Viruses and Bacteria

The Difference in Definition BacteriaBacteria: Prokaryotic Organisms –Pro: Primitive or “prior to” –Karyon: Nucleus or “kernel” –Single-celled organisms –Has circular DNA; often has “plasmid” DNA that helps codes for genes to increase fitness (ex. Antibiotic resistance) VirusesViruses: Submicroscopic, parasitic, acellular entity composed of a nucleic acid core surrounded by a protein coat. –Below the resolution of a microscope –Relies on a host –Does not have the properties of cellular life Prokaryo Submicroscopicparasiticacellular

The Difference in Size Bacteria can be measured in micrometers – m or Viruses are measured in nanometers – m or 10 -9

Comparing the size of a virus, a bacterium, and an animal cell 0.25  m Virus Animal cell Bacterium Animal cell nucleus

Bacteria Two main “domains” or groups 1.Bacteria Cell walls with peptidoglycan 2.Archaebacteria Cell walls lack peptidoglycan Adapted to extreme environments: - Extremely hot and cold, salty, without oxygen, etc. peptidoglycan Made up of types of peptide and sugar bonds

Bacteria: Shapes Three basic shapes: –Rod-shaped (Bacilli) Bacillus anthracis (Anthrax), Yersinia pestis (Bubonic plague) -Comma-shaped (Vibrios) Vibrio cholerae –Spherical (Cocci) Streptococcus, Staphylococcus –Spiral (Spirilla) Treponema pallidum (Syphillis)

Bacterial Staining Gram-positive: Retains the crystals of violet dye in the peptidoglycan layer Infection by this type can be treated by antibiotics such as penicillin

Gram-negative: Will not pick up the violet dye Infection by this type must be treated by a broad-spectrum antibiotic such as ciprofloxacin Bacterial Staining peptidoglycan

Bacterial Growth and Reproduction Binary Fission: (video)Binary Fission Asexual division DNA replicates and cytoplasm divides Conjugation (video)Conjugation “Sexual” reproduction Sex Pilus extends between bacteria plasmid DNA is transferred from one bacterium to another Spore Formation: occurs when growth conditions are unfavorable An endospore is a “spore” with a thick internal wall of membrane that encloses and protects its DNA

Viral Shapes and structure 18  250 mm 70–90 nm (diameter) 80–200 nm (diameter) 80  225 nm 20 nm50 nm (a) Tobacco mosaic virus(b) Adenoviruses(c) Influenza viruses (d) Bacteriophage T4 RNA Capsomere of capsid DNA Capsomere Glycoprotein Membranous envelope Capsid DNA Head Tail fiber Tail sheath

Viruses Reproduction Viruses reproduce by infecting other cells. Two types of viral infections: 1. Lytic Infection 2. Lysogenic Infection

Figure 18.1 T4 bacteriophage infecting an E. coli cell 0.5  m

The Lytic Infection Step 1: Attachment of virus to host cell Step 2: Injection of viral DNA into cell Step 3: Replication of viral DNA and Synthesis of Protein Capsule using cellular “machinery” –DNA and RNA polymerases, ribosomes, etc. Step 4: Assembly of new viruses inside host cell Step 5: New viruses “lyse” the host cell and are released for further infection

Characteristics of Lytic Infections 1.Fast acting 2.Symptoms emerge within 24 – 48 hours 3.Examples – influenza, west-nile

The Lysogenic Infection Step 1: Virus attaches and inserts its DNA inside host Step 2: Viral DNA attaches to the host DNA (prophage) Step 3: The viral DNA lies “dormant” and only replicates each time the cell replicates Step 4: Stress or other “factors” causes the infection to progress to the “lytic” phase

Characteristics of Lysogenic Infections 1.Slow Acting - Viral DNA can lie “dormant” for many years as proghage 2.The host are “symptom-free” during dormancy 3.Infection is fast acting when the infection progresses to the lytic phase 4. Example: HIV