Bacteria and Viruses• Bacteria and viruses are often lumped together into one group

by the general public as “things that make you sick”.• Even so, bacteria and viruses are structured much differently

and function much differently because of this.• In fact, there are some types of viruses that infect bacteria

(bacteriophages)Generalized pictures:

Bacteria Virus

Bacteria• Bacteria are considered living because they are made of cells

(and thus can perform the 7 functions of life [MRS. GOCH])• Bacteria can live independently on their own or can be

dependent upon a living host• Bacterial infections can be treated with antibiotics.• Some antibiotics work by targeting the ribosomes of the

prokaryote (which are smaller than ribosomes of the eukaryotic host); therefore, the ribosomes of the bacteria are inhibited from making proteins while the eukaryotic ribosomes continue to function properly

• Antibiotic resistance – class discussion• Problems with overusing antibiotics

Bacterial reproduction• Bacteria typically reproduce asexual through binary fission but

can transfer DNA to other organisms.• Bacteria can transfer DNA in 3 ways1. Transformation – uptake of DNA from surrounding other

cells or other organisms (Griffith’s expt)2. Transduction – bacteriophage (virus) DNA taken up by

bacteria (Hershey and Chase)3. Conjugation – bacterial cells mating; Male has sex pili which

attaches to female, outside layers of cells fuse and create cytoplasmic bridge, DNA from male “donor” cell passes to female and male copies his DNA as it transfers so he doesn’t lose any genes• F factor – has genes to make sex pili and other things necessary

for conjugation as well as having an origin of replication

Viruses• Viruses are acellular (without cells)• This means that they are non-living (because they cannot

perform all 7 of the MRS. GOCH functions)• Viruses are made only of DNA and a protein coat (called a

capsid)• This is what made them perfect for the Hershey and Chase

experiment. We knew that viruses had the ability to make a host produce more viruses by injecting either their DNA or proteins into them (therefore, one of these 2 had to be the hereditary material)

Life cycle of a virus• Viruses reproduce by 1 of 2 cycles:1. Lytic cycle – breaks open host cell and releases viruses

made by host cells organelles• Virus immediately turns cell into virus making factory• Cell swells with virus and lyses

2. Lysogenic cycle – does not destroy host cell• Virus DNA inserted into host cells

DNA, phase DNA called prophage

• Virus then reproduced each time cell replicates

Types of Viruses1. DNA virus – virus that uses DNA as its hereditary material • The virus injects its DNA into the host.• The host then takes up the viral DNA into its own genome.• The host cell then translates and transcribes the viral DNA every time it

does the same processes for itself. • May lay dormant in nerve cells until stimulated by stress

• Ex. Herpes

Types of Viruses Continued

2. RNA virus – virus that uses RNA as its hereditary material • These viruses inject their mRNA into the host cell and then can

use the ribosomes of the host cell to manufacture more of their proteins

Types of Viruses Continued3. Retrovirus – special kind of RNA virus that replicate through reverse transcription• A retrovirus uses mRNA as its genetic material as well. What makes it

different is that once inside the host cell, the retrovirus uses its own reverse transcriptase enzyme to make DNA from its mRNA (the reverse of the usual transcription process, hence the “retro”virus)

• The newly made “viral DNA” is then incorporated into the host cells genome.

• The host cell then translates and transcribes the viral DNA every time it does the same processes for itself.

• Ex. AIDS• Outwardly the AIDS virus looks like the flu or mumps (membranous envelope and glycoprotein spikes)• Inwardly, it has 2 identical copies of its RNA and reverse transcriptase enzymes