2There are four classes of biological molecules 3.3 Cells make a huge number of large molecules from a small set of small moleculesThere are four classes of biological molecules1. Carbohydrates2. Proteins3. Lipids4. Nucleic acids
83.4 Monosaccharides are the simplest carbohydrates Carbohydrates range from small sugar molecules (monomers) to large polysaccharidesSugar monomers are monosaccharides, such as glucose and fructoseThese are linked together to form the polysaccharidesMonosaccharides have molecular formulae that are multiples of CH2O.
93.5 Cells link two single sugars to form disaccharides Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reactionAn example is a glucose monomer bonding to a fructose monomer to form sucrose, a common disaccharideDi- = twoSucrose is the sugar (disaccharide) we keep around the kitchen to sweeten coffee or use for dozens of other things.Animation: Disaccharides
10GlucoseGlucoseFigure 3.5 Disaccharide formation by a dehydration reaction.
11Glucose Glucose Maltose Figure 3.5 Disaccharide formation by a dehydration reaction.Maltose
123.7 Polysaccharides are long chains of sugar units Polysaccharides are polymers of monosaccharidesPoly- = manyAnimals and plants store sugars for later use. Plants store starch while animals store glycogen.
13Starch is a storage polysaccharide composed of glucose monomers and found in plants Glycogen is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is neededCellulose is a polymer of glucose that forms plant cell wallsChitin is a polysaccharide used by insects and crustaceans to build an exoskeleton
14Starch granules in potato tuber cells STARCH Glucose monomer Glycogen in muscletissueGLYCOGENCELLULOSECellulose fibrils ina plant cell wallFigure 3.7 PolysaccharidesHydrogen bondsCellulosemolecules
163.8 Fats are lipids that are mostly energy-storage molecules Lipids are water insoluble (hydrophobic, or water fearing) compounds that are important in energy storageThey contain twice as much energy as a polysaccharideFats are lipids made from glycerol and fatty acidsHydro- = of waterPhob- = fear (i.e. phobia)Lipids are generally not big enough to be macromolecules. They are grouped together because they mix poorly, if at all, with water.
17Figure 3.8A Water beading on the only coating of feathers.
18Fatty acids link to glycerol by a dehydration reaction A fat contains one glycerol linked to three fatty acidsFats are often called triglycerides because of their structureAnimation: Fats
19GlycerolFatty acidFigure 3.8B A dehydration reaction linking a fatty acid to glycerol.
20Figure 3.8C A fat molecule made from glycerol and three fatty acids.
21PhospholipidsThe polar, hydrophilic heads are in contact with the watery environment on both sides of the membraneThe hydrophobic fatty acid ‘tails’ band together in the center
22Some fatty acids contain double bonds This causes kinks or bends in the carbon chain because the maximum number of hydrogen atoms cannot bond to the carbons at the double bondThese compounds are called unsaturated fats because they have fewer than the maximum number of hydrogensFats with the maximum number of hydrogens are called saturated fatsMost animal fat is saturated fat. Saturated fats, such as butter and lard, will pack tightly together and will be solid at room temperature.Plant and fish fats are usually unsaturated fats. They are usually liquid at room temperature. Olive oil and cod liver oil are examples.Peanut butter, margarine, and many other products are hydrogenated to prevent lipids from separating out in liquid (oil) form.
23Saturated fats tend to be solid at room temperature Unsaturated fats are liquid at room temperature
283.9 Phospholipids and steroids are important lipids with a variety of functions Phospholipids are structurally similar to fats and are an important component of all cellsThey are a major part of cell membranes, in which they cluster into a bilayer of phospholipidsThe hydrophilic heads are in contact with the water of the environment and the internal part of the cellThe hydrophobic tails band in the center of the bilayerThe phospholipid bilayer provides the cell with a structure that separates the outside from the inside of the cell. The integrity of the membrane is necessary for life functions. Because of the nature of the phospholipid, many molecules cannot move across the membrane without help.
29Phospholipids of a cell membrane The phospholipid bilayer provides the cell with a structure that separates the outside from the inside of the cell; many molecules cannot move across the membrane without helpWater (outside cell)HydrophilicheadsHydrophobictailsinterior of cell membraneHydrophilicheadsWater (inside cell)
30Steroids are lipids composed of fused ring structures 3.9 Phospholipids and steroids are important lipids with a variety of functionsSteroids are lipids composed of fused ring structuresCholesterol is an example of a steroid that plays a significant role in the structure of the cell membraneUnfortunately, a high level of cholesterol in the blood can lead to atherosclerosis. This is a heart disease that results when deposits form in the arteries that supply the heart muscle with oxygen. The deposits block blood flow, and a heart attack results. Both saturated fats and trans fats promote higher levels of cholesterol.
31In addition, cholesterol is the compound from which we synthesize sex hormones Figure 3.9B Cholesterol, a steroid.
323.10 CONNECTION: Anabolic steroids pose health risks Anabolic steroids are synthetic variants of testosterone that can cause a buildup of muscle and bone massThey can be sold as prescription drugs and used to treat certain diseasesThey may also be abused with serious consequences, such as liver damage that can lead to cancerThere are several important adverse consequences to steroid use to gain an athletic edge. Sports organizations and the public have come out against their use as a means to enhance performance. Athletic governing bodies prohibit their use.The consequences of steroid abuse will likely be of great interest to your students. However, the reasons for the damaging consequences might not be immediately clear. As time permits, consider noting the diverse homeostatic mechanisms that normally regulate the traits affected by steroid abuse.
33Anabolic SteroidsTestosterone causes a build-up of muscle and bone mass in males and maintains masculine traits Anabolic steroids mimic testosterone because of their similar structure Anabolic steroids are prescribed to treat anemia and diseases that destroy muscle mass; birth control pills usually contain synthetic variants of estrogen and progesterone
34The good, the bad and the ugly.. Anabolic steroids increase protein synthesis within cells resulting in a massive buildup of cellular tissue (“anabolism”) especially in muscle cellsAnabolic steroid use has adverse side effects:Violent mood swings (“roid rage”) and deep depression, elevated blood pressure, increases in cholesterol levels, increased risk of heart attack, liver damage, reduced sexual function, infertility, breast development (in men), and more….
373.11 Proteins are essential to the structures and functions of life A protein is a polymer built from various combinations of 20 amino acid monomersProteins have unique structures that are directly related to their functionsEnzymes, proteins that serve as metabolic catalysts, regulate the chemical reactions within cellsProteins are called polypeptidesProteins account for more than 50% of the dry mass of cells.
38Many polypeptides strung together PolypetideA chain of amino acidsA proteinMany polypeptides strung together
39Structural proteins provide associations between body parts and contractile proteins are found within muscleDefensive proteins include antibodies of the immune system, and signal proteins are best exemplified by the hormonesReceptor proteins serve as antenna for outside signals, and transport proteins carry oxygen
40Proteins Antibodies are defensive proteins Hair and nails are made of proteins (“keratin”)Muscles are pure protein (actin and myosin)Venom is proteinHemoglobin is a proteinInsulin and glucagon are regulatory proteinsThe human growth hormone is a protein that regulates growth
41Figure 3.11 Structural proteins of hair, tendons, and ligaments; and contractile proteins of muscles.
423.12 Proteins are made from amino acids linked by peptide bonds Amino acids, the building blocks of proteins, have an amino group and a carboxyl groupBoth of these are covalently bonded to a central carbon atomAlso bonded to the central carbon is a hydrogen atom and other chemical group symbolized by “R”The “R” determines the type of amino acid and what it can build
433.12 Proteins are made from amino acids linked by peptide bonds Amino acids, the building blocks of proteinsI.e. The 26 letters of the alphabet are the building block for the English language
44Amino group Carboxyl group Figure 3.12A General structure of an amino acid.
45Amino acids are classified as hydrophobic or hydrophilic Some amino acids have a nonpolar R group and are hydrophobicOthers have a polar R group and are hydrophilic, which means they easily dissolve in aqueous solutions
46Leucine (Leu) Serine (Ser) Aspartic acid (Asp) Hydrophobic Hydrophilic Figure 3.12B Examples of amino acids with hydrophobic and hydrophilic R groups.Leucine (Leu)Serine (Ser)Aspartic acid (Asp)HydrophobicHydrophilic
47Amino acids link together to form polymeric proteins polymeric-consisting of many repeating structural unitsLinkage is accomplished by an enzyme-mediated dehydration reactionThis links the carboxyl group of one amino acid to the amino group of the next amino acidThe covalent linkage resulting is called a peptide bond
48Carboxyl group Amino group Amino acid Amino acid Figure 3.12C Peptide bond formation.As more and more amino acids are added, a chain of amino acids called a polypeptide results. The combination of amino acids is determined by expression of genes on DNA. Although there seems to be an unlimited number of combinations of 20 amino acids, the combinations are limited in an individual because of inheritance.
49Peptide bond Carboxyl group Amino group Dehydration reaction Amino acidAmino acidDipeptideFigure 3.12C Peptide bond formation.As more and more amino acids are added, a chain of amino acids called a polypeptide results. The combination of amino acids is determined by expression of genes on DNA. Although there seems to be an unlimited number of combinations of 20 amino acids, the combinations are limited in an individual because of inheritance.
503.13 A protein’s specific shape determines its function A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bondsThe amino acid sequence causes the polypeptide to assume a particular shapeThe shape of a protein determines its specific functionBecause of the molecular structure of specific proteins on brain cells, endorphins bind to them. This gives us a feeling of euphoria and pain relief. Morphine, heroin, and other opiate drugs are able to mimic endorphins and bind to the endorphin receptors in the brain. Because of the euphoria that results, we become addicted.
51AddictionEndorphins bind to specific protein receptors on our brains, causing us to feel a sense of euphoria However, many drugs mimic these endorphins and bind to the same protein receptors.
52GrooveFigure 3.13A Ribbon model of the protein lysozyme.
53GrooveFigure 3.13B Space-filling model of lysozyme.
543.13 A protein’s specific shape determines its function If for some reason a protein’s shape is altered, it can no longer functionDenaturation will cause polypeptide chains to unravel and lose their shape and, thus, their functionProteins can be denatured by changes in salt concentration, temperature and pH
55It is VERY easy to denatureate a protein , but VERY difficult to renaturate a protein
573.14 A protein’s shape depends on four levels of structure A protein can have four levels of structure1. Primary structure2. Secondary structure3. Tertiary structure4. Quaternary structureFor the BLAST Animation Alpha Helix, go to Animation and Video Files.
58The primary structure of a protein is its unique amino acid sequence The correct amino acid sequence is determined by the cell’s genetic information (genes)The slightest change in this sequence affects the protein’s ability to function, or makes an entirely new protein with a different functionSickle cell disease is manifested by an inability of hemoglobin in red blood cells to carry oxygen, the primary function of hemoglobin. This blood disorder is the result of change in a single amino acid.
59Single amino acid changes can result in severe diseases Single amino acid changes can result in severe diseases. Some amino acid changes result in no negative effects.
60Protein secondary structure results from coiling or folding of the polypeptide Coiling results in a helical structure called an alpha helixFolding may lead to a structure called a pleated sheetCoiling and folding result from hydrogen bonding between certain areas of the polypeptide chainHydrogen bonding is an important component of the silk protein of a spider’s web. The many hydrogen bonds makes the web as strong as steel.
61Many hydrogen bonds are responsible for the strength of spider silk. Figure 3.14UN01 Spider in web.Many hydrogen bonds are responsible for the strength of spider silk.
63The overall three-dimensional shape of a protein is called its tertiary structure Tertiary structure generally results from interactions between the R groups of the various amino acidsDisulfide bridges are covalent bonds that further strengthen the protein’s shape
64Two or more polypeptide chains (subunits) associate providing quaternary structure Collagen is an example of a protein with quaternary structureIts triple helix gives great strength to connective tissue, bone, tendons, and ligamentsAnimation: Protein Structure IntroductionMisfolding of proteins cause diseases, such as Alzheimer’s and Parkinson’s. Both are manifested by accumulations of misfolded proteins.Consider an assignment to review the organic molecules in our diets. Have students, working individually or in small groups, analyze a food label listing the components of a McDonald’s Big Mac or other fast food sandwich. Note the most abundant organic molecule class (perhaps by weight) found in each component.Animation: Primary Protein StructureAnimation: Secondary Protein StructureAnimation: Tertiary Protein StructureAnimation: Quaternary Protein Structure
65Four Levels of Protein Structure Primary structureAmino acidsFigure 3.14A Primary structure.
66Four Levels of Protein Structure Primary structureAmino acidsHydrogenbondSecondary structureAlpha helixPleated sheetFigure 3.14A Primary structure.Figure 3.14B Secondary structure.
72Transthyretin, with four identical polypeptide subunits Figure 3.14D Quaternary structure.Quaternary structure
73Proteins gone bad So what happens is a protein folds incorrectly? Many diseases, such as Alzheimer’s and Parkinson’s involve an accumulation of misfolded proteinsPrions are infectious agents composed of proteinsPrion diseases are currently untreatable and always fatal
74PrionsPrions infect and propogate by refolding abnormally into a structure that is able to convert normally-folded molecules into abnormally-structured formThis altered form accumulates in infected tissue, causing tissue damage and cell deathPrions are resistant to denaturation due to their extremely stable, tightly packed structure
75PrionsPrions are implicated in a number of diseases in a variety of mammals:Bovine Spongiform Encephalopathy (“Mad Cows Disease”) – spread by feed containing ground-up infected cattleCreutzfeldt-Jakob Disease – degenerative neurological disorder spread by skin grafts or human growth hormone products; Kuru is a similar disease spread by cannibalism among the Fore tribe of Papua New Guinea
76PrionsChronic Wasting Disease – found in deer, moose, elk in U.S. and CanadaFatal Familial Insomnia – very rare, inherited prion disease (50 families worldwide have the responsible gene mutation); insoluble protein causes plaques to develop in the thalamus, the region of brain responsible for the regulation of sleep; fatal within several months
773.15 TALKING ABOUT SCIENCE: Linus Pauling contributed to our understanding of the chemistry of life After winning a Nobel Prize in Chemistry, Pauling spent considerable time studying biological moleculesHe discovered an oxygen attachment to hemoglobin as well as the cause of sickle-cell diseasePauling also discovered the alpha helix and pleated sheet of proteinsPauling was also an advocate for halting nuclear weapons testing and won the Nobel Peace Prize for his work. He was very close to reporting the structure of DNA when Watson and Crick scooped him and correctly described its structure.
78Figure 3.15 Linus Pauling with a model of the alpha helix in 1948.
803.16 Nucleic acids are information-rich polymers of nucleotides DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotidesNucleotides have three parts1. A five-carbon sugar called ribose in RNA and deoxyribose in DNA2. A phosphate group3. A nitrogenous baseStudent Misconceptions and ConcernsModule 3.16 is the first time the authors present the concept of transcription and translation, discussed extensively in later chapters. The basic conceptual flow of information from DNA to RNA to proteins is essential to these later discussions.
81Nitrogenous base (adenine) Phosphate group Sugar Figure 3.16A A nucleotide, consisting of a phosphate group, sugar, and a nitrogenous base.PhosphategroupSugar
823.16 Nucleic acids are information-rich polymers of nucleotides There are four DNA nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G)RNA also has A, C, and G, but instead of T, it has uracil (U)
833.16 Nucleic acids are information-rich polymers of nucleotides A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate of one nucleotide bonds to the sugar of the next nucleotideThe result is a repeating sugar-phosphate backbone with protruding nitrogenous bases
84NucleotideFigure 3.16B Part of a nucleotide.Sugar-phosphatebackbone
853.16 Nucleic acids are information-rich polymers of nucleotides Two polynucleotide strands wrap around each other to form a DNA double helixThe two strands are associated because particular bases always hydrogen bond to one anotherA pairs with T, and C pairs with G, producing base pairsRNA is usually a single polynucleotide strand
873.16 Nucleic acids are information-rich polymers of nucleotides A particular nucleotide sequence that can instruct the formation of a polypeptide is called a geneMost DNA molecules consist of millions of base pairs and, consequently, many genesThese genes, many of which are unique to the species, determine the structure of proteins and, thus, life’s structures and functions
88PolymersThe key to the great diversity of proteins and DNA is arrangement – the variation in the sequence in which monomers are strung together DNA is built of only four monomers (nucleotides) and proteins are built from only 20 kinds of amino acids; both of which are incredibly diverse: the proteins in you and a fungus are made with the same 20 amino acids
89Mutations are alterations in bases or the sequence of bases in DNA 3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolutionMutations are alterations in bases or the sequence of bases in DNALactose tolerance is the result of mutationsIn many people, the gene that dictates lactose utilization is turned off in adulthoodApparently, mutations occurred over time that prevented the gene from turning offThis is an excellent example of human evolutionMutations that lead to lactose tolerance are relativity recent events. The mutation was useful because it allowed people to drink milk when other foods were unavailable. In other words, it provided a survival advantage.