Presentation on theme: "Bacteria and Viruses Chapter 19. 19-1 Bacteria Common name for all prokaryotes unicellular organisms without a nucleus Were all in Monera Eubacteria live."— Presentation transcript:
19-1 Bacteria Common name for all prokaryotes unicellular organisms without a nucleus Were all in Monera Eubacteria live nearly everywhere normally protected by cell wall containing peptidoglycan - cell membrane inside of cell wall Archaebacteria lack peptidoglycan DNA similar to eukaryotic DNA most are extremophiles – live in harsh environments methanogens; halophiles; extreme thermophiles
Prokaryotic Body Plan bacterial flagellum pilus capsule cell wall plasma membrane cytoplasm DNA ribosomes in cytoplasm
Identifying Prokaryotes 1.Shape a. bacilli(us) – rod-shaped b. cocci(us) – spherical c. spirilla(us) – spiral and corkscrew shaped 2. Cell Walls a. Gram-positive – have thick peptidoglycan cell walls that take and hold stain b. Gram-negative – thinner cell walls with lipids on outside – does not hold stain 3. Movement
Metabolic Diversity 1.Chemoheterotrophs – must take in organic molecules for energy and a supply of carbon 2. Photoheterotrophs – use photosynthesis for energy, but take in organic compounds for carbon source 3. Photoautotrophs – use photosynthesis for both energy and carbon source 4. Chemoautotrophs – use chemosynthesis – get energy from chemical reactions and use carbon dioxide as carbon source
Releasing Energy -bacteria release energy by cellular respiration and fermentation A.Obligate Aerobes - require a constant supply of oxygen B. Obligate Anaerobes - must live in the absence of oxygen C. Facultative Anaerobes - can survive with or without oxygen
Growth and Reproduction -under good conditions bacteria can reproduce every 20 minutes Binary Fission -normal asexual reproduction of bacteria -replicate DNA and then divide Conjugation -exchange of genetic material between bacterial cells -increases genetic diversity Spore Formation - allows survival of bad conditions for a long time
Prokaryotic Fission - 1 DNA replication begins Bacterium before DNA replication bacterial chromosome Figure 21.7 Page 350
Prokaryotic Fission - 2 parent DNA molecule DNA copy DNA replication completed Membrane growth moves DNA molecules apart
Prokaryotic Fission - 3 New membrane and cell- wall material deposited Cytoplasm divided in two
Conjugation nicked plasmid in donor cell conjugation tube to recipient cell Transfer of plasmid
Importance of Bacteria -while we usually think of bacteria negatively they are actually essential to correct functioning in ecosystems A.Decomposers - primary decomposers who make nutrients available to plants - used in sewage treatment plants also B. Nitrogen Fixers - Rhizobium in nodules of legume roots fix nitrogen in a form the plants can use
C. Human Uses in food production in industry – can clean-up oil spills to synthesize drugs and chemicals genetic engineering now has them producing human hormones Mutualism with Eschecaria coli in our colon where they help us make vitamins
19-2 Viruses - virus means “poison” What is a Virus? non-living – no metabolism and can’t reproduce on their own DNA or RNA core surrounded by a protein coat use a living cell’s internal structures to reproduce themselves Capsid – protein coat - often with proteins on it that help it invade a host cell – often highly specific once inside the host the viral genes get the host cell to make viral proteins and DNA/RNA
-bacteriophage – a virus that attacks bacteria Viral Infection 1.Lytic Infection - virus enters a cell; has copies of itself made; and causes cell to burst and release more viruses 2. Lysogenic Infection - virus enters a cell and has its DNA integrated into the DNA of the host cell - as cell replicates its DNA it also replicates the viral DNA - prophage – viral DNA embedded in host DNA
Lytic Pathway Stepped Art Fig. 21.20 Page 358 Virus particles bind to wall of suitable host. Viral genetic material enters cell cytoplasm. Viral DNA directs host machinery to produce viral proteins and viral DNA. Viral protein molecules are assembled into coats; DNA is packaged inside. Tail fibers and other parts are added to coats. Lysis of host cell is induced; infectious particles escape.
Lysogenic Pathway Stepped Art Fig 21.20 (2) Page 358 Viral DNA usually becomes integrated into the bacterial chromosome. Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated. After binary fission, each daughter cell will have recombinant DNA. Viral DNA is excised from chromosome and cell enters lytic pathway.
- may stay inactive for a long time - eventually something causes the DNA of the prophage to be activated and it enters the Lytic cycle and destroys the host cell Retroviruses Viruses which have RNA as genetic material When they infect a cell the cell first makes DNA from RNA template (reverse transcription) DNA inserts into cell’s DNA and can stay dormant Can cause some cancers, HIV causes AIDS, colds (Copy Figure 19-11)
19-3 Diseases Caused by Bacteria and Viruses While most bacteria and viruses are not harmful a few are pathogens (disease causing) -Disease results when a virus or bacteria interfere with the host’s ability to get enough nutrients or energy -Louis Pasteur developed the Germ Theory of Disease when he proved that bacteria can cause disease Bacteria cause disease by directly breaking down cells for food or by releasing toxins that travel throughout the body and interfere with normal activity in the host.
-Vaccines are used to stimulate the immune system by exposing it to a dead or weakened pathogen. -Antibiotics are used against bacterial infections that the immune system doesn’t beat. -Bacteria can be controlled by sterilization with heat; disinfectants; and correct food processing and handling.
Viral Disease -Viruses produce disease by disrupting the body’s normal equilibrium -Most viruses are very specific in what cells they attack – polio only attacks motor neurons -Viral infections cannot be treated with antibiotics.