules. Organisms prefer fats in their diets because of the high calories, but this also causes obesity and illness in today’s modern world. 2.14 Cholesterol and phospholipids are used to build sex hormones and membranes. Not all lipids are fats The sterols Cholesterol Important component of most cell membranes. Can attach to blood vessel walls and cause them to thicken. Cells in our liver produce almost 90% of the circulating cholesterol. Steroid Hormones Estrogen Testosterone • synthetic variants of testosterone Phospholipids and Waxes Phospholipids are the major component of the cell membrane. Waxes are strongly hydrophobic. Take-home message 2.14 Cholesterol and phospholipids are lipids that are not fats. Both are important components in cell membranes. Cholesterol also serves as a precursor to steroid hormones, important regulators of growth and development. 2.15 Proteins are versatile macromolecules that serve as building blocks. Amino Acids Twenty Strung different amino acids together to make proteins Take-home message 2.15 Unique combinations of 20 amino acids give rise to proteins, the chief building blocks of physical structures that make up all organisms. Proteins perform myriad functions. 2.16 Proteins are an essential dietary component. Growth Repair Replacement Food labels indicate an item’s protein content. Why is this insufficient for you to determine whether you are protein deficient, even if your protein intake exceeds your recommended daily amount? Complete Proteins Have all essential amino acids Incomplete proteins Complementary proteins Take-home message 2.16 Eight of the 20 amino acids are essential amino acids and cannot be made by the body so must be consumed in the diet. Complete proteins contain all eight essential amino acids, while incomplete proteins do not. 2.17 Protein functions are influenced by their three-dimensional shape. Peptide bonds Primary Structure The sequence of amino acids Secondary Structure Hydrogen bonding between amino acids The two most common patterns: • twist in a corkscrew-like shape • zig-zag folding Tertiary Structure Folding and bending of the secondary structure Due to bonds such as hydrogen bonds or covalent sulfursulfur bonds. Quaternary Structure When two or more polypeptide chains are held together by bonds between the amino acids on the different chains. Hemoglobin Egg whites contain much protein. Why does beating them change their texture, making them stiff? Egg whites contain much protein. Why does beating them change their texture, making them stiff? Why is wet hair easier to style than dry hair? Why do some people have curly hair and others have straight hair? Take-home message 2.17 The particular amino acid sequence of a protein determines how it folds into a particular shape. This shape determines many of the protein's features, such as which molecules it will interact with. When a protein's shape is deformed, the protein usually loses its ability to function. 2.18 Enzymes are proteins that initiate and speed up chemical reactions. “Misspelled” Proteins Incorrect Active amino acid sequence site disruptions Phenylketonuria Why do some adults get sick when they drink milk? Take-home message 2.18 Enzymes are proteins that help initiate and speed up chemical reactions. They aren't permanently altered in the process but rather can be used again and again. 2.19 Nucleic acids are macromolecules that store information. Two Types of Nucleic Acids Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) Both play central roles in directing the production of proteins. Information Storage The information in a molecule of DNA is determined by its sequence of bases. Adenine, guanine, cytosine, and thymine • CGATTACCCGAT Take-home message 2.19 The nucleic acids DNA and RNA are macromolecules that store information by having unique sequences of molecules. Both play central roles in directing protein production in organisms. 2.20 DNA holds the genetic information to build an organism. Base-Pairing A &T G &C What is the complimentary strand to this strand: CCCCTTAGGAACC? Take-home message 2.20 DNA is like a ladder in which the long vertical element of the ladder is made from a sequence of sugar-phosphatesugar-phosphate molecules and rungs are nucleotide bases. The sequence of nucleotide bases contains the information about how to produce a particular protein. 2.21 RNA is a universal translator, reading DNA and directing protein production. RNA differs from DNA in three important ways. The sugar molecule of the sugarphosphate backbone Single-stranded Uracil (U) replaces thymine (T) Take-home message 2.21 RNA acts as a middleman molecule— taking the instructions for protein production from DNA to another part of the cell where, in accordance with the RNA instructions, amino acids are pieced together into proteins. Learning Objectives Describe what atoms are, their structure, and how they bond. Understand water’s features that help it support all life. Describe carbohydrates—their structure and function. Describe lipids—their structure and function. Describe proteins—their structure and function. Describe nucleic acids—their structure and function.