Bacteria and Viruses

Bacteria are prokaryotes• Pro – before

• Karyon – nucleus

• The simplest forms of life

• Earth’s first cells

Prokaryote Review• Single-celled

• No nucleus

• No membrane bound organelles

• Divided into 2 kingdoms– Archaebacteria

– Eubacteria

A. Prokaryote Cell Structure

• cell membrane• cytoplasm• ribosomes• Single loop of

DNA

Most have a cell wall

All prokaryotes have:

• plasmids• pili• flagella

Some prokaryotes form endospores that enable them to survive harsh conditions.

Some prokaryotes have:

Bacteria Shape

• Cocci (ball-shaped)

• Bacillus (rod-shaped)

• Spirilli (spiral-shaped)

Bacteria & Disease

• Pathogen – a disease causing agent

• Bacteria are harmful because they damage their host’s tissues by– A direct attack on the host’s tissue– By releasing poisonous toxins

Controlling Bacteria

• Pasteurization – heating product to a temperature that will kill most bacteria

• Sanitation

• Vaccines – a preparation of killed or weakened pathogens introduced into the body to produce immunity

• Antibiotics – chemical that destroys or inhibits the growth of bacteria

Viruses• Virus: “poison” (Latin); infectious

particles consisting of a nucleic acid in a protein coat

Viruses

• Viruses are not cells.

• They are not alive

• Reproduce only within a host cell.

• They do not have– Enzymes for metabolism– Do not have ribosomes– Do not have the equipment to make

proteins

Viral structure

• Basic structure:– Protein coat - capsid– Nucleic acid core

(RNA or DNA)– Envelope

• (second coat – only in enveloped viruses)

envelope

RNA

Proteincoat

Lytic Cycle

• Virus attaches to host cell’s membrane and injects its nucleic acid into the host cell.

• The viral nucleic acid takes over protein synthesis, creating new viruses.

• The host cell bursts, lyses, releasing the newly formed viruses.

The Lysogenic Cycle• Replication of the viral genome

without destroying the host cell.• Virus DNA enters host, becomes part

of Hosts DNA.• Host Cell copies its DNA and Virus

DNA and reproduces normally but passes on Virus DNA to all its offspring. Cell with Virus DNA but not active is called a prophage.

• Prophage can become active and become lytic at anytime

Controlling Viruses• Antibiotics don’t work against viruses

– Antibiotics work by interfering with cellular processes such as protein synthesis

• Vaccinations– Help build up your immune system– Work well against viruses that don’t mutate