Sinh học - Chapter 3: The molecules of cells

Chapter 3The Molecules of Cells0IntroductionMost of the world’s population cannot digest milk-based foods.These people are lactose intolerant, because they lack the enzyme lactase.This illustrates the importance of biological molecules, such as lactase, in the daily functions of living organisms.© 2012 Pearson Education, Inc.Figure 3.0_1Chapter 3: Big IdeasIntroduction to OrganicCompoundsCarbohydratesLipidsProteinsNucleic AcidsINTRODUCTION TO ORGANIC COMPOUNDS© 2012 Pearson Education, Inc.3.1 Life’s molecular diversity is based on the properties of carbonDiverse molecules found in cells are composed of carbon bonded toother carbons andatoms of other elements.Carbon-based molecules are called organic compounds.© 2012 Pearson Education, Inc.3.1 Life’s molecular diversity is based on the properties of carbonBy sharing electrons, carbon canbond to four other atoms andbranch in up to four directions.Methane (CH4) is one of the simplest organic compounds.Four covalent bonds link four hydrogen atoms to the carbon atom.Each of the four lines in the formula for methane represents a pair of shared electrons.© 2012 Pearson Education, Inc.3.1 Life’s molecular diversity is based on the properties of carbonMethane and other compounds composed of only carbon and hydrogen are called hydrocarbons.Carbon, with attached hydrogens, can bond together in chains of various lengths.© 2012 Pearson Education, Inc.Figure 3.1AStructuralformulaBall-and-stickmodelSpace-fillingmodelThe four single bonds of carbon point to the corners of a tetrahedron.A carbon skeleton is a chain of carbon atoms that can bebranched orunbranched.Compounds with the same formula but different structural arrangements are call isomers.3.1 Life’s molecular diversity is based on the properties of carbon© 2012 Pearson Education, Inc.Figure 3.1BLength. Carbon skeletons vary in length.EthanePropaneButaneIsobutaneBranching.Skeletons may be unbranchedor branched.Double bonds. Skeletons may have double bonds.1-Butene2-ButeneCyclohexaneBenzeneRings. Skeletons may be arranged in rings.3.2 A few chemical groups are key to the functioning of biological moleculesAn organic compound has unique properties that depend upon thesize and shape of the molecule andgroups of atoms (functional groups) attached to it.A functional group affects a biological molecule’s function in a characteristic way.Compounds containing functional groups are hydrophilic (water-loving).© 2012 Pearson Education, Inc.3.2 A few chemical groups are key to the functioning of biological moleculesThe functional groups arehydroxyl group—consists of a hydrogen bonded to an oxygen,carbonyl group—a carbon linked by a double bond to an oxygen atom,carboxyl group—consists of a carbon double-bonded to both an oxygen and a hydroxyl group,amino group—composed of a nitrogen bonded to two hydrogen atoms and the carbon skeleton, andphosphate group—consists of a phosphorus atom bonded to four oxygen atoms.© 2012 Pearson Education, Inc.Table 3.2_1Table 3.2_23.2 A few chemical groups are key to the functioning of biological moleculesAn example of similar compounds that differ only in functional groups is sex hormones.Male and female sex hormones differ only in functional groups.The differences cause varied molecular actions.The result is distinguishable features of males and females.© 2012 Pearson Education, Inc.Figure 3.2TestosteroneEstradiol3.3 Cells make a huge number of large molecules from a limited set of small moleculesThere are four classes of molecules important to organisms:carbohydrates,proteins,lipids, andnucleic acids.© 2012 Pearson Education, Inc.3.3 Cells make a huge number of large molecules from a limited set of small moleculesThe four classes of biological molecules contain very large molecules.They are often called macromolecules because of their large size.They are also called polymers because they are made from identical building blocks strung together.The building blocks of polymers are called monomers.© 2012 Pearson Education, Inc.3.3 Cells make a huge number of large molecules from a limited set of small moleculesMonomers are linked together to form polymers through dehydration reactions, which remove water.Polymers are broken apart by hydrolysis, the addition of water.All biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells.© 2012 Pearson Education, Inc.A cell makes a large number of polymers from a small group of monomers. For example,proteins are made from only 20 different amino acids andDNA is built from just four kinds of nucleotides.The monomers used to make polymers are universal.3.3 Cells make a huge number of large molecules from a limited set of small molecules© 2012 Pearson Education, Inc.Figure 3.3A_s1Short polymerUnlinkedmonomerFigure 3.3A_s2Short polymerUnlinkedmonomerDehydration reactionforms a new bondLonger polymerFigure 3.3B_s1Figure 3.3B_s2Hydrolysisbreaks a bondCARBOHYDRATES© 2012 Pearson Education, Inc.3.4 Monosaccharides are the simplest carbohydratesCarbohydrates range from small sugar molecules (monomers) to large polysaccharides.Sugar monomers are monosaccharides, such as those found in honey,glucose, andfructose.Monosaccharides can be hooked together to formmore complex sugars andpolysaccharides.© 2012 Pearson Education, Inc.3.4 Monosaccharides are the simplest carbohydratesThe carbon skeletons of monosaccharides vary in length.Glucose and fructose are six carbons long.Others have three to seven carbon atoms.Monosaccharides arethe main fuels for cellular work andused as raw materials to manufacture other organic molecules.© 2012 Pearson Education, Inc.Figure 3.4BGlucose(an aldose)Fructose(a ketose)3.4 Monosaccharides are the simplest carbohydratesMany monosaccharides form rings.The ring diagram may beabbreviated by not showing the carbon atoms at the corners of the ring anddrawn with different thicknesses for the bonds, to indicate that the ring is a relatively flat structure with attached atoms extending above and below it. © 2012 Pearson Education, Inc.Figure 3.4CStructuralformulaAbbreviatedstructureSimplifiedstructure6543213.5 Two monosaccharides are linked to form a disaccharideTwo monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction.The disaccharide sucrose is formed by combininga glucose monomer anda fructose monomer.The disaccharide maltose is formed from two glucose monomers.© 2012 Pearson Education, Inc.Figure 3.5_s1GlucoseGlucoseFigure 3.5_s2GlucoseGlucoseMaltose3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity?Sodas or fruit drinks probably contain high-fructose corn syrup (HFCS).Fructose is sweeter than glucose.To make HFCS, glucose atoms are rearranged to make the glucose isomer, fructose.© 2012 Pearson Education, Inc.3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity?High-fructose corn syrup (HFCS) isused to sweeten many beverages andmay be associated with weight gain.Good health is promoted bya diverse diet of proteins, fats, vitamins, minerals, and complex carbohydrates andexercise.© 2012 Pearson Education, Inc.Figure 3.63.7 Polysaccharides are long chains of sugar unitsPolysaccharides aremacromolecules andpolymers composed of thousands of monosaccharides.Polysaccharides may function asstorage molecules orstructural compounds.© 2012 Pearson Education, Inc.3.7 Polysaccharides are long chains of sugar unitsStarch isa polysaccharide,composed of glucose monomers, andused by plants for energy storage.Glycogen isa polysaccharide,composed of glucose monomers, andused by animals for energy storage.© 2012 Pearson Education, Inc.3.7 Polysaccharides are long chains of sugar unitsCelluloseis a polymer of glucose andforms plant cell walls.Chitin isa polysaccharide andused by insects and crustaceans to build an exoskeleton.© 2012 Pearson Education, Inc.Figure 3.7Starch granulesin potato tuber cellsGlycogen granulesin muscletissueGlycogenGlucosemonomerStarchCelluloseHydrogen bondsCellulosemoleculesCellulose microfibrilsin a plant cell wall3.7 Polysaccharides are long chains of sugar unitsPolysaccharides are usually hydrophilic (water-loving).Bath towels areoften made of cotton, which is mostly cellulose, andwater absorbent.© 2012 Pearson Education, Inc.LIPIDS© 2012 Pearson Education, Inc.3.8 Fats are lipids that are mostly energy-storage moleculesLipidsare water insoluble (hydrophobic, or water-fearing) compounds,are important in long-term energy storage,contain twice as much energy as a polysaccharide, andconsist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds.© 2012 Pearson Education, Inc.Figure 3.8A3.8 Fats are lipids that are mostly energy-storage moleculesLipids differ from carbohydrates, proteins, and nucleic acids in that they arenot huge molecules andnot built from monomers.Lipids vary a great deal instructure andfunction.© 2012 Pearson Education, Inc.3.8 Fats are lipids that are mostly energy-storage moleculesWe will consider three types of lipids:fats,phospholipids, andsteroids.A fat is a large lipid made from two kinds of smaller molecules,glycerol andfatty acids.© 2012 Pearson Education, Inc.3.8 Fats are lipids that are mostly energy-storage moleculesA fatty acid can link to glycerol by a dehydration reaction.A fat contains one glycerol linked to three fatty acids.Fats are often called triglycerides because of their structure.© 2012 Pearson Education, Inc.Figure 3.8BFatty acidGlycerolFigure 3.8CFatty acidsGlycerol3.8 Fats are lipids that are mostly energy-storage moleculesSome fatty acids contain one or more double bonds, forming unsaturated fatty acids thathave one fewer hydrogen atom on each carbon of the double bond,cause kinks or bends in the carbon chain, andprevent them from packing together tightly and solidifying at room temperature.Fats with the maximum number of hydrogens are called saturated fatty acids.© 2012 Pearson Education, Inc.3.8 Fats are lipids that are mostly energy-storage moleculesUnsaturated fats include corn and olive oils.Most animal fats are saturated fats.Hydrogenated vegetable oils are unsaturated fats that have been converted to saturated fats by adding hydrogen.This hydrogenation creates trans fats associated with health risks.© 2012 Pearson Education, Inc.3.9 Phospholipids and steroids are important lipids with a variety of functionsPhospholipids arestructurally similar to fats andthe major component of all cells.Phospholipids are structurally similar to fats.Fats contain three fatty acids attached to glycerol.Phospholipids contain two fatty acids attached to glycerol.© 2012 Pearson Education, Inc.Figure 3.9A-BWaterHydrophobic tailsWaterHydrophilic headsSymbol for phospholipidPhosphategroupGlycerol3.9 Phospholipids and steroids are important lipids with a variety of functionsPhospholipids cluster into a bilayer of phospholipids.The hydrophilic heads are in contact withthe water of the environment and the internal part of the cell.The hydrophobic tails band in the center of the bilayer.© 2012 Pearson Education, Inc.Figure 3.9BWaterHydrophobic tailWaterHydrophilic headSymbol for phospholipid3.9 Phospholipids and steroids are important lipids with a variety of functionsSteroids are lipids in which the carbon skeleton contains four fused rings.Cholesterol is acommon component in animal cell membranes andstarting material for making steroids, including sex hormones.© 2012 Pearson Education, Inc.Figure 3.9C3.10 CONNECTION: Anabolic steroids pose health risksAnabolic steroidsare synthetic variants of testosterone,can cause a buildup of muscle and bone mass, andare often prescribed to treat general anemia and some diseases that destroy body muscle.© 2012 Pearson Education, Inc.3.10 CONNECTION: Anabolic steroids pose health risksAnabolic steroids are abused by some athletes with serious consequences, includingviolent mood swings,depression,liver damage, cancer,high cholesterol, andhigh blood pressure.© 2012 Pearson Education, Inc.PROTEINS© 2012 Pearson Education, Inc.3.11 Proteins are made from amino acids linked by peptide bondsProteins areinvolved in nearly every dynamic function in your body andvery diverse, with tens of thousands of different proteins, each with a specific structure and function, in the human body.Proteins are composed of differing arrangements of a common set of just 20 amino acid monomers.© 2012 Pearson Education, Inc.3.11 Proteins are made from amino acids linked by peptide bondsAmino acids havean amino group anda carboxyl group (which makes it an acid).Also bonded to the central carbon isa hydrogen atom anda chemical group symbolized by R, which determines the specific properties of each of the 20 amino acids used to make proteins.© 2012 Pearson Education, Inc.Figure 3.11AAminogroupCarboxylgroup3.11 Proteins are made from amino acids linked by peptide bondsAmino acids are classified as eitherhydrophobic orhydrophilic.© 2012 Pearson Education, Inc.Figure 3.11BHydrophobicHydrophilicAspartic acid (Asp)Serine (Ser)Leucine (Leu)3.11 Proteins are made from amino acids linked by peptide bondsAmino acid monomers are linked togetherin a dehydration reaction,joining carboxyl group of one amino acid to the amino group of the next amino acid, andcreating a peptide bond.Additional amino acids can be added by the same process to create a chain of amino acids called a polypeptide.© 2012 Pearson Education, Inc.Figure 3.11C_s1CarboxylgroupAminogroupAmino acidAmino acidFigure 3.11C_s2CarboxylgroupAminogroupAmino acidAmino acidDipeptidePeptidebondDehydrationreaction3.12 A protein’s specific shape determines its functionProbably the most important role for proteins is as enzymes, proteins thatserve as metabolic catalysts andregulate the chemical reactions within cells.© 2012 Pearson Education, Inc.3.12 A protein’s specific shape determines its functionOther proteins are also important.Structural proteins provide associations between body parts.Contractile proteins are found within muscle.Defensive proteins include antibodies of the immune system.Signal proteins are best exemplified by hormones and other chemical messengers.Receptor proteins transmit signals into cells.Transport proteins carry oxygen.Storage proteins serve as a source of amino acids for developing embryos.© 2012 Pearson Education, Inc.3.12 A protein’s specific shape determines its functionA polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds.The amino acid sequence causes the polypeptide to assume a particular shape.The shape of a protein determines its specific function.© 2012 Pearson Education, Inc.Figure 3.12BGrooveFigure 3.12CGroove3.12 A protein’s specific shape determines its functionIf a protein’s shape is altered, it can no longer function.In the process of denaturation, a polypeptide chainunravels,loses its shape, andloses its function.Proteins can be denatured by changes in salt concentration, pH, or by high heat.© 2012 Pearson Education, Inc.3.13 A protein’s shape depends on four levels of structureA protein can have four levels of structure:primary structuresecondary structuretertiary structurequaternary structure© 2012 Pearson Education, Inc.3.13 A protein’s shape depends on four levels of structureThe primary structure of a protein is its unique amino acid sequence.The correct amino acid sequence is determined by the cell’s genetic information.The slightest change in this sequence may affect the protein’s ability to function.© 2012 Pearson Education, Inc.3.13 A protein’s shape depends on four levels of structureProtein secondary structure results from coiling or folding of the polypeptide.Coiling results in a helical structure called an alpha helix.A certain kind of folding leads to a structure called a pleated sheet, which dominates some fibrous proteins such as those used in spider webs.Coiling and folding are maintained by regularly spaced hydrogen bonds between hydrogen atoms and oxygen atoms along the backbone of the polypeptide chain.© 2012 Pearson Education, Inc.Figure 3.13_1Figure 3.13_2PolypeptidechainCollagen3.13 A protein’s shape depends on four levels of structureThe overall three-dimensional shape of a polypeptide is called its tertiary structure.Tertiary structure generally results from interactions between the R groups of the various amino acids.Disulfide bridges may further strengthen the protein’s shape.© 2012 Pearson Education, Inc.3.13 A protein’s shape depends on four levels of structureTwo or more polypeptide chains (subunits) associate providing quaternary structure.Collagen is an example of a protein with quaternary structure.Collagen’s triple helix gives great strength to connective tissue, bone, tendons, and ligaments.© 2012 Pearson Education, Inc.Figure 3.13A_s1Primary structureAminoacidsAmino acidsFour Levels of Protein StructureFigure 3.13A-B_s2Primary structureAminoacidsAmino acidsFour Levels of Protein StructureBeta pleatedsheetAlpha helixHydrogenbondSecondary structureFigure 3.13A-C_s3Primary structureAminoacidsAmino acidsFour Levels of Protein StructureBeta pleatedsheetAlpha helixHydrogenbondSecondary structureTertiary structureTransthyretinpolypeptideFigure 3.13A-D_s4Primary structureAminoacidsAmino acidsFour Levels of Protein StructureBeta pleatedsheetAlpha helixHydrogenbondSecondary structureTertiary structureTransthyretinpolypeptideQuaternary structureTransthyretin, with fouridentical polypeptidesFigure 3.13APrimary structureAminoacidFigure 3.13BSecondary structureAmino acidAmino acidHydrogenbondAlpha helixBeta pleatedsheetFigure 3.13CTertiary structureTransthyretinpolypeptideFigure 3.13DQuaternary structureTransthyretin, with fouridentical polypeptidesNUCLEIC ACIDS© 2012 Pearson Education, Inc.3.14 DNA and RNA are the two types of nucleic acidsThe amino acid sequence of a polypeptide is programmed by a discrete unit of inheritance known as a gene.Genes consist of DNA(deoxyribonucleic acid), a type of nucleic acid.DNA is inherited from an organism’s parents.DNA provides directions for its own replication.DNA programs a cell’s activities by directing the synthesis of proteins.© 2012 Pearson Education, Inc.3.14 DNA and RNA are the two types of nucleic acidsDNA does not build proteins directly.DNA works through an intermediary, ribonucleic acid (RNA).DNA is transcribed into RNA.RNA is translated into proteins.© 2012 Pearson Education, Inc.Figure 3.14_s1GeneDNAFigure 3.14_s2GeneDNATranscriptionRNANucleic acidsFigure 3.14_s3GeneDNATranscriptionRNAProteinTranslationAminoacidNucleic acids3.15 Nucleic acids are polymers of nucleotidesDNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides.Nucleotides have three parts:a five-carbon sugar called ribose in RNA and deoxyribose in DNA,a phosphate group, anda nitrogenous base.© 2012 Pearson Education, Inc.Figure 3.15APhosphategroupSugarNitrogenousbase(adenine)3.15 Nucleic acids are polymers of nucleotidesDNA nitrogenous bases areadenine (A),thymine (T),cytosine (C), andguanine (G).RNAalso has A, C, and G,but instead of T, it has uracil (U).© 2012 Pearson Education, Inc.3.15 Nucleic acids are polymers of nucleotidesA nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers,when the phosphate of one nucleotide bonds to the sugar of the next nucleotide,by dehydration reactions, andby producing a repeating sugar-phosphate backbone with protruding nitrogenous bases.© 2012 Pearson Education, Inc.Figure 3.15BATCGTNucleotideSugar-phosphatebackbone3.15 Nucleic acids are polymers of nucleotidesTwo polynucleotide strands wrap around each other to form a DNA double helix.The two strands are associated because particular bases always hydrogen bond to one another.A pairs with T, and C pairs with G, producing base pairs.RNA is usually a single polynucleotide strand.© 2012 Pearson Education, Inc.Figure 3.15CBasepairACTGCCGTACGATTAGCTATAAT3.16 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolutionThe majority of peoplestop producing the enzyme lactase in early childhood anddo not easily digest the milk sugar lactose.Lactose tolerance represents arelatively recent mutation in the human genome andsurvival advantage for human cultures with milk and dairy products available year-round.© 2012 Pearson Education, Inc.3.16 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolutionResearchers identified three mutations that keep the lactase gene permanently turned on.The mutations appear to have occurredabout 7,000 years ago andat the same time as the domestication of cattle in these regions.© 2012 Pearson Education, Inc.