Description
TABLE OF CONTENTS
1Â The Chemical Foundations of Biochemistry 1
Chemistry in Context 1
1.1 General Chemical Principles 2
1.1.1 The basic principles of thermodynamics describe all systems 2
1.1.2 Equilibrium describes a specific thermodynamic state 7
1.1.3 Kinetics describes the rate of chemical reactions 8
1.1.4 Thermodynamics, equilibrium, and kinetics are used together to describe biochemical reactions and systems 9
1.2 Fundamental Concepts of Organic Chemistry 11
1.2.1 Chemical properties and reactions can be sorted by functional groups 11
1.2.2 The solubility and polarity of a molecule can be determined from its structure 12
1.2.3 Reaction mechanisms attempt to explain how a reaction occurs 13
1.2.4 Many biochemical molecules are polymers 14
1.3 The Chemistry of Water 15
1.3.1 The structure of water provides clues about its properties 16
1.3.2 Hydrogen bonding among water molecules is one of the most important weak forces in biochemistry 17
1.3.3 Water can ionize to acids and bases in biochemical systems 18
2Â Nucleic Acids 26
Nucleic Acids in Context 26
2.1 Nucleic Acids Have Distinct Structures 27
2.1.1 Nucleic acids can be understood at the chemical level 28
2.1.2 The complex shapes of nucleic acids are the result of numerous weak forces 30
2.2 Nucleic Acids Have Many Cellular Functions 37
2.2.1 Replication is the process by which cells copy DNA 37
2.2.2 Transcription is the copying of DNA into an RNA message 40
2.2.3 Translation is the synthesis of proteins by ribosomes using an mRNA code 41
2.2.4 Regulation of replication, transcription, and translation is critical to an organism’s survival and propagation 42
2.2.5 Viruses and retroviruses use the cell’s own machinery to reproduce 43
2.3 The Manipulation of Nucleic Acids Has Transformed Biochemistry 45
2.3.1 DNA can be easily manipulated and analysed in vitro 45
2.3.2 DNA can be used to drive protein expression 53
2.3.3 Techniques can be used to silence genes in organisms 59
3Â Proteins I: An Introduction to Protein Structure and Function 67
Proteins in Context 67
3.1 Amino Acid Chemistry 69
3.1.1 The structure of amino acids dictates their chemical properties 69
3.1.2 The side chains of amino acids impart unique properties 70
3.1.3 Amino acids have various roles in biochemistry 72
3.2 Proteins Are Polymers of Amino Acids 74
3.2.1 Both peptides and proteins are polymers of amino acids 74
3.2.2 The peptide bond has special characteristics 76
3.2.3 Many proteins require inorganic ions or small organic molecules to function 76
3.2.4 Amino acids can be modified within proteins 77
3.3 Proteins Are Molecules of Defined Shape and Structure 79
3.3.1 The primary structure of a protein is its amino acid sequence 79
3.3.2 The secondary structure of a protein is comprised of a few conserved structures 81
3.3.3 The tertiary structure of a protein is the organization of secondary structures into conserved motifs 84
3.3.4 The quaternary structure of a protein describes how individual subunits interact 88
3.4 Examples of Protein Structures and Functions 89
3.4.1 Aquaporin, a transmembrane pore 90
3.4.2 Chymotrypsin, an enzyme 90
3.4.3 Collagen, a structural protein 91
3.4.4 Hemoglobin, a transport protein 92
3.4.5 Immunoglobulins, binding proteins 92
3.4.6 Insulin, a signaling protein 93
3.4.7 Myosin, a molecular motor 94
4Â Proteins II: Enzymes 101
Enzymes in Context 101
4.1 Regarding Enzymes 103
4.1.1 Enzymes are protein catalysts 103
4.1.2 Enzymatically catalyzed reactions can be categorized 105
4.1.3 How do enzymes work? 106
4.2 Enzymes Increase Reaction Rate 108
4.2.1 A review of chemical rates 108
4.2.1 A review of chemical rates 108
4.2.2 The Michaelis-Menten equation relates enzymatic rates to measurable parameters 109
4.2.3 The Michaelis constant has several meanings 111
4.2.4 Kinetic data can be graphically analyzed 112
4.2.5Â kcat/KMÂ is a measure of catalytic efficiency 112
4.2.6 Some enzymes approach catalytic perfection 112
4.2.7 Enzymatic reactions may be inhibited through one of several different mechanisms 113
4.2.8 Many reactions have more than one substrate 116
4.3 The Mechanism of an Enzyme Can Be Deduced from Structural, Kinetic, and Spectral Data 117
4.3.1 Enzymatically catalyzed reactions have common properties 118
4.3.2 Examining examples of enzymatic reaction mechanisms illustrates underpinning principles 119
4.3.3 Mechanisms are elucidated using a combination of experimental techniques 125
4.4 Examples of Enzyme Regulation 127
4.4.1 Covalent modifications are a common means of enzyme regulation 127
4.4.2 Allosteric regulators bind at sites other than the active site 129
5Â Membranes and an Introduction to Signal Transduction 138
Biochemistry in Context 138
5.1 Membrane Structure and Function 139
5.1.1 The chemical properties of the membrane components dictate the characteristics of the membrane 140
5.1.2 Other aspects of membrane structure 145
5.1.3 Membrane fusion and membrane budding 146
5.2 Signal Transduction 149
5.2.1 General principles underlie signal transduction 149
5.2.2 The protein kinase A (PKA) signaling pathway is activated by cyclic AMP 150
5.2.3 Insulin is an important metabolic regulator and growth factor 153
5.2.4 The AMP kinase (AMPK) signaling pathway coordinates metabolic pathways in the cell and in the body 154
6Â Carbohydrates I: Mono- and Disaccharides, Glycolysis, Gluconeogenesis, and the Fates of Pyruvate 161
Carbohydrates in Context 161
6.1 Properties, Nomenclature, and Biological Functions of Monosaccharides 163
6.1.1 Monosaccharides are the simplest carbohydrates 163
6.1.2 Monosaccharides form hemiacetals and hemiketals 165
6.1.3 Monosaccharides form heterocyclic structures 165
6.1.4 Monosaccharides can be chemically modified 167
6.1.5 Carbohydrates can be classified as reducing sugars or nonreducing sugars 168
6.2 Properties, Nomenclature, and Biological Functions of Complex Carbohydrates 170
6.2.1 Common disaccharides include lactose, sucrose, and maltose 170
6.2.2 Trisaccharides and oligosaccharides contain three or more monosaccharide units bound by glycosidic linkages 173
6.2.3 Common polysaccharides function to store energy or provide structure 174
6.3 Glycolysis and an Introduction to Metabolic Pathways 177
6.3.1 Metabolic pathways describe how molecules are built up or broken down 178
6.3.2 Glycolysis is the process by which glucose is broken into pyruvate 180
6.4 Gluconeogenesis 193
6.4.1 Gluconeogenesis differs from glycolysis at four reactions 193
6.4.2 The regulation of gluconeogenesis takes place at several different levels 195
6.5 The Fates of Pyruvate 196
6.5.1 Pyruvate can be decarboxylated to acetyl-CoA by pyruvate dehydrogenase 197
6.5.2 Pyruvate can be converted to lactate by lactate dehydrogenase 200
6.5.3 Pyruvate can be transaminated to alanine 201
6.5.4 Pyruvate can be carboxylated to oxaloacetate by pyruvate carboxylase 201
6.5.5 Microbes can decarboxylate pyruvate into acetaldehyde 201
7Â The Common Catabolic Pathway: Citric Acid Cycle, the Electron Transport Chain, and ATP Biosynthesis 209
Electron Transport in Context 209
7.1 The Citric Acid Cycle 211
7.1.1 There are eight reactions in the citric acid cycle 212
7.1.2 The citric acid cycle is regulated at multiple places and by several different mechanisms 218
7.1.3 Anaplerotic reactions of the citric acid cycle replenish intermediates 219
7.2 The Electron Transport Chain 223
7.2.1 Electron transport occurs through a series of redox active centers from higher to lower potential energy 224
7.2.2 Complex I (NADH dehydrogenase) transfers electrons from NADH to ubiquinone via a series of iron-sulfur centers 229
7.2.3 Complex II is the citric acid cycle enzyme succinate dehydrogenase 231
7.2.4 Complex III is ubiquinone/cytochrome c reductase 233
7.2.5 Cytochrome c is a soluble electron carrier 235
7.2.6 In complex IV, oxygen is the terminal electron carrier 235
7.2.7 The entire complex working as one: the respirasome 238
7.3 ATP Biosynthesis 241
7.3.1 The structure of ATP synthase underlies its function 241
7.3.2 ATP synthase acts as a molecular machine driving the assembly of ATP molecules 243
7.3.3 Other ATPases serve as ion pumps 245
7.3.4 Inhibitors of the ATPases can be powerful drugs or poisons 246
8Â Carbohydrates II: Glycogen Metabolism, the Pentose Phosphate Pathway, Glycoconjugates, and Extracellular Matrices 253
Polysaccharides in Context 253
8.1 Glycogen Metabolism 255
8.1.1 Glycogenesis is glycogen biosynthesis 256
8.1.2 Glycogenolysis is glycogen breakdown 257
8.1.3 The regulation of glycogenesis and glycogenolysis 259
8.2 The Pentose Phosphate Pathway 264
8.2.1 The oxidative phase of the pentose phosphate pathway produces NADPH and ribulose-5-phosphate 264
8.2.2 The nonoxidative phase of the pentose phosphate pathway results in rearrangement of monosaccharides 266
8.2.3 Regulation of the pentose phosphate pathway 267
8.2.4 The pentose phosphate pathway in health and disease 268
8.2.5 Xylulose-5-phosphate is a master regulator of carbohydrate and lipid metabolism 271
8.3 Carbohydrates in Glycoconjugates 273
8.3.1 Glycoproteins 273
8.3.2 Glycolipids 276
8.3.3 Proteoglycans and non-proteoglycan polysaccharides 279
8.3.4 Peptidoglycans 282
8.4 Extracellular Matrices and Biofilms 284
8.4.1 Eukaryotic extracellular matrix proteins 284
8.4.2 Biofilms are composed of microbes living in a secreted matrix 290
9Â Lipids I: Fatty Acids, Steroids, and Eicosanoids; Beta-Oxidation and Fatty Acid Biosynthesis 300
Lipids in Context 300
9.1 Properties, Nomenclature, and Biological Functions of Lipid Molecules 302
9.1.1 Fatty acids are a common building block of many lipids 302
9.1.2 Neutral lipids are storage forms of fatty acids or cholesterol 305
9.1.3 Phospholipids are important in membrane formation 306
9.1.4 All steroids and bile salts are derived from cholesterol 309
9.1.5 Eicosanoids are potent signaling molecules derived from 20-carbon polyunsaturated fatty acids 310
9.2 Fatty Acid Catabolism 311
9.2.1 Fatty acids must be transported into the mitochondrial matrix before catabolism can proceed 312
9.2.2 Fatty acids are oxidized to acetyl-CoA by β-oxidation 312
9.2.3 Beta-oxidation is regulated at two different levels 316
9.3 Fatty Acid Biosynthesis 317
9.3.1 Two major enzyme complexes are involved in fatty acid biosynthesis 318
9.3.2 Elongases and desaturases in the endoplasmic reticulum increase fatty acid diversity 326
9.3.3 The formation of malonyl-CoA by acetyl-CoA carboxylase is the regulated and rate-determining step of fatty acid biosynthesis 327
9.4 Ketone Body Metabolism 329
9.4.1 Ketone bodies are made from acetyl-CoA 330
9.4.2 Ketone bodies can be thought of as a water-soluble fuel source used in the absence of carbohydrates 330
9.5 Steroid Metabolism 332
9.5.1 Cholesterol is synthesized in the liver through the addition of energetically activated isoprene units 332
9.5.2 Steroid hormones are derived from cholesterol 336
9.5.3 Bile salts are steroid detergents used in the digestion of fats 337
9.6 Eicosanoid and Endocannabinoid Metabolism 339
9.6.1 Eicosanoids are classified by the enzymes involved in their synthesis 339
9.6.2 Endocannabinoids such as anandamide are also arachidonate derivatives 341
10Â Lipids II: Metabolism and Transport of Complex Lipids 351
Complex Lipids in Context 351
10.1 Phospholipid Metabolism 353
10.1.1 Glycerophospholipids are derived from phosphatidate or diacylglycerol using activated carriers 354
10.1.2 Sphingolipids are synthesized from ceramide 355
10.1.3 Phospholipases and sphingolipases cleave at specific sites 358
10.2 Digestion of Triacylglycerols 361
10.2.1 Triacylglycerol digestion begins in the gastrointestinal tract 361
10.2.2 Dietary lipids are absorbed in the small intestine and pass into lymph before entering the circulation 363
10.2.3 Several molecules affect neutral lipid digestion 365
10.3 Transport of Lipids in the Circulation 367
10.3.1 Lipoproteins have a defined structure and composition, and transport lipids in the circulation 367
10.3.2 The trafficking of lipoproteins in the blood can be separated conceptually into three different paths 369
10.3.3 Brain lipids are transported on apo E-coated discs 372
10.3.4 Fatty acids and hydrophobic hormones are transported by binding to carrier proteins 374
10.4 Entry of Lipids into the Cell 377
10.4.1 Fatty acids can enter the cell via diffusion or by protein-mediated transport 377
10.4.2 Lipoprotein particles and many other complexes enter the cell via receptor-mediated endocytosis 377
10.5 Neutral Lipid Biosynthesis 380
10.5.1 Triacylglycerols are synthesized by different pathways depending on the tissue 380
10.5.2 Triacylglycerol metabolism and phosphatidate metabolism are enzymatically linked 382
10.6 Lipid Storage Droplets, Fat Storage, and Mobilization 384
10.6.1 Bulk neutral lipids in the cell are stored in a specific organelle, the lipid storage droplet 384
10.6.2 Specific phosphorylation of lipases and lipid droplet proteins regulate lipolysis (triacylglycerol breakdown) 384
10.6.3 Triacylglycerol metabolism is regulated at several levels 387
10.7 Lipid Rafts as a Biochemical Entity 388
10.7.1 Lipid rafts are loosely associated groups of sphingolipids and cholesterol found in the plasma membrane 388
10.7.2 Lipid rafts have been broadly grouped into two categories: caveolae and non-caveolar rafts 388
11Â Amino Acid and Amine Metabolism 397
Amine Metabolism in Context 397
11.1 Digestion of Proteins 399
11.1.1 Protein digestion begins in the stomach 399
11.1.2 Protein digestion continues in the small intestine, aided by proteases 401
11.1.3 Amino acids are absorbed in the small intestine 401
11.1.4 Amino acids serve many biological roles in the organism 403
11.2 Transamination and Oxidative Deamination 404
11.2.1 Ammonia can be removed from an amino acid in two different ways 405
11.2.2 The glucose–alanine shuttle moves nitrogen to the liver and delivers glucose to tissues that need it 405
11.2.3 Glutamine is also important in nitrogen transport 406
11.3 The Urea Cycle 409
11.3.1 Ammonia detoxification begins with the synthesis of carbamoyl phosphate 409
11.3.2 The urea cycle synthesizes urea and other metabolic intermediates 409
11.3.3 Nitrogen metabolism is regulated at different levels 412
11.3.4 Mechanisms for elimination of nitrogenous wastes differ between mammals and non-mammals 412
11.3.5 Some mammals have adapted to high- or low-protein diets 413
11.4 Pathways of Amino Acid Carbon Skeleton Scavenging 414
11.4.1 Three-carbon skeletons produce pyruvate 416
11.4.2 Four-carbon skeletons produce oxaloacetate 417
11.4.3 Five-carbon skeletons produce α-ketoglutarate 418
11.4.4 Methionine, valine, and isoleucine produce succinyl-CoA 418
11.4.5 Other amino acids produce acetyl-CoA, acetoacetate, or fumarate 418
11.5 The Detoxification of Other Amines and Xenobiotics 423
11.5.1 Phase I metabolism makes molecules more hydrophilic through oxidative modification 424
11.5.2 Phase II metabolism couples molecules to bulky hydrophilic groups 427
11.6 The Biochemistry of Renal Function 429
11.6.1 Molecules smaller than proteins are filtered out of the blood by the glomerulus 430
11.6.2 Water, glucose, and electrolytes are reabsorbed in the proximal convoluted tubule, loop of Henle, and distal convoluted tubule 431
12Â Regulation and Integration of Metabolism 440
Metabolism in Context 440
12.1 A Review of the Pathways and Crossroads of Metabolism 442
12.1.1 The pathways of metabolism are interconnected 442
12.1.2 Several metabolites are at the intersection of multiple pathways 443
12.2 Organ Specialization and Metabolic States 446
12.2.1 Different organs play distinct roles in metabolism 447
12.2.2 The organism shifts between different metabolic states depending on access to food 450
12.3 Communication between Organs 455
12.3.1 Organs communicate using hormones 455
12.3.2 Hormonal signals to the brain regulate appetite and metabolism 458
12.3.3 Transcription factors and histone acetylases and deacetylases regulate metabolism in the longer term 460
12.4 Metabolic Disease 463
12.4.1 Diseases of excess: obesity, diabetes, and metabolic syndrome 463
12.4.2 Diseases of absence: starvation, cachexia, and cancer 467
12.4.3 Diseases of indulgence: alcohol overconsumption 468
12.4.4 Other metabolic states 469
13Â Nucleotide and Deoxynucleotide Metabolism 477
Nucleotides and Deoxynucleotides in Context 477
13.1 Purine Biosynthesis 478
13.1.1 The de novo biosynthetic pathway builds the purine backbone from phosphoribose 478
13.1.2 The salvage biosynthetic pathway recycles hypoxanthine into adenosine and guanosine 482
13.1.3 Purine biosynthesis is tightly regulated 483
13.2 Pyrimidine Biosynthesis 484
13.2.1 The de novo pathway of pyrimidine biosynthesis generates UMP 485
13.2.2 The pyrimidine salvage pathway converts CMP back into UMP 486
13.2.3 Pyrimidine biosynthesis is regulated allosterically 486
13.3 Deoxyribonucleotide Biosynthesis 489
13.3.1 The simplest active structure of ribonucleotide reductase is a dimer of dimers 489
13.3.2 Ribonucleotide reductase reduces the 2′ carbon of the NDPs 489
13.3.3 Ribonucleotide reductase employs a free radical and a series of redox-active thiols to synthesize deoxyribonucleotides 490
13.3.4 Regulation of ribonucleotide reductase balances deoxynucleotide concentrations and impacts the rate of DNA synthesis 491
13.3.5 Thymidine is synthesized from dUMP 492
13.4 Catabolism of Nucleotides 495
13.4.1 Purines are catabolized to nucleosides and then uric acid 496
13.4.2 Pyrimidines are catabolized to malonyl-CoA and methylmalonyl-CoA 500
14Â DNA Replication, Damage, and Repair 506
DNA in Context 506
14.1 Challenges of DNA Replication 507
14.1.1 The structure of DNA creates several challenges for replication 508
14.1.2 DNA replication addresses the challenges posed by its structure 509
14.2 DNA Replication in Prokaryotes 512
14.2.1 Initiation of replication begins at an ori sequence 512
14.2.2 Elongation replicates the E. coli genome 512
14.2.3 Topoisomerases relieve strain in the DNA helix 514
14.2.4 DNA polymerases synthesize and proofread DNA 515
14.3 DNA Replication in Eukaryotes 517
14.3.1 In eukaryotes replication originates in multiple sites 517
14.3.2 DNA replication systems in eukaryotes are more complex than in prokaryotes 518
14.3.3 Histones must be removed before replication and then reincorporated afterward 519
14.3.4 Telomeres present a problem for DNA replication 520
14.4 DNA Damage and Repair 523
14.4.1 DNA damage occurs in various ways and through different agents 523
14.4.2 Prokaryotes have various mechanisms for DNA repair 527
14.5 Homologous Recombination 534
14.5.1 Homologous recombination generates genetic diversity 534
14.5.2 Recombination in prokaryotes is mediated by Rec proteins 535
14.5.3 Recombination in eukaryotes can proceed through several different models 536
14.5.4 Transposons are hopping genes 537
14.5.5 VDJ recombination generates genetic diversity in the immune system 539
15Â RNA Synthesis and Processing 546
RNA Synthesis in Context 546
15.1 Transcription: RNA Synthesis 548
15.1.1 Different types of RNA polymerase catalyze synthesis of different types of RNA 548
15.1.2 Transcription involves five stages 550
15.1.3 RNA polymerase inhibitors can be powerful drugs or poisons 554
15.1.4 Retroviruses employ reverse transcription 555
15.2 Processing of Nascent Eukaryotic RNA Messages 557
15.2.1 Messenger RNA molecules receive a 5′-methylguanine cap 558
15.2.2 Messenger RNA molecules receive a 3′ poly(A) tail 559
15.2.3 The nascent mRNA is spliced into different messages 559
15.2.4 Transfer RNA molecules have several uncommon modifications 564
15.3 RNA Export from the Nucleus 566
15.3.1 Transit into and out of the nucleus is regulated by the nuclear pore complex 566
15.3.2 Importins and exportins transport molecules in the Ran cycle 568
15.3.3 Different classes of RNA molecules employ different protein adapters for transport 569
16Â Protein Synthesis 576
Protein Synthesis in Context 576
16.1 The Genetic Code 577
16.1.1 The genetic code translates nucleic acids into amino acids 578
16.1.2 Codon degeneracy and wobble benefit protein synthesis 579
16.1.3 The genetic code is almost universal 579
16.2 RNA Structure Function in Protein Biosynthesis 580
16.2.1 Messenger RNA contains structural information 580
16.2.2 Transfer RNAs act as adapters for the genetic code 581
16.2.3 Ribosomal RNA molecules provide both structure and catalysis 583
16.3 Protein Biosynthesis 585
16.3.1 Activation is the coupling of amino acids to tRNA 585
16.3.2 Initiation is the binding of the ribosome and the beginning of protein biosynthesis 589
16.3.3 Elongation is the addition of more amino acids to the growing polypeptide chain 591
16.3.4 The final step in protein synthesis is termination of translation 593
16.3.5 Proteins may be made on free polysomes or translated into a membrane 594
16.3.6 Nascent proteins fold and undergo processing 595
16.3.7 Inhibitors of protein biosynthesis may be lifesaving
drugs or deadly toxins 597
17Â Control and Regulation of Gene Expression 606
Gene Regulation in Context 606
17.1 DNA–Protein Interactions 607
17.1.1 DNA structure determines the interactions that regulate genes 608
17.1.2 DNA promoter sequences regulate gene expression 609
17.1.3 Transcription factors use specific protein motifs to interact with DNA 610
17.2 Regulation of Expression in Prokaryotes 613
17.2.1 Sigma factors regulate large groups of genes 613
17.2.2 Operons regulate small groups of genes that code for proteins with a common purpose 614
17.2.3 Riboswitches are regulatory elements found in mRNA 619
17.3 Regulation of Expression in Eukaryotes 623
17.3.1 Eukaryotic DNA is organized into chromosomes 623
17.3.2 Histones and other proteins organize and give structure to the chromosome 626
17.3.3 Epigenetic gene regulation can affect expression by modifying histones or DNA 628
17.3.4 Eukaryotic transcription factors can be classified based on their mechanism of action 631
17.3.5 MicroRNAs regulate gene expression at the message level 639
17.3.6 Regulation of the ferritin and transferrin genes occurs at the mRNA level 641
18Â Determination of Macromolecular Structure 649
Macromolecular Structure in Context 649
18.1 An Introduction to Structure Determination 650
18.1.1 Resolution is a key feature of structure determination 651
18.1.2 Contrast is important in some techniques for structure determination 652
18.1.3 The means of depicting structures have evolved along with advances in structure determination 653
18.2 Electron Microscopy 654
18.2.1 There are parallels between light microscopy and electron microscopy 654
18.2.2 Sample preparation is essential to visualization in electron microscopy 655
18.2.3 Advances in electron microscopy have dramatically improved resolution 656
18.3 X-Ray Diffraction and Neutron Scattering 658
18.3.1 A two-dimensional example illustrates the principles of diffraction 658
18.3.2 Diffraction from a crystal occurs in three dimensions 659
18.3.3 The determination of structures by X-ray diffraction can be broken into four steps 660
18.3.4 A table of data describes the quality of an X-ray crystallography structure 665
18.3.5 Neutron scattering is similar to X-ray diffraction 667
18.4 Nuclear Magnetic Resonance 668
18.4.1 NMR relies on the quantum-mechanical property of nucleus spin 668
18.4.1 NMR relies on the quantum-mechanical property of nucleus spin 668
18.4.2 An NMR spectrometer generates a magnetic field 669
18.4.3 NMR spectra are interpreted by analysing peaks 670
18.4.4 The Overhauser effect describes the through-space effects of one nuclei on others 670
18.4.5 Multidimensional NMR techniques are used to probe three-dimensional structure 671
18.4.6 NMR is developing as a technology 672
19 Allosterism and Receptor–Ligand Interactions 679
Allosterism in Context 679
19.1 Allosterism and Cooperativity 680
19.1.1 Allosterism is a means of regulating protein function 680
19.1.2 Multiple models describe cooperative allosteric interactions 682
19.1.3 Allosteric molecules can operate in different ways 685
19.2 Hemoglobin 686
19.2.1 Hemoglobin and myoglobin have related structures 687
19.2.2 Hemoglobin is regulated allosterically by oxygen 688
19.2.3 Other molecules also bind to hemoglobin 690
19.2.4 Several diseases arise from mutations in haemoglobin genes 692
19.3 Receptor–Ligand Interactions 696
19.3.1 Nuclear hormone receptors bind ligands within the cell 697
19.3.2 Membrane-bound receptors bind ligands outside the cell 698
19.3.3 Ligand binding can activate or inhibit receptors 700
19.3.4 Receptor–ligand interactions can involve simple or allosteric binding 701
20Â Designer Proteins and Protein Folding 706
Protein Engineering and Folding in Context 706
20.1 Protein Production 707
20.1.1 Solid-phase peptide synthesis is a means of chemically synthesizing proteins 707
20.1.2 Proteins can be biologically overexpressed 711
20.1.3 Different organisms can be used for protein expression 712
20.2 Protein Engineering 714
20.2.1 Site-directed mutagenesis is a way to alter precisely the amino acid sequence of a protein 715
20.2.2 Chimeric or fusion proteins are the result of inframe combination of mRNAs that code for different proteins 718
20.2.3 Epitope tags are modifications made to proteins to assist in detection or purification 720
20.2.4 Amber codon suppression is a way to incorporate unnatural amino acids into proteins 722
20.3 Protein Folding 724
20.3.1 There is debate about the mechanisms by which proteins fold 725
20.3.2 Protein folding can be analyzed using thermodynamics 728
20.3.3 Computational predictions have yet to model protein folding fully 729
21Â Biomolecule Purification 736
Protein Purification in Context 736
21.1 Protein Purification Basics 737
21.1.1 The first step of purifying a protein is to identify a source 737
21.1.2 Purification schemes detail each step in a purification 739
21.1.3 Purification begins with crude steps of separation and becomes more refined 740
21.1.4 Protein chromatography separates proteins based on physical or chemical properties 742
21.2 Size-Exclusion Chromatography 745
21.2.1 Size-exclusion chromatography uses the size and shape of a protein to achieve separation 745
21.2.2 Size-exclusion chromatography is based on hydrodynamic properties 747
21.3 Affinity Chromatography 751
21.3.1 Affinity chromatography takes advantage of numerous weak forces to separate molecules 751
21.3.2 Different resins are used to separate proteins 753
21.3.3 Proteins can be used to bind to a molecule of interest 756
22Â Bioinformatics and Omics 764
Bioinformatics in Context 764
22.1 Introduction to Bioinformatics 765
22.1.1 A classical approach to a problem can be reformulated using a bioinformatics approach 765
22.1.2 Bioinformatics or omics experiments can be used to test all aspects of biochemistry 766
22.1.3 Bioinformatics experiments differ in the volume of data generated and the methods used to process the data 768
22.2 Generating Bioinformatic Data 769
22.2.1 High-throughput sequencing is used to study the genome
769
22.2.2 The transcriptome can be studied using microarrays or RNA sequencing 771
22.2.3 Mass spectrometry is used to quantify proteins, lipids, carbohydrates, and metabolites 774
22.3 Analyzing Bioinformatic Data 778
22.3.1 Several computational tools are used in bioinformatic data analysis 778
22.3.2 Search algorithms are important inbioinformatics 779
22.3.3 Interaction maps indicate how proteins interact 785
23Â Signal Transduction 790
Cell Signaling in Context 790
23.1 A Review of Signal Transduction 791
23.1.1 Signal transduction follows certain basic principles 792
23.1.2 The PKA signaling pathway involves a second messenger 793
23.1.3 The insulin signaling pathway has multiple functions 794
23.1.4 The AMP kinase signaling pathway regulates cell metabolism 795
23.2 An Overview of Regulation of Signal Transduction 797
23.2.1 Second messengers regulate certain pathways 797
23.2.2 Kinase cascades are an alternative to second messengers 798
23.2.3 SH2 domains are common structural motifs found in signaling proteins 799
23.3 Six New Signal Transduction Pathways 800
23.3.1 The JAK-STAT pathway is involved in inflammation 800
23.3.2 Mitogen-activated protein kinases help to regulate cell proliferation 803
23.3.3 Toll-like receptor signaling is critical to the innate immune response 806
23.3.4 PKC and the phosphoinositide cascade affect gene expression and enzyme activity 807
23.3.5 The cyclin-dependent kinases regulate cell growth and replication 811
23.3.6 Nitric oxide signals via protein kinase G 813
24Â Protein Trafficking 821
Protein Trafficking in Context 821
24.1 Molecular Aspects of Protein Trafficking 822
24.1.1 Signal sequences direct proteins to specific organelles 822
24.1.2 Many proteins are trafficked using vesicles 823
24.1.3 Proteins are sorted and modified in the Golgi apparatus 825
24.2 Molecular Motors 827
24.2.1 Myosins move along actin microfilaments 827
24.2.2 Kinesins move along tubulin microtubules 829
24.2.3 Dyneins move cargo back to the ER 831
24.2.4 Other proteins also generate motion 831
24.3 Vesicular Fusion 834
24.3.1 SNARE proteins are essential mediators of vesicular fusion with the plasma membrane 834
24.3.2 The structure of the SNARE proteins serves their function 835
24.3.3 Vesicular fusion involves the formation and disassociation of the SNARE complex 835
25Â Photosynthesis and Nitrogen Fixation 841
Photosynthesis and Nitrogen Fixation in Context 841
25.1 Photosynthesis 842
25.1.1 An overview of photosynthesis reveals several important reactions 842
25.1.2 Photosynthesis takes place in the chloroplast 843
25.1.3 The light-dependent reactions of photosynthesis generate ATP, NADPH, and oxygen 844
25.1.4 The light-independent reactions of photosynthesis fix CO2Â and generate carbohydrates 852
25.2 Nitrogen Fixation 859
25.2.1 Nitrogen levels in Earth’s atmosphere changed over time 859
25.2.2 The nitrogen cycle describes nitrogen chemistry in the environment 860
25.2.3 Nitrogenase employs unique structural features to catalyze the reduction of nitrogen gas 862
Techniques T-1
solutions A-1
Glossary G-1
Index I-1
