Transcript How are bacteria different from viruses?

Viruses and Bacteria
The Difference in Definition
• Bacteria: Pro
Prokaryotic
karyo 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)
Submicroscopic parasitic
• Viruses: 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
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
Virus
Bacterium
Animal
cell
Animal cell nucleus
0.25 m
Bacteria
Two main “domains” or groups
1. Bacteria
Cell walls with peptidoglycan
Made up of types of peptide and sugar bonds
2. Archaebacteria
Cell walls lack peptidoglycan
Adapted to extreme environments:
- Extremely hot and cold, salty, without
oxygen, etc.
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
Bacterial Staining
• Gram-negative: Will not pick up the violet dye
• Infection by this type must be treated by a
broad-spectrum antibiotic such as ciprofloxacin
peptidoglycan
Bacterial Growth and Reproduction
• Binary Fission: (video)
Asexual division
DNA 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 unfavorable
An endospore is a “spore” with a thick internal wall of
membrane that encloses and protects its DNA
Viral Shapes and structure
Capsomere
of capsid
RNA
Capsomere
Membranous
envelope
DNA
Head
Capsid Tail
sheath
RNA
DNA
Tail
fiber
Glycoprotein
18  250 mm
20 nm
(a) Tobacco mosaic virus
Glycoprotein
70–90 nm (diameter)
80–200 nm (diameter)
50 nm
50 nm
(b) Adenoviruses
(c) Influenza viruses
80  225 nm
50 nm
(d) Bacteriophage T4
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
Step
1:3:Attachment
5:Replication
New viruses
of
virus
to
thehost
host
cell
cell
Step
of “lyse”
viral DNA
and
and areof
released
furtherusing
infection
Synthesis
Proteinfor
Capsule
cellular “machinery” –DNA and RNA
polymerases, ribosomes, etc.
Step
of viral
new DNA
virusesinto
inside
Step 4:2: Assembly
Injection of
cell
host cell
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