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Viruses and Bacteria - Ch19 and Ch27 - Coggle Diagram
Viruses and Bacteria - Ch19 and Ch27
Viruses
What They Are
Basic Facts
Not cells
Do not have ribosomes
Do not do their own metabolism
Main Parts
Capsid: protein coat that protects genome
Genetic material: DNA or RNA
Envelope
Some viruses have an envelope
Envelope comes from host cell membrane
Envelope has viral proteins to attach to new cells
Dependence on Host
Cannot reproduce without a host cell
Use host enzymes and ribosomes
Use host ATP for energy
Shapes
Helical
Long and tube shaped
Example: Tobacco Mosaic Virus
Icosahedral
Round with many flat faces
Example: Adenovirus
Complex
Have head and tail parts
Example: bacteriophages that infect bacteria
Infection
Host Range
Host range = which species and cells a virus can infect
Based on matching receptors on host cell surface
Example: flu virus binds to receptors in lung cells
Entry Methods
Some viruses inject DNA or RNA into cell
Some enter by endocytosis
Some fuse their envelope with host membrane
Limits
Viruses cannot multiply in air by themselves
They must enter a living cell to make copies
Reproduction Cycles
Lytic Cycle
Step 1: Virus attaches to host cell
Step 2: Virus injects DNA or RNA
Step 3: Host cell makes viral parts
Step 4: Viral parts assemble into new viruses
Step 5: Cell bursts and releases many viruses
Lysogenic Cycle
Viral DNA joins host DNA
Called a prophage in bacteria
Copied when host cell divides
Can switch later to lytic cycle
Prophage vs Provirus
Prophage: viral DNA in bacterial chromosome
Provirus: viral DNA in animal cell genome
Provirus usually stays in host cell permanently
Retroviruses
Basic Info
Have RNA as genetic material
Use enzyme called reverse transcriptase
Steps
Virus enters host cell
Reverse transcriptase makes DNA from viral RNA
Viral DNA enters host genome
Host makes new viral RNA and proteins
Example
HIV is a retrovirus
HIV infects certain white blood cells
Leads to disease called AIDS
Prions
What They Are
Misfolded versions of normal brain proteins
Do not contain DNA or RNA
Still infectious
How They Spread
Spreading Mechanism
Prion touches normal protein
Normal protein changes shape
Chain reaction of misfolding
Properties
Very hard to destroy by heat and chemicals
Cause slow brain damage
Often fatal
Diseases
Animal Diseases
Scrapie in sheep
Mad Cow Disease in cows
Human Diseases
Creutzfeldt Jakob Disease
Bacterial Growth and Gene Transfer
Binary Fission
Steps
DNA is copied
Cell grows longer
Cell splits into two cells
Notes
Can happen every few minutes in good conditions
Daughter cells are clones unless mutations occur
Gene Transfer Methods
Transformation
Bacteria take DNA from environment
DNA can give new traits
Transduction
Virus infects bacteria and carries bacterial DNA
DNA from one bacterium moves to another
Conjugation
Bacteria connect using pilus
DNA passes from donor to receiver
Hfr Cells
Have F factor in main chromosome
Can transfer large parts of chromosome
Increase genetic variety in population
Horizontal Gene Transfer
Results
Genes move between unrelated bacteria
Spreads antibiotic resistance
Helps bacteria adapt quickly
Diversity and Ecology
Domains
Bacteria
Very common in soil, water, and living things
Archaea
Often live in extreme environments
Halophiles
Live in very salty places
Thermophiles
Live in very hot places
Methanogens
Make methane gas
Live in guts of cows and in swamps
Ecological Roles
Decomposers
Break down dead organisms
Return nutrients to soil
Nutrient Recycling
Cycle carbon, nitrogen, and other elements
Oxygen Makers
Cyanobacteria do photosynthesis
Release oxygen into environment
Symbiosis
Mutualism
Both partners benefit
Example: gut bacteria help digest food
Commensalism
One benefits, other not helped or harmed
Parasitism
One benefits and the other is harmed
Example: disease causing bacteria
Human Impact
Helpful Uses
Make foods like yogurt and cheese
Used in CRISPR and other biotech
Used in bioremediation to clean spills
Harmful Effects
Cause diseases like TB, cholera, Lyme disease
Some release toxins that damage cells
Virus Protection and Disease
Vaccines and Antibiotics
How Vaccines Work
Contain weak or dead virus or just virus pieces
Body makes memory cells
Later, body can attack real virus faster
When To Use
Best if given before infection
Vaccines help prevent disease
What Vaccines Are Not
Vaccines are not antibiotics
Vaccines do not cure active infection
Antibiotics
Antibiotics kill bacteria
Antibiotics do not work on viruses
Virus Spread
Epidemic
Large outbreak in one region or country
Pandemic
Outbreak across many countries or the world
COVID pandemic started in 2020
Vectors
Animals or insects that carry pathogens
Example: mosquitoes carry some viruses
Viral Diseases
Older Vaccinated Diseases
Smallpox
Polio
Newer and Recent Examples
HIV
Ebola
Zika
H1N1 flu
SARS
MERS
Why Nets Work
Mechanism
Nets and screens block mosquitoes and flies
Insects cannot bite humans as easily
Less chance to pass virus in blood
Note
Nets do not block single virus particles
They block the insect carriers
Bacteria
Structure
Cell Wall
Made of peptidoglycan
Gram positive: thick wall
Gram negative: thin wall plus outer membrane
Capsule
Sticky outer layer
Helps bacteria stick to surfaces
Helps protect from immune system
Endospore
Thick coated resistant cell
Keeps DNA safe in harsh conditions
Can survive heat and dryness
Movement Structures
Flagella spin to move bacteria
Attachment Structures
Fimbriae help bacteria stick
Pili move DNA between cells
Gram Stain
Steps
Add crystal violet
Add iodine
Wash with alcohol
Add safranin
Results
Gram positive = purple
Gram negative = pink
Shapes
Coccus: round shaped
Bacillus: rod shaped
Spirillum: spiral shaped
Inside Cell
Nucleoid
Region with main DNA loop
Plasmids
Small extra DNA circles
Can carry genes for resistance or special traits
Special Plasmids
F plasmid: helps form pili for conjugation
R plasmid: carries antibiotic resistance
Nutrition and Metabolism
Energy Types
Phototroph: uses light for energy
Chemotroph: uses chemicals for energy
Carbon Types
Autotroph: uses carbon dioxide as carbon source
Heterotroph: uses organic carbon from other organisms
Four Nutrition Types
Photoautotroph
Energy from light
Carbon from carbon dioxide
Example: cyanobacteria
Photoheterotroph
Energy from light
Carbon from organic molecules
Chemoautotroph
Energy from chemicals
Carbon from carbon dioxide
Chemoheterotroph
Energy from chemicals
Carbon from organic molecules
Example: many bacteria and animals
Oxygen Use
Obligate aerobes
Need oxygen to live
Obligate anaerobes
Oxygen poisons them
Use fermentation or other final acceptors
Facultative anaerobes
Can live with or without oxygen
Use aerobic respiration when oxygen is present
Nitrogen Fixation
Process
Turns nitrogen gas into ammonia
Ammonia can be used to build proteins
Examples
Some soil bacteria
Anabaena with special cells called heterocysts
Virus vs Bacteria Comparison
Living or Not
Viruses are not truly alive
Bacteria are living cells
Structure
Viruses: capsid and genome, no cell organelles
Bacteria: full cells with wall, membrane, ribosomes
Reproduction
Viruses: must enter host cell to copy
Bacteria: reproduce by binary fission
Treatment
Viruses: vaccines and some antiviral drugs
Bacteria: antibiotics and sometimes vaccines
Size
Viruses are much smaller than bacteria
Bacteria are larger and visible under light microscope