Chapter 16: Microbial life Flashcards
Prokaryotes’ contribution to life :)
- First cells were single-celled organisms with no membrane-bound organelles that existed alone 🙁 for 1.5 billion years.
- Cyanobacteria (photosynthetic) introduced oxygen into Earth’s atmosphere, which permitted diversification of life.
Define autotroph, heterotroph
Autorophs (like plants) make their own food. Heterorophs (like animals) get their foods from elsewhere.
Explain how eukaryotic life arose out of endosymbiosis
Organelles (mitochondria, chloroplasts, nuclei) were prokaryotes that were engulfed by other prokaryotes. Started to depend on one another for resources.
Explain the significance of prokaryotes to life on Earth
Maintain ecological balance:
* Live on and in humans and animals (like stomach and skin).
* Produces food and chemicals.
* Causes disease 🙁
What is microbiology
Study of microorganisms
Classify organisms based on trophy (photoautotroph, chemoautotroph, photoheterotroph, chemoheteroph).
see chart on GD
Photoautotroph
* Harness solar energy.
* Harness carbon from CO2 to build organic compounds.
Ex. cyanobacteria, plants, algae.
Chemoautotroph
* Harness chemical energy
* Harness carbon from CO2 to build organic compounds.
Ex. some archea, nitrogen-fixing bacteria.
Photoheterorophs
* Harness solar energy.
* Harness carbon from organic source.
Ex. halobacteria.
Chemoheterotroph
* Harness chemical energy.
* Harness carbon from organic source.
* Ex. common in Archaea, bacteria, protists, fungi, animals, some plants.
Classify organisms based on their oxygen requirements
Obligate aerobes: require oxygen.
Obligate anaerobes: can’t use oxygen and are poisoned by it:
* Some exclusively get energy from fermentation.
* Others perform respiration using inorganic molecule other than oxygen.
Facultative anaerobes use oxygen if available
* Can also get energy by fermentation in anaerobic environments.
Classify organisms into domains
prokaryotic: archaea, bacteria.
Eukaryotic: eukarya.
Compare and contrast bacteria and archaea
Main difference is their nucleic acid sequence (plus ribosomal RNA, cell wall structure, lipids in cell membranes).
Bacteria have peptidoglycan in their cell wall, Archaea doesn’t
Shapes of bacteria
Cocci: spherical
Bacilli: rod-shaped
Spiralli: spiral
What is gram stain
see GD
A stain that classifies bacteria by cell wall structure:
* Thick walls of peptidoglycan traps dye → stains purple (gram-positive).
* Complex walls with less peptidoglycan that don’t retain dye → stains pink (gram-negative).
Structure and function of bacterial cell wall
see GD
External to plasma membrane that protect bacteria from osmotic changes
* Have peptidoglycan (large mesh-like polymer that forms the bacterial cell wall).
Function of capsule
see GD
External of cell wall; made of sugars.
* protects bacteria from immune detection by phagocytes
* assists in adhesion to surfaces
* colony formation,
* formation of biofilm.
Biofilm, how does it form?
What does it protect from?
Forms from bacterial capsules fusing togather.
Protects bacteria from chemicals like antibiotics.
Function of flagella
se GD
Helps bacterial cell move:
* Taxis: movement towards or away from stimulus.
Function of pili
see GD
Common in gram-neg. bacteria.
* Attachment to surfaces, colonization/infection, conjugation.
Conjugation
- F pilus of one cell attaches to other cell.
- Plasmid (extrachromocomal pieces of DNA that encode new functions, like antibiotic resistance) is transferred
Define and explain the process of binary fission
see GD
Type of asexual reproduction:
* Cell replicates its DNA.
* Plasma forms and separates the DNA molecules, resulting in 2 identical cells; leads to exponential growth.
Function endospore
A thick protective coating around the cell’s genetic material that forms under harsh conditions.
* Cell is damaged and is metabolically inctive.
* Endospore can absorb water and resum life.
Symbiosis
Ecological relationship between species in direct contact.
Types of symbiotic relationships
- Mutualism: both symbionts benefit.
- Commensalism: one symbiont benefits, the other receives no harm or benefit (like in human bodies).
- Parasitism: one symbiont (parasite) benefits at the expense of the other (host).
function of normal microbiota in the skin
Some bacteria can convert sebum to fatty acids → creates acidic environment that prevents growth of other bacteria.
Normal microbiota in digestive system
Saliva contains millions of bacteria per mL, stomach contains relatively few due to lower pH.
Large intestine contains alot:
* Mostly anaerobes or facultative anaerobes.
* Breakdown molecules, some provide with vitamins.
To be consider pathogenic, bacteria must:
- Invade a host.
- Resist internal defenses in order to grow.
- Cause harm to host.
Koch’s postulates
see GD
- The pathogen must be found in diseased organism, but not healthy organisms.
- The pathogen must be isolated from the diseased organism and grown in a pure culture.
- The pathogen must induce disease when introduced to healthy organisms.
- The pathogen must then be reisolated from the diseased organism and be identified as identical to the original causative agent.
What is an opportunisic pathogen?
Non-pathogenic microorganisms that act as pathogens in certain circumstances (given the opportunity, like an impaired immune system).
How do pathogenic bacteria cause disease?
Physical growth and invasion of tissue:
By releasing toxins:
* Exotoxins: proteins secreted by bacteria. (ex. Staphylococus aureus)
* Endotoxins: components of bacterial membranes that are released when the cells die. (ex. borrelia that causes Lyme disease)
What are antibiotics?
Drugs that kill or slow the growth of bacteria.
How does antibiotic resistance develop?
- Within a number of bacteria, a few are resistant to antibiotics.
- Antibiotics kill the pathogens but not the resistant bacteria.
- The remaining resistant bacteria develop freely (can also transfer drug-resistance to other bacteria)
Human use of bacteria
- E. coli is a model organism for genetics.
- Many species make antibiotics, vitamins.
- Decompose plastic, sewage, pesticides.
- Make food like yogurt, cheese, beer.
- Make useful chemicals like butanol, acetone, acetic acid.
- Use recombinant DNA technology to make insulin, lactase, human growth hormone.
How does food become spoiled?
When contaminated with microorganisms.
* Break down food and produce acids and other harmful wastes (the microorganism themselves may not be harmful).
Microorganisms that can cause foodborne illnesses
See GD
- Salmonella enterica in eggs, poulty. Endotoxin.
- Staphylococcus aureus in meat, dairy. Heat-stable exotoxin.
Explain how food preservation methods prevent food spoilage
- Freezing slows down microbial growth.
- Pickling: acidic conditions prevents growth.
- Fermenting: microbes metabolize food and produce acids that prohibit the growth of some microbes.
- Dehydrating removes water.
- Canning: seals and heat food to kill all organisms (some anaerobes, clostridium botulinum, makes exotoxin that causes botulism, can grow in improperly canned foods).
- Pasteurization: milk heated quickly, then cooled rapidly.
- No sterilization, but reduces microbial load and rids most pathogens.
- Chemical food additives
- Very few approved for use and safe for human consumption (e.g. antibiotics, sodium nitrites, ethylene, and propylene oxides).
Describe the basic structure of a virus
Surrounded by capsid (protective protein coat)
* Genetic material DNA or RNA, double- or single-stranded.
Why are virus considered non-living?
Because they rely on organisms (host) to mutiply as they lack the biological ability to do so themselves. Also not made of cells.
Life cycle of viruses
- Host entry (usually bind sugars and proteins on host cell surface).
- Replication of genetic material (use host’s enzymes and materials).
- Make capsid proteins using viral genes.
- Assembly of new viral particles.
- Exist host cell.
Explain how viruses target specific host cells
Viral infections can be species-, tissue-, or organ-specific:
* Depends on molecular interactions between viral surface proteins and host cell surface receptors.
What causes hamburger disease? What causes acne?
- Escherichia coli found in cow intestines. Causes diarrhea and stomach cramps.
- Propionibacterium acnes.
Describe the structure of SARS-CoV-2
- Capsid surrounded by lipid layer (envelope) with spike proteins.
- Spike proteins bind to epithelial cells in lungs using human receptor ACE2.
Food perishibility
Highly perishable: meat, dairy, fruits, & veggies.
Semi-perishable foods: potatoes, apples, carrots & nuts.
Non-perishable: sugars, grains, rice, flour, & dry beans.
Why do prokaryotes reproduce faster than eukaryotes?
In order to reproduce, cells need nutrients. Small cells like prokaryotes have a higher surface-to-area ratio than eukaryotes, allowing nutrients to quickly diffuse in to other parts of the cell.
