Bacteria and Viruses

Chapter 19

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 flagellumpilus

capsule

cell wall

plasma membrane

cytoplasm

DNA

ribosomes in cytoplasm

Identifying Prokaryotes1.Shape

a. bacilli(us) – rod-shapedb. cocci(us) – sphericalc. spirilla(us) – spiral and corkscrew shaped

2. Cell Wallsa. 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 Diversity1.Chemoheterotrophs – must take in organic

molecules for energy and a supply of carbon2. 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 fermentationA.Obligate Aerobes

- require a constant supply of oxygenB. Obligate Anaerobes

- must live in the absence of oxygenC. Facultative Anaerobes

- can survive with or without oxygen

Growth and Reproduction-under good conditions bacteria can reproduce every 20 minutesBinary Fission-normal asexual reproduction of bacteria-replicate DNA and then divideConjugation-exchange of genetic material between bacterial

cells-increases genetic diversitySpore Formation- allows survival of bad conditions for a long time

Prokaryotic Fission - 1

DNA replication

begins

Bacterium before

DNA replication bacterial chromosome

Figure 21.7Page 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

Conjugationnicked plasmid

in donor cellconjugation tubeto 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 bacteriaViral Infection1.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 ArtFig. 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 ArtFig 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 VirusesWhile 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 diseaseBacteria 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.

Lyme Disease

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.