1.3 Classification and Structure of Prokaryotic Cells***

Question 1

prokaryotes

Answer 1

• no membrane-bound organelles
• genetic material organized in a single, circular molecule of DNA (plasmid)
• DNA is concentrated in the nucleoid region
• simplest of all organisms
• include all bacteria

Question 2

domains of life

Answer 2

1. Archaea (prokaryotes)
2. Bacteria (prokaryotes)
3. Eukarya

Question 3

Archaea

Answer 3

• single-celled organisms
  
  • visually similar to bacteria but…
    
    • contain genes and several metabolic pathways which are more similar to eukaryotes and bacteria
• extremophiles: extremely high temps, high salinity, and no light
  
  • also found in a variety of habitats, including the human body
• ability to use alternative sources of energy:
  
  • photosynthetic → light
  • chemosynthetic → inorganic compounds such as sulfur and nitrogen compounds (i.e. ammonia)

Question 4

Archaea continued…

Answer 4

• Archaea more similar to eukaryotes than prokaryotes
  
  • hypothesized → eukaryotes and archaea share a common origin
    
    • both start translation with methionine, contain similar RNA polymerases, and associate histones with DNA
• however → archaea contain a single, circular chromosome, divide via binary fission or budding, and share a similar structure to bacteria
  
  • also, resistant to many antibiotics

Question 5

bacteria

Answer 5

• all bacteria contain:
  
  • a cell membrane
  • cytoplasm
• some have flagella or fimbriae
• bacteria and eukaryotes share analogous structures → difficult to target only bacteria with medications
  
  • however, some seemingly similar structures have great enough biochemical differences
    
    • eukaryote vs bacterial flagella and ribosomes

Question 6

bacteria continued…

Answer 6

• 5 x 10³⁰ bacteria on earth
• bacteria outnumber human cells 10:1

Question 7

bacteria continued…

Answer 7

• some bacteria are mutualistic symbiotes
  
  • ex: bacteria in human gut produce vitamin K and vitamin B (biotin) → prevent opportunistic pathogens
    
    • produce vitamin K in the intestine → vit K required for production of plasma proteins required for blood clotting → newborns don’t have colonized gut → can’t produce clotting factors → risk for hemorrhage → newborns injected with vitamin K

Question 8

bacteria continued…

Answer 8

• some bacteria are pathogens or parasites → cause disease
  
  • can live intracellularly or extracellularly
    
    • ex: Chlamydia trachomatis → lives inside cells of reproductive tract
    • ex: Clostridium tetani → lives outside of cells and produces toxins which enter the bloodstream

Question 9

classification of bacteria by shape

Answer 9

• cocci → spherical
  
  • Streptococcus pyogenes
• bacilli → rod
  
  • Escherichia coli
• spirilli → spiral
  
  • Treponema pallidum (syphilis)

Question 10

Aerobes and Anaerobes

Answer 10

obligate aerobes vs aerobes

Question 11

obligate aerobe

Answer 11

require O₂ for metabolism

Question 12

anaerobes (3 types)

Answer 12

do not require O₂

Question 13

obligate anaerobes

Answer 13

die in O2 containing environments

(reactive O2-containing radicals → cell death)

Question 14

facultative anaerobes

Answer 14

can do both aerobic and anaerobic metabolism

Question 15

aerotolerant anaerobes

Answer 15

unable to use O2 for metabolism but are not harmed by O2

Question 16

prokaryotic cell structure

Answer 16

• cell wall
• cell membrane
• envelope
• ribosome
• nucleoid DNA region
• plasmids
• flagellum

Question 17

cell wall

Answer 17

• two types of cell walls:
  
  • gram positive
  • gram negative

Question 18

gram positive vs gram negative staining

Answer 18

1. violet stain
2. safranin counterstain
3. deep purple → absorbed crystal violet stain → gram positive
4. pink-red → absorbed safranin counterstain → gram negative

Question 19

gram positive cell walls

Answer 19

• thick layer of peptidoglycan (polymer of AA and sugars)
• contains lipoteichoic acid (Fx unknown, but may trigger human immune response)

Question 20

gram negative cell walls

Answer 20

• thin layer of peptidoglycan
• contain outer membranes
• contain lipopolysaccharide (triggers stronger human immune system response)

Question 21

flagella (insert figure 1.9 from page 19)

Answer 21

made up of:

1. filament → hollow, helical structure composed of flagellin
2. hook → connects the filament to the basal body to create torque
3. basal body → anchors flagellum to the cytoplasmic membrane and is the rotating motor

Question 22

DAN nucleoid region

Answer 22

single, circular chromosome of DNA which is not coiled around histones

Question 23

plasmid

Answer 23

DNA acquired from external sources

(not necessary for survival → not considered part of the genome)

Question 24

prokaryotes lack mitochondria

Answer 24

electron transport chain / generation of ATP occurs in the cell membrane

Question 25

prokaryotes have different ribosomes than eukaryotes

Answer 25

pro → 30S and 50S subunits

eu → 40S and 60S subunits

Question 26

1.3 Concept Check

Answer 26

Question 27

1.3 Concept Check

Answer 27