18.1 Studying Viruses and Prokaryotes KEY CONCEPT Infections can be caused in several ways.

18.1 Studying Viruses and Prokaryotes Discovery of Viruses Beijerinck (1897) coined the Latin name “virus” meaning poison He studied filtered plant juices & found they caused healthy plants to become sick 2

18.1 Studying Viruses and Prokaryotes Tobacco Mosaic Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants He discovered viruses were made of nucleic acid and protein 3

18.1 Studying Viruses and ProkaryotesSmallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Deadly viruses are said to be - virulent Smallpox had been eradicated in the world today, but is now coming back 4

18.1 Studying Viruses and Prokaryotes Viruses are smaller than the smallest cellViruses are smaller than the smallest cell Measured in nanometersMeasured in nanometers Viruses couldn’t be seen until the electron microscope was invented in the 20 th centuryViruses couldn’t be seen until the electron microscope was invented in the 20 th century 5

18.1 Studying Viruses and Prokaryotes Size of Viruses 6

18.1 Studying Viruses and Prokaryotes Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen. viruses nm prokaryotics cells ,000 nm prion 2-10 nm viroids nm eukaryotics cells 10, ,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter

18.1 Studying Viruses and Prokaryotes A virus is made of DNA or RNA and a protein coat. –non-living pathogen –can infect many organisms A viroid is made only of single-stranded RNA. –causes disease in plants –passed through seeds or pollen

18.1 Studying Viruses and ProkaryotesViroids Small, circular RNA molecules without a protein coat Infect plants Potato famine in Ireland Resemble introns 9

18.1 Studying Viruses and Prokaryotes A prion is made only of proteins. –causes misfolding of other proteins –results in diseases of the brain

18.1 Studying Viruses and ProkaryotesPrions Prions are “infectious proteins” They are normal body proteins that get converted into an alternate configuration by contact with other prion proteins They have no DNA or RNA The main protein involved in human and mammalian prion diseases is called “PrP”11

18.1 Studying Viruses and Prokaryotes Prion Diseases Causes neurons to rapidly degenerate.Causes neurons to rapidly degenerate. Examples:Examples: Mad cow disease (bovine spongiform encephalitis: BSE)Mad cow disease (bovine spongiform encephalitis: BSE) People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemiesPeople in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies12

18.1 Studying Viruses and Prokaryotes Clicker Question Prions can be contracted by… A: Eating leftovers from the fridge. B: Eating the brain of an infected animal. C: Eating meat that has come into contact with the brain or spinal cord of an infected animal. D: Both B and C

18.1 Studying Viruses and Prokaryotes Clicker Question! What infectious element causes Mad Cow Disease? A: Phages B: Prions C: Viroids D: Plasma E: Virus

18.2 Viral Structure and Reproduction KEY CONCEPT Viruses exist in a variety of shapes and sizes.

18.2 Viral Structure and Reproduction Viruses differ in shape and in ways of entering host cells. Viruses have a simple structure. –genetic material –capsid, a protein shell –maybe a lipid envelope, a protective outer coat capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

18.2 Viral Structure and Reproduction Viral Characteristics Noncellular Have a protein coat called the capsid Have a nucleic acid core containing DNA or RNA Capable of reproducing only when inside a HOST cell17

18.2 Viral Structure and Reproduction Characteristics Some viruses are enclosed in a protective envelope Some viruses may have spikes to help attach to the host cell Most viruses infect only SPECIFIC host cells18 CAPSID ENVELOPE DNA SPIKES

18.2 Viral Structure and Reproduction Helical Viruses 19

18.2 Viral Structure and Reproduction Polyhedral Viruses 20

18.2 Viral Structure and Reproduction Complex Viruses 21

18.2 Viral Structure and Reproduction Used for Virus Identification RNA or DNA Virus Do or do NOT have an envelope Capsid shape HOST they infect22

18.2 Viral Structure and Reproduction Bacteriophages infect bacteria. capsid DNA tail sheath tail fiber

18.2 Viral Structure and Reproduction Viruses enter cells in various ways. colored SEM; magnifications: large photo 25,000; inset 38,000x –bacteriophages pierce host cells

18.2 Viral Structure and Reproduction25

26 Clicker Question - Phages A Bacteriophage or a phage is: A virus that infects a __________ cell. A.Plant B.Animal C.Bacteria D.Protista E.Fungi

18.2 Viral Structure and Reproduction –viruses of eukaryotes enter by endocytosis Viruses enter cells in various ways.

18.2 Viral Structure and Reproduction –viruses of eukaryotes also fuse with membrane Viruses enter cells in various ways.

18.2 Viral Structure and Reproduction host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle. Viruses cause two types of infections. A lytic infection causes the host cell to burst. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

18.2 Viral Structure and Reproduction 5 Steps of Lytic Cycle 1. Attachment to the cell 2. Penetration (injection) of viral DNA or RNA 3. Replication (Biosynthesis) of new viral proteins and nucleic acids 4. Assembly (Maturation) of the new viruses 5. Release of the new viruses into the environment (cell lyses)30

18.2 Viral Structure and Reproduction One-step Growth Curve 31

18.2 Viral Structure and Reproduction A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

18.2 Viral Structure and Reproduction The Lysogenic Cycle 33

18.2 Viral Structure and Reproduction Viral Latency Some viruses have the ability to become dormant inside the cell Called latent viruses They may remain inactive for long periods of time (years) Later, they activate to produce new viruses in response to some external signal HIV and Herpes viruses are examples34

18.2 Viral Structure and Reproduction Latency in Eukaryotes Some eukaryotic viruses remain dormant for many years in the nervous system tissues Chickenpox (caused by the virus Varicella zoster) is a childhood infection It can reappear later in life as shingles, a painful itching rash limited to small areas of the body35 SHINGLES

18.2 Viral Structure and Reproduction Latency in Eukaryotes Herpes viruses also becomes latent in the nervous system A herpes infection lasts for a person’s lifetime Genital herpes (Herpes Simplex 2) Cold sores or fever blisters (Herpes Simplex1)36 SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY

18.2 Viral Structure and Reproduction Clicker Question! Viruses replicate: A. On their own B. With other viruses by joining pili C. When ever they want to D. In a host cell only

18.2 Viral Structure and Reproduction38 All Viruses ONLY contain RNA. A. True B. False Clicker Question!

18.2 Viral Structure and Reproduction Retroviruses39

Characteristics of Retroviruses Contain RNA, not DNA Contain enzyme called Reverse Transcriptase When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell40

18.2 Viral Structure and Reproduction41 ENZYME

18.2 Viral Structure and Reproduction Retroviruses The enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) using virus RNA as a template42 RTase

18.2 Viral Structure and Reproduction Retroviruses HIV, the AIDS virus, is a retrovirus Feline Leukemia Virus is also a retrovirus43

18.2 Viral Structure and Reproduction Clicker Question! Retroviruses contain: A. tRNA B. DNA C. RNA D. rRNA E. mRNA

18.3 Viral Diseases KEY CONCEPT Some viral diseases can be prevented with vaccines.

18.3 Viral Diseases Viruses cause many infectious diseases There are many examples of viral infections. –common cold

18.3 Viral Diseases –influenza Viruses cause many infectious diseases There are many examples of viral infections. –common cold

18.3 Viral Diseases –influenza Viruses cause many infectious diseases There are many examples of viral infections. –common cold –SARS

18.3 Viral Diseases –HIV HIV-infected white blood cell Viruses cause many infectious diseases There are many examples of viral infections. The body has natural defenses against viruses.

18.3 Viral Diseases Characteristics Some viruses cause disease such as: Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola Some viruses may cause some cancers like leukemia50 MEASLES

18.3 Viral Diseases Vaccines are made from weakened pathogens. A vaccine stimulates the body’s own immune response. Vaccines prepare the immune system for a future attack. Vaccines are the only way to control the spread of viral disease.

18.3 Viral Diseases Herpes Virus 52 SIMPLEX I and II

18.3 Viral Diseases Adenovirus53 COMMON COLD

18.3 Viral Diseases Influenza Virus 54

18.3 Viral Diseases Chickenpox Virus 55

18.3 Viral Diseases Papillomavirus – Warts! 56