Virus Objectives

• What is a virus?

• What is the structure of a typical virus?

• How do viruses reproduce?

• C/C lytic and lysogenic cycles

• What happens to viruses once they infect

an organism?

* Name some viruses and what they do

History

• Iwanowski and Beijernick (1890’s) – Worked on Tobacco Mosaic Virus (infects tobacco and

tomato leaves). – Creates mosaic pattern on leaves. – Made a juice of the infected leaves and then put this

juice through a filter. • Rubbed the filtered juice onto leaves. • Still became infected. • Concluded that whatever these disease causing

particles were, they were very small (smaller than bacteria).

• Named them viruses meaning “poison”.

• Stanley (1935) – Purified TMV into a

crystal. – Living particles don’t

crystallize therefore, viruses are non-living pathogenic (disease causing) particles.

Viruses• Particles of nucleic acid, protein and

sometimes a lipid envelope.

• Obligate intracellular parasite (can only replicate within a living cell)

Structure of a virus

• Small – 20nm (polio virus) – 350nm (small pox virus)

• Single type of nucleic acid (RNA or or DNA but never both)

• Protein coat – capsid• Some have envelopes (made of lipids)outside

of capsid• Surface projections made up of lipids for

attachment onto host cells• Are specific to their host

Shapes

• Shapes are – Rod– Helical– Icosahedral (20 sides)

HIVRetrovirus

Envelope Projections

Bacteriophage

Infect E. coli bacteria

Attach with tail fibers onto cell.

Inject nucleic acid into cell

Capsid

Tail

The Lytic Cycle • Get in, replicate and get out to invade other host cells• Virulent (Disease causing)• The cold, rubella (German measles), mumps

ReleaseAttachment at Receptor site

Entry

Replication

Assembly

The Lytic Virus infection

Attaches onto host cell Injects DNA into host cell Replication of Viral parts

Reassembly of virons Lysis – bursting out

Viruses that reproduce only by the lytic cycle are called Virulent

Lysogenic InfectionLysogenic Infection• Virus embeds its DNA into hosts DNA which is

replicated with host cell’s DNA. • Remains unnoticed for sometimes years• AIDS, cold sores, chicken pox, hepatitis

Prophage

Attachment Integration Cell multiplication & Injection of nucleic acid Prophage remains unnoticed and not transcribed

Lytic and Lysogenic Cycles

Viral Diseases • Measles, Mumps, Rubella, Rabies, the Cold,

the Flu, Influenza, Hepatitis, AIDS, Chicken pox, Small pox, Polio, Yellow fever, Meningititis, some cancers, Swine flu

• Vaccines are small doses of either killed, altered or live viruses. Body builds up antibodies against virus

Diseases caused by viruses

• AIDS• The Cold• Measles• Mumps• Rubella• Chicken pox/Shingles• Small Pox• Hepatitis• SARS• The Flu• Ebola• HPV• Bird Flu• Polio

Polio and the Iron Lung

The Different forms of Viruses• RetrovirusesRetroviruses – AIDS. Contains RNA instead

of DNA. Goes from RNA to DNA to RNA to protein. Normal is DNA to RNA to protein.

• ViroidsViroids – another disease causing agent but no capsid, only the RNA. – Found only in plants

• PrionPrion – viral proteins that cause diseases. Scrapie in sheep degrades nervous system. Mad Cow disease (Bovine spongiform encephalopathy) in cows – puts holes into brain.– In humans, its Creutzfeld-Jakob disease & Kuru.

Bacterial Objectives• What are the two bacterial

kingdoms/domains? How are they different?• Describe the structure of a typical bacterial

cell and the 3 main shapes• How do bacteria reproduce and metabolize?• Name some common bacterial disease and

their causative agents.• How are bacteria important to us?

• Formally known as Kingdom – Monera

• Unicellular,

• Prokaryotic cell (no nucleus or membrane bound organelles.

• Have Ribosomes and a cell wall ,

• Single long, circular strand of DNA

• Auto or Heterotrophic

Kingdom – ArchaebacteriaKingdom – Archaebacteria

• Lack Peptidoglycan in cell wall – a sugar/protein substance

• Extremophiles

• First organisms to colonize primitive earth

Kingdom – EubacteriaKingdom – Eubacteria• Larger of the two kingdoms

• Have Peptidoglycan in cell wall

• 3 basic shapes

– Bacilli – Rod shaped. E. coli, Bacillus anthracis

– Cocci – Spherical shaped. • Staphylococcus aureus, Streptococcus pyogenes

Strepto – Chains Tetra - 4 Staphylo –clusters• Diplo – 2

• Spirilla – Spiral shaped. Spirochette, Syphilis

Staining properties • Groups Eubacteria in two groups

– Gram Staining• Gram Positive – Gram stain purple with Crystal

violet due to thick layer of peptidoglycan. Easier to kill with antibiotics

• Gram Negative – Gram stain pink with Safarin. Hard to kill with antibiotics due to thin layer of peptidoglycan

Basic Structure

EndosporesEndospores

• Produced by Gram + (usually Bacillus & Clostridium)

• Dormant structure to survive adverse conditions (heat, cold, dryness).

Bacillus anthracis

Methods of Respiration

• Obligate aerobic bacteria must have oxygen.

– Streptococcus

• Obligate anaerobes die if oxygen is present.

– Clostridium

• Facultative anaerobes w/ or w/o oxygen.

– E. coli

Reproduction

• Asexually by binary fission

• Conjugation - Sexual repro method . Two bacteria form a conjugation bridge or tube between them. DNA is transferred from one bacteria to the other 

Bacteria and Humans

• Pathogens – disease causing agents (Pathology – science of studying diseases)

• Can produce poisonous toxins (poisons) like the botulism toxin

• Destroy food crops

To fight them:

• Antibiotics interfere with cell wall or protein synthesis. Penicillin, tetracycline

• Bacteria can mutate and become antibiotic resistant (often results from overuse of antibiotics)

Helpful Bacteria:

1. Bacteria of decay - major decomposers (Saprophytes)

2. Symbiosis – Nitrogen Fixing bacteria - Convert atmospheric N2 to NH3, Rhizobium in root nodules of legumes

3. Fermentation: Food processing of sour cream, yogurt, buttermilk, wine, sauerkraut, pickles, cheese

4. Industrial – “oil eating bacteria”, mining gold, cleaning up pollutants - Bioremediation

5. Biotechnology

Diseases caused by bacteria

• Anthrax• Botulism• Cholera• Cavities• Gonorrhea• Syphilis• Tetanus• Staph Infection (MRSA)• Food Poisoning• Lyme Disease• Diphtheria• Tuberculosis• Escherichia coli O157: H7• Leprosy• Meningitis• Strep throat• Whooping cough (Pertussis)

Food poisoningFood poisoning • Results from decay of foods and

production of toxins

• 33 million people/yr get “stomach flu”

• Seafood accounts for 20 – 25% of cases

• 33% of all raw poultry tests + for Staphylococcus

• 1 in every 200 eggs has Salmonella

4 C’s of Food Safety

Chill your foods

Cook your food to the proper

temperature

Clean food and cooking surfaces

Combat Cross Contamination

Antibacterial AgentsAntibacterial Agents

• Antibiotics – organic substance that inhibits growth in/on living material. Penicillin

• Disinfectants – inhibits growth on a non-living surface – bleach, ammonia

• Antiseptics– inhibits growth on a living surface – alcohol, hydrogen peroxide

• Sterilization – high heat or chemicals that kills bacteria

Antimicrobial agentsAntimicrobial agents

• DisinfectantsDisinfectants– 1 – Bleach– 2 – Ammonia– 3 – 409– 4 – Sterile water

• AntisepticsAntiseptics– 1 – Hand gel– 2 – Iodine– 3 – Alcohol– 4 – Sterile water

• AntibioticsAntibiotics– 1 – Streptomycin– 2 – Erythromycin– 3 – Tetracycline– 4 – Sterile water

• Bacteria Bacteria (indicate which on you have on your lab)– Bacillus cereus– E. coli– Serratia marcescens

Antiseptic CCDisinfectant CC Antibiotic CC