Biology/O’Connor

Virus/Bacteria Notes

O’Connor

• Viruses are named after the disease

they cause or by what tissue they infect.

Polio

• Viruses are composed of nucleic acids

enclosed in a protein coat (capsid)

Smallpox

Viruses are considered to be nonliving because:

• Don’t carry out respiration

• Don’t grow

• Don’t develop

Smallpox

• They do replicate… however they

require a host cell to carry out

replication.

Viral Structure:

Virus is either RNA or DNA

How does a virus infect a cell?

• Virus recognizes host cell

Attachment to a recognized cell.

• The virus and cell fit like a key and lock

Hepatitis C

• Virus enters cell by injecting nucleic

acid (RNA or DNA) into host cell.                 

AIDS/HIV

• Replication begins by viral nucleic acid

using the host cell’s equipment.                                          

Ebola Virus

Two Different Cycles of viruses:

• Lytic Cycle

• Lysogenic cycle

Lytic Cycle

Cell dies quickly

1. Attachment of virus

2. Nucleic Acid invades host cell

3. Replication

4. Assembly of new virus particles

5. Cell lyses (ruptures) and virus is released into environment

Lytic Cycle

Lysogenic Cycle

Cell does not die quickly

1. Attachment of virus

2. Nucleic Acid invades host cell

3. Virus becomes part of host chromosome –(PROVIRUS)

4. Cell divides splitting chromosomes and creating new cell with the virus.

5. Provirus leaves chromosome cont.

6. Viral Nucleic Acid and proteins are assembled

7. Cell lyses (ruptures) and virus is released into environment to infect other cells.

Lysogenic Cycle

Retroviruses:

• RNA viruses

1. Viral RNA injected into host cell

2. Host cell’s DNA is used to make viral DNA from viral RNA

3. Viral RNA uses reverse transcriptase to make viral DNA

4. Viral DNA becomes a provirus

5. Keeps producing new virus without killing cell first

• To test for a retrovirus like HIV a blood

test will be done to test for reverse

transcriptase.

Viroids

• RNA strand no protein coat

• Cause diseases in plants

Prions

• Are composed of proteins but have no nucleic acids to carry genetic information.

• They act like viruses

• Cause diseases such as mad cow disease & Creutzfeldt-Jakob disease.

Tobacco Mosaic Virus

• First virus to be identified

Archaebacteria & Eubacteria

* (quick review) Prokaryotes are unicellular organisms that do not have a nucleus or membrane-bound organelles. They are classified as two kingdoms archaebacteria and eubacteria.

Archaebacteria The extremists

• live mainly in habitats where there is usually no free oxygen available.

»Three types:

1. methane-producing archaebacteria

2. salt-loving archaebacteria

3. heat & acid loving archaebacteria

Eubacteria

• Prokayotes that live in places more hospitable than archaebacteria inhabit and that vary in nutritional needs.

Types:

• Heterotrophic Eubacteria live almost everywhere.

• Photosynthetic autotrophs- make their own energy by sunlight, so they live in places with sunlight.

• Chemosynthetic autotrophs- make their own energy, but do not require sun.

Bacterium

• Consists of very small cell. A bacterial cell has all the structures necessary to carry out its life functions.

Fighting bacteria

• Most bacteria live in hypotonic environments, where water is always trying to enter the cell. If you can damage the cell wall and allow the water in it will cause the cell to burst.

Penicillin

• Sir Alexander Flemming discovered by mistake that penicillin would cause the cell walls of bacteris he was growing to be damaged.

• Damaged cell wall = burst bacteria cell

Identifying Bacteria

• Gram staining- the stain allows you to distinguish two groups because of their difference in the composition of bacteria cell walls.

• Gram-stain positive turn purple• Gram-stain negative turn pink

• Positive & negative react to different antibiotics.

Shape also identifies bacteria

• Three most common:

• Spheres- called cocci

• Rods- called bacilli

• Spirals – called spirilla

Patterns of Growth

• Bacteria cells often grow in characteristic patterns.

• Diplo – paired

• Staphylo – resemble grapes

• Strepto - chains

Binary Fission

• Bacteria reproduces asexually & rapidly

• Copies chromosome• They attach• Grow larger• 2 chromosomes separate, pull apart• Move to opposite ends of cell• Partition forms and you have 2 similar cells

Sexual Reproduction of Bacteria

• Conjugation- some bacteria can do this. Transfers DNA through a bridge like structure called a pilus.

Importance of Bacteria

• Disease causing bacteria are actually few compared to harmless and beneficial bacteria.

• They help fertilize fields

• Recycle nutrients on Earth

• Produce foods & medicines.

“Good” Bacteria

• Some bacteria convert N2 into ammonia by nitrogen fixation and others that convert the ammonia into nitrites & nitrates which plants use.

• Swiss cheese, pickles, yogart all made by bacteria

• Some produce antibiotics, like bacitracin

“Bad” Bacteria

Can cause diseases like:

• Strep throat

• Tuberculosis

• Tetanus

• Lyme disease

• Cavities

• diptheria