BIOLOGY 101. CHAPTER 5: The Structure and Function of Large Biological Molecules: The Molecules of Life

BIOLOGY 101 CHAPTER 5: The Structure and Functin f Large Bilgical Mlecules: The Mlecules f Life

Structure and Functin f Large Bi Mlecules: Mlecules f Life CONCEPTS: 5.1 Macrmlecules are plymers, built frm mnmers 5.2 Carbhydrates serve as fuel and building material 5.3 Lipids are a very diverse grup f hydrphbic mlecules 5.4 Prteins prvide a diversity f structures, resulting in a wide range f functins 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.1 Macrmlecules are plymers, built frm mnmers Three f the fur classes f macrmlecules carbhydrates, prteins, and nucleic acids frm chainlike mlecules called plymers. A plymer is a lng mlecule cnsisting f many similar r identical building blcks linked by cvalent bnds. The repeated units are small mlecules called mnmers. Sme f the mlecules that serve as mnmers have ther functins f their wn. These plymers are created thrugh a dehydratin reactin

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.1 Macrmlecules are plymers, built frm mnmers The cvalent bnds that cnnect mnmers in a bilgical plymer are disassembled by hydrlysis, a reactin that is effectively the reverse f dehydratin. In hydrlysis, bnds are brken by the additin f water mlecules. A hydrgen atm attaches t ne mnmer, and a hydrxyl grup attaches t the adjacent mnmer.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.1 Macrmlecules are plymers, built frm mnmers The chemical mechanisms which cells use t make and break plymers are similar fr all classes f macrmlecules. These prcesses are facilitated by enzymes, specialized macrmlecules (catalysts) that speed up chemical reactins in cells. Enzymes bind t ther substances (substrates), s their shape is critical fr their functin

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.1 Macrmlecules are plymers, built frm mnmers The cvalent bnds that cnnect mnmers in a plymer are disassembled by hydrlysis, a reactin that is effectively the reverse f dehydratin. The prcess f digestin is an example f hydrlysis within the human bdy. We take in fd as rganic plymers that are t large fr ur cells t absrb. In the digestive tract, enzymes direct the hydrlysis f specific plymers. The resulting mnmers are absrbed by the cells lining the gut and transprted t the bldstream fr distributin t bdy cells. The cells f ur bdy then use dehydratin reactins t assemble the mnmers int new and different plymers that carry ut functins specific t the particular cell type.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.1 Macrmlecules are plymers, built frm mnmers An immense variety f plymers can be built frm a small number f mnmers. Each cell has thusands f different kinds f macrmlecules. Macrmlecules vary amng cells f the same individual. They vary mre amng unrelated individuals f a species, and even mre between species. This diversity cmes frm varius cmbinatins f the 40 50 cmmn mnmers and sme thers that ccur rarely. These mnmers can be cnnected in a great many cmbinatins, just as the 26 letters in the alphabet are used t create a whle dictinary f wrds. The mlecular lgic f life is simple but elegant: Small mlecules cmmn t all rganisms are rdered int unique macrmlecules.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Despite the great diversity in rganic macrmlecules, members f each f the fur majr classes f macrmlecules have similarities in structure and functin. Carbhydrates, Lipids, Prteins, and Nucleic Acids Carbhydrates include sugars and their plymers. The simplest carbhydrates are Mnsaccharides, r simple sugars. Disaccharides, r duble sugars, cnsist f tw mnsaccharides jined by a cvalent bnd. Plysaccharides are plymers f many mnsaccharides.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Sugars, the smallest carbhydrates, serve as fuel and a surce f carbn. Mnsaccharides generally have mlecular frmulas that are sme multiple f the unit CH 2 O. Fr example, glucse has the frmula C 6 H 12 O 6. Mnsaccharides have a carbnyl grup (>C=O) and multiple hydrxyl grups (-OH). Depending n the lcatin f the carbnyl grup, the sugar is an aldse (aldehyde sugar) r a ketse (ketne sugar). Mst names fr sugars end in -se.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Sugars, the smallest carbhydrates, serve as fuel and a surce f carbn. Glucse exists as enantimeric ismers in slutin, exhibiting bth D-glucse and L-glucse frms L-Glucse des nt ccur naturally in higher living rganisms, but can be synthesized in the labratry. Only D-glucse is bilgically active as an energy surce The chain, r pen frm f D-glucse can clse t frm a ring, when it des this it will present as either r ismers

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Plysaccharides are plymers f hundreds t thusands f mnsaccharides jined by glycsidic linkages. Sme plysaccharides serve fr strage and are hydrlyzed as sugars are needed. Other plysaccharides serve as building materials fr the cell r the whle rganism. The architecture and functin f a plysaccharide are determined by its sugar mnmers and by the psitins f its glycsidic linkages.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Plysaccharides are plymers f hundreds t thusands f mnsaccharides jined by glycsidic linkages. Starch and cellulse are tw examples f different types f linkages between the glucse mnmers in cmplex carbhydrates

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Starch is a strage plysaccharide cmpsed entirely f glucse mnmers. Plants stre surplus glucse as starch granules within plastids, including chlrplasts, and withdraw it as needed fr energy r carbn. Animals that feed n plants, especially parts rich in starch, have digestive enzymes that can hydrlyze starch t glucse, making the glucse available as a nutrient fr cells. Grains and ptat tubers are the main surces f starch in the human diet.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Mst f the glucse mnmers in starch are jined by 1 4 linkages (number 1 carbn t number 4 carbn). The simplest frm f starch, amylse, is unbranched.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Mst f the glucse mnmers in starch are jined by 1 4 linkages (number 1 carbn t number 4 carbn). The simplest frm f starch, amylse, is unbranched. Animals stre glucse in a plysaccharide called glycgen. Glycgen is similar t amylpectin, but mre highly branched. Humans and ther vertebrates stre a day s supply f glycgen in the liver and muscles, hydrlyzing it t release glucse t meet the bdy s demand fr sugar.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Cellulse is a majr cmpnent f the tugh walls f plant cells. Plants prduce almst 1014 kg (100 billin tns) f cellulse per year. It is the mst abundant rganic cmpund n Earth.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Like starch, cellulse is a plymer f glucse. Hwever, the glycsidic linkages in these tw plymers differ. The linkages are different because glucse has tw slightly different ring structures. These tw ring frms differ in whether the hydrxyl grup attached t the number 1 carbn is fixed abve ( glucse) r belw ( glucse) the plane f the ring. Starch is a plysaccharide f alpha ( ) glucse mnmers.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Like starch, cellulse is a plymer f glucse. Hwever, the glycsidic linkages in these tw plymers differ. The linkages are different because glucse has tw slightly different ring structures. These tw ring frms differ in whether the hydrxyl grup attached t the number 1 carbn is fixed abve ( glucse) r belw ( glucse) the plane f the ring. Starch is a plysaccharide f alpha ( ) glucse mnmers. Cellulse is a plysaccharide f beta ( ) glucse mnmers Due t the psitin f the hydrxyl grup s near t the carbxyl grup, chains f -glucse alternate in rientatin

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Enzymes that digest starch by hydrlyzing its linkages cannt hydrlyze the linkages in cellulse. Animals cannt hydrlyze chains f -glucse Cellulse in human fd passes thrugh the digestive tract and is eliminated in feces as insluble fiber. As it travels thrugh the digestive tract, cellulse abrades the intestinal walls and stimulates the secretin f mucus, which aids in the passage f fd.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Sme micrbes can digest cellulse t its glucse mnmers thrugh the use f cellulase enzymes Many eukarytic herbivres, frm cws t termites, have symbitic relatinships with cellulsedigesting prkarytes and prtists, prviding the micrbes and the hst animal access t a rich surce f energy.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.2 Carbhydrates serve as fuel and building material Plysaccharides, the plymers f sugars, have strage and structural rles. Anther imprtant structural plysaccharide is chitin, fund in the exskeletns f arthrpds (including insects, spiders, and crustaceans). Chitin is similar t cellulse, except that it has a nitrgencntaining appendage n each glucse mnmer. Pure chitin is leathery but can be hardened by the additin f calcium carbnate. Chitin als prvides structural supprt fr the cell walls f many fungi.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Lipids: Unlike ther macrmlecules, lipids d nt frm plymers. The unifying feature f lipids is that they have little r n affinity fr water because they cnsist f mstly hydrcarbns, which frm nnplar cvalent bnds. Lipids are highly diverse in frm and functin. Diverse types include Fats, Phsphlipids and Sterids

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats stre large amunts f energy Althugh fats are nt strictly plymers, they are large mlecules assembled frm smaller mlecules via dehydratin reactins. A fat is cnstructed frm tw kinds f smaller mlecules: glycerl and fatty acids. Glycerl is a three-carbn alchl with a hydrxyl grup attached t each carbn. A fatty acid cnsists f a carbxyl grup attached t a lng carbn skeletn, ften 16 t 18 carbns lng. The many nnplar cvalent C-C and C-H bnds in the lng hydrcarbn skeletn make fats nnplar. Fats separate frm water because the water mlecules hydrgen-bnd t ne anther and exclude the fats.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats stre large amunts f energy In a fat, three fatty acids are jined t glycerl by an ester linkage, creating a triacylglycerl, r triglyceride. The three fatty acids in a fat can be the same r different. Fatty acids vary in length (number f carbns) and in the number and lcatins f duble bnds. If the fatty acid has n carbn-carbn duble bnds, then the mlecule is a saturated fatty acid, saturated with hydrgens at every pssible psitin. If the fatty acid has ne r mre carbn-carbn duble bnds frmed by the remval f hydrgen atms frm the carbn skeletn, then the mlecule is an unsaturated fatty acid.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats stre large amunts f energy A saturated fatty acid is a straight chain, but an unsaturated fatty acid has a kink wherever there is a cis duble bnd. The kinks caused by the cis duble bnds prevent the mlecules frm packing tightly enugh t slidify at rm temperature. Fats made frm saturated fatty acids are saturated fats. Fats made frm unsaturated fatty acids are unsaturated fats. Mst animal fats are saturated and are slid at rm temperature. Plant and fish fats are liquid at rm temperature and are knwn as ils. Mst f these ils are unsaturated, but ccnut, ccnut il, palm il and palm kernel il and cca butter are saturated plant ils

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats stre large amunts f energy A gram f fat can stre mre than twice as much energy as a gram f a plysaccharide such as starch. In general, as saturatin increases, fats are cnsidered t be less healthy fr yur heart Plyunsaturated fats are the healthiest dietary surce f fat While mnunsaturated fats are better fr yu than saturated fats, they are still may nt be gd fr yur cardiac health! Saturated fats are unhealthy fr yur cardiac health Trans-fats are the least healthy ptin fr fat intake

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: Plyunsaturated fats are essential, meaning that they are a physilgical requirement, but we cannt manufacture them. Plyunsaturated fats have duble bnds that prduce kinks in their structure. The kinks prevent clse packing and result in liquid states at rm temperature Eating plyunsaturated fats in place f saturated fats reduces harmful LDL chlesterl and imprves the chlesterl prfile. It als lwers triglycerides.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: There are tw main types f plyunsaturated fats: Omega-3 and Omega-6 fatty acids The designatin has t d with the lcatin f the first duble bnd frm the methyl (terminal) end f a fatty acid Omega-3 Fatty Acids: Surces f mega-3 fatty acids include fatty fish such as salmn, mackerel, and sardines, flaxseeds, walnuts, canla il, and unhydrgenated sybean il. Ptential benefits: May help prevent r even treat heart disease and strke - reducing bld pressure, raising HDL, and lwering triglycerides. EPA/DHA may help depressin (dpamine levels) and inflammatry prcesses (bth are cntrversial) Omega-3: EPA and DHA -- are primarily fund in certain fish ALA (alpha-linlenic acid), anther mega- 3 fatty acid, is fund in plant surces such as nuts and seeds.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: Mnunsaturated fats are cntrversial as t hw beneficial they are fr cardiac health The American Heart Assciatin recmmends replacing saturated fats with either mnunsaturated r plyunsaturated fats. Sme primate studies suggest mnunsaturated fat intake is n better than saturated fat intake, regardless f the influence t LDL and HLD levels

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: Saturated fats are generally cnsidered t be bad fr cardiac health. They increase ttal chlesterl, tipping the balance between HDL and LDL levels twards an increase t less healthy LDL

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: The phrase hydrgenated vegetable ils n fd labels means that unsaturated fats have been synthetically cnverted t saturated fats by the additin f hydrgen. When vegetable il is heated in the presence f hydrgen and a heavy-metal catalyst such as palladium, hydrgen atms are added t the carbn chain. Hydrgenating vegetable ils prduces saturated fats and als unsaturated fats with trans duble bnds. Eating fds rich in trans fats: Increases the amunt f harmful LDL (reducing HDL). Causes inflammatin, which is linked t heart disease, strke, diabetes, and ther chrnic cnditins. Cntribute t insulin resistance, which increases the risk f develping type 2 diabetes.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Fats and cardiac health: The phrase hydrgenated vegetable ils n fd labels means that unsaturated fats have been synthetically cnverted t saturated fats by the additin f hydrgen. Peanut butter and sme margarines are hydrgenated t prevent lipids frm separating ut as il. The prcess f hydrgenating vegetable ils prduces saturated fats and als unsaturated fats with trans duble bnds. These trans fat mlecules cntribute mre than saturated fats t athersclersis. Nte: nt all margarines are created equal sme margarines cntain trans fat. In general, the mre slid the margarine, the mre trans fat it cntains. S stick margarines usually have mre trans fat than tub margarines d

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Phsphlipids are majr cmpnents f cell membranes. Phsphlipids have tw fatty acids attached t glycerl and a phsphate grup at the third psitin. The phsphate grup carries a negative charge. Additinal smaller grups (usually charged r plar) may be attached t the phsphate grup t frm a variety f phsphlipids.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Phsphlipids are majr cmpnents f cell membranes. The interactin f phsphlipids with water is cmplex The fatty acid tails are hydrphbic, but the phsphate grup and its attachments frm a hydrphilic head. When phsphlipids are added t water, they frm assemblages with the hydrphbic tails pinting tward the interir.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.3 Lipids are a diverse grup f hydrphbic mlecules Phsphlipids are majr cmpnents f cell membranes. Phsphlipids are arranged as a bilayer at the surface f a cell. The hydrphilic heads are n the utside f the bilayer, in cntact with the aqueus slutin, and the hydrphbic tails pint tward the interir f the bilayer. The phsphlipid bilayer frms a barrier between the cell and the external envirnment. Phsphlipids are the majr cmpnent f all cell membranes.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prteins accunt fr mre than 50% f the dry mass f mst cells. They are instrumental in almst everything an rganism des. Prtein functins include structural supprt, strage, transprt, cellular cmmunicatin, mvement, and defense against freign substances. Mst imprtant, prtein enzymes functin as catalysts in cells, regulating metablism by selectively accelerating certain chemical reactins withut being cnsumed.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Humans have tens f thusands f different prteins, each with a specific structure and functin. Prteins are the mst structurally cmplex mlecules knwn. Each type f prtein has a cmplex three-dimensinal shape. All prteins are unbranched plymers cnstructed frm the same 20 amin acid mnmers.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Amin acids are the mnmers frm which prteins are cnstructed Amin acids are rganic mlecules with bth carbxyl and amin grups. At the center f an amin acid is an asymmetric carbn atm called the alpha ( ) carbn. Fur cmpnents are attached t the α carbn: a hydrgen atm, a carbxyl grup, an amin grup, and a variable R grup (r side chain). Different R grups characterize the 20 different amin acids. An R grup may be as simple as a hydrgen atm (as in the amin acid glycine), r it may be a carbn skeletn with varius functinal grups attached (as in glutamine).

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Amin acids are the mnmers frm which prteins are cnstructed. Amin acids are jined tgether when a dehydratin reactin remves a hydrxyl grup frm the carbxyl end f ne amin acid and a hydrgen atm frm the amin grup f anther. The resulting cvalent bnd is called a peptide bnd. Repeating the prcess ver and ver creates a plypeptide chain. At ne end is an amin acid with a free amin grup (the N-terminus), and at the ther end is an amin acid with a free carbxyl grup (the C-terminus).

What type f bnds hld mnsaccharides tgether t frm plysaccharides? 1, 4 Glycsidic bnds (culd be α r β)

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. A functinal prtein cnsists f ne r mre plypeptides precisely twisted, flded, and ciled int a unique shape. It is the rder f amin acids that determines the three-dimensinal structure f the prtein under nrmal cellular cnditins. A prtein s specific structure determines its functin.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. In almst every case, the functin f a prtein depends n its ability t recgnize and bind t sme ther mlecule. Fr example, an antibdy binds t a particular freign substance.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. In almst every case, the functin f a prtein depends n its ability t recgnize and bind t sme ther mlecule. Fr example, an antibdy binds t a particular freign substance. Natural signal mlecules called endrphins bind t specific receptr prteins n the surface f brain cells in humans, prducing euphria and relieving pain. Mrphine, herin, and ther piate drugs mimic endrphins because they are similar in shape and can bind t the brain s endrphin receptrs.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. When a cell synthesizes a plypeptide, the chain generally flds spntaneusly t assume the functinal structure fr that prtein. The flding is reinfrced by a variety f bnds between parts f the chain, which in turn depend n the sequence f amin acids.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Three levels f structure - primary, secndary, and tertiary structures - rganize the flding within a single plypeptide. Quaternary structure arises when tw r mre plypeptides jin t frm a prtein. Nt all prteins will have a quaternary structure Vide Links: Intrductin Primary Structure Secndary Structure Tertiary Structure Quaternary Structure

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Each plypeptide has a unique linear sequence f amin acids. This linear sequence is called the Primary Structure It is the primary structure, r specific sequence f amin acids that determines the verall shape f a prtein Because there are nearly unlimited pssible sequences, there are nearly unlimited pssible prtein shapes

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Mst prteins have segments f their plypeptide chains repeatedly ciled r flded. These cils and flds are referred t as secndary structure and result frm hydrgen bnds between the repeating cnstituents f the plypeptide backbne. Each hydrgen bnd is weak, but the sum f many hydrgen bnds stabilizes the structure f part f the prtein.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. One secndary structure is the helix, a delicate cil held tgether by hydrgen bnding between every furth amin acid, as fund in transthyretin. Sme fibrus prteins, such as -keratin, the structural prtein f hair, have the helix frmatin ver mst f their length. The ther main type f secndary structure is the pleated sheet. Pleated sheets are fund in bth glbular prteins and sme fibrus prteins, including the silk prtein f a spider s web. The presence f s many hydrgen bnds makes each silk fiber strnger than a steel strand f the same weight.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Tertiary structure is determined by interactins amng varius R grups. Much f this flding is due t the interactin f plar r nnplar amin acids with their watery envirnment. This drives the frmatin f tertiary structure Althugh these three interactins are relatively weak, their cumulative effect helps give the prtein a unique shape. Strng cvalent bnds called disulfide bridges that frm between the sulfhydryl grups (SH) f tw cysteine mnmers act t rivet parts f the prtein tgether.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Quaternary structure results frm the aggregatin f tw r mre plypeptide subunits. Only sme prteins pssess a quaternary structure Fr example, the plasma prtein hemglbin is made up f fur plypeptide chains.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. A plypeptide chain with a given amin acid sequence can spntaneusly arrange itself int a threedimensinal shape determined and maintained by the interactins respnsible fr secndary and tertiary structure. The flding ccurs as the prtein is synthesized within the cell.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Prtein structure als depends n the physical and chemical cnditins f the prtein s envirnment. Alteratins in ph, salt cncentratin, temperature, r ther factrs can unravel r denature a prtein. These frces disrupt the weak chemical bnds and interactins within a prtein that maintain its shape. Because it is misshapen, a denatured prtein is bilgically inactive

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. Mst prteins becme denatured if they are transferred frm an aqueus envirnment t a nnplar slvent. The plypeptide chain reflds s that its hydrphbic regins face utward, tward the slvent. Other denaturatin agents include chemicals that disrupt the hydrgen bnds, inic bnds, and disulfide bridges that maintain a prtein s shape. Denaturatin can als be caused by heat, which disrupts the weak interactins that stabilize cnfrmatin. This explains why extremely high fevers can be fatal. Prteins in the bld becme denatured by the high bdy temperatures

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.4 Prteins include a diversity f structures, resulting in a wide range f functins Prtein cnfrmatin determines prtein functin. The flding f many prteins is assisted by chapernins, r chaperne prteins. Chapernins d nt specify the final structure f a plypeptide but rather wrk t segregate and prtect the plypeptide while it flds spntaneusly. Mlecular systems in the cell interact with chapernins, marking incrrectly flded prteins fr reflding r fr destructin. Accumulatin f incrrectly flded plypeptides is assciated with many diseases, including Alzeimer s, Parkinsn s, and mad cw disease

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin The amin acid sequence f a plypeptide is prgrammed by a discrete unit f inheritance knwn as a gene. A gene cnsists f DNA, a plymer knwn as a nucleic acid. DNA is cmbined with prteins t frm chrmsmes in the nucleus f eukarytic cells Nucleic acids are made f mnmers called nucletides.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin There are tw types f nucleic acids: RNA and DNA The tw types f nucleic acids are ribnucleic acid (RNA) and dexyribnucleic acid (DNA). RNA and DNA are the mlecules that enable living rganisms t reprduce their cmplex cmpnents frm generatin t generatin. DNA prvides directins fr its wn replicatin. DNA als directs RNA synthesis. Subsequently, RNA directs prtein synthesis This entire prcess is called gene expressin.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin There are tw types f nucleic acids: RNA and DNA Althugh DNA encdes the infrmatin that prgrams all the cell s activities, it is nt directly invlved in the day-t-day peratins f the cell. Each gene alng a DNA mlecule directs the synthesis f a specific type f RNA called messenger RNA (mrna).

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin There are tw types f nucleic acids: RNA and DNA Prtein synthesis is directed by cellular structures called ribsmes. In eukarytes, DNA is lcated in the nucleus, but mst ribsmes are in the cytplasm. Thse that flat free in cytplasm make prteins that stay inside the cell mrna functins as an intermediary, mving genetic instructins fr building prteins frm the nucleus t the cytplasm.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin The Central Dgma f Genetics Cpying DNA nucletides t new strands f nucletides is called DNA Replicatin, as the new duble stranded mlecules are exact cpies f the riginal Cpying ne type f Nucleic Acid (DNA) t anther (RNA) is called Transcriptin

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin A nucleic acid strand is a plymer f nucletides. Nucleic acids are plymers made f nucletide mnmers rganized as plynucletides, mlecules f either DNA r RNA Each nucletide cnsists f three parts: a nitrgenus base, a pentse sugar, and ne r mre phsphate grups. There are tw classes f nitrgenus bases

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin A nucleic acid strand is a plymer f nucletides. The nitrgenus bases are rings f carbn and nitrgen that cme in tw types: purines and pyrimidines. Pyrimidines have a single six-membered ring f carbn and nitrgen atms. There are three different pyrimidines: cytsine (C), thymine (T), and uracil (U) Thymine is fund nly in DNA and uracil is fund nly in RNA. Purines have a six-membered ring jined t a five-membered ring. The tw purines are adenine (A) and guanine (G).

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin DNA Pairing Rules: The nitrgenus bases are rings f carbn and nitrgen that cme in tw types: purines and pyrimidines. Pairing f purines and pyrimidines between duble strands f DNA accunt fr unifrm width f DNA mlecules This creates a pairing rule, in which (A-T) pyrimidines nly bnd t (G-C) purines Due t pairing, the tw strands are referred t as being cmplementary

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin A nucleic acid strand is a plymer f nucletides. The pentse jined t the nitrgenus base is ribse in nucletides f RNA and dexyribse in DNA. The nly difference between the sugars is the lack f an xygen atm n carbn 2 in dexyribse. Because the atms in bth the nitrgenus base and the sugar are numbered, the sugar atms are distinguished by a prime ( ) after the number. Thus, the secnd carbn in the sugar ring is the 2 (2 prime) carbn, and the carbn that sticks up frm the ring is the 5 carbn. The cmbinatin f a pentse and a nitrgenus base is a nucleside.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin A nucleic acid strand is a plymer f nucletides. The additin f a phsphate grup creates a nucleside mnphsphate r nucletide. Plynucletides are nucletides jined by cvalent bnds called phsphdiester linkages that frm between the OH grup n the 3 f ne nucletide and the phsphate n the 5 carbn f the next. This prcess creates a repeating backbne f sugarphsphate units, with appendages cnsisting f the nitrgenus bases.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin A nucleic acid strand is a plymer f nucletides. The sequence f bases alng a DNA r mrna plymer is unique fr each gene. Because genes are nrmally hundreds t thusands f nucletides lng, the number f pssible base cmbinatins is virtually limitless. The linear rder f bases in a gene specifies the rder f amin acids the primary structure f a prtein, which in turn determines three-dimensinal structure and functin.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin Inheritance is based n replicatin f the DNA duble helix An RNA mlecule is usually a single plynucletide chain. DNA mlecules have tw plynucletide strands that spiral arund an imaginary axis t frm a duble helix. The sugar-phsphate backbnes f the tw plynucletides are n the utside f the helix. The tw backbnes run in ppsite 5 t 3 directins frm each ther, an arrangement referred t as antiparallel. The tw plynucletides r strands are held tgether by hydrgen bnds between the paired bases.

Structure and Functin f Large Bi Mlecules: Mlecules f Life 5.5 Nucleic acids stre, transmit, and help express hereditary infrmatin Inheritance is based n replicatin f the DNA duble helix Prir t cell divisin, each f the strands serves as a template t rder nucletides in a new cmplementary strand. This results in tw identical cpies f the riginal duble-stranded DNA mlecule, which are then distributed t the daughter cells. This mechanism ensures that a full set f genetic infrmatin is transmitted whenever a cell reprduces This type f cpying is called semicnservative replicatin because each new mlecule cnserves ne f the riginal strands