Section 20.1

1. Section 20.1 Bacteria

2. What are Prokaryotes? • Prokaryotes – single-celled organisms that DO NOT have membrane bound organelles • Found in 3 shapes: • Rod shaped (bacillus) • Sphere shaped (coccus) • Spiral shaped (spirillum) • Prokaryotes divided into 2 groups: Archaea and Bacteria • Bacteria most common • 1 square inch of skin has about 100,000 bacteria!!

3. Bacterial Structure • Have internal structures, even though not surrounded by membranes • Have DNA • In a single chromosome clustered in a mass called a nucleoid • Often have small extra loops of DNA called plasmids • Plasmids – have ‘special’ genes that are not related to basic life functions • Ex) antibiotic resistance

4. Bacterial Structure • Have ribosomes and many types of enzymes • Have granules of stored nutrients • Have lipid bilayers • Surrounded by a rigid cell wall • 1-2 layers thick • Made of peptidoglycan • Can also be covered by a membrane

5. Bacterial Structure • The presences of this membrane allows biologists to group bacteria into two categories using Gram staining: • Gram-positive – have a large amount of peptidoglycan and no outer membrane • Stain dark purple b/c thick cell wall absorbs dye • Gram-negative – have a small amount of peptidoglycan can have an outer membrane • Stain pink • Useful, b/c gram-negative bacteria are more resistant to host defenses and to medicine

7. Obtaining Energy and Nutrients • Bacteria differ in how they obtain energy and nutrients • Separated into 3 groups • Photoautotrophs • Chemoautotrophs • Heterotrophs

8. Obtaining Energy and Nutrients • Photoautotrophs • Get energy from sunlight through photosynthesis • Include: • Purple sulfur and nonsulfur bacteria • Green sulfur bacteria • Cyanobacteria • Green and purple sulfur bacteria can grow only in oxygen-free environments

9. Obtaining Energy and Nutrients • Cyanobacteria are abundant today • Major component of plankton • Produce a great deal of our oxygen • Probably formed Earth’s oxygen atmosphere

10. Obtaining Energy and Nutrients • Chemoautotrophs • Only organisms that can get their energy from inorganic sources • Use molecules that contain sulfur or nitrogen • Can make their own amino acids and proteins from hydrogen-rich chemicals

11. Obtaining Energy and Nutrients • Heterotrophs • What most prokaryotes are • Get energy from both their nutrients and other organisms • Most absorb nutrients from dead organisms • But some are parasites or pathogens • Ex) Salmonella, anthrax, syphilis, staph infections

12. http://www.youtube.com/watch?v=iResq8dA3Eg

13. Reproduction an Adaptation • Prokaryotes usually reproduce asexually through binary fission • Makes identical cells • BUT mutations do occur during reproduction and new forms emerge frequently • There are 3 ways that prokaryotes can form new genetic combinations

14. Reproduction an Adaptation • Conjugation • Occurs when two bacteria exchange genetic material • http://www.youtube.com/watch?v=EtxkcSGU698 • Transformation • Occurs when bacteria take up DNA fragments from their environment • Transduction • Occurs when genetic material is transferred by a virus • Often convey antibiotic resistance • http://www.youtube.com/watch?v=-QeMZQCD22w

15. Reproduction an Adaptation • Endospore Formation • Some bacteria survive harsh conditions by forming thick walled structures called endospores • Form inside the bacteria • Surround the DNA and a small bit of cytoplasm • Endospores can survive boiling, radiation, and acid • Show no signs of life • Can be revived after hundreds of years

16. REVIEW • Explain the difference between Gram-positive and Gram-negative bacteria • List AND describe the 3 ways that bacteria can obtain energy • List AND describe the different shapes of bacteria • Which type of bacteria gets energy from inorganic molecules? • Coccus bacteria • Chemoautotrophs • Heterotrophs • Photoautotrophs

17. Section 20.2 Viruses

18. Is a Virus Alive? • Viruses are NOT considered living • Have genetic material, but CANNOT reproduce on their own • Reproduce by infecting cells • Use the cell’s ribosomes, ATP, enzymes, and other molecules to make more viruses

19. Is a Virus Alive? • Viruses do not grow • Are assembled into their full size w/i a cell • Viruses do not carry out metabolic activities • Viruses do not have any cytoplasm or organelles • Viruses do not maintain homeostasis

20. Viral Structure • All viruses have 2 structures • Capsid – a protein coat that surrounds the genetic material • Viruses recognize their hosts by specific proteins on the host cell’s surface • Must match the proteins on the virus • Envelope – membrane-like layer that covers the capsid

21. Viral Structure • The genetic material of a virus can be either RNA or DNA • DNA viruses • The genetic material can become inserted into the host cell’s DNA • The virus makes copies of its DNA by using the host cell’s enzymes and nucleotides • Viral DNA also directs production of mRNA and proteins that are assembled into new viruses

22. Viral Structure • RNA Viruses • Reproduction occurs by 1 of 2 methods • Method 1: viral RNA is used directly to make mRNA • Then used to make more viral RNA • Method 2: viral RNA is transcribed into DNA • Then inserted into the host cell’s DNA • Then transcribed into viral mRNA

23. Reproduction • A viral infection begins when the genetic material of a virus enters a host cell • Once inside the cell, a virus can reproduce by 2 different processes • Lytic Life Cycle • Lysogenic Life Cycle

24. Reproduction • Lytic Cycle • Viral genetic material enters a cell but remains separate from the host cell’s DNA • The virus uses the host cell’s organelles to replicate the virus’s DNA and to make viral proteins • Proteins are assembled and form complete viruses • The host cell breaks open, releases newly made viruses, and dies

26. Reproduction • Lysogenic Cycle • Viral DNA becomes part of the host cell’s DNA • When host cell replicates its own DNA, also replicates the virus • New virus particles are not assembled, and the host cell is not destroyed • After days, months, or years, the virus may leave the host’s DNA and enter the lytic cycle • If the virus never enters the lytic cycle, it may become a permanent part of its host’s genome

28. Viroids and Prions • Viroid – single strand of RNA that has no capsid • Can replicate inside a host’s cell to make new viroids • Cause abnormal development and stunted growth in plants • Prions – nonfunctioning, misshapen versions of proteins • Attach to normal proteins in the brain • The misfolding spreads and destroys brain tissue • Transmitted by eating food contaminated w/ infected brain tissue

29. Koch’s Postulates and Disease Transmission • German physician Robert Koch developed a technique for diagnosing the cause of an infection • His 4-step procedure is known as Koch’s postulates • This technique is still used today to identify a disease-causing agent (pathogen)

30. Koch’s Postulates and Disease Transmission • Step 1: The pathogen must be found in an animal w/ the disease and not in a healthy animal • Step 2: The pathogen must be isolated from the sick animal and grown in a laboratory culture • Step 3: When the isolated pathogen is injected into a healthy animal, the animal must develop the disease • Step 4: The pathogen should be taken from the second animal, grown in the lab, and shown to be the same as the original pathogen

32. Koch’s Postulates and Disease Transmission • Diseases that can spread from person to person are considered contagious • Some contagious diseases must be transmitted directly from one host to another by contact • Others can survive outside the host for a period of time • These are transmitted through air, food or water, or contaminated objects

33. Bacterial Diseases • Bacteria can cause disease by producing toxins and by destroying body tissues • The most common way that bacteria cause disease is by producing poisonous chemicals called toxins • Released or stored inside the bacteria until it dies • Second way: producing enzymes • These break down the host’s tissues into nutrients the bacteria can use

34. Antibiotic Resistance • Antibiotics – chemicals that inhibit the growth of or kill microorganisms • Antibiotic resistance is the ability of bacteria to tolerate antibiotics • Mutations for antibiotic resistance arise naturally and often • Plasmids containing antibiotic-resistance genes can pass between bacteria during conjugation

35. Antibiotic Resistance • Disease that were once easy to treat with antibiotics are now more difficult to • Some bacteria are resistant to multiple antibiotics • Once resistant to one, physicians must switch to a different antibiotic • Bacteria will probably develop resistance to those • Cycle continues

36. Viral Diseases • Viruses cause disease in bacteria, plants, and animals • It is difficult to develop a drug that kills the virus without harming the living host • Viruses have been shown to cause some types of cancer

37. Viral Diseases • Symptoms of viral illness can be caused by several factors • Common: aches and fever • Result from the body’s response to infection • Many viral diseases can be prevented through vaccination • Vaccine – a weakened form of a pathogen that prepares the immune system to recognize and destroy the pathogen

38. Vaccine • Inactivated vaccine • Made by growing virus in tissue culture • Then treating the virus w/ formaldehyde • This causes the virus to not reproduce in the person who receives the vaccine • The use of the whole virus stimulates immunity to antigens on the virus surface • Ex) polio vaccine

39. Vaccine • Weakened Vaccine • More potent than killed ones • The pathogen is grown in animals or tissue culture under conditions that make it less virulent

40. Vaccine • Weakened vaccines stimulate generation of memory cells in the human immune system • Disadvantage: may very rarely revert back to its virulent form and cause disease

41. Emerging Diseases • Emerging diseases are: • Diseases that are newly recognized • Diseases that have spread to new areas or to a new host • Diseases that have reemerged when a disease that was once considered under control begins to spread

42. Emerging Diseases • Diseases can spread to new areas or a new host when people come into contact w/ a pathogen in a different way than in the past • Environmental changes can play a role • Human behavior also can cause disease emergence

43. Roles of Bacteria and Viruses • Both bacteria and viruses play a vital role in all of Earth’s ecosystems • Make oxygen, decomposing stuff • Bacteria are important in industries such as food production, chemical production, mining, and environmental cleanup • Bacteria and viruses also have been important in genetic research

44. REVIEW • List the four steps of Koch’s postulates • Explain why it is difficult to develop a cure for viral diseases • Explain why viruses are not considered to be living organisms • A virus kills its host cell during • Conjugation • The lytic cycle • The lysogenic cycle • Assembly of the capsid