C-18-The Genetics of Bacteria and Viruses

Chapter 18

The Genetics of Viruses and Bacteria

Bacteria and Viruses represent life at its simplest levels.

Understanding what is happening in bacteria and viruses helps us to understand more complicated organisms such as ourselves.

Bacteria and Viruses can cause many diseases.

Bacteria and viruses are important tools in biotechnology and genetic engineering.

Viral Structure and Function

Viruses are composed of DNA or RNA surrounded by a protective protein coat. The DNA or RNA can be single or double stranded and can contain from 4 to several hundred genes.

Viruses cannot metabolize or multiply on their own. They are not composed of cells.

Viruses utilize the living cells of other organisms to carry out their life processes. (trans-P 18.3)

Viruses come in a variety of shapes and sizes. (trans-p 18.2)

Viruses have 2 methods of multiplying

1. Lytic cylce (trans-p 18.4)

2. Lysogenic cycle (trans-p 18.5)

Viruses are classified according their DNA or RNA

DS-DNA

SS-DNA

DS-RNA

SS-RNA

See table 18.1

Defenses against Viruses

Antibiotics work against bacterial infections but not against virus infections.

To combat viral infections we rely upon our immune systems and vaccines.

Bacterial Structure and Function

Bacteria are simple unicellular organisms and they are the most abundant organisms on earth. They are both beneficial and pathogenic.

Bacteria occur as rods, spheres or spirals.

They have a single circular DNA molecule (the chromosome). Some have an additional small ring of DNA called the plasmid. The plasmid carries additional accessory genes that confer additional characteristics on the bacteria.

(Trans-P 7.4 and 20.1)

Bacterial Reproduction

1.Binary Fission- a type of cell division by which single bacterial cells reproduce asexually.

In this process the single replicated chromosome is partitioned into each of the two daughter cells. The daughter cells are separated by pinching in of the plasma membrane.(trans-p 12.10)

2. Conjugation-a type of mating that bacteria undergo in which DNA is transferred between two cells that are temporarily joined. In conjugation one cell is the donor and the other is the recipient of genetic information.

Donor cell is called the F+ cell

Recipient cell is called the F- cell

3. Transformation- occurs when bacterial cells take up DNA directly from their surroundings. Trans-p 16.1

4. Transduction-occurs when bacteriophages (viruses that attack bacteria) carry bacterial genes from one host cell to another.

Infectious agents other than Viruses and Bacteria

1. Viroids-tiny molecules of naked circular RNA that infect plants.

2. Prions- infectious brain proteins.

(Trans-p 18.10)