* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Life and Chemistry: Large Molecules
Citric acid cycle wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Gel electrophoresis wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Gene expression wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Signal transduction wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Western blot wikipedia , lookup
Point mutation wikipedia , lookup
Peptide synthesis wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Metalloprotein wikipedia , lookup
Size-exclusion chromatography wikipedia , lookup
Fatty acid synthesis wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Protein structure prediction wikipedia , lookup
Genetic code wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Proteolysis wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Life and Chemistry: Large Molecules 3 Life and Chemistry: Large Molecules • Theories of the Origin of Life • Macromolecules: Giant Polymers • Condensation and Hydrolysis Reactions • Proteins: Polymers of Amino Acids • Carbohydrates: Sugars and Sugar Polymers • Lipids: Water-Insoluble Molecules • Nucleic Acids: Informational Macromolecules That Can Be Catalytic • All Life from Life 3 Theories of the Origin of Life • Living things are composed of the same elements as the inanimate universe. • The arrangement of these elements in biological systems is unique. • There are two theories for the origin of life during the 600 million years of the Hadean: Life from extraterrestrial sources Chemical evolution 3 Theories of the Origin of Life • Could life have come from outside Earth? • The composition of meteorites suggests that some of life’s complex molecules could have come from space. • There is no proof, however, that living things have ever traveled to Earth by way of a comet or meteorite. 3 Theories of the Origin of Life • The theory of chemical evolution holds that conditions on the primitive Earth led to the formation of the large molecules unique to life. • In the 1950s, Stanley Miller and Harold Urey set up an experimental “primitive” atmosphere and used a spark to simulate lightning. • Within days, the system contained numerous complex molecules. Figure 3.1 Synthesis of Prebiotic Molecules in an Experimental Atmosphere 3 Theories of the Origin of Life • The results of the Miller-Urey experiments have undergone several interpretative refinements. • The earliest stages of chemical evolution resulted in the emergence of monomers and polymers that probably have remained generally unchanged for 3.8 billion years. 3 Macromolecules: Giant Polymers • There are four major types of biological macromolecules: Proteins - silk, hair, tendons Carbohydrates - starch, cellulose, chitin, glycogen Lipids - fats, oils, waxes Nucleic acids - DNA, RNA, ATP 3 Macromolecules: Giant Polymers • These macromolecules are made the same way in all living things, and are present in all organisms in roughly the same proportions. • An advantage of this biochemical unity is that organisms acquire needed biochemicals by eating other organisms. 3 Macromolecules: Giant Polymers • Macromolecules are giant polymers. • Polymers are formed by covalent linkages of smaller units called monomers. • Molecules with molecular weights greater than 1,000 daltons (atomic mass units) are usually classified as macromolecules. Table 3.1 The Building Blocks of Organisms 3 Macromolecules: Giant Polymers • The functions of macromolecules are related to their shape and the chemical properties of their monomers. • Some of the roles of macromolecules include: Energy storage Structural support Transport Protection and defense Regulation of metabolic activities Means for movement, growth, and development Heredity 3 Condensation and Hydrolysis Reactions • Macromolecules are made from smaller monomers by means of a condensation or dehydration reaction in which an OH from one monomer is linked to an H from another monomer. • Energy must be added to make or break a polymer. • The reverse reaction, in which polymers are broken back into monomers, is a called a hydrolysis reaction. Figure 3.3 Condensation and Hydrolysis of Polymers (Part 1) Figure 3.3 Condensation and Hydrolysis of Polymers (Part 2) 3 Proteins: Polymers of Amino Acids • Proteins are polymers of amino acids. They are molecules with diverse structures and functions. • Each different type of protein has a characteristic amino acid composition and order. • Proteins range in size from a few amino acids to thousands of them. • Folding is crucial to the function of a protein and is influenced largely by the sequence of amino acids. • 50% or more of the dry weight of animals and bacteria 3 Proteins: Polymers of Amino Acids • An amino acid has four groups attached to a central carbon atom: A hydrogen atom An amino group (NH3+) The acid is a carboxyl group (COO–). Differences in amino acids come from the side chains, or the R groups. 3 Proteins: Polymers of Amino Acids • Amino acids can be classified based on the characteristics of their R groups. Five have charged hydrophilic side chains. Five have polar but uncharged side chains. Seven have nonpolar hydrophobic side chains. Cysteine has a terminal disulfide (—S—S—). Glycine has a hydrogen atom as the R group. Proline has a modified amino group that forms a covalent bond with the R group, forming a ring. Table 3.2 The Twenty Amino Acids Found in Proteins (Part 1) Table 3.2 The Twenty Amino Acids Found in Proteins (Part 2) Table 3.2 The Twenty Amino Acids Found in Proteins (Part 3) 3 Proteins: Polymers of Amino Acids • Proteins are synthesized by condensation reactions between the amino group of one amino acid and the carboxyl group of another. This forms a peptide linkage. • Proteins are also called polypeptides. A dipeptide is two amino acids long; a tripeptide, three. A polypeptide is multiple amino acids long. Figure 3.5 Formation of Peptide Linkages 3 Proteins: Polymers of Amino Acids • There are four levels of protein structure: primary, secondary, tertiary, and quaternary. • The precise sequence of amino acids is called its primary structure. • The peptide backbone consists of repeating units of atoms: N—C—C—N—C—C. • Enormous numbers of different proteins are possible. Figure 3.6 The Four Levels of Protein Structure (Part 3) 3 Proteins: Polymers of Amino Acids • Other factors determining tertiary structure: The nature and location of secondary structures Hydrophobic side-chain aggregation and van der Waals forces, which help stabilize them The ionic interactions between the positive and negative charges deep in the protein, away from water 3 Proteins: Polymers of Amino Acids • It is now possible to determine the complete description of a protein’s tertiary structure. • The location of every atom in the molecule is specified in three-dimensional space. Figure 3.7 Three Representations of Lysozyme 3 Proteins: Polymers of Amino Acids • Quaternary structure results from the ways in which multiple polypeptide subunits bind together and interact. • This level of structure adds to the threedimensional shape of the finished protein. • Hemoglobin is an example of such a protein; it has four subunits. Figure 3.8 Quaternary Structure of a Protein 3 Proteins: Polymers of Amino Acids • Shape is crucial to the functioning of some proteins: Enzymes need certain surface shapes in order to bind substrates correctly. Carrier proteins in the cell surface membrane allow substances to enter the cell. Chemical signals such as hormones bind to proteins on the cell surface membrane. • The combination of attractions, repulsions, and interactions determines the right fit. Figure 3.9 Noncovalent Interactions between Proteins and Other Molecules 3 Proteins: Polymers of Amino Acids • Changes in temperature, pH, salt concentrations, and oxidation or reduction conditions can change the shape of proteins. • This loss of a protein’s normal three-dimensional structure is called denaturation ( i.e. an egg). Figure 3.11 Denaturation Is the Loss of Tertiary Protein Structure and Function 3 Enzymes • Enzymes are proteins that act as a catalyst (increase the rate of a chemical reaction). • Enzymes have an active site ( example of a lock and key) 3 Carbohydrates: Sugars and Starches • Carbohydrates are carbon molecules with hydrogen and hydroxyl groups. • They act as energy storage and transport molecules. • They also serve as structural components and building material (i.e. chitin and cellulose). 3 Carbohydrates: Sugars and Sugar Polymers • There are four major categories of carbohydrates: Monosaccharides Disaccharides, which consist of two monosaccharides Oligosaccharides, which consist of between 3 and 20 monosaccharides Polysaccharides, which are composed of hundreds to hundreds of thousands of monosaccharides 3 Carbohydrates: Sugars and Sugar Polymers • The general formula for a carbohydrate monomer is multiples of CH2O, maintaining a ratio of 1 carbon to 2 hydrogens to 1 oxygen. • During the polymerization, which is a condensation reaction, water is removed. • Carbohydrate polymers have ratios of carbon, hydrogen, and oxygen that differ somewhat from the 1:2:1 ratios of the monomers. 3 Carbohydrates: Sugars and Sugar Polymers • All living cells contain the monosaccharide glucose (C6H12O6). • Glucose exists as a straight chain and a ring, with the ring form predominant. • The two forms of the ring, a-glucose and bglucose, exist in equilibrium when dissolved in water. Figure 3.13 Glucose: From One Form to the Other 3 Carbohydrates: Sugars and Sugar Polymers • Different monosaccharides have different numbers or different arrangements of carbons. • Most monosaccharides are optical isomers. • Hexoses (six-carbon sugars) include the structural isomers glucose, fructose, mannose, and galactose. • Pentoses are five-carbon sugars. Figure 3.14 Monosaccharides Are Simple Sugars (Part 1) Figure 3.14 Monosaccharides Are Simple Sugars (Part 2) 3 Carbohydrates: Sugars and Sugar Polymers • Monosaccharides are bonded together covalently by condensation reactions. The bonds are called glycosidic linkages. • Disaccharides have just one such linkage: sucrose, lactose, maltose, cellobiose. • Maltose and cellobiose are structural isomers. Figure 3.15 Disaccharides Are Formed by Glycosidic Linkages 3 Carbohydrates: Sugars and Sugar Polymers • Polysaccharides are giant polymers of monosaccharides connected by glycosidic linkages. • Cellulose is a giant polymer of glucose joined by b-1,4 linkages. • Starch is a polysaccharide of glucose with a-1,4 linkages. Figure 3.16 Representative Polysaccharides (Part 1) Figure 3.16 Representative Polysaccharides (Part 2) 3 Carbohydrates: Sugars and Sugar Polymers • Starches vary by amount of branching. • Some plant starch, such as amylose, is unbranched. Others, such as amylopectin, are moderately branched. • Animal starch, called glycogen, is a highly branched polysaccharide. 3 Carbohydrates: Sugars and Sugar Polymers • Carbohydrates are modified by the addition of functional groups: Glucose can acquire a carboxyl group (—COOH), forming glucuronic acid. Phosphate added to one or more hydroxyl (—OH) sites creates a sugar phosphate such as fructose 1,6-bisphosphate. Amino groups can be substituted for —OH groups, making amino sugars such as glucosamine and galactosamine. Figure 3.17 Chemically Modified Carbohydrates (Part 1) Figure 3.17 Chemically Modified Carbohydrates (Part 2) Figure 3.17 Chemically Modified Carbohydrates (Part 3) Figure 3.17 Chemically Modified Carbohydrates (Part 4) 3 Typical Hamburger QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 3 Lipids: Water-Insoluble Molecules • Lipids are insoluble in water. • This insolubility results from the many nonpolar covalent bonds of hydrogen and carbon in lipids. • Lipids aggregate away from water, which is polar, and are attracted to each other via weak, but additive, van der Waals forces. • Hydrophobic end- water hating • Hydrophilic end - water loving 3 Lipids: Water-Insoluble Molecules • Roles for lipids in organisms include: Energy storage (fats and oils) Cell membranes (phospholipids) Capture of light energy (carotinoids) Hormones and vitamins (steroids and modified fatty acids) Thermal insulation Electrical insulation of nerves Water repellency (waxes and oils) 3 Lipids: Water-Insoluble Molecules • Fats and oils store energy. • Fats and oils are triglycerides, composed of three fatty acid molecules and one glycerol molecule. • Glycerol is a three-carbon molecule with three hydroxyl (—OH) groups, one for each carbon. • Fatty acids are long chains of hydrocarbons with a carboxyl group (—COOH) at one end. Figure 3.18 Synthesis of a Triglyceride 3 Lipids: Water-Insoluble Molecules • Saturated fatty acids have only single carbon-tocarbon bonds and are said to be saturated with hydrogens. • Saturated fatty acids are rigid and straight, and solid at room temperature. Animal fats are saturated. 3 Lipids: Water-Insoluble Molecules • Unsaturated fatty acids have at least one double-bonded carbon in one of the chains —the chain is not completely saturated with hydrogen atoms. • The double bonds cause kinks that prevent easy packing. Unsaturated fatty acids are liquid at room temperature. Plants commonly have unsaturated fatty acids. Figure 3.19 Saturated and Unsaturated Fatty Acids 3 Lipids: Water-Insoluble Molecules • Phospholipids - similar to fats, except one or two of the fatty acids are replaced by a phosphate group which is connected to a nitrogen group. • As a result, phospholipids orient themselves so that the phosphate group faces water and the tail faces away. • In aqueous environments, these lipids form bilayers, with heads facing outward, tails facing inward. Cell membranes are structured this way. Figure 3.20 Phospholipid Structure Figure 3.21 Phospholipids Form a Bilayer 3 Lipids: Water-Insoluble Molecules • Carotenoids are light-absorbing pigments found in plants and animals. • One, b-carotene, is a plant pigment used to trap light in photosynthesis. • In animals, this pigment, when broken into two identical pieces, becomes vitamin A. Figure 3.22 b –Carotene is the Source of Vitamin A 3 Lipids: Water-Insoluble Molecules • Steroids are signaling molecules. • Classified as a lipid because they are insoluble in water. • Steroids are organic compounds with a series of fused rings. • The steroid cholesterol is a common part of animal cell membranes. • Cholesterol is also is an initial substrate for synthesis of the hormones testosterone and estrogen. Figure 3.23 All Steroids Have the Same Ring Structure 3 Lipids: Water-Insoluble Molecules • Some lipids are vitamins: small organic molecules essential to health. • Vitamin A is important for normal development, maintenance of cells, and night vision. • Vitamin D is important for absorption of calcium in the intestines. • Vitamin E, an antioxidant, protects membranes. • Vitamin K is a component required for normal blood clotting. 3 Lipids: Water-Insoluble Molecules • Waxes are highly nonpolar molecules consisting of saturated long fatty acids bonded to long fatty alcohols via an ester linkage. • A fatty alcohol is similar to a fatty acid, except for the last carbon, which has an —OH group instead of a —COOH group. • Waxy coatings repel water and prevent water loss from structures such as hair, feathers, and leaves. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Nucleic acids are polymers that are specialized for storage and transmission of information. • Two types of nucleic acid are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). • DNA encodes hereditary information and transfers information to RNA molecules. • The information in RNA is decoded to specify the sequence of amino acids in proteins. • Largest biological molecules. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Nucleic acids are polymers of nucleotides. • A nucleotide consists of a pentose sugar, a phosphate group, and a nitrogen-containing base. • In DNA, the pentose sugar is deoxyribose; in RNA it is ribose. Figure 3.24 Nucleotides Have Three Components 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • DNA typically is double-stranded. • The two separate polymer chains are held together by hydrogen bonding between their nitrogenous bases. • The base pairing is complementary: At each position where a purine is found on one strand, a pyrimidine is found on the other. • Purines have a double-ring structure. Pyrimidines have one ring. Figure 3.25 Distinguishing Characteristics of DNA and RNA 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • The linkages that hold the nucleotides in RNA and DNA are called phosphodiester linkages. • These linkages are formed between carbon 3 of the sugar and a phosphate group that is associated with carbon 5 of the sugar. • The backbone consists of alternating sugars and phosphates. • In DNA, the two strands are antiparallel. • The DNA strands form a double helix, a molecule with a right-hand twist. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Most RNA molecules consist of only a single polynucleotide chain. • Instead of the base thymine, RNA uses the base uracil. • Hydrogen bonding between ribonucleotides in RNA can result in complex three-dimensional shapes. Figure 3.26 Hydrogen Bonding in RNA 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • DNA is an information molecule. The information is stored in the order of the four different bases. • This order is transferred to RNA molecules, which are used to direct the order of the amino acids in proteins. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Closely related living species have DNA base sequences that are more similar than distantly related species. • The comparative study of base sequences has confirmed many of the traditional classifications of organisms. • DNA comparisons confirm that our closest living relatives are chimpanzees: We share more than 98 percent of our DNA base sequences. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Certain RNA molecules called ribozymes can act as catalysts. • The discovery of ribozymes provided a solution to the question of whether proteins or nucleic acids came first when life originated. • Since RNA can be informational and catalytic, it could have acted as a catalyst for its own replication as well as for the synthesis of proteins. 3 Nucleic Acids: Informational Macromolecules That Can Be Catalytic • Nucleotides have other important roles: The ribonucleotide ATP supplies energy for biochemical reactions. The ribonucleotide GTP powers protein synthesis. cAMP (cyclic AMP) is a special ribonucleotide that is essential for hormone action and the transfer of information by the nervous system. 3 All Life from Life • Should we expect to see new life forms arise from the biochemical environment? • During the Renaissance, most people thought that some forms of life arose directly from inanimate or decaying matter by spontaneous generation. • In 1668, Francisco Redi did an experiment to test this hypothesis. 3 All Life from Life • The invention of the microscope unveiled a vast new biological world which some scientists believed arose spontaneously from their rich chemical environment. • Louis Pasteur completed experiments to disprove this idea. • Environmental and planetary conditions that exist on Earth today prevent life from arising from nonliving materials, as it might have during the Hadean. Figure 3.28 Disproving the Spontaneous Generation of Life (Part 1) Figure 3.28 Disproving the Spontaneous Generation of Life (Part 2)