Lecture 9: Prokaryotes

Question 1

What two groups on the tree of life constitute prokaryotes?

Is this a monophyletic group?

Answer 1

Bacteria and Archaea

No, archaea are more related to eukarya than bacteria

Question 2

What are the most abundant organisms on earth? How many are in your mouth/intestines?

Answer 2

The most abundant organisms are prokaryotes. There are about 1000 species in our intesting and 700 in our mouths.

Question 3

What are examples of diseases caused by bacterial pathogens?

Answer 3

1. Strep throat
2. Diarrhea
3. Black Plague
4. Gonorrhea

Question 4

What are the five ways we can study prokaryote diversity?

Answer 4

1. Enrichment culture
2. DNA Sequencing
3. Shape
4. Gram Stain
5. Modes of Nutrition

Question 5

What is enrichment culture?

Answer 5

Enrichment culture is when bacteria are cultured (grown) in the lab. The classic approach is to try to use growing conditions to try to coax bacteria to grow.

Question 6

How are prokaryotes studied through DNA sequencing?

Answer 6

One takes an environmental sample and sequences the DNA (can be ribosomal or just any DNA). This allows for a reflection of this bacteria’s phylogenetic history and one can decipher how manyspecies are in the sample and their relative amounts.

Question 7

How is shape used to distinguish among prokaryotes? What are the 3 shapes?

Answer 7

Prokaryotes can either be:
- spherical (coccus)
- rod-shaped (bacilli)
- helical

Question 8

What is Treponema pallidum? What is its shape?

Answer 8

Treponema pallidum is the bacteria responsible for causing the disease syphillus. Its shape, the corkscrew shape, is important to its mode of infection. The bacterium “screws” its way into slight breaks in the skin and multiplies prolifically.

Question 9

How is the Gram stain used to distinguish among bacteria?

Answer 9

The gram stain provides insights into the composition of the cell wall and plasma membrane. Various chemicals are applied to bacteria (including a violet-colored dye and iodine).

The gram positive bacteria are violet. Gram negative bacteria do not retain the violet dye.

Question 10

What is the difference between gram+ and gram- bacteria?

Why is penicillin, an antibiotic, more effective on gram+ bacteria?

Answer 10

Gram+ and gram- bacteria differ in the morphology and structure of their cell walls. Gram+ bacteria contain more peptidoglycan, which absorbs the violet dye.
Gram-bacteria have much less peptidoglycan, and therefore do not look violet.

Penicillin is an antibiotic that inhibits the synthesis and cross-linking of peptidoglycans.

Question 11

Do Archaea have peptidoglycan in their cell walls?

Answer 11

No, only bacteria have peptidoglycan.

Question 12

3 examples of gram+ disease-causing bacteria

Answer 12

Streptococcus pyogenes - strep throat, scarlet fever, rheumatic fever
Streptococcus pneumoniae - bacterial pneumonia
Staphylococcus aureus - skin infections, toxic-shock syndrome

Strepto = chain of cells
Staphylo = “bunch of grapes” organization

Question 13

3 examples of gram+ disease-causing bacteria

Answer 13

Streptococcus pyogenes - strep throat, scarlet fever, rheumatic fever
Streptococcus pneumoniae - bacterial pneumonia
Staphylococcus aureus - skin infections, toxic-shock syndrome

Strepto = chain of cells
Staphylo = “bunch of grapes” organization

Question 14

2 examples of gram- disease-causing bacteria

Answer 14

Salmonella enterica - food poisoning
Neiserria gonorrheae - causes gonorrhea

Question 15

How is modes of nutrition used to distinguish among prokaryotes?

Answer 15

All prokaryotes fall into two categories in terms of nutrition:
Autotrophs and Heterotrophs
Autotrophs: need only CO2 and an energy source to synthesize nutrients
Heterotrophs: need a source of organic carbon for their food

Question 16

What are the two kinds of autotrophs?

Answer 16

Photoautotrophs: use light as the source of energy that drives the synthesis of organic compounds from CO2. use photosynthesis.

Chemoautotrophs: get energy from chemical bonds by oxidation of electron donors in the environment.
Energy can come from H2S (hydrogen sulfide), NH3 (ammonia), organic compounds

Question 17

Deep-sea vent community depends on chemoautrotophic bacteria for energy

What must we know about these deep-sea communities?

Answer 17

1. They depend ultimately upon Bacteria and Archaea
2. Most of the larger organisms there live in symbiosis with chemoautotrophic bacteria. This symbiosis is mutualistic.
3. Most freeliving bacteria in the deep-sea vent communities are Archaea, because they are adapted to extreme environments.

Question 18

What are the two types of heterotrohps?

Answer 18

Photoheterotrophs: these organisms capture energy from light via photosynthesis but also need organic compounds to survive. They make glucose but can’t make the rest of the organic compounds needed from a glucose precursor.

Chemoheterotrophs: these organisms consume organic compounds. Most prokaryotes are chemoheterotrophs.

Question 19

What is the difference between Archaea and Bacteria?

Answer 19

RNA Polymerase: Bacteria’s has five subunits and archaea has 13 (similar to humans)
Peptidoglycan: only bacteria have it
First amino acid: Bacteria uses formylmethionine and archaea uses methionine
Histones associated with DNA: only in Archaea

Question 20

What are the similarities among Archaea and bacteria?

Answer 20

1. Both divide by binary fission
2. Organize DNA in a circular form
3. Are haploid
4. Are all unicellular