Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and Jane Reece Chapter 18 The Genetics of Viruses and Bacteria

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.1 T4 bacteriophage infecting an E. coli cell 0.5  m

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.2 Comparing the size of a virus, a bacterium, and an animal cell 0.25  m Virus Animal cell Bacterium Animal cell nucleus

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.3 Infection by tobacco mosaic virus (TMV)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.4 Viral structure 18  250 mm 70–90 nm (diameter) 80–200 nm (diameter) 80  225 nm 20 nm50 nm (a) Tobacco mosaic virus(b) Adenoviruses(c) Influenza viruses (d) Bacteriophage T4 RNA Capsomere of capsid DNA Capsomere Glycoprotein Membranous envelope Capsid DNA Head Tail fiber Tail sheath

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.5 A simplified viral reproductive cycle VIRUS Capsid proteins mRNA Viral DNA HOST CELL Viral DNA Entry into cell and uncoating of DNA Replication Transcription DNA Capsid Self-assembly of new virus particles and their exit from cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.6 The lytic cycle of phage T4, a virulent phage Attachment. The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell. Entry of phage DNA and degradation of host DNA. The sheath of the tail contracts, injecting the phage DNA into the cell and leaving an empty capsid outside. The cell’s DNA is hydrolyzed. Synthesis of viral genomes and proteins. The phage DNA directs production of phage proteins and copies of the phage genome by host enzymes, using components within the cell. Assembly. Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms. Release. The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles Phage assembly Head Tails Tail fibers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.7 The lytic and lysogenic cycles of phage, a temperate phage Many cell divisions produce a large population of bacteria infected with the prophage. The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages. Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Certain factors determine whether The phage attaches to a host cell and injects its DNA. Phage DNA circularizes The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered Lysogenic cycleLytic cycle or Prophage Bacterial chromosome Phage DNA

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.8 The reproductive cycle of an enveloped RNA virus Capsid and viral genome enter cell 2 The viral genome (red) functions as a template for synthesis of complementary RNA strands (pink) by a viral enzyme. 3 New virus 8 RNA Capsid Envelope (with glycoproteins) Glycoproteins on the viral envelope bind to specific receptor molecules (not shown) on the host cell, promoting viral entry into the cell. 1 New copies of viral genome RNA are made using complementary RNA strands as templates. 4 Vesicles transport envelope glycoproteins to the plasma membrane. 6 A capsid assembles around each viral genome molecule. 7 Complementary RNA strands also function as mRNA, which is translated into both capsid proteins (in the cytosol) and glycoproteins for the viral envelope (in the ER). 5 HOST CELL Viral genome (RNA) Template Capsid proteins Glyco- proteins mRNA Copy of genome (RNA) ER

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 18.9 The structure of HIV, the retrovirus that causes AIDS Reverse transcriptase Viral envelope Capsid Glycoprotein RNA (two identical strands)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure SARS (severe acute respiratory syndrome), a recently emerging viral disease (a) Young ballet students in Hong Kong wear face masks to protect themselves from the virus causing SARS. (b) The SARS-causing agent is a coronavirus like this one (colorized TEM), so named for the “corona” of glycoprotein spikes protruding from the envelope.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Viral infection of plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Model for how prions propagate Prion Normal protein Original prion New prion Many prions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Replication of a bacterial chromosome Replication fork Origin of replication Termination of replication

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Generalized transduction Phage DNA Donor cell A+A+ B+B+ A+A+ B+B+ A+A+ Phage infects bacterial cell that has alleles A + and B + Host DNA (brown) is fragmented, and phage DNA and proteins are made. This is the donor cell. A bacterial DNA fragment (in this case a fragment with the A + allele) may be packaged in a phage capsid

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Generalized transduction Phage DNA Donor cell Recipient cell A+A+ B+B+ A+A+ B+B+ A+A+ A+A+ B–B– A–A– B–B– A+A+ Recombinant cell Crossing over Phage infects bacterial cell that has alleles A + and B + Host DNA (brown) is fragmented, and phage DNA and proteins are made. This is the donor cell. A bacterial DNA fragment (in this case a fragment with the A + allele) may be packaged in a phage capsid. Phage with the A + allele from the donor cell infects a recipient A – B – cell, and crossing over (recombination) between donor DNA (brown) and recipient DNA (green) occurs at two places (dotted lines). The genotype of the resulting recombinant cell (A + B – ) differs from the genotypes of both the donor (A + B + ) and the recipient (A – B – )

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Bacterial conjugation Sex pilus 1  m

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Transposable genetic elements in bacteria (a) Insertion sequences, the simplest transposable elements in bacteria, contain a single gene that encodes transposase, which catalyzes movement within the genome. The inverted repeats are backward, upside-down versions of each other; only a portion is shown. The inverted repeat sequence varies from one type of insertion sequence to another. (b) Transposons contain one or more genes in addition to the transposase gene. In the transposon shown here, a gene for resistance to an antibiotic is located between twin insertion sequences. The gene for antibiotic resistance is carried along as part of the transposon when the transposon is inserted at a new site in the genome. Insertion sequence Transposase gene Inverted repeat Inverted repeat Inverted repeats Transposase gene Insertion sequence Antibiotic resistance gene Transposon A T C C G G T… T A G G C C A … A C C G G A T… T G G C C T A …

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure The trp operon: regulated synthesis of repressible enzymes (a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes. Genes of operon Inactive repressor Protein Operator Polypeptides that make up enzymes for tryptophan synthesis Promoter Regulatory gene RNA polymerase Start codon Stop codon Promoter trp operon 5 3 mRNA 5 trpD trpE trpCtrpB trpA trpR DNA mRNA ED C BA

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA mRNA Protein Tryptophan (corepressor) Active repressor No RNA made Tryptophan present, repressor active, operon off. As tryptophan accumulates, it inhibits its own production by activating the repressor protein. (b)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure The lac operon: regulated synthesis of inducible enzymes DNA mRNA Protein Active repressor RNA polymerase No RNA made lacZ lacl Regulatory gene Operator Promoter Lactose absent, repressor active, operon off. The lac repressor is innately active, and in the absence of lactose it switches off the operon by binding to the operator. (a) 5 3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings mRNA 5' DNA mRNA Protein Allolactose (inducer) Inactive repressor lacl lacz lacYlacA RNA polymerase PermeaseTransacetylase  -Galactosidase 5 3 (b) Lactose present, repressor inactive, operon on. Allolactose, an isomer of lactose, derepresses the operon by inactivating the repressor. In this way, the enzymes for lactose utilization are induced. mRNA 5 lac operon

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Positive control of the lac operon by catabolite activator protein (CAP) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized. If glucose is scarce, the high level of cAMP activates CAP, and the lac operon produces large amounts of mRNA for the lactose pathway. (a) CAP-binding site Operator Promoter RNA polymerase can bind and transcribe Inactive CAP Active CAP cAMP DNA Inactive lac repressor lacl lacZ

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized. When glucose is present, cAMP is scarce, and CAP is unable to stimulate transcription. Inactive lac repressor Inactive CAP DNA RNA polymerase can’t bind Operator lacl lacZ CAP-binding site Promoter

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The viral cycle that causes cell death quickly is 1.Lysogenic 2.Lytic 3.Reverse transcription 4.Mitosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The viral cycle that replicates without killing the host is 1.Lysogenic 2.Lytic 3.Reverse transcription 4.Mitosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prions are tiny particles that affect 5 1.Bacteria 2.Plants 3.Animals 4.Protists

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Viroids are tiny particles that affect 5 1.Bacteria 2.Plants 3.Animals 4.Protists

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prions are tiny particles that affect 5 1.Bacteria 2.Plants 3.Animals 4.Protists

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What are the parts of an operon? 5 1.RPG 2.POG 3.PIG 4.GOP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The P in an operon stands for 5 1.Promoter 2.Protein 3.Prion 4.Polymerization