Viruses

Viruses are not living organisms

Special enzymes that viruses utilize are:

1.       RNA replicase, which is an enzyme that uses viral DNA to make complimentary RNA strands

2.       Reverse transcriptase, which is an enzyme that uses RNA

Bacterial viruses are called bacteriophages

Lysogenic and Lytic cycles of DNA viruses:

LYTIC: (immediate action)

Phage (virus) DNA destroys host DNA. Modifies the DNA with cytosine bases. Takes over reproductive processes. Virus proteins destroy nucleus membrane to further aid in its reproduction.

LYSOGENIC: (virus takes its time)

Phage DNA integrates with host DNA to form prophage, if prokaryotic. If eukaryotic, then it's called an oncogene. Doesn't cause immediate problems in the host's DNA. Remains embedded for a while. (e.g. HIV virus)

Restriction enzymes stop the translation and transcription of DNA and RNA at certain points. They break up the DNA. We have found over 200 types of these restriction enzymes. One example that has been useful is using the restriction enzymes to break up the DNA of icefish and take their "antifreeze" gene and incorporate it into tomato plants so the plants don't freeze when the weather drops below freezing.

Endocytosis- when the virus enters the membrane of a cell

Retro Virus (e.g. AIDS)

·         contains 2 RNA identical strands and reverse transcriptase

·         utilize reverse transcriptase to copy DNA from RNA template, then uses strand to make double helix

·         DNA enters nucleus and integrates into host DNA, which becomes provirus

·         proviral DNA transcribed into viral protein

·         virus surrounded by host cell membrane, which pinches off. Allows it to interact with other cells.

·         enveloped virus

Bacterial Genomes

·         single circular chromosomes

·         plasmids- smaller rings of DNA that carry accessory genes

·         transcription and translation are coupled in bacteria. (i.e. RNA attaches to ribosome before it has left the DNA.)

·         replication is by rolling circle

·         how do bacterial cells produce variation if DNA being replicated is the same?

1.       Transduction by virus

2.       Conjugation - sexual connection?

·         bacteria can gain genes from other bacteria- morphs into a mutant bacteria. This process is called transduction

·         conjugation- cells attach to each other and replicate