BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 10 Molecular Biology of the Gene Modules 10.1 – 10.5
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory –The herpesvirus hijacks the host cell’s molecules and organelles to produce new copies of the virus Saboteurs Inside Our Cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Viruses provided some of the earliest evidence that genes are made of DNA Molecular biology studies how DNA serves as the molecular basis of heredity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA THE STRUCTURE OF THE GENETIC MATERIAL 10.1 Experiments showed that DNA is the genetic material Head Tail Tail fiber DNA Figure 10.1A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Hershey-Chase Experiment Figure 10.1B Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Phage Bacterium Radioactive protein DNA Empty protein shell 12 Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 3 Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 4 Measure the radioactivity in the pellet and liquid. Batch 1 Radioactive protein Batch 2 Radioactive DNA Radioactive DNA Phage DNA Centrifuge Pellet Radioactivity in liquid Radioactivity in pellet Pellet Centrifuge
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phage reproductive cycle Figure 10.1C Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA is a nucleic acid, made of long chains of nucleotides 10.2 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 –RNA has a slightly different sugar –RNA has U instead of T 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 10.3 DNA is a double-stranded helix Figure 10.3A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix Figure 10.3C Twist 1 chocolate coat, Blind (PRA)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen bonds between bases hold the strands together –Each base pairs with a complementary partner –A pairs with T –G pairs with C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Three representations of DNA Figure 10.3D Ribbon modelPartial chemical structureComputer model Hydrogen bond
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In DNA replication, the strands separate –Enzymes use each strand as a template to assemble the new strands DNA REPLICATION 10.4 DNA replication depends on specific base pairing Parental molecule of DNA Figure 10.4A Both parental strands serve as templates Two identical daughter molecules of DNA Nucleotides A A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Untwisting and replication of DNA Figure 10.4B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA replication begins at specific sites 10.5 DNA replication: A closer look 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 How DNA daughter strands are synthesized 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 The daughter strands are identical to the parent molecule
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The information constituting an organism’s genotype is carried in its sequence of bases THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN 10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A specific gene specifies a polypeptide –The DNA is transcribed into RNA, which is translated into the polypeptide Figure 10.6A DNA Protein TRANSCRIPTION TRANSLATION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Studies of inherited metabolic disorders first suggested that phenotype is expressed through proteins Studies of the bread mold Neurospora crassa led to the one gene-one polypeptide hypothesis Figure 10.6B
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 10.7 Genetic information written in codons is translated into amino acid sequences
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virtually all organisms share the same genetic code 10.8 The genetic code is the Rosetta stone of life Figure 10.8A
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 10.9 Transcription produces genetic messages in the form of RNA 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, the DNA helix unzips –RNA nucleotides line up along one strand of the DNA following the base-pairing rules –The single-stranded messenger RNA peels away and the 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 Noncoding segments called 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 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
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 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
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
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 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are changes in the DNA base sequence –These are caused by errors in DNA replication or by mutagens –The 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 VIRUSES: GENES IN PACKAGES Viral DNA may become part of the host chromosome Phage New phage DNA and proteins are synthesized Phage DNA inserts into the bacterial chromosome by recombination Attaches to cell Phage DNA Bacterial chromosome Phage injects DNA Occasionally a prophage may leave the bacterial chromosome Many cell divisions Lysogenic bacterium reproduces normally, replicating the prophage at each cell division Prophage Phage DNA circularizes LYSOGENIC CYCLE Cell lyses, releasing phages Phages assemble LYTIC CYCLE OR
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many viruses have RNA, rather than DNA, as their genetic material –Example: flu viruses Connection: Many viruses cause disease in animals Figure 10.18A Membranous envelope RNA Protein coat Glycoprotein spike
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some animal viruses steal a bit of the host cell’s membrane Figure 10.18B VIRUS Glycoprotein spike Protein coat Envelope Viral RNA (genome) 1 Plasma membrane of host cell Entry 2 Uncoating Viral RNA (genome) 3 RNA synthesis by viral enzyme 4 Protein synthesis 5 RNA synthesis (other strand) mRNA New viral protein New viral proteins 6 Assembly 7 Exit Template New viral genome
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most plant viruses have RNA –Example: tobacco mosaic disease Connection: Plant viruses are serious agricultural pests Figure ProteinRNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The deadly Ebola virus causes hemorrhagic fever –Each virus is an enveloped thread of protein-coated RNA Hantavirus is another enveloped RNA virus Connection: Emerging viruses threaten human health Figure 10.20A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings HIV is a retrovirus The AIDS virus makes DNA on an RNA template Figure 10.21A Envelope Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Inside a cell, HIV uses its RNA as a template for making DNA to insert into the host chromosome Figure 10.21B Viral RNA DNA strand Double- stranded DNA Viral RNA and proteins CYTOPLASM NUCLEUS Chromosomal DNA Provirus DNA RNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virus studies help establish molecular genetics Molecular genetics helps us understand viruses –such as HIV, seen here attacking a white blood cell Virus research and molecular genetics are intertwined Figure 10.22