ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty Outline INTRODUCTION Simplest Organisms Are Bacteria Viruses Are Not Living Organisms Are fragments of a genome Cannot grow or replicate on their own Replicate only utilizing host cell`s machinery Important due to disease producing potential THE VIRUSES Viruses Are Unique Entities Are strands of nucleic acid encased in protein coats Cannot grow or replicate on their own, use machinery of host cell to reproduce Possess only one form of nucleic acid, either DNA or RNA True organisms contain both DNA and RNA Could never have existed independently as preexisting organisms The Discovery of Viruses Earliest observations near end of nineteenth century Concluded infectious agents of some diseases were not bacteria Included tobacco mosaic and hoof-and-mouth disease Infectious agents were not filtered out with fine porcelain filters Purification on tobacco mosaic virus by Stanley in 1933 Purified virus formed crystals fig 30.1 Considered agent chemical matter rather than living organism Structure of a basic virus fig 30.2 Protein coat in combination with a nucleic acid Rod about 300 nanometers long Tobacco mosaic virus specifically contained RNA Plant viruses have similar composition Most other viruses contain DNA Nearly all viruses form a protein sheath or capsid around nucleic acid core Many viruses form an envelope around capsid, rich in protein, lipid, glycoprotein Simple structure of viruses enhance study of genetics and molecular biology Viruses may be future means by which genetic traits are carried from one organism to another to treat human genetic diseases The Nature of Viruses Usually produce no disease or outward sign of presence Viruses are often highly host-specific, reproduce only within a certain host An organism may have more than one kind of virus May be many more viruses than there are kinds of organisms Mode of action Transmit nucleic acid component from one host cell to another Nucleic acid takes over host cell and produces more viruses Virulent viruses cause host cell to lyse and release new virus particles Temperate viruses become established in genome of host cell Viruses possess limited nucleotide sequences Ones associated with enzymes needed to replicate viral parts Make possible invasion of new cells Existence of prions demonstrated and under great study Infectious proteins not associated with nucleic acids Implicated as infectious agents in Alzheimer's disease Control of viruses Difficult as they completely integrate into host`s metabolism Immunization most effective control Antibiotics are useless because they act on features of living organisms Viruses being used as control agents for some kinds of bacteria The Structure of Viruses fig 30.3 Size Smallest = 17 nanometers in diameter Largest = 1000 nanometers in greatest dimension Few barely visible at light microscope level Most are visible only through electron microscopy Variable in appearance fig 30.2 Simplest is single molecule of nucleic acid surrounded by capsid More complex are many molecules surrounded by many different proteins fig 30.4 Two different shapes identified Helical have rod-like appearance Isometric have spherical appearance Form icosahedron structural pattern fig 30.3 Efficient symmetrical arrangement Bacteriophages fig 30.5 Infect bacteria, structurally and functionally diverse Double-stranded DNA viruses important in molecular biology Among most complex viruses T3 and T7 varieties are icosahedral with short tails Structure of T-even (T2, T4, T6) varieties Icosahedral head Capsid composed of three primary proteins Long tail Connecting neck with collar, long whiskers and complex base plate Progression of infection by T4 bacteriophage One of tail fibers contacts bacterial cell wall lipoproteins Other tail fibers set phage perpendicular to bacterial surface Base plate contacts cell surface Tail contracts, tail tube pierces bacterial cell wall Contents of head (DNA) injected into host cell cytoplasm fig 30.6 T -series bacteriophages are all virulent Lambda phage of Escherichia coli is a temperate phage Much known about its structure Complete sequence of bases identified, 23 proteins identified Viral Replication Occurs only when they enter host cells and use host's cellular machinery Carry genes that are translated into proteins by host cell Leads to production of more viruses Viruses contain only DNA or RNA, no ribosomes or other enzymes for protein synthesis or energy production Analogous to operation of a computer via a specific set of instructions Introduction of a new program will cause all operations to cease Computer will spend time making new copies of that introduced program Introduced program is not a computer, but merely a set of instructions Viruses and Disease tbl 30.1 Smallpox, chickenpox, measles, German measles, viral encephalitis, mononucleosis, mumps, shingles, influenza, colds, infectious hepatitis, yellow fever, fig 30.7 polio, rabies, AIDS Implicated in some cancers, leukemias, autoimmune diseases like multiple sclerosis, rheumatoid arthritis, diabetes Variolation practiced in China thousands of years ago Exposure to skin scabs of people who had survived smallpox Resulted in protection against contracting disease Observation and treatment by Edward Jenner Milkmaids exposed to milder cowpox rarely developed smallpox Deliberately vaccinated patients with cowpox viruses Smallpox was not contracted; treatment considered successful Lacked knowledge of antibodies and viruses Marberg virus cause some of most lethal diseases known to man fig 30.8 Include Ebola virus with lethality of over 90% Outbreak in 1995 threatened to spread worldwide A Viral Case Study: HIV AIDS first reported in U.S. in 1982 Infectious agent: human immunodeficiency virus (HIV) Closely related to African green monkey virus Etiology of the disease Affected individuals have no resistance to infection Rarely survive more than a few years, die of otherwise nonlethal diseases Transfer of body fluids poses most significant threat Incidence growing rapidly Clinical symptoms do not develop until after long period of latency How HIV compromises the immune system Normally a series of cells patrols bloodstream for invaders These cells are destroyed in AIDS patients, most specifically T4 cells The HIV infection cycle fig 30.9 Attachment HIV infects only T4 cells fig 30.10 Infects T4 cell by recognizing glycoprotein surface marker HIV glycoprotein precisely fits CD4 protein on T4 surface Cells lacking CD4 cannot be infected Entry Penetrates cell membrane, enters cell via endocytosis Protein coat shed Replication Single strand RNA with reverse transcriptase enzyme inside cell Viral RNA made into double-stranded DNA via reverse transcriptase Double-stranded DNA inserts itself into chromosomes of T4 cell Infected cell can remain latent or become active Latent cell: incorporates viral DNA into cell genome Active cell: virus directs production of copies of its genome Cell dies and lyses New viruses released to infect other T4 cells Latent cell can become active at later time Trigger to activate unknown, but associated with infections Latent cell activated by external stimuli Ultraviolet radiation Chemicals and carcinogens Other kinds of viruses Retroviruses (HIV) contain both RNA and reverse transcriptase Other viruses (cold virus) contain RNA but not reverse transcriptase Work without enzyme by using host's ribosomes and using RNA like mRNA Other viruses contain DNA: herpesviruses (cold sores and genital herpes), papillomaviruses (warts) Viruses: Particles of Genomes Origin as fragments of bacterial and eukaryotic genomes explains diversity New forms of viruses are evolving continuously THE BACTERIA Bacteria Are a Unique Group of Living Organisms Represent the oldest form of life fig 4.11 Only representatives of the prokaryotes Used to be classified as the only member of the kingdom Monera Present classification identifies two kingdoms of bacteria Archaebacteria Eubacteria Bacteria Are an Extremely Diverse Group of Organisms fig 30.11 Few major structural differences Species differentiation based on metabolic processes Characterized by growth on certain defined media Activities altered by growth conditions and chemicals Role of Bacteria Responsible for creating properties of atmosphere and soils Are autotrophic, photosynthetic and chemosynthetic, contribute to world carbon balance Are heterotrophic and break down organic compounds Only a few genera of bacteria are capable of fixing atmospheric nitrogen Involved in industrial processes and chemical syntheses Produce acetic acid, vinegar, amino acids, enzymes Production of various milk products, bread and ethanol Antibiotics derived from bacterial sources Genetic engineering applications PROKARYOTES VERSUS EUKARYOTES Structural Differences Multicellularity: bacteria are fundamentally single-celled fig 30.11e, 12 May adhere within matrix, some form filaments Few integrated activities between cells Primitive colonial forms include gliding bacteria fig 30.11d Cell size: extremely small individual cell size Chromosomes: non-membrane bound DNA is circular and lacks proteins Cell division and genetic recombination Simple division via binary fission True sexual reproduction absent, genetic recombination irregular Internal compartmentalization: Lack membrane-bound organelles Enzymes are bound to cell membrane Only organelles present are ribosomes Flagella: possess simple flagella fig 30.1a,c,13 Composed of single flagellin fiber Lack 9 + 2 structure of eukaryotic flagella and cilia fig 5.26 Flagellar motion resembles spinning propeller, not whip-like motion Metabolic Diversity: Eukaryotes exhibit only one form of photosynthesis Bacteria exhibit several patterns of photosynthesis, aerobic and anaerobic Bacteria undergo chemosynthesis and fix atmospheric nitrogen BACTERIAL STRUCTURE Cell Wall Structure Polysaccharide network with polypeptide crosslinks fig 30.14 Classed as gram-positive or gram-negative Gram-positive composed of polysaccharide network Gram-negative have additional lipopolysaccharide chains Gram-negative are less susceptible to antibiotics May be surrounded by gelatinous capsule General Morphology Cell shape Rod-shaped: bacilli Spherical: cocci Spirally coiled: spirilla Some form stalked structures that give rise to spores fig 30.11d After division individual cells may adhere forming chains Cyanobacteria regularly form large filamentous masses fig 30.12 Connected by outer walls or gelatinous sheaths May exhibit coordinated gliding or rotational movements Rigid, helical flagella composed of flagellin protein fig 5.8 Hairlike pili function in attachment and identification fig 30.13 Thick-walled endospores fig 30.15 Resistant to desiccation Resistant to heat, killed only by extremely high temperatures BACTERIAL VARIATION Mutation One in 200 bacteria will have mutant characteristics fig 30.16 Many mutants result from great number of individual cells Rapid multiplication in short time period Increase number with favorable mutations Rapidly changes characteristics of a population Plays important role in genetic diversity Example: development of antibiotic resistance Genetic Recombination Transfer of genes via viruses, plasmids, other DNA fragments Examples Rapid transfer of antibiotic resistant plasmids Transfer of pathogenic characteristics among enteric bacteria Rapid generation time is an alternative evolutionary strategy BACTERIA AS PLANT PATHOGENS Cause Costly Plant Diseases Symptoms are generally spots on stems, leaves or fruit Include blights, soft rots and wilts Most pathogens are rod-shaped pseudomonads fig 30.11a Example: Citrus Canker Caused by pseudomonad Xanthomonas campestris Introduced from abroad, causes serious economical damage in Florida BACTERIA AS HUMAN PATHOGENS Cause Many Human Diseases tbl 30.1 Examples: cholera, leprosy, tetanus, bacterial pneumonia, whooping cough, diphtheria Generally related to one of several genera Streptococcus: pneumonia, scarlet and rheumatic fevers fig 30.1b Staphylococcus: cause widespread infections Many bacterial diseases spread through food or water Insect vectors spread diseases like typhus Humans can contract disease from drinking cow milk, causes brucellosis in animals Tuberculosis One-third of all people worldwide infected with Mycobacterium tuberculosis Eight million new cases each year, three million deaths Leading cause of death from a single infectious agent Eradication programs dismantled in U.S. in 1980's Experiencing a dramatic resurgence of the disease Complicated by social factors, declining public health infrastructure Associated with prevalence of HIV Multidrug resistant strains of TB are developing Dental Caries Causes tooth decay and cavities Dental plaque composed of bacteria and polysaccharide matrix Involves many species of bacteria High sugar diets harmful Bacteria convert sugars to lactic acid Acid destroys hard tissue of tooth Control via fluoride by retarding loss of calcium Sexually Transmitted Diseases STDs caused by bacteria and viruses Viral STDs have no cure Bacterial STDs frequently mutate to drug-resistant strains Gonorrhea Most prevalent communicable disease, cause by Neisseria gonorrhoeae bacterium Transmitted during sexual activities through transfer of body fluids Can spread to eyes (conjunctivitis) and internal organs, cause arthritic meningitis Symptoms in women and men are generally mild and go unnoticed Treatment via combination of antibiotics Syphilis Less common as a result of blood-screening procedures and antibiotic treatment Caused by spirochaete bacterium, Treponema palladum Transmitted during intercourse, direct contact with sore or from mother to fetus Disease progresses in four distinct stages Primary stage characterized by chancre sore, highly infectious stage Secondary stage distinguished by body rash Third stage shows no symptoms, may last years Fourth stage is heart disease, mental deficiency, nerve damage, loss of motor functions, blindness Treated via antibiotics Genital herpes Caused by two types of closely related viruses Herpes simplex Type 1 causes cold sores and fever blisters Herpes simplex type 2 causes genital lesions of genital herpes Transmitted through sexual contact when open sores are evident Herpes virus in body travels along nerve endings to base of spine May remain dormant with no symptoms May become active and produce painful symptoms Initial outbreak produces measle-like lesions, flu-like symptoms May become dormant, outbreaks reappear with stress or exposure to sun Antiviral drugs can lessen severity of outbreaks, not a cure Transmission possible during outbreaks Chlamydia "Silent STD" caused by Chlamydia trachomatis bacterium Has both bacterial and viral characteristics Susceptible to antibiotics like bacterium Depends on host cell to replicate, like virus Transmitted via sexual intercourse Women usually do not experience symptoms until infection is established Can cause pelvic inflammatory disease Can lead to sterility, increase risk of acquiring HIV Symptoms in men include watery discharge, burning or itching Tests exist to identify bacteria in discharge Treatment via antibiotics mostly tetracycline, penicillin not effective Genital warts Caused by human papillomavirus (HPV) Transmission through contact with infected person fig 30.17 More than 30 strains, three known to cause cervical cancer Warts appear in genital region three weeks to three months after exposure Treatment through various agents to remove warts Archaebacteria and Eubacteria Archaebacteria are distinctly different from all other bacteria Base sequences of rRNA virtually identical in all members Differ from sequences in other bacteria and eukaryotes Cell walls lack muramic acid Have distinctive membranes, unusual cell walls, unique metabolic cofactors Capable of living in anaerobic atmosphere rich in CO2 and H2 Include oldest life forms, ancestral to Eubacteria and eukaryotes Independent evolution of each group Some have ribosomes similar to eukaryotes Others have smaller ribosomes like Eubacteria Include methanogens that produce methane gas Produce marsh gas, natural gas and reduce elemental sulfur Produce own anaerobic environment, cannot function in presence of oxygen Include other bacteria able to survive in inhospitable environments Thermoacidophiles Hot springs, deep sea thermal vents Use hydrogen sulfide as energy source Halophiles Salt-loving bacteria Use salt to generate ATP SIMPLE BUT VERSATILE ORGANISMS Simple Organisms with Diverse Metabolisms First Life on Earth and Only Life for Two Billion Years