Biology Chapter 19: Viruses, Bacteria, and Archaea PDF

Biology Concepts and Applications | 9e Starr | Evers | Starr Chapter 19 Viruses, Bacteria, and Archaea © Cengage Learning 2015 © Cengage Learning 2015  19.1 What Are Viruses? Viruses: noncellular infectious agents...

Biology Concepts and Applications | 9e Starr | Evers | Starr Chapter 19 Viruses, Bacteria, and Archaea © Cengage Learning 2015 © Cengage Learning 2015  19.1 What Are Viruses? Viruses: noncellular infectious agents – Consists of a protein coat around a core of DNA or RNA The coat is enveloped in a bit of plasma membrane derived from a previous host – Replicates only in a host cell – A virus is far smaller than any cell – Has no ribosomes or other metabolic machinery © Cengage Learning 2015  What Are Viruses? (cont’d.) Viral structure – Either enveloped or non-enveloped Most animal viruses are enveloped Most plant viruses are non-enveloped Herpes viruses are enveloped DNA viruses HIV is an enveloped RNA virus Tobacco mosaic virus has a helical structure, with coat proteins arranged around RNA to form a rod – Many animal viruses have a 20-sided protein coat © Cengage Learning 2015  What Are Viruses? (cont’d.) viral RNA viral RNA and enzymes envelope protein coat (a bit of beneath membrane envelope protein subunit from host) of coat A B © Cengage Learning 2015 © Cengage Learning 2015  What Are Viruses? (cont’d.) Viral replication – Each type of virus has structural adaptations that allow it to infect and replicate in hosts of a particular type – Replication begins when a virus attaches to membrane proteins on host cell – Genetic material enters cell – Results in cellular hijacking © Cengage Learning 2015  What Are Viruses? (cont’d.) Bacteriophage (phages) – A virus that infects bacteria and archaea – Have two replication pathways Lytic: multiplication is rapid, and new viral particles are released by lysis Lysogenic: the virus enters a latent state that extends the cycle © Cengage Learning 2015 © Cengage Learning 2015  What Are Viruses? (cont’d.) HIV replication – HIV is an enveloped RNA virus that causes the disease AIDS – HIV replicates inside human white blood cells – Spikes of viral protein attach to proteins in the cell’s plasma membrane – Drugs that fight HIV interfere with viral binding to the host, reverse transcription, integration of DNA, or formation of viral proteins © Cengage Learning 2015  What Are Viruses? (cont’d.) Nine steps in HIV replication 1. Virus binds to a host cell 2. Viral RNA and enzymes enter cell 3. Viral reverse transcriptase uses viral RNA to make double-stranded viral DNA 4. Viral DNA integrates into host genome 5. Transcription produces viral RNA © Cengage Learning 2015  What Are Viruses? (cont’d.) Nine steps in HIV replication (cont’d.) 6. Some viral RNA is translated to produce viral proteins 7. Other viral RNA forms the new viral genome 8. Viral proteins and RNA self-assemble at the host membrane 9. New virus buds with an envelope of host membrane © Cengage Learning 2015  What Are Viruses? (cont’d.) RNA viruses that use reverse transcriptase to produce viral DNA in a host are called retroviruses © Cengage Learning 2015 © Cengage Learning 2015  What Are Viruses? (cont’d.) viral glycoprotein (binds to host proteins) viral coat proteins one of two strands of viral RNA lipid envelope © Cengage Learning 2015 with proteins  19.2 How Do Viruses Affect Human Health? Viral diseases – Pathogens: disease-causing agents – Usually produce mild symptoms persist in body for long periods – Can be latent and then reawaken © Cengage Learning 2015  How Do Viruses Affect Human Health? (cont’d.) © Cengage Learning 2015  How Do Viruses Affect Human Health? (cont’d.) Common viral diseases – Nonenveloped viruses: Adenoviruses (colds) Viral gastroenteritis (stomach flu) Human papillomavirus (genital warts, cervical cancer) © Cengage Learning 2015  How Do Viruses Affect Human Health? (cont’d.) Enveloped viruses – Herpes viruses (cold sores, genital herpes, infectious mononucleosis, chicken pox) – Influenza (flu) – Mumps, measles, and German measles © Cengage Learning 2015  How Do Viruses Affect Human Health? (cont’d.) Emerging viral diseases – Changes to viral genomes as a result of mutation or gene exchanges can alter the properties of a viral disease – A disease that was previously unknown, is new to humans, or has recently begun spreading to a new region © Cengage Learning 2015  How Do Viruses Affect Human Health? (cont’d.) West nile fever – An enveloped RNA virus that replicates in birds – Mosquitoes carry the virus from host to host (the vector for this virus) – Attacks the nervous system and can be fatal – An endemic disease throughout the continental United States © Cengage Learning 2015  How Do Viruses Affect Human Health? Ebola hemorrhagic fever – Ebola virus is highly contagious to humans – Symptoms include fever, muscle pain, and massive internal bleeding – Death rate is 90 percent © Cengage Learning 2015  How Do Viruses Affect Human Health? Viral recombination – Viruses have genomes that can mutate – RNA viruses can mutate quickly – Viral genomes can also exchange genes when two viruses infect a host at the same time © Cengage Learning 2015  How Do Viruses Affect Human Health? Viral recombination (cont’d.) – Avian influenza H5N1 (bird flu) occasionally infects people who are in contact with birds, and has a high mortality rate – Influenza H1N1 (swine flu) first appeared in 2009, can cause severe respiratory symptoms, and is easily transmitted © Cengage Learning 2015  19.3 How Do Viruses Affect Plant Health? Viroids – A new type of plant pathogen – A small RNA, circular and single-stranded without a protein coat – Are ribozymes (RNAs with enzymatic activity) – Discovered in 1971 – Viroids do not encode proteins © Cengage Learning 2015  How Do Viruses Affect Plant Health? A B © Cengage Learning 2015  19.4 How Are Bacteria and Archaea Similar? Bacteria and archaea – Prokaryotes – Small, structurally simple and single-celled – Three cell shapes Coccus (spherical) Bacillus (rod-shaped) Spirillum (spiral) © Cengage Learning 2015 © Cengage Learning 2015  How Are Bacteria and Archaea Similar? Prokaryotic traits – No nucleus, endoplasmic reticulum, or Golgi bodies – Single chromosome (a circular DNA molecule); many species also contain plasmids – Cell wall (in most species) © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) Prokaryotic traits (cont’d.) – Ribosomes distributed in the cytoplasm – Asexual reproduction by binary fission – Capacity for gene exchange among existing cells through conjugation, transduction, and transformation © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) Reproduction and gene exchange – Reproduce by binary fission: Asexual reproduction Replication of a single, circular chromosome Division of a parent cell into two genetically equivalent descendants © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) Four steps in binary fission – Circular chromosome attaches to inside of plasma membrane – Cell duplicates chromosome, attaches copy beside the original, and adds membrane and wall material between them – When cell has almost doubled in size, new membrane and wall are deposited – Two genetically identical cells result © Cengage Learning 2015 © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) Horizontal gene transfers – Move genes between existing individuals (cells) Conjugation – One cell gives a plasmid to the other – One cell extends a sex pilus out to another cell – The cell that made the sex pilus passes a copy of its plasmid to its partner © Cengage Learning 2015 © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) Metabolic diversity of prokaryotes Mode of Nutrition Energy Source Carbon Source Photoautotrophic # & Sunlight Carbon dioxide -Chemoautotrophic Inorganic 2 ① substances Carbon dioxide & Photoheterotrophic Sunlight & -Organic compounds -- Chemoheterotrophic & Organic Scompounds Organic compounds © Cengage Learning 2015 © Cengage Learning 2015  How Are Bacteria and Archaea Similar? (cont’d.) g [ 2 E © Cengage Learning 2015  19.5 What Are Some Major Bacterial Lineages? Bacteria are widespread, abundant, and diverse – Most either harmless or beneficial Many bacteria have essential ecological roles: – Decomposers – Cycle nutrients – Form partnerships with other species © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Cyanobacteria – Produce oxygen during photosynthesis – Carry out nitrogen fixation, producing ammonia that algae and plants need as a nutrient – Partner with fungi and form lichens – Spirulina is grown commercially © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) nitrogen- photosynthetic resting cell fixing cells (forming) cell © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Proteobacteria are the largest bacterial lineage – Some are nitrogen-fixers (Rhizobium) – Myxobacteria show remarkable cooperative behavior (multicelled fruiting bodies with spores) – Escherichia coli are part of our normal flora © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Thiomargarita namibiensis – The largest known bacterium – Has an enormous vacuole that holds sulfur and nitrate Some important pathogens: Salmonella, Campylobacter, Helicobactor pylori, Vibrio cholerae Rickettsias (intracellular parasites) are the closest relatives of mitochondria © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) B A © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Gram staining – Method used to prepare bacteria for examination under a microscope – Process used to distinguish groups based on cell wall structure Thick-walled Gram-positive bacteria are tinted purple Thinner-walled Gram-negative bacteria such as cyanobacteria and proteobacteria are stained pink © Cengage Learning 2015 © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Gram-positive bacteria have thick walls Gram-negative bacteria have thinner walls Some Gram-positive soil bacteria (Clostridium, Bacillus) produce endospores – Allow them to survive Boiling, freezing, radiation, and disinfectants © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) Spirochetes – Spiral-shaped bacteria – Include aquatic decomposers, nitrogen fixers, and bacteria that live in cattle gut and break down cellulose – Some are pathogens Cause of sexually-transmitted disease syphilis Cause of Lyme disease, transmitted by ticks © Cengage Learning 2015  What Are Some Major Bacterial Lineages? (cont’d.) © Cengage Learning 2015  19.6 How Do Bacteria Affect Human Health? Normal flora – Normally harmless or beneficial microorganisms that typically live in or on a body Some endospore-forming bacteria make deadly toxins: – Bacillus anthracis: anthrax – Clostridium tetani: tetanus – C. botulinum: botulism © Cengage Learning 2015  How Do Bacteria Affect Human Health? (cont’d.) Dangerous infections: – Mycobacterium tuberculosis: tuberculosis – Streptococcus: & strep throat, “flesh-eating bacteria” & – Staphylococcus: Antibiotic-resistant staph infections © Cengage Learning 2015  How Do Bacteria Affect Human Health? (cont’d.) © Cengage Learning 2015  19.7 How Were Archaea Discovered? Biologists historically divided all life into two groups, prokaryotes and eukaryotes New evidence revealed differences in structure, organization, and gene sequences between bacteria and archaeans The three domain model is now considered correct © Cengage Learning 2015  How Were Archaea Discovered? (cont’d.) prokaryotes eukaryotes bacteria archaea eukaryotes A B © Cengage Learning 2015  How Were Archaea Discovered? (cont’d.) © Cengage Learning 2015  19.8 Where Do Archaea Live? Archaeans are more diverse and widely distributed than previously thought – Many archaeans are: Methanogens (methane makers) Extreme halophiles (salt lovers) Extreme thermophiles (heat lovers) Archaeans coexist with bacteria in many habitats and can exchange genes with them © Cengage Learning 2015  Where Do Archaea Live? (cont’d.) A B © Cengage Learning 2015 C  19.9 Sharing Viruses Scientists use the knowledge of evolution to investigate how a new disease such as AIDS can arise and spread in the human population – By sequencing the HIV-1 genome and comparing it to genomes of primate viruses, researchers found that the human virus evolved from simian immunodeficiency virus (SIV), which infects wild chimpanzees © Cengage Learning 2015  Sharing Viruses (cont’d.) © Cengage Learning 2015