Bio Lecture ppt Viruses and Bacteria CC BY, Leslie Orzetti-Gollhofer

1. Viruses and Bacteria

2. Simple Yet Complex
• Virus – collection of genetic material and
proteins
– Causes infections in ALL life forms
• Bacteria – prokaryotic cell
– First “life” on earth

3. What is a Virus?
• Infectious agents, NOT CELLS
• No nucleus, organelles, cytoplasm
• Can replicate ONLY inside a living cell
– Obligate Intracellular Parasites
• Contain only 1 type of genetic molecule,
either DNA OR RNA
• Do not grow
• NOT ALIVE

4. Other Virus Characteristics
• Some viruses have:
– Envelop – lipid rich layer outside protein coat
• Envelop may have proteins that help infect cells
• Ex. HIV, Flu
• Can use presence or absence of envelop to classify
– Tails
– Spikes
– Legs

5. HIV
Chicken Pox
Common
Cold
Influenza

6. Other Virus Characteristics
• Host Range – kind of cells or organisms it can
infect
– Can ONLY infect cell that has target protein on the
outside
– Ex. HIV only infects human helper T cells
– Ex. Rabies can infect any mammal
• Reservoir – Place where viruses exist in
nature, acts as source of virus for host
– Ex. Birds – Bird flu, Mosquitos – yellow fever

7. Are Viruses Alive
• NO
– Does not metabolize
– Does not respond to stimuli
– Does not reproduce on its own
• How is it like things that are alive?
– Has genetic material (DNA or RNA)
– Viruses can evolve
– Classified similarly (Family, Genus, Species)

8. How Do Viruses Replicate?
• Uses host cell to make new viral particles
1. Attachment – attaches to host cell by sticking to
receptor on cell’s surface
2. Penetration – Viral genetic material enters host cell
(engulfing, injecting)
3. Synthesis – Virus produces lots of copies of genetic
material in host cell. Host cell provides all needed
materials
4. Assembly – subunits of capsid join, genetic material
packed
5. Release – Exocytosis, breakdown cell wall, bud from
host particle

9. 1
2
3
4
5
Attachment:
Virus binds cell surface receptor.
Penetration:
Viral nucleic acid is released inside
host cell.
Synthesis:
Host cell manufactures viral nucleic
acids and proteins.
Assembly:
New viruses are assembled from
newly synthesized coat proteins,
enzymes, and nucleic acids.
Release:
New viruses leave the host cell.

10. Does the Host Cell Die?
• Immediate Death
– Lytic Infection – virus enters cell, immediately replicates,
causes host cell to burst
– Newly released viruses infect other cells
• Delayed Death
– Lysogenic Infection – genetic material enters host cell,
replicates WITH host cells chromosomes
– Eventually switch to lytic infection
– Prophage – bacteriophage’s DNA inserted into host cells
DNA
– Only few copies are made that will determine if infection
becomes lytic

12. Severity of Infection
• Cell death causes symptoms
• Amount of cell death determines severity of
symptoms
• Symptoms not around host cells from immune
reaction
• Some viruses stick around for A LONG TIME
– Virus lays dormant as cell divides
– Latent infection – does not produce symptoms
• Herpes type I, HIV, HPV, Epstein-Barr

13. Fighting Off Infections
• Antiviral Drugs
– Interfere with enzymes, genetic information
– HOWEVER – body rarely ever is cured from a virus
b/c drugs kill host cell as well
• Vaccinations – teach body how to fight
infection when they see it again
– Some confer immunity for life (ex. Measles)
– Some have to get every year (ex. Flu)

14. Plant Viruses
• Must penetrate outer waxy leaf layers & thick
cell walls
– Usually spread by leaf eating insects
– Infection starts at site of infection spread by
plasmodesmata, vascular tissue
– Ex. Tobacco mosaic virus

15. Pepper Mild Mottle Virus
Plant Viruses
Tobacco Mosaic Virus

16. Viroids
• Highly wound circle of RNA without protein
coat
– Naked RNA that can infect cell
• Does not encode for protein
• Interferes with plant’s ability to produce
needed proteins
• Transmitted by seeds or pollen

17. Reported Viral Diseases

18. Bacteria: The First LIVE Organisms

19. What is a Prokaryotic Cell?
• Lack true nucleus or other membrane bound
organelles
• Belong to Domains:
– Archaea - Archaebacteria
– Bacteria – Eubacteria
• Parts of Prokaryotic Cell
– Cell membrane
– Cell wall
– Cytoplasm
– Ribosomes
– Granules, vessicles
– External structures – capsule, flagella, pili

20. Bacterial Cell Parts

21. Bacterial Classification
• Size – 0.5 – 2.0µm, surface/volume 3:1
• Shape – can sometimes change during lifetime
– Coccus – spherical
– Bacillus – rod shaped
– Spiral
• Comma – vibrio
• Rigid, wavy – spirilum
• Corkscrew – spirochaete
– Irregular

22. Common Shapes of Bacteria

23. Bacterial Classification
• Arrangement – distinctive arrangements/groups of
cells
– Form when cells divide without separating
• Division in one plane:
– Diplo – pairs of cells
– Strepto – chains of cells
• Division in two planes:
– Tetrads
• Division in three planes
– Sarcinae
• Random Division
– Staphylo

24. Common Arrangements of Bacteria

25. Prokaryotic Cell Wall
• Outside cell membrane
• Rigid but porous
• Functions:
– Maintains shape of cell
– Prevents cell from bursting
• Components
– Peptidoglycan – VERY large molecule, most important
component
– Teichoic Acid – gram positive, extend beyond cell wall
– Outer Membrane – gram negative, bilayer at outermost layer of
cell wall
– Lipopolysaccharide (LPS) – endotoxin, part of outer membrane
released when cell dies
– Periplasmic Space – gap between cell membrane and cell wall,
active area of cell metabolism

26. Gram Negative vs. Gram Positive
Anthracis bacillus
Bacillus subtilis

27. Typical Bacterial Parts
• Cell Membrane – similar to eukaryotic, fluid mosaic
model, semi-permeable
• Cytoplasm – mainly water (80%), other 20% = enzymes,
proteins, carbohydrates, lipids, ions
– Does NOT carryout streaming
• Ribosomes – protein synthesis, can be found in chains
(polyribosomes)
• Nuclear Region – centrally located, NOT bounded by
membrane
– Consists mainly of DNA, little RNA
– Can have 1 or 2 circular chromosomes, some with small
plasmids (small circular DNA molecules)

28. Typical Bacterial Parts
• Internal Membrane System
– Chromatophores – photosynthetic, has pigments,
used to capture light
– Nitrifying bacteria – enzymes used to derive
energy from nitrogen compounds
• Inclusions
– Granules – not bound by membrane, glycogen,
polyphosphate
– Vesicles – vacuoles – bound by membrane, air or
lipid deposits for energy

29. Typical Bacterial Parts
• Endospores – resting stage bacteria, NOT
reproductive, just used to stay alive
– Contain VERY little water
– Resistant to heat, desiccation, acids, bases,
disinfectants, radiation
– Bacteria induced to form endospore when some
nutrient missing

30. Typical Bacterial Parts
• Flagella – thin, helical EXTERNAL structure for
movement
– Chemotaxis – using flagella to move toward or away
from substances
– Phototaxis – using flagella to move toward or away
from light
• Axial Filaments – endoflagella
– Flagella that does not extend beyond cell wall
• Pili – small, hollow projections used to attach
bacteria to surfaces, transfer genetic material

31. Typical Bacterial Parts
• Glycocalyx – any polysaccharide containing
substance external to cell wall
– Capsule – protective structure outside wall, thick,
tightly bound, makes it difficult to destroy bacterial
cell
• Ex. Anthrax – naturally occurring in cattle, only has capsule
when infecting organism
– Slime Layer – outside wall, thin, but less tightly bound
to wall, protects cell from drying, helps bind cells
together and to their environment
• Ex. Slime layers, biofilms, tooth plaques

32. Common Bacterial Diseases