Bacterial Diversity and Biology

Question 1

Why are bacterial ribosomes targets for phylogenetic studies?

Answer 1

They contain 16s RNA (rRNA) which has a low mutation rate

Question 2

Name a difference between the eukaryotic and prokaryotic cell membranes.

Answer 2

prokaryotic cell membranes do not contain steroids such as cholesterol

Question 3

Define an acid-fast cell envelope.

Answer 3

neither gram-positive or gram-negative due to thick layer of mycolic acids that protect bacteria
forms a hydrophobic layer
reduced rate of nutrient uptake

Question 4

What do gram-positive and gram-negative bacterial cell membranes differ in levels of?

Answer 4

peptidoglycan

Question 5

How is peptidoglycan cross-linked to one another?

Answer 5

via a tetrapeptide

Question 6

What is the role of teichoic acids in gram-positive bacteria?

Answer 6

provides rigidity
promotes interaction w host cells and biofilm formation
promote adherence to host cells

bound covalently to peptidoglycan
major surface antigen

Question 7

How does the structure of gram-negative bacteria differ to that of gram positive?

Answer 7

absence of teichoic and lipotechoic acids
has an outer membrane
thin layer of peptidoglycan
periplasmic space
have lipopolysaccharides on surface

Question 8

What is the role of lipopolysaccharides on gram-negative bacteria?

Answer 8

essential for bacterial viability
hydrophilic o-polysaccharide repels hydrophobic molecules, including antibiotics
LPS structure used to classify bacteria

Question 9

Define what a plasmid is.

Answer 9

circular or linear extrachromosomal DNAs not usually essential for bacterial survival capable of autonomous replication that often provide a selective advantage eg antibiotic resistance

Question 10

What is the structure of bacterial flagella?

Answer 10

1. long helical filament
2. connecting hook
3. basal body –> rotor to turn the flagellum

filament is a hollow structure composed solely of flagellin protein
basal body is a complex structure > 15 proteins

Question 11

What is the structure and role of pili and fimbriae?

Answer 11

both are protein spikes that extend from surface
pili are longer but less abundant

fimbriae used for adhesion (type I)
pili used for twitching motility (type IV), extension and retraction allows movement on solid surface

pili also allow for horizontal gene transfer

Question 12

What are capsules?

Answer 12

polysaccharide slime surrounding bacterial cells
present in both gram positive and gram negative
barrier to toxic hydrophobic molecules
contain water -> prevent dessication

major virulence factor for effective host colonisation
allows resistance to phagocytosis

Question 13

What is a serotype?

Answer 13

groups within a single species of bacteria that share distinctive surface structures

Question 14

What is passive transport?

Answer 14

simple diffusion of small hydrophobic molecules
hydrophilic molecules require facilitated diffusion via channel or carrier proteins

Question 15

What is ion-coupled transport?

Answer 15

eg proton symport
- driven by electrochemical transmembrane proton gradient (proton or sodium motive force)
- co-transport in same direction
- active transport

eg ABC transport
- ATP-binding cassette
- hydrolysis of ATP drives transport
- specific binding proteins
- active transport

Question 16

What is group translocation?

Answer 16

substrate is modified, generally phosphorylated during transport eg phosphotransferase system (PTS system)
energy provided by the PEP passed along chain of enzymes
modification of the sugar –> maintains the concentration gradient

Question 17

How is ATP generated in bacteria?

Answer 17

1. electrons generated during glycolysis are transferred to NAD+, a cytoplasmic electron carrier molecule that is reduced to NADH
2. electrons are carried to electron transport chain in the plasma membrane where proton motive force fuels ATP synthesis from ADP by ATP synthase

Question 18

How does bacterial fermentation cause dental disease?

Answer 18

high sugar content diets provide sugars for bacteria on our teeth to ferment
this produces lactic acid which dissolves calcium phosphate
bacterial proteolytic enzymes degrade supporting matrix

Question 19

What are the main components involved in bacterial cell division?

Answer 19

Fts proteins interact to form divisome
- form septal ring and define the cell division plane

Min proteins (C, D, and E)
- cytoskeletal-like coiled in poles
- bipolar gradient that help localise the ring

proteins move around the cell to prevent attachment of Fts proteins in certain places

Question 20

What protein initiates formation of DNA replication complex and how?

Answer 20

DnaA
binds to the DNA origin of replication (oriC) to initiate formation

Question 21

What is endospore formulation?

Answer 21

genome is sequestered in highly protected spore until environmental conditions improve
mother cell secretes coat (composed of calcium dipicolinate) then lyses to release spore
occurs mainly in gram+ bacteria

Question 22

Properties of bacterial ribosome?

Answer 22

Smaller than mammalian
70s compound of 2 subunits (30s + 50s)
No membrane between ribosomes and DNA so transcription and translation are coupled
Major antibiotic target

Question 23

Bacteria cell wall properties?

Answer 23

Peptidoglycan (mucopeptide or murein) polysaccharide chains with peptide cross links (tetrapeptide)
Resists osmotic pressure and determines cell shape
Signals innate immune system

Question 24

Gram negative vs positive staining

Answer 24

Negative - pink (due to thin layer of peptigoglycan)
Positive - purple (due to many layers of peptidoglycan)

Question 25

Plasmid properties?

Answer 25

Circular/linear extrachromosomal DNA
Not usually survival essential
Capable of autonomous replication
Often provide selective advantage