1. DNA, RNA structure 2. DNA replication 3. Transcription, translation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA is a nucleic acid, made of long chains of nucleotides DNA and RNA are polymers of nucleotides Figure 10.2A Nucleotide Phosphate group Nitrogenous base Sugar PolynucleotideSugar-phosphate backbone DNA nucleotide Phosphate group Nitrogenous base (A, G, C, or T) Thymine (T) Sugar (deoxyribose)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA has four kinds of bases, A, T, C, and G Figure 10.2B Pyrimidines Thymine (T)Cytosine (C) Purines Adenine (A)Guanine (G)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA is also a nucleic acid –different sugar –U instead of T –Single strand, usually Figure 10.2C, D Phosphate group Nitrogenous base (A, G, C, or U) Uracil (U) Sugar (ribose)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin DNA is a double-stranded helix Figure 10.3A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen bonds between bases hold the strands together: A and T, C and G Figure 10.3D Ribbon modelPartial chemical structureComputer model Hydrogen bond

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Untwisting and replication of DNA each strand is a template for a new strand Figure 10.4B helicase DNA polymerase

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA replication begins at many specific sites How can entire chromosomes be replicated during S phase? Figure 10.5A Parental strand Origin of replication Bubble Two daughter DNA molecules Daughter strand

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each strand of the double helix is oriented in the opposite direction Figure 10.5B 5 end3 end 5 end P P P P P P P P

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA polymerase works in only one direction 5 end P P Parental DNA Figure 10.5C DNA polymerase molecule Daughter strand synthesized continuously Daughter strand synthesized in pieces DNA ligase Overall direction of replication 5 3 Telomere sequences are lost with each replication. Cancer, aging telomeres

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –The DNA is transcribed into RNA, which is translated into the polypeptide Figure 10.6A DNA RNA Protein TRANSCRIPTION TRANSLATION The information constituting an organism’s genotype is carried in its sequence of bases

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transcription produces genetic messages in the form of mRNA Figure 10.9A RNA polymerase RNA nucleotide Direction of transcription Newly made RNA Template strand of DNA

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In transcription, DNA helix unzips –RNA nucleotides line up along one strand of DNA, following the base-pairing rules –single-stranded messenger RNA peels away and DNA strands rejoin RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Area shown in Figure 10.9A Growing RNA RNA polymerase Completed RNA Figure 10.9B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA transcripts of DNA

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Noncoding segments, introns, are spliced out A cap and a tail are added to the ends Eukaryotic RNA is processed before leaving the nucleus Figure DNA RNA transcript with cap and tail mRNA ExonIntron Exon Transcription Addition of cap and tail Introns removed Exons spliced together Coding sequence NUCLEUS CYTOPLASM Tail Cap

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The “words” of the DNA “language” are triplets of bases called codons –The codons in a gene specify the amino acid sequence of a polypeptide Translation of nucleic acids into amino acids

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid

UCAG U C A G G A C U G A C U G A C U G A C U UUUUUU UUCUUC UUAUUA UUGUUG CUUCUU CUCCUC CUACUA CUGCUG AUUAUU AUCAUC AUAAUA AUGAUG GUUGUU GUCGUC GUAGUA GUGGUG phe leu ile met (start) val UCUUCU UCCUCC UCAUCA UCGUCG CCUCCU CCCCCC CCACCA CCGCCG ACUACU ACCACC ACAACA ACGACG GCUGCU GCCGCC GCAGCA GCGGCG ser pro thr ala UAUUAU UACUAC UAAUAA UAGUAG CAUCAU CACCAC CAACAA CAGCAG AAUAAU AACAAC AAGAAG AAAAAA GAUGAU GACGAC GAAGAA GAGGAG tyr stop his gln asn lys asp glu UGUUGU UGCUGC UGAUGA UGGUGG CGUCGU CGCCGC CGACGA CGGCGG AGUAGU AGCAGC AGAAGA AGGAGG GGUGGU GGCGGC GGAGGA GGGGGG cys stop trp arg ser arg gly First Base Third Base Second Base Virtually all organisms share the same genetic code “unity of life”

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An exercise in translating the genetic code Figure 10.8B Start codon RNA Transcribed strand Stop codon Translation Transcription DNA Polypeptide

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide The process is aided by transfer RNAs Transfer RNA molecules serve as interpreters during translation Figure 10.11A Hydrogen bond Amino acid attachment site RNA polynucleotide chain Anticodon

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Figure 10.11B, C Anticodon Amino acid attachment site

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ribosomes build polypeptides Figure 10.12A-C Codons tRNA molecules mRNA Growing polypeptide Large subunit Small subunit mRNA mRNA binding site P siteA site PA Growing polypeptide tRNA Next amino acid to be added to polypeptide

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An initiation codon marks the start of an mRNA message Figure 10.13A End Start of genetic message AUG = methionine

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Figure 10.13B 1 Initiator tRNA mRNA Start codon Small ribosomal subunit 2 P site Large ribosomal subunit A site

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The mRNA moves a codon at a time relative to the ribosome –A tRNA pairs with each codon, adding an amino acid to the growing polypeptide –A STOP codon causes the mRNA-ribosome complex to fall apart Elongation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure Codon recognition Amino acid Anticodon A site P site Polypeptide 2 Peptide bond formation 3 Translocation New peptide bond mRNA movement mRNA Stop codon

b a Red object = ? What molecules are present in this photo?

Table 14.2 Types of RNA Type of RNA Functions inFunction Messenger RNA (mRNA) Nucleus, migrates to ribosomes in cytoplasm Carries DNA sequence information to ribosomes Transfer RNA (tRNA) Cytoplasm Provides linkage between mRNA and amino acids; transfers amino acids to ribosomes Ribosomal RNA (rRNA) Cytoplasm Structural component of ribosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The sequence of codons in DNA spells out the primary structure of a polypeptide –Polypeptides form proteins that cells and organisms use Review: The flow of genetic information in the cell is DNA  RNA  protein

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are changes in the DNA base sequence –caused by errors in DNA replication or by mutagens –change of a single DNA nucleotide causes sickle-cell disease Mutations can change the meaning of genes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.16A Normal hemoglobin DNA mRNA Normal hemoglobin Glu Mutant hemoglobin DNA mRNA Sickle-cell hemoglobin Val

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of mutations Figure 10.16B mRNA NORMAL GENE BASE SUBSTITUTION BASE DELETION ProteinMetLysPheGlyAla MetLysPheSerAla MetLysLeuAlaHis Missing

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.23A, B Deletion Duplication Inversion Homologous chromosomes Reciprocal translocation Nonhomologous chromosomes Chromosomal changes can be large or small

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Summary of transcription and translation Figure Stage mRNA is transcribed from a DNA template. Anticodon DNA mRNA RNA polymerase TRANSLATION Enzyme Amino acid tRNA Initiator tRNA Large ribosomal subunit Small ribosomal subunit mRNA Start Codon 2 Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 3 Stage Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. TRANSCRIPTION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure (continued) 4 Stage Elongation Growing polypeptide Codons 5 Stage Termination mRNA New peptide bond forming Stop Codon The ribosome recognizes a stop codon. The poly- peptide is terminated and released. A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Polypeptide