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.