02 Prokaryotes Flashcards
How old are prokaryotes?
~3.5 billion years old
How large are prokaryotes?
0.5-5.5 micrometers
What is the function of the prokaryotic cell wall?
Maintain cell shape, prevent bursting in hypotonic environments – but NOT hypertonic environments
What is peptidoglycan?
Polymer ONLY in domain bacteria. Polymer structure with sugars cross-linked by short polypeptides.
Makes up cell wall.
What do plants and fungi have instead of peptidoglycan?
plants - cellulose
fungi - chitin
What are the two prokaryotic stains?
1: crystal-violet – stains purple, retained by gram-positive bacteria
2: safranin – pink, retained by gram-negative bacteria
What is a gram-positive bacterium?
- Cell wall with thick peptidoglycan
- Vulnerable to antibiotics which inhibit peptidoglycan synthesis
- Stained purple by crystal-violet stain
What is a gram-negative bacterium?
- Cell wall has thin peptidoglycan
- Much less vulnerable to antibiotics
- Stained pink by safranin stain
- Also produces lipopolysaccharide (LPS) – toxic, causes fever
What is a prokaryotic capsule / slime layer?
- Provides defense against dehydration / phagocytosis
- Consists of polysaccharides, proteins
- Capsule = rigid, strong
- Slime layer = looser protection
What is taxis?
Motility
Positive taxis = towards stimulus
Negative taxis = away from stimulus
Phototaxis = response to light
Chemotaxis = response to chemical
What are flagella?
Found in bacteria, eukaryotes, archaea BUT all developed independently => analogous traits
What are some differences between prokaryotic and eukaryotic flagella?
- Prokaryotic one tenth size of eukaryotic
- Prokaryotic not covered in plasma membrane
- Composed of different proteins
- Different propulsion methods
What are the constituent parts of the prokaryotic flagellum?
- Motor rings embedded in cell wall / membrane
- Hook
- Filament – which rotates / propels cell
SEQ prokaryotic taxis
H+ ions pumped out of cell across plasma membrane by electron transport chain => forms chemiosmotic gradient
H+ diffuse back into cell through motor
=> hook turns
==> filament rotates
====> cell moves
Use E Coli in the human intestine as an example of how rapid reproduction can be an effective prokaryotic reproductive strategy despite small probabilities of individual gene mutation
probability of mutation = 1/10 million per gene per cell per division
c. 2^10 new cells produced in human intestine per day
= 2000 mutations of each individual gene per day
= ~9 million total mutations per day
Name three modes of prokaryotic genetic recombination
Transformation, transduction, conjugation
What is genetic transformation?
Prokaryotic cell taking in foreign DNA from environment, e.g. in the Griffith experiment
What is genetic transduction?
Either: phage transfers prokaryotic genes from one host to another
Or: viral replication – fragment of host DNA accidentally packaged into virus and injected into new host
SEQ genetic conjugation in prokaryotes
Prokaryotic cells with F plasmid (F+ cells) = donor cells
F plasmid codes for production of pilis.
F+ uses pilis to attach to F- cell (recipient)
Pilis pull F- cell close to F+ cell
Mating bridge produced
One-way horizontal DNA transfer from donor to recipient
Discuss prokaryotic metabolic diversity
Energy sources: photo, chemo
Carbon sources: inorganic (autotrophs); organic (heterotrophs)
Role of oxygen:
obligate aerobes - require for respiration
obligate anaerobes:
- either produce ATP without an electron transport chain (fermentation) OR use substance other than oxygen as final electron acceptor, e.g. nitrate, sulfate (= anaerobic respiration)
facultative aerobes - do both
What does molecular evidence indicate regarding prokaryotic diversity?
Two domains: bacteria and archaea
- Archaea closer to eukaryotes than prokaryotes are
- strong evidence for horizontal gene transfer
What are the primary groups in domain bacteria?
Proteobacteria
Chlamydia
- all parasites
Spirachetes
- lyme, syphillis
Cyanobacteria
- gram negative, photosynthetic, choloroplast precursors
Gram positive bacteria
What are some examples of archaea?
Extremphiles - e.g. halophiles (salt), thermophiles
Methanogens - release methane
