The Structure and Function of DNA

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1 Chapter 0 The Structure and Function of PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko Animation: and RNA Structure Right click slide / select Play : STRUCTURE AND REPLICATION was known to be a chemical in cells by the end of the nineteenth century, has the capacity to store genetic information, and can be copied and passed from generation to generation. The discovery of as the hereditary material ushered in the new field of molecular biology, the study of heredity at the molecular level. Animation: Hershey-Chase Experiment Right click slide / select Play and RNA Structure Figure 0. and RNA are nucleic acids. Phosphate group Nitrogenous base They consist of chemical units called nucleotides. A nucleotide polymer is a polynucleotide. Sugar nucleotide Nitrogenous base (can be A, G, C, or T) Thymine (T) Nucleotides are joined by covalent bonds between the sugar of one nucleotide and the phosphate of the next, forming a sugar-phosphate backbone. double helix Phosphate group Sugar (deoxyribose) nucleotide Polynucleotide Sugar-phosphate backbone

2 Figure 0.a Phosphate group Nitrogenous base Figure 0. RNA polynucleotide Cytosine Sugar nucleotide Nitrogenous base (can be A, G, C, or T) Thymine (T) Guanine Adenine Uracil Phosphate group Sugar (deoxyribose) Phosphate nucleotide Sugar (ribose) Polynucleotide Sugar-phosphate backbone and RNA Structure Watson and Crick s Discovery of the Double Helix The sugar in is deoxyribose. Thus, the full name for is deoxyribonucleic acid. James Watson and Francis Crick determined that is a double helix. Watson and Crick used X-ray crystallography data to reveal the basic shape of. Rosalind Franklin produced the X-ray image of. and RNA Structure Figure 0.3b The four nucleotides found in differ in their nitrogenous bases. These bases are thymine (T), cytosine (C), adenine (A), and guanine (G). RNA has uracil (U) in place of thymine. Rosalind Franklin X-ray images of

3 Figure 0.3a Watson and Crick s Discovery of the Double Helix bases pair in a complementary fashion: adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). James Watson (left) and Francis Crick Watson and Crick s Discovery of the Double Helix Figure 0.5 The model of is like a rope ladder twisted into a spiral. Hydrogen bond The ropes at the sides represent the sugarphosphate backbones. Each wooden rung represents a pair of bases connected by hydrogen bonds. (a) Ribbon model (b) Atomic model (c) Computer model Figure Twist Blast Animation: Structure of Double Helix Select Play

4 Figure 0.6 Parental (old) molecule Daughter (new) strand Parental (old) strand Blast Animation: Hydrogen Bonds in Select Play Daughter molecules (double helices) Replication Replication When a cell reproduces, a complete copy of the must pass from one generation to the next. Watson and Crick s model for suggested that replicates by a template mechanism. can be damaged by X-rays and ultraviolet light. polymerases are enzymes, make the covalent bonds between the nucleotides of a new strand, and are involved in repairing damaged. Replication replication ensures that all the body cells in multicellular organisms carry the same genetic information. 4 Bioflix Animation: Replication

5 Replication replication in eukaryotes begins at specific sites on a double helix (called origins of replication) and proceeds in both directions. Animation: Lagging Strand Right click slide / select Play Figure 0.7 Origin of replication Parental strands Origin of replication Origin of replication Parental strand Daughter strand Bubble Animation: Origins of Replication Right click slide / select Play Two daughter molecules THE FLOW OF GENETIC INFORMATION FROM TO RNA TO PROTEIN provides instructions to a cell and an organism as a whole. 5 Animation: Leading Strand Right click slide / select Play

6 How an Organism s Genotype Determines Its Phenotype An organism s genotype is its genetic makeup, the sequence of nucleotide bases in. Figure 0.8- The phenotype is the organism s physical traits, which arise from the actions of a wide variety of proteins. Cytoplasm How an Organism s Genotype Determines Its Phenotype specifies the synthesis of proteins in two stages: Figure 0.8- TRANSCRIPTION. transcription, the transfer of genetic information from into an RNA molecule and. translation, the transfer of information from RNA into a protein. RNA Cytoplasm Figure TRANSCRIPTION RNA Cytoplasm 6 TRANSLATION Bioflix Animation: Protein Synthesis Protein

7 From Nucleotides to Amino Acids: An Overview From Nucleotides to Amino Acids: An Overview Genetic information in is transcribed into RNA, then translated into polypeptides, which then fold into proteins. Experiments have verified that the flow of information from gene to protein is based on a triplet code. A codon is a triplet of bases, which codes for one amino acid. From Nucleotides to Amino Acids: An Overview The Genetic Code What is the language of nucleic acids? In, it is the linear sequence of nucleotide bases. A typical gene consists of thousands of nucleotides in a specific sequence. When a segment of is transcribed, the result is an RNA molecule. The genetic code is the set of rules that convert a nucleotide sequence in RNA to an amino acid sequence. Of the 64 triplets, 6 code for amino acids and 3 are stop codons, instructing the ribosomes to end the polypeptide. RNA is then translated into a sequence of amino acids in a polypeptide. Figure 0.0 Figure 0. Second base of RNA codon U C A G Gene Gene Gene 3 strand TRANSCRIPTION RNA TRANSLATION Codon Polypeptide Amino acid molecule First base of RNA codon UUU UUC U UUA UUG CUU CUC C CUA CUG AUU AUC A AUA AUG GUU GUC G GUA GUG Phenylalanine (Phe) Leucine (Leu) Leucine (Leu) Isoleucine (Ile) Met or start Valine (Val) UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG Serine (Ser) Proline (Pro) AAC Threonine (Thr) AAA AAG GAU Alanine (Ala) UAU UAC UAA UAG CAU CAC CAA CAG AAU GAC GAA GAG Tyrosine (Tyr) Stop Stop Histidine (His) Glutamine (Gln) Asparagine (Asn) Lysine (Lys) Aspartic acid (Asp) Glutamic acid (Glu) UGU UGC Cysteine (Cys) U C UGA Stop A UGG Tryptophan (Trp) G CGU U CGC Arginine C CGA (Arg) A CGG G AGU Serine U AGC (Ser) C AGA Arginine A AGG (Arg) G GGU U GGC Glycine C GGA (Gly) A GGG G Third base of RNA codon 7

8 The Genetic Code Transcription: From to RNA Because diverse organisms share a common genetic code, it is possible to program one species to produce a protein from another species by transplanting. RNA nucleotides are linked by the transcription enzyme. Figure 0. Animation: Transcription Right click slide / select Play Transcription: From to RNA Figure 0.3a Transcription makes RNA from a template, uses a process that resembles the synthesis of a strand during replication, and substitutes uracil (U) for thymine (T). Newly made RNA RNA nucleotides RNA polymerase Direction of transcription Template strand of (a) A close-up view of transcription 8

9 Figure 0.3b Termination of Transcription Promoter Initiation of gene Terminator During the third phase of transcription, called termination, RNA Elongation reaches a special sequence of bases in the template called a terminator, signaling the end of the gene, 3 Termination Growing RNA polymerase detaches from the RNA and the gene, and Completed RNA the strands rejoin. (b) Transcription of a gene Initiation of Transcription The Processing of Eukaryotic RNA The start transcribing signal is a nucleotide sequence called a promoter, which is located in the at the beginning of the gene and a specific place where attaches. The first phase of transcription is initiation, in which attaches to the promoter and RNA synthesis begins. In the cells of prokaryotes, RNA transcribed from a gene immediately functions as messenger RNA (), the molecule that is translated into protein. The eukaryotic cell localizes transcription in the nucleus and modifies, or processes, the RNA transcripts in the nucleus before they move to the cytoplasm for translation by ribosomes. RNA Elongation The Processing of Eukaryotic RNA During the second phase of transcription, called elongation, the RNA grows longer and the RNA strand peels away from its template. RNA processing includes adding a cap and tail consisting of extra nucleotides at the ends of the RNA transcript, removing introns (noncoding regions of the RNA), and RNA splicing, joining exons (the parts of the gene that are expressed) together to form messenger RNA (). 9

10 The Processing of Eukaryotic RNA Messenger RNA () RNA splicing is believed to play a significant role in humans in allowing our approximately,000 genes to produce many thousands more polypeptides and by varying the exons that are included in the final. Translation requires, ATP, enzymes, ribosomes, and transfer RNA (trna). Figure 0.4 Transfer RNA (trna) RNA transcript with cap and tail Cap Transcription Addition of cap and tail s removed Tail Exons spliced together Coding sequence Transfer RNA (trna) acts as a molecular interpreter, carries amino acids, and matches amino acids with codons in using anticodons, a special triplet of bases that is complementary to a codon triplet on. Cytoplasm Translation: The Players Figure 0.5 Amino acid attachment site Translation is the conversion from the nucleic acid language to the protein language. Hydrogen bond RNA polynucleotide chain 0 trna polynucleotide (ribbon model) trna (simplified representation)

11 Ribosomes Ribosomes are organelles that coordinate the functions of and trna and are made of two subunits. Figure 0.6b Growing polypeptide Next amino acid to be added to polypeptide Each subunit is made up of proteins and a considerable amount of another kind of RNA, ribosomal RNA (rrna). trna Codons (b) The players of translation Ribosomes Translation: The Process A fully assembled ribosome holds trna and for use in translation. Translation is divided into three phases:. initiation,. elongation, and 3. termination. Figure 0.6a Initiation trna binding sites Initiation brings together P site A site, binding site Large subunit Small subunit Ribosome the first amino acid with its attached trna, and two subunits of the ribosome. The molecule has a cap and tail that help the bind to the ribosome. (a) A simplified diagram of a ribosome

12 Figure 0.7 Cap Start of genetic message End Tail Blast Animation: Translation Select Play Initiation Figure 0.8 Initiation occurs in two steps.. An molecule binds to a small ribosomal subunit, then a special initiator trna binds to the start codon, where translation is to begin on the. Initiator trna Met P site Large ribosomal subunit A site. A large ribosomal subunit binds to the small one, creating a functional ribosome. Start codon Small ribosomal subunit Elongation Elongation occurs in three steps. Step : Codon recognition. The anticodon of an incoming trna pairs with the codon at the A site of the ribosome. Animation: Translation Right click slide / select Play

13 Figure 0.9 Polypeptide Amino acid Elongation P site A site Step 3: Translocation. The P site trna leaves the ribosome. Codons Codon recognition The trna carrying the polypeptide moves from the A to the P site. ELONGATION Stop codon Peptide bond formation New peptide bond movement 3 Translocation Elongation Figure 0.9b Step : Peptide bond formation. The polypeptide leaves the trna in the P site and attaches to the amino acid on the trna in the A site. New peptide bond The ribosome catalyzes the bond formation between the two amino acids. movement Translocation ELONGATION Stop codon Figure 0.9a Termination Polypeptide Amino acid Elongation continues until a stop codon reaches the ribosome s A site, P site A site Codons Codon recognition Peptide bond formation ELONGATION the completed polypeptide is freed, and the ribosome splits back into its subunits. 3

14 Review: RNA Protein Figure Transcription In a cell, genetic information flows from to RNA in the nucleus and RNA to protein in the cytoplasm. Tail RNA processing Cap Amino acid trna ATP Enzyme 3 Amino acid attachment Figure 0.0- Figure Transcription Transcription RNA processing Tail Cap Amino acid trna Enzyme ATP 3 Amino acid attachment 4 A Initiation of translation Ribosomal subunits Figure 0.0- Figure Transcription Transcription Tail RNA processing Cap Tail RNA processing Cap Codon 5 Elongation Amino acid 4 trna Enzyme ATP 3 Amino acid attachment 4 A Initiation of translation Ribosomal subunits

15 Figure Transcription Tail RNA processing Cap Codon 5 Elongation Polypeptide Amino acid trna Enzyme ATP 3 Amino acid attachment A Ribosomal subunits 4 Initiation of 6 translation Termination Stop codon Review: RNA Protein As it is made, a polypeptide coils and folds and assumes a three-dimensional shape, its tertiary structure. Transcription and translation are how genes control the structures and activities of cells. 5