Download - Viruses – Chp. 25
VIRUSES – CHP. 25
Pathogen – any organism that causes disease. Exs.) virus, bacteria, protozoan.
Some Examples of VIRUS Illnesses : Polio, Chicken Pox, Shingles, Hepatitis, Flu, AIDS, Common Cold.
Are Viruses Living or Non-Living?? :
- Scientists debate this because viruses do not require food, oxygen, water……yet they can reproduce (note – they only reproduce inside a living host cell).
Bacteriophage – viruses that only attack bacteria. Ex.) T-4 virus
T-4 Virus – a famous virus in scientific circles.
- It only attacks bacteria – it is safe to humans.
- It is easy to grow in petri dishes and cost is minimal.
- Because of the above factors, T-4 makes a good research specimen.
- T-4 is famous because it has been widely studied. Most of our early knowledge about viruses came from studying T-4.
Virus Structure – made up of a coat and a core.
- Coat is outer protective covering made of protein.
- Core is made up of the genetic material DNA or RNA.
Lytic Cycle – reproductive cycle for regular viruses. See figure 25-5 on page 492 in book.
Stages of Lytic Cycle:1. Attachment – virus latches onto cell.2. Entry – virus injects its DNA into cell.3. Replication – virus DNA takes over the
cell’s machinery and directs it to make virus parts.
4. Assembly – virus parts get put together.5. Release – newly made viruses break out
of cell and can now go and attack more cells. (note – the cell dies in the process).
Lysogenic Cycle – reproductive cycle for LATENT viruses.
Latent Viruses – infect you now, but do not make you sick for a period of time. Exs.) HIV, Herpes, Shingles.
3 Major Ways That Germs are Transmitted
1. Airborne Transmission – enter the body with the air breathed in. Exs.) smallpox, chicken pox, polio, measles, flu, common cold.Prevention – vaccines, avoid sick people, cover your mouth when sneezing and coughing.
2. Food and Water Transmission – most effect stomach and intestines. Gets into food/water from intestinal wastes. Exs.) hepatitis A, salmonella, botulism, E. coli.
Prevention – good hygiene, wash hands, check canned food for damage, keep foods refrigerated/frozen, cook meats/eggs well done, have drinking water tested.
3. Contact Transmission – shaking hands, kissing, touching, sex, sharing cups, towels, etc.
- Watch wounds of all kindsPrevention – practice safe sex, good hygiene,
disinfect wounds.
Chapter 25 - Bacteria
Classification Kingdoms of Bacteria
1. Archaebacteria – rare – only found in a few places on earth. Exs.) in the boiling water of hot springs, in very salty waters where no other bacteria thrive, at the ocean vents where water is superheated.
Eubacteria – “true” bacteria – common, everyday bacteria. They are found just about everywhere, including in and on our bodies.
Prokaryotic Cells (Prokaryotes) = Bacteria- Thought to be the oldest cells on earth.- Do not have a true nucleus that houses the DNA.
Bacterial DNA just floats unprotected inside the cell.
- Very simple structure. They do not have any parts that are seen in more complex cells.
- ***BACTERIA ARE THE ONLY CELLS ON EARTH THAT ARE PROKARYOTIC.***
Bacterial Shapes – Used for Identification
1. Coccus (Cocci) 2. Bacillus (Bacilli) 3. Spirillum (Spirilla)
1. Coccus (Cocci) – round, sphere shaped.
- Diplococcus – 2 joined in a pair.- Staphylococcus – clumps/clusters of
cells…many cause “staph” infection.- Streptococcus – strips/chains of
cells…. cause “strep” throat.- Tetrad – 4 cells arranged in a square.
2. Bacillus (Bacilli) – elongated rod shapes
- Diplobacillus – 2 joined.- Streptobacillus – strips/chains.
3. Spirillum (Spirilla) – bent rods like a boomerang, or corkscrew shaped. Spirilla only occur in the single form, they do not join together in any way.
See top of page 470 in book.
Nutrition in Bacteria
Autotrophs – “Cyanobacteria” – SOME bacteria are photosynthetic and can make there own food.
Heterotrophs – MOST bacteria rely on other organisms to make food for them. 2 types:
- Saprophytes – get food from dead organisms….many of these bacteria compete with us for our food and spoil it.
- Parasites – get food from living cells. These are the pathogens that infect us and make us sick.
Respiration in Bacteria
Obligate Aerobes – require oxygen and cannot live without it…….most bacteria.
Obligate Anaerobes – do not grow in the presence of oxygen. They use other gases such as methane or they conduct fermentation.
Facultative Bacteria – live with or without oxygen. They grow faster with oxygen.
Factors That Affect the Growth of Bacteria
1. Temperature :- 79 – 100 degrees Fahrenheit – optimum growth
range for many bacteria.- Refrigeration/cooking inhibits bacteria.- Body uses fever as defense mechanism to kill off
temperature sensitive bacteria.2. Moisture:- Bacteria are 90% water and dryness makes them
inactive- We dry many foods to preserve them such as
pasta, dried fruit and beans, cereal, rice, potatoes.
3. Radiation – sunlight and ultraviolet light kills bacteria by mutating their DNA.
- We put ultraviolet lights in operating rooms to kill germs.
4. Chemicals – many kill bacteria. Exs.) chlorine, vinegar (acetic acid) to pickle foods, sugar, salt, artificial preservatives.
Factors That Affect the Growth of Bacteria
Bacteria Reproduction and SurvivalBinary Fission =
simple cell division….the bacterium splits in 2.- This is how bacteria
REPRODUCE when growth conditions are good.
Bacteria Reproduction and SurvivalSpore Formation – Bacterium makes a
tough protein wrapper to protect only its DNA when conditions are not good. This is called a SPORE.
- This is how bacteria SURVIVE when conditions are not suited for growth. Spores can survive quite harsh conditions.