General intro/Impact of microorganisms on human

Question 1

What are some general characteristics of microorganisms?

Answer 1

• defined as life forms too small to be seen by human eyes
• they are diverse in shape and metabolic capacity
• they inhabit every environment
• they can be unicellular, multicellular or form complex structures
• they are the oldest form of life
• they represent a major fraction of Earth’s biomass
• more complex life forms (animals and plants) have been and are influenced by microbes via symbiosis and pathogens

Question 2

What are the structural characteristics that all microbial cells have?

Answer 2

• cytoplasmic membrane – separate the outside from the cytoplasm
• genome – either DNA or RNA
• ribosomes

Question 3

What is the difference between eukaryotic and prokaryotic microbial cells?

Answer 3

• Eukaryotic cells have membrane-enclosed organelles (nucleus, golgi, ER … ) and their genome is organised in linear structures (chromosomes) and is very large (contains lots of junk DNA
• Prokaryotic cells lacks of nucleus and organelles, genome is organised in nucleoid, and is small, but all genes are expressed. Some cells contain extrachromosomal, circular DNA (plasmid) and some bacteria have cell walls (external proteiction)

Question 4

What are the activities that all microbial cells posses?

Answer 4

• metabolic activities; nutrients are acquired from the environment and transformed into cellular material and waste (catabolic and anabolic metabolism)
• growth; the genome contains all the information for metabolism, allowing growth
• evolution; genes can change within a population, leading to phenotypic modification

Question 5

What are the activities that some cells posses?

Answer 5

• motility; some cells posses the ability to self-repulsion in response to environmental conditions
• differentiation; cells can form specialised cells (spores)
• intercellular communication; cells can communicate with other cells via chemical signals
• horizontal gene transfer; some cells can interchange genes with other cells

Question 6

What are morphological characteristics of microbial cells?

Answer 6

• morphology is defined by cell size and shape
• most prokaryotes range between 0.5-10 micrometer
• some prokaryotes can reach 600 micrometer
• eukaryotes cells range between 5-100 micrometer
• the smaller the cell is, the higher is surface-to-volume ratio (the larger the cell is, the slower it grows)

Question 7

What are some typical cell shapes microbial cells can have?

Answer 7

• coccus
• rod/bacillus
• spirillus
• spirochete
• appenaged
• some are clustered

Question 8

What are the 3 domains? And what characteristics they have that allow differentiation?

Answer 8

1. Bacteria
   
   • prokaryotes
   • 80+ phyla known
2. Archaea
   
   • prokaryotes
   • 15+ phyla, of which 5 are well described
   • extremophiles/tolerate extreme environments
   • lack of disease-causing species
3. Eukarya
   
   • eukaryotes
   • 6 kingdoms (plants, fungi, animals …)
   • originated from algae and protozoa (unicellular)

All three domains have a common ancestor (LUCA = last universal common ancestor)

Question 9

Why viruses are not considered life?

Answer 9

viruses are parasite that need to infect host cells to activate metabolism, which processes are carried by host’s machineries.

Question 10

What is the difference between anoxygenic and oxygenic bacteria? And what is a common characteristic that the first bacteria had?

Answer 10

The first bacteria were phototrophic microorganisms (they were able to harvest energy from the sunlight) and anoxygenic, thus were able to produce photosynthetic products in absence of oxygen (anaerobic respiration). As oxygen was present in the atmosphere, cyanobacteria evolved, which were able to do photosynthesis and produce oxygen (oxygenic environment)

Question 11

How microorganisms affect human life?

Answer 11

Microorganisms affect human’s everyday life in both harmful and beneficial way:

1. Agents of disease; bacterial and viral pathogens are the cause of infectious diseases
2. Agriculture; humans have exploited microbial nutrient cycles in agriculture (nitrogen, sulfur, carbon)
3. Mammals; mammals live in symbiosis with microbes (gut in humans and rumen in ruminent animals – allow cellulose digestion)
4. Food; microbes have both harmful (spoilage and foodborne diseases) and beneficial (improvement of safety and preservation) function
5. Industries; humans use microbes as tools in the major industries (biotechnologies, bioremediation … )