1. Ch. 19 Bacteria and Viruses

2. Ch. 19 Outline 19-1: Bacteria Classifying prokaryotes
Identifying Prokaryotes
Metabolic Diversity
Growth and Reproduction
Importance of Bacteria

3. Ch. 19 Outline
19-2: Viruses
What is a virus?
Viral Infection
Retroviruses
Viruses and Living Cells
19-3 Diseases caused by bacteria and viruses
Bacterial Diseases in Humans
Controlling Bacteria
Viral Diseases
Viroids and Prions

4. Bacteria
Once microscopes were invented, scientists discovered a world of microorganisms.
Prokaryotes: Single celled organisms that lack a nucleus
All prokaryotes are bacteria

5. Classifying Prokaryotes
Bacteria
are classified into the kingdoms of
Eubacteria
Archaebacteria
include a variety of lifestyles such as
live in harsh environments such as
Infecting large organisms
Thick mud
Living in soil
Animal digestive tracts
Salty lakes
Hot springs

6. Classifying Prokaryotes
Two kingdoms of bacteria: Eubacteria, archaebacteria
Eubacteria: the larger of the two kingdoms
Cell walls have peptidoglycan
Found almost everywhere
Archaebacteria: lack peptidoglycan
DNA Sequences more like eukaryotes than eubacteria
Live in extreme environments (Some with no oxygen)
Ex. Methanogens  produce methane gas

7. Identifying Prokaryotes
Prokaryotes are identified by characteristics such as shape, the chemical nature of their cell walls, the way they move, and the way they obtain energy.

8. Identifying Prokaryotes
Shapes
Rod-shaped  Bacillus
Spherical  Coccus
Spiral  Spirillum
If a Bacterial species tends to collect into long strands, so that they look long strings under the microscope, they will be named with the prefix strepto-
If a Bacterial species forms clumps or clusters, they will be named with the prefix staphylo-

9. Bacterial Structure

10. Identifying Prokaryotes
Cell Walls
The Method called Gram Staining can reveal if a bacteria’s cell wall has peptidoglycan in it.
Gram positive bacteria  have thick cell walls with peptidoglycan and turn violet after the test.
Gram negative bacteria  thin cell walls and turn pink after the test

11. Gram Staining

12. Cell Walls
What does the type of cell wall have to do with a bacterium’s susceptibility to antibiotics?
Gram negative bacteria’s extra layer outside the cell wall can make it hard for some antibiotics to get inside the cell (where they can work). That makes it important for a doctor to know what kind of bacteria is causing the infection so that most effective antibiotic can be used to treat it.

13. Identifying Prokaryotes
Movement:
Some don’t move at all; some move by flagella; glide over slime-like material they secrete; snake or spiral forward.

14. Metabolic Diversity Bacteria obtain energy in different ways.
Heterotrophs
Chemoheterotrophs – must take in organic molecules for food and energy
Photoheterotrophs – photosynthetic but also must take in organic compounds (small group)

15. Metabolic Diversity Autotrophs Photoautotrophs – photosynthetic
Chemoautotrophs – make their own food using the energy in chemicals (not the sun)

16. Metabolic Diversity Releasing Energy
Bacteria need a constant supply of energy just like all other living organisms. (CR/fermentation)
Obligate aerobes: require a constant supply of oxygen to live
Obligate anaerobes: must live in the absence of oxygen
Facultative aerobes: can survive with or without oxygen
Can live almost anywhere!

17. Growth and Reproduction
Bacteria grow and divide very rapidly. Their method of division is called binary fission
Grows until double in size, copies DNA and simply splits into two daughter cells
Asexual form of reproduction (no exchange of genetic material)

18. Growth and Reproduction
Conjugation: A process of exchanging genetic info in bacteria
A bridge forms between two bacterial cells and genes move from one cell to the other
Lead to Genetic diversity of bacteria

19. Conjugation

20. Growth and Reproduction
When growth conditions are unfavorable, many bacteria produce spores, which can remain dormant until the right conditions are there.
Endospore: one type of spore formed when a bacterium produced a thick internal wall that encloses its DNA and some cytoplasm

21. Endospores

22. Importance of Bacteria
We could not survive without bacteria. Some are producers, others are decomposers, and some are used by humans for various things.
Decomposers
Bacteria help recycle nutrients in the environment
Breakdown complex molecules in sewage

23. Importance of Bacteria
Nitrogen Fixers
Plants and animals need nitrogen to make amino acids, but they can’t get it from the air
Bacteria convert N2 from the air into a molecule that plants can absorb (and animals then get it from eating plants)

24. Importance of Bacteria
Human Uses of Bacteria
Produce foods and beverages
Industry  cleaning up oil spills
Remove waste and poisons from water
Synthesize drugs and chemicals (genetic engineering)
Produce vitamins in human intestines

25. Pathogenic bacteria How do bacteria cause damage or disease?
a. Your body contains plenty of protein, minerals, carbohydrates, vitamins, and many other resources that bacteria need to survive and when they compete with your body for those nutrients, it can make you sick.

26. Pathogenic Bacteria
Heterotrophic bacteria secrete enzymes that break down the organic structures (usually our cells) in their environment so they can absorb the nutrients in them; it is this destruction of cells that causes you problems
Another way bacteria can make us sick is by secreting toxins (poisons) either directly in our bodies or in the food we eat, which is often the case with types of food poisoning.

27. Food Poisoning
Staphylococcus aureus causes the most common type of food poisoning, which results in painful diarrhea, nausea, and vomiting
Botulism (Clostridium botulinum) from canned food that has not been sterilized properly can cause paralysis and death.
Salmonella bacteria (from undercooked pork, poultry, eggs) cause vomiting, diarrhea, and stomach cramps, which can lead to dehydration and death (especially in the very young or very old)

28. Food Poisoning
Eschericha coli are normal inhabitants of our intestines, but a new strain of E. coli (O157:H7) has caused illness and death for people who ate undercooked hamburger meat.
Pasteurization – heating food to a temperature that kills most bacteria – helps reduce the risk of food poisoning.

29. Bacteria Table

30. What is a Virus?
Viruses: particles of nucleic acids, proteins (and sometimes lipids)
Viruses are NON-LIVING, but they do reproduce. They infect a living cell and use its machinery to replicate itself.
Structure of a virus:
A typical virus is composed of a core of DNA or RNA surrounded by a protein coat.
Capsid: the protein coat

31. Viral Structures

32. What is a Virus?
Viruses bind to proteins on the surface of cells. They “trick” the cell into allowing it inside. Once inside, the viral genes are expressed, producing copies of the virus (and sometimes killing the cell).

33. What is a Virus? What can be infected by a virus?
Animals
Plants
Bacteria
Fungi
Bacteriophages: viruses that infect bacteria

34. Viral Infection
There are two types of viral infections: lytic and lysogenic
Lytic Infection
The virus enters the cell, makes copies of itself, and causes the cell to burst
Lysogenic Infection
The Viral DNA becomes part of the host DNA and is replicated along with it (Prophage: viral DNA in the host DNA)
The prophage stays part of the DNA for many generations before it becomes active.

35. Lytic Vs. Lysogenic

36. Retroviruses
Retroviruses: viruses that have RNA as their genetic material.
They get their name from how their genetic material is copied … backwards!
When they infect a cell, their RNA is copied into DNA
Ex. AIDS is a retrovirus

37. Viruses and Living Cells
Like living things, viruses reproduce and evolve. However, they are not considered living things for the following reasons:
They are not made of cells
They do not metabolize
They do not grow

38. Bacterial Diseases in Humans
Pathogen: disease-causing agents
Louis Pasteur was the first scientist to show the bacteria causes disease.
Bacteria produce disease in one of two ways:
Damage the cells and tissue of the infected organism by breaking down the cells for food
Release toxins that travel throughout the body and interfere with normal activity of the host.

39. Preventing bacterial disease
Vaccine: preparation of weakened of killed pathogen
Prompts body’s immune system (more in Ch. 40!)
Antibiotics: compounds the block the growth of reproduction of bacteria

40. Preventing bacterial disease
Controlling Bacteria
There are various methods used to control bacterial growth:
Sterilization (killing them with heat)
Disinfectants (chemicals that kill bacteria)
Food Processing (storing food in refrigerators, cooking food)

41. Antibiotics
Antibiotic-resistant bacteria – bacteria that have genes that make them no longer susceptible to the effects of antibiotics
Genetic mutations for antibiotic resistance happen spontaneously as a result of errors in DNA replication
Taking Antibiotics eliminates the susceptible bacteria from the population and leaves the resistant bacteria, allowing them to reproduce and pass on their resistant traits (bacteria reproduce very rapidly!!!)

42. Antibiotics
Antibiotic misuse: Usually, if a full course of an Antibiotic is taken, all the targeted bacteria are killed and there is no chance for a resistant strain to develop; but if the antibiotic is stopped early, the surviving bacteria will be the ones that were most resistant to the antibiotic

43. Antibiotics
There are now strains of tuberculosis and S. aureus that are resistant to multiple drugs = hard to treat!
Widespread use of antibacterial soaps can encourage antibiotic resistant strains of bacteria.

44. Viral Diseases
Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium.
Viral diseases cannot be treated with antibiotics, but there are some vaccines against viruses.

45. Viral Diseases Some viruses can also cause cancer:
Hepatitis B (transmitted by blood or sexual contact, it attacks the liver) – liver cancer
Epstein-Barr virus – (the virus that causes mono or even chronic fatigue syndrome) – Burkitt’s lymphoma
Human papilloma virus (causes warts) – the sexually transmitted genital warts can lead to cervical cancer in women.

46. Virus Disease Table

47. Viroids and Prions
Scientists have discovered two other virus-like particles that also cause disease: Viroids and Prions
Viroids: Single-stranded RNA molecules that have no surrounding capsids
Affect Plant Cells

48. Prions Prions – a molecule made of protein, but with no nucleic acid
Disease-causing prions are folded into the wrong shape, which does not allow it to function as it should.
If a normal prion comes into contact with a disease-causing one, the normal one will also change its shape so that it is folded wrong and no longer functions either; in this way, the disease spreads
Ex: Scrapie (sheep), mad cow disease, Creutzfeldt-Jacob disease (in humans) are all brain diseases that can be distributed by eating meat that contains the disease-causing prion.