Molecules of Life: BiomoleculesSlide 2What Is a Nucleic Acid?Slide 4Nucleotides Polymerize to Form Nucleic AcidsThe Polymerization of Nucleic Acids Is EndergonicSlide 7Slide 8The Sugar-Phosphate Backbone Is DirectionalDNA and the gene:Watson and Crick’s Model of DNA’s Secondary StructureSlide 12Slide 13What Is the Nature of DNA's Secondary Structure?Importance of H-bonding: In proteins and nucleic acidsSummary of DNA’s Secondary StructureHow Does DNA Replicate?RNA Structure and FunctionSlide 19RNA’s Secondary StructureIs DNA a Catalytic Molecule?RNA’s VersatilityWhat Are the Chemical Structures and Functions of Nucleic Acids?Key Concepts Learned:Slide 25© 2011 Pearson Education, Inc.Molecules of Life: BiomoleculesProteins: Building blocks of proteins are the amino acids (C, H, O, N) (monomer=amino acid)example: enzymes catalyzing biochemical reactions, antibodies protecting against diseases… Nucleic acids: RNA, DNA (C, H,O, P, N) Storing/ transferring genetic information (monomer=nucleotide)Carbohydrates: Monosaccharides & derivatives (C, H, O) Cn(H2O)n (monomer= monosaccharide)example: Starch, cellulose…(phosphorylated / sulphated sugars)lipids: Fatty acids, Cholesterol (C,H,[O]) membrane components (phosphorylated lipids)© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.What Is a Nucleic Acid?•A nucleic acid is a polymer of nucleotide monomers.•Nucleotides are each composed of a phosphate group, a sugar, and a nitrogenous base.–The sugar is ribose in ribonucleotides and deoxyribose in deoxyribonucleotides. (it is a 5C sugar = pentose)•There are two groups of nitrogenous bases: –purines (adenine, guanine)–pyrimidines (cytosine, uracil, and thymine)•Uracil (U) is found only in ribonucleotides, and thymine (T) is found only in deoxyribonucleotides.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Nucleotides Polymerize to Form Nucleic Acids Nucleic acids form when nucleotides polymerize.•A condensation reaction forms a phosphodiester linkage (phosphodiester bond) between the phosphate group on the 5′ carbon of one nucleotide and the –OH group on the 3′ carbon of another.•Types of nucleotides involved: 1. Ribonucleotides, which contain the sugar ribose and form RNA 2. Deoxyribonucleotides, which contain the sugar deoxyribose and form DNA© 2011 Pearson Education, Inc.The Polymerization of Nucleic Acids Is Endergonic•Polymerization of nucleic acids is an endergonic process catalyzed by enzymes.•Energy for polymerization comes from the phosphorylation of the nucleotides.–Phosphorylation is the transfer of one or more phosphate groups to a substrate molecule. This raises the potential energy of the substrate and enables endergonic reactions.In nucleic acid polymerization, two phosphates are transferred, creating a nucleoside triphosphate.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.The Sugar-Phosphate Backbone Is Directional•The sugar-phosphate backbone of a nucleic acid is directional—one end has an unlinked 5′ carbon, and the other end has an unlinked 3′ carbon. •The nucleotide sequence is written in the 5′  3′ direction. This reflects the sequence in which nucleotides are added to a growing molecule.•This nucleotide sequence comprises the nucleic acid’s primary structure.© 2011 Pearson Education, Inc.DNA is an informational molecule: information is encoded in the sequences of bases.RNA uses the information to determine the sequence of amino acids in proteins.•PROTEINS and DNA/RNA: These are two cellular components with the Proteins being the executors of the cell’s specific functions while DNA is the repository of the information needed to produce proteins. •FLOW OF BIOLOGICAL INFORMATION: DNA  RNA  POLYPEPTIDE (protein) STRUCTURE / FUNCTIONDNA and the gene:© 2011 Pearson Education, Inc.Watson and Crick’s Model of DNA’s Secondary Structure•James Watson and Francis Crick determined: 1. DNA strands run in an antiparallel configuration.2. DNA strands form a double helix.–The hydrophilic sugar-phosphate backbone faces the exterior.–Nitrogenous base pairs face the interior.3. Purines always pair with pyrimidines.–Specifically, strands form complementary base pairs A-T and G-C.–A-T have two hydrogen bonds.–C-G have three hydrogen bonds.4. DNA has two different sized grooves: the major groove and the minor groove.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.A=TC=G© 2011 Pearson Education, Inc.What Is the Nature of DNA's Secondary Structure? •Erwin Chargaff established two empirical rules for DNA: 1.The total number of purines and pyrimidines is the same.2.The numbers of A’s and T’s are equal and the numbers of C’s and G’s are equal.•Complementary strand for: ATCCAGT ?The DNA Double Helix© 2011 Pearson Education, Inc.Importance of H-bonding: In proteins and nucleic acids© 2011 Pearson Education, Inc.Summary of DNA’s Secondary StructureDNA’s secondary structure consists of two antiparallel strands twisted into a double helix. The molecule is stabilized by hydrophobic interactions in its interior and by hydrogen bonding between the complementary base pairs A-T and G-C.___________________________________________________DNA can store and transmit biological information.The language of nucleic acids is contained in the sequence of the bases.DNA carries the information required for the growth and reproduction of all cells.DNA Contains Biological Information:© 2011 Pearson Education, Inc.How Does DNA Replicate? •Complementary base pairing provides a simple mechanism for DNA replication – each strand can serve as a template for the formation of a new complementary strand.•DNA replication requires two steps: 1. Separation of the double helix2. Hydrogen bonding of deoxyribonucleotides with complementary bases on the original template strand, followed by phosphodiester bond formation to form the complementary strand© 2011 Pearson Education, Inc.RNA Structure and FunctionLike DNA, RNA has a primary structure consisting of a sugar-phosphate backbone formed by phosphodiester linkages and, extending from that backbone, a sequence of four types of nitrogenous bases.•The primary structure of RNA differs from DNA in two ways:1. RNA contains uracil instead of thymine.2. RNA contains ribose instead of deoxyribose. –The presence of the 2’–OH group on