Biology Fall 2009--Rozema
Unit 2: Cell Structure & Function
Viruses & Bacteria Notes
Viruses:
- Recall that some scientists still debate whether or not viruses are living (cells) or
not.
- Some scientists argue that they are because they use energy, reproduce, and
evolve like living cells. However, other scientists argue that because viruses do
not contain all of the characteristics of life, they are not living.
- Viruses are considered a type of parasite. A parasite is something which can
functions by using another living organism for all of their resources. A parasite
only takes, but does not give back.
- Viruses cannot “function” without a living cell. They are by most of the scientific
community considered non-living, and only display living-characteristics when
infecting cells.
- Viruses contain genetic information (nucleic acids) in a protein coated capsule.
They are also 100x smaller than bacteria.
- Viruses are the cause of “common colds” and many serious diseases.
Bacteria:
- Bacteria are a type of living cell, they are technically prokaryotic cells (meaning
they do not have a true-nucleus or complex organelles).
- Bacteria are living. They can survive and function completely on their own.
- Bacteria have a cell wall and a cell membrane on the outside.
- Their genetic information (nucleic acids) float freely around on the inside.
- Many bacteria have two pieces of genetic information (DNA and plasmids).
- Plasmids promote antibiotic resistance. Plasmids are extra chunks of DNA, often
containing antibodies against the antibiotic medicines.
- Bacteria can exchange plasmids through binary fission. When you stop taking
your antibiotics before the pills are gone, you allow the “strongest” and “most fit”
bacteria to reproduce, and share their resistance.
- Bacteria often get a bad rap, but most bacteria are necessary for life since they
help cycle nutrients.
- However, some bacteria, in large quantities are harmful to organisms.