02 Prokaryotes

Question 1

How old are prokaryotes?

Answer 1

~3.5 billion years old

Question 2

How large are prokaryotes?

Answer 2

0.5-5.5 micrometers

Question 3

What is the function of the prokaryotic cell wall?

Answer 3

Maintain cell shape, prevent bursting in hypotonic environments – but NOT hypertonic environments

Question 4

What is peptidoglycan?

Answer 4

Polymer ONLY in domain bacteria. Polymer structure with sugars cross-linked by short polypeptides.
Makes up cell wall.

Question 5

What do plants and fungi have instead of peptidoglycan?

Answer 5

plants - cellulose

fungi - chitin

Question 6

What are the two prokaryotic stains?

Answer 6

1: crystal-violet – stains purple, retained by gram-positive bacteria
2: safranin – pink, retained by gram-negative bacteria

Question 7

What is a gram-positive bacterium?

Answer 7

• Cell wall with thick peptidoglycan
• Vulnerable to antibiotics which inhibit peptidoglycan synthesis
• Stained purple by crystal-violet stain

Question 8

What is a gram-negative bacterium?

Answer 8

• Cell wall has thin peptidoglycan
• Much less vulnerable to antibiotics
• Stained pink by safranin stain
• Also produces lipopolysaccharide (LPS) – toxic, causes fever

Question 9

What is a prokaryotic capsule / slime layer?

Answer 9

• Provides defense against dehydration / phagocytosis
• Consists of polysaccharides, proteins
• Capsule = rigid, strong
• Slime layer = looser protection

Question 10

What is taxis?

Answer 10

Motility

Positive taxis = towards stimulus
Negative taxis = away from stimulus
Phototaxis = response to light
Chemotaxis = response to chemical

Question 11

What are flagella?

Answer 11

Found in bacteria, eukaryotes, archaea BUT all developed independently => analogous traits

Question 12

What are some differences between prokaryotic and eukaryotic flagella?

Answer 12

• Prokaryotic one tenth size of eukaryotic
• Prokaryotic not covered in plasma membrane
• Composed of different proteins
• Different propulsion methods

Question 13

What are the constituent parts of the prokaryotic flagellum?

Answer 13

• Motor rings embedded in cell wall / membrane
• Hook
• Filament – which rotates / propels cell

Question 14

SEQ prokaryotic taxis

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Name three modes of prokaryotic genetic recombination

Answer 16

Transformation, transduction, conjugation

Question 17

What is genetic transformation?

Answer 17

Prokaryotic cell taking in foreign DNA from environment, e.g. in the Griffith experiment

Question 18

What is genetic transduction?

Answer 18

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

Question 19

SEQ genetic conjugation in prokaryotes

Answer 19

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

Question 20

Discuss prokaryotic metabolic diversity

Answer 20

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

Question 21

What does molecular evidence indicate regarding prokaryotic diversity?

Answer 21

Two domains: bacteria and archaea

• Archaea closer to eukaryotes than prokaryotes are
• strong evidence for horizontal gene transfer

Question 22

What are the primary groups in domain bacteria?

Answer 22

Proteobacteria

Chlamydia
- all parasites

Spirachetes
- lyme, syphillis

Cyanobacteria
- gram negative, photosynthetic, choloroplast precursors

Gram positive bacteria

Question 23

What are some examples of archaea?

Answer 23

Extremphiles - e.g. halophiles (salt), thermophiles

Methanogens - release methane