Viruses and Bacteria. The Difference in Definition BacteriaBacteria: Prokaryotic Organisms –Pro:...
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Transcript of Viruses and Bacteria. The Difference in Definition BacteriaBacteria: Prokaryotic Organisms –Pro:...
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
Submicroscopic parasitic acellular
The Difference in Size
• Bacteria can be measured in micrometers– 0.000001m or 10-6
• Viruses are measured in nanometers– 0.000000001m or 10-9
Comparing the size of a virus, a bacterium, and an animal cell
0.25 m
Virus
Animalcell
Bacterium
Animal cell nucleus
Bacteria
Two main “domains” or groups1. Bacteria
Cell walls with peptidoglycan
2. ArchaebacteriaCell walls lack peptidoglycanAdapted 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)
Asexual divisionDNA replicates and cytoplasm divides
• Conjugation (video) “Sexual” reproduction
Sex Pilus extends between bacteria plasmid DNA is transferred from one bacterium to another
• Spore Formation:occurs when growth conditions are unfavorableAn 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 nm 50 nm 50 nm 50 nm
(a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4
RNA
RNACapsomereof capsid
DNACapsomere
Glycoprotein Glycoprotein
Membranousenvelope
CapsidDNA
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 InfectionStep 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