1 / 37

Fig. 19-1

Chapter 19. Fig. 19-1. 1.The simplest form of life 2.Exist on the borderline between the living and the inanimate, non-biological world 3. Reveal more complex life 4. Human disease. 0.5 µm. Fig. 19-9. (a) The 1918 flu pandemic. 0.5 µm. (b) Influenza A H5N1 virus. (c) Vaccinating ducks.

vadin
Download Presentation

Fig. 19-1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 19 Fig. 19-1 1.The simplest form of life 2.Exist on the borderline between the living and the inanimate, non-biological world 3. Reveal more complex life 4. Human disease 0.5 µm

  2. Fig. 19-9 (a) The 1918 flu pandemic 0.5 µm (b) Influenza A H5N1 virus (c) Vaccinating ducks

  3. RESULTS Fig. 19-2 Extracted sap from tobacco plant with tobacco mosaic disease Passed sap through a porcelain filter known to trap bacteria Rubbed filtered sap on healthy tobacco plants 3 1 2 • In 1935, Wendell Stanley confirmed this hypothesis by crystallizing the infectious particle, now known as tobacco mosaic virus (TMV) Healthy plants became infected 4

  4. Some evolutionary biologist: make more copies of their genome Viruses : nucleic acid + a protein coat (capsid), protection andentrance Viral genomes may consist of either Double- or single-stranded DNA, or Double- or single-stranded RNA Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus NA+ protein coat= nucleocapsid, in animal virus +a membranous envelope (the lipid membrane) A good source of pure DNA before the advent of gene cloning eg: SV40 virus (a ds DNA virus , 5 genes Obligate parasite (either as degenerate cells or renegade cellular genes) Rapid genetic change has obscured or erased ant relationships Structure of Viruses

  5. Virus particle or virion RNA Membranous envelope Head DNA RNA DNA Capsomere Fig. 19-3 Capsid Tail sheath Tail fiber Capsomere of capsid Glycoproteins Glycoprotein 18  250 nm 70–90 nm (diameter) 80  225 nm 80–200 nm (diameter) 20 nm 50 nm 50 nm 50 nm (a) Tobacco mosaic virus (b) Adenoviruses (d) Bacteriophage T4 (c) Influenza viruses

  6. Some viruses have membranous envelopes that help them infect hosts (membrane-scavenging strategy) These viral envelopes surround the capsids of influenza viruses and many other viruses found in animals (encephalitis virus, smallpox, rabies, herpes virus and the HIV) Viral envelopes, which are derived from the host cell’s membrane, contain a combination of viral (virus-encoded proteins) and host cell molecules (N-terminal protrude outwrd, C-terminal ofter contact the nucleocapsid) Easily dissolved by detergents but gastrointestinal viruses (including poliovirus) have purely protein viral envelopes

  7. Bacteriophages, also called phages, are viruses that infect bacteria They have the most complex capsids found among viruses Phages have an elongated capsid head that encloses their DNA A protein tail piece attaches the phage to the host and injects the phage DNA inside Bacteriophages

  8. The lytic cycle is a phage reproductive cycle that culminates in the death of the host cell The lytic cycle produces new phages and digests the host’s cell wall, releasing the progeny viruses A phage that reproduces only by the lytic cycle is called a virulent phage Bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA The Lytic Cycle

  9. The lysogenic cycle • The lysogenic cycle replicates the phage genome without destroying the host • The viral DNA molecule is incorporated into the host cell’s chromosome • This integrated viral DNA is known as a prophage • Every time the host divides, it copies the phage DNA and passes the copies to daughter cells

  10. Temperate phages • An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode • Phages that use both the lytic and lysogenic cycles are called temperate phages

  11. VIRUS Entry and uncoating 1 DNA Capsid Transcription and manufacture of capsid proteins 3 Fig. 19-4 Replication 2 HOST CELL • Adsorption penetration • cytoplasm (smallpox and RNA virus) or • nucleus (DNA virus) Viral DNA mRNA Capsid proteins Viral DNA Self-assembly of new virus particles and their exit from the cell 4

  12. The phage attaches to a host cell and injects its DNA Phage DNA Fig. 19-UN1 Bacterial chromosome Prophage Lytic cycle Lysogenic cycle • Virulent or temperate phage • Destruction of host DNA • Production of new phages • Lysis of host cell causes release • of progeny phages • Temperate phage only • Genome integrates into bacterial • chromosome as prophage, which • (1) is replicated and passed on to • daughter cells and • (2) can be induced to leave the • chromosome and initiate a lytic cycle

  13. Daughter cell with prophage Fig. 19-6 Phage DNA The phage injects its DNA. Cell divisions produce population of bacteria infected with the prophage. Phage DNA circularizes. Phage Bacterial chromosome Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lytic cycle Lysogenic cycle The bacterium reproduces, copying the prophage and transmitting it to daughter cells. The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered or Prophage Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages.

  14. There are two key variables used to classify viruses that infect animals: DNA or RNA? Single-stranded or double-stranded? Reproductive Cycles of Animal Viruses

  15. The Baltimore classification of viruses is based on the mechanism of mRNA production. Viruses must generate mRNAs from their genomes to produce proteins and replicate themselves, but different mechanisms are used to achieve this in each virus family. Viral genomes may be single-stranded (ss) or double-stranded (ds), RNA or DNA, and may or may not use reverse transcriptase (RT). Additionally, ssRNA viruses may be either sense (+) or antisense (−). This classification places viruses into seven groups:

  16. Table 19-1

  17. Host cell DNA polymerase and RNA polymerase to transcribe • The enzymes of DNA replication are generally not expressed in quiescent ceel (G0) most of the cell infected will be in G0 • : have large genomes that contain greater than 60 genes, encode rheir own DNA polymerase and ensure their ability replicate in quiescent cells. • Other viruses circumvent this problem by producing a protein that induces the resting host cell to enter the active cell cycle • 5. the virus and the viral growth-promoting proteins can drive the host cell into unceasing growth and cell division (oncogene) • HPV: cervical carcinoma • EB: mononucleosis • Burkitt’s lymphoma (a childhood tumor) in central Africa • Nasopharyngeal carcinoma in Southeast Asia Table 19-1a google

  18. SS DNA • A simple genome • Have a simple genome—one gene for a viral nucleocapside protein and another gene for a DNA replication enzyme • only template for transcription  ds DNA, 3’ as a primer + Table 19-1b 德國麻疹 馬象皮病毒 - Fig 19-7 • (+) ssRNA+ an mRNA • pico—small • mRNA make viral proteins  that can replicate the ssRNA genome as well as the proteins needed for the capsid.

  19. Capsid and viral genome enter the cell Capsid RNA Fig. 19-7 HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA Capsid proteins ER Copy of genome (RNA) Glyco- proteins The reproductive cycle of an enveloped RNA virus (Class V) --- Template for mRNA synthesis New virus

  20. 2009 flu pandemic

  21. Influenza hemagglutinin (HA) or haemagglutinin (British English) • is a type of hemagglutinin found on the surface of the influenzaviruses. • 2. It is an antigenicglycoprotein. It is responsible for binding the virus to the cell that is being infected. • 3. The name "hemagglutinin" comes from the protein's ability to cause red blood cells (erythrocytes) to clump together ("agglutinate") in vitro

  22. Viral neuraminidase is an enzyme on the surface of influenza viruses that enables the virus to be released from the host cell. Drugs that inhibit neuraminidase, known as neuraminidase inhibitors, are used to treat influenza. When influenza virus reproduces, it attaches to the cell surface using hemagglutinin, a molecule found on the surface of the virus which binds to sialic acid groups. Sialic acids are found on various glycoproteins at the host cell surface, and the virus exploits these groups to bind the host cell. In order for the virus to be released from the cell, neuraminidase must enzymatically cleave the sialic acid groups from host glycoproteins. In some viruses, a hemagglutinin-neuraminidase protein combines the neuraminidase and hemagglutinin functions in a single protein.

  23. Influenza virus replication

  24. De Clercq Nature Reviews Drug Discovery5, 1015–1025 (December 2006) | doi:10.1038/nrd2175

  25. The broadest variety of RNA genomes is found in viruses that infect animals Retroviruses use reverse transcriptase to copy their RNA genome into DNA HIV (human immunodeficiency virus) is the retrovirus that causes AIDS (acquired immunodeficiency syndrome) RNA as Viral Genetic Material

  26. Viral envelope Glycoprotein Capsid RNA (two identical strands) Reverse transcriptase HIV Fig. 19-8 Membrane of white blood cell HIV HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid 0.25 µm DNA HIV entering a cell NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus New HIV leaving a cell

  27. Viral envelope Glycoprotein Capsid RNA (two identical strands) Fig. 19-8a HOST CELL Reverse transcriptase HIV Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus

  28. Membrane of white blood cell HIV Fig. 19-8b 0.25 µm HIV entering a cell New HIV leaving a cell

  29. Emerging viruses are those that appear suddenly or suddenly come to the attention of scientists Severe acute respiratory syndrome (SARS) recently appeared in China Outbreaks of “new” viral diseases in humans are usually caused by existing viruses that expand their host territory Emerging Viruses

  30. Structure of the Virus

  31. Hypothesis: naked bits of cellular nucleic acisds that moved from one cell to another Mobile genetic elements Plasmid transposons Evolution of viruses

  32. 1.A specific cellular tRNA acts as a primer and hybridizes to a complementary part of the virus genome called the primer binding site or PBS 2.Complementary DNA then binds to the U5 (non-coding region) and R region (a direct repeat found at both ends of the RNA molecule) of the viral RNA 3.A domain on the reverse transcriptase enzyme called RNAse H degrades the 5’ end of the RNA which removes the U5 and R region 4.The primer then ‘jumps’ to the 3’ end of the viral genome and the newly synthesised DNA strands hybridizes to the complementary R region on the RNA 5.The first strand of complementary DNA (cDNA) is extended and the majority of viral RNA is degraded by RNAse H 6.Once the strand is completed, second strand synthesis is initiated from the viral RNA 7.There is then another ‘jump’ where the PBS from the second strand hybridizes with the complementary PBS on the first strand 8.Both strands are extended further and can be incorporated into the hosts genome by the enzyme integrase

  33. Reverse transcriptase Specific tRNA as primer 1.RNase H 2. RNA-dependent RNAP 1.RNase H 3. DNA-dependent DNAP

  34. Viral infection of plants Fig. 19-10

  35. Fig. 19-11 Model for how prions propagate Original prion Prion Aggregates of prions New prion Normal protein

  36. Fig. 19-UN3

More Related