Chapter 16: Microbial life

Question 1

Prokaryotes’ contribution to life :)

Answer 1

• 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.

Question 2

Define autotroph, heterotroph

Answer 2

Autorophs (like plants) make their own food. Heterorophs (like animals) get their foods from elsewhere.

Question 3

Explain how eukaryotic life arose out of endosymbiosis

Answer 3

Organelles (mitochondria, chloroplasts, nuclei) were prokaryotes that were engulfed by other prokaryotes. Started to depend on one another for resources.

Question 4

Explain the significance of prokaryotes to life on Earth

Answer 4

Maintain ecological balance:
* Live on and in humans and animals (like stomach and skin).
* Produces food and chemicals.
* Causes disease 🙁

Question 5

What is microbiology

Answer 5

Study of microorganisms

Question 6

Classify organisms based on trophy (photoautotroph, chemoautotroph, photoheterotroph, chemoheteroph).

see chart on GD

Answer 6

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.

Question 7

Classify organisms based on their oxygen requirements

Answer 7

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.

Question 8

Classify organisms into domains

Answer 8

prokaryotic: archaea, bacteria.
Eukaryotic: eukarya.

Question 9

Compare and contrast bacteria and archaea

Answer 9

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

Question 10

Shapes of bacteria

Answer 10

Cocci: spherical
Bacilli: rod-shaped
Spiralli: spiral

Question 11

What is gram stain

see GD

Answer 11

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).

Question 12

Structure and function of bacterial cell wall

see GD

Answer 12

External to plasma membrane that protect bacteria from osmotic changes
* Have peptidoglycan (large mesh-like polymer that forms the bacterial cell wall).

Question 13

Function of capsule

see GD

Answer 13

External of cell wall; made of sugars.
* protects bacteria from immune detection by phagocytes
* assists in adhesion to surfaces
* colony formation,
* formation of biofilm.

Question 14

Biofilm, how does it form?
What does it protect from?

Answer 14

Forms from bacterial capsules fusing togather.
Protects bacteria from chemicals like antibiotics.

Question 15

Function of flagella

se GD

Answer 15

Helps bacterial cell move:
* Taxis: movement towards or away from stimulus.

Question 16

Function of pili

see GD

Answer 16

Common in gram-neg. bacteria.
* Attachment to surfaces, colonization/infection, conjugation.

Question 17

Conjugation

Answer 17

• F pilus of one cell attaches to other cell.
• Plasmid (extrachromocomal pieces of DNA that encode new functions, like antibiotic resistance) is transferred

Question 18

Define and explain the process of binary fission

see GD

Answer 18

Type of asexual reproduction:
* Cell replicates its DNA.
* Plasma forms and separates the DNA molecules, resulting in 2 identical cells; leads to exponential growth.

Question 19

Function endospore

Answer 19

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.

Question 20

Symbiosis

Answer 20

Ecological relationship between species in direct contact.

Question 21

Types of symbiotic relationships

Answer 21

• 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).

Question 22

function of normal microbiota in the skin

Answer 22

Some bacteria can convert sebum to fatty acids → creates acidic environment that prevents growth of other bacteria.

Question 23

Normal microbiota in digestive system

Answer 23

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.

Question 24

To be consider pathogenic, bacteria must:

Answer 24

• Invade a host.
• Resist internal defenses in order to grow.
• Cause harm to host.

Question 25

Koch's postulates ## Footnote see GD

Answer 25

1. The pathogen must be found in diseased organism, but not healthy organisms. 1. The pathogen must be isolated from the diseased organism and grown in a pure culture. 1. The pathogen must induce disease when introduced to healthy organisms. 1. The pathogen must then be reisolated from the diseased organism and be identified as identical to the original causative agent.

Question 26

What is an opportunisic pathogen?

Answer 26

Non-pathogenic microorganisms that act as pathogens in certain circumstances (given the opportunity, like an impaired immune system).

Question 27

How do pathogenic bacteria cause disease?

Answer 27

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)

Question 28

What are antibiotics?

Answer 28

Drugs that kill or slow the growth of bacteria.

Question 29

How does antibiotic resistance develop?

Answer 29

* 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)

Question 30

Human use of bacteria

Answer 30

* 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.

Question 31

How does food become spoiled?

Answer 31

When contaminated with microorganisms. * Break down food and produce acids and other harmful wastes (the microorganism themselves may not be harmful).

Question 32

Microorganisms that can cause foodborne illnesses ## Footnote See GD

Answer 32

* *Salmonella enterica* in eggs, poulty. Endotoxin. * *Staphylococcus aureus* in meat, dairy. Heat-stable exotoxin.

Question 33

Explain how food preservation methods prevent food spoilage

Answer 33

* **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).

Question 34

Describe the basic structure of a virus

Answer 34

Surrounded by **capsid** (protective protein coat) * Genetic material DNA or RNA, double- or single-stranded.

Question 35

Why are virus considered non-living?

Answer 35

Because they rely on organisms (host) to mutiply as they lack the biological ability to do so themselves. Also not made of cells.

Question 36

Life cycle of viruses

Answer 36

1. Host entry (usually bind sugars and proteins on host cell surface). 1. Replication of genetic material (use host’s enzymes and materials). 1. Make capsid proteins using viral genes. 1. Assembly of new viral particles. 1. Exist host cell.

Question 37

Explain how viruses target specific host cells

Answer 37

Viral infections can be species-, tissue-, or organ-specific: * Depends on molecular interactions between viral surface proteins and host cell surface receptors.

Question 38

What causes hamburger disease? What causes acne?

Answer 38

1. *Escherichia coli* found in cow intestines. Causes diarrhea and stomach cramps. 2. *Propionibacterium acnes*.

Question 39

Describe the structure of SARS-CoV-2

Answer 39

* Capsid surrounded by lipid layer (envelope) with spike proteins. * Spike proteins bind to epithelial cells in lungs using human receptor ACE2.

Question 40

Food perishibility

Answer 40

**Highly perishable**: meat, dairy, fruits, & veggies. **Semi-perishable foods**: potatoes, apples, carrots & nuts. **Non-perishable**: sugars, grains, rice, flour, & dry beans.

Question 41

Why do prokaryotes reproduce faster than eukaryotes?

Answer 41

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.