Module 2 - Bacterial Structure and Function Flashcards
What is the “simplest” bacterial cell shape?
Coccus (spherical)
What is the typical scale of a bacterial cell?
A few micrometres across
What is the name of the star-shaped genus?
Stella
Name the three “arrangements” of cells described in the lecture
Streptococcus (chains); Staphylococcus (clusters); Pairs of Rods (e.g., E. coli)
What are the two main architectural differences between Gram-positive and Gram negative bacteria?
GP - thicker layer of peptidoglycan which forms the outer layer
GN - less peptidoglycan, outer layer is lipopolysaccharides and proteins
Name the 5 steps of the Gram Staining process
- Heat fixing
- Crystal Violet
- Fix with Gram’s Iodine
- Decolourise with ethanol/acetone
- Counterstain
Why are bacteria gently heated at the start of the Gram Staining process?
To fix them to the surface of the microscope slide
Why is iodine added during the Gram Staining process?
To form a larger iodine-crystal violet complex within the cell walls of the bacteria (fixing)
Why do ethanol/acetone decolourise GN cells but not GP?
The solvents readily dissolve the outer lipid layer of GN bacteria, allowing the CV-Iodine complex to be washed away.
The thicker peptidoglycan layer in GP is dehydrated and shrinks but retains the stain
What is the main role of peptidoglycan?
To prevent cells from osmotic lysis (high internal osmotic pressure)
Which two amino sugars form the glycan backbone of Peptidoglycan?
N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM)
Which elements of peptidoglycan are more and less conserved across species?
Glycan backbone is very conserved, peptides are more variable
What is unusual about the forms of amino acids found in peptidoglycan?
It can contain both L- and D-form amino acids
Which of the following are true of the inner- and outer membrane in a gram-negative cell wall?
- Less fluid
- Contains LPS
- Porins are a prominent feature
- Asymetric
- Less fluid = outer wall (due to LPS)
- Contains LPS = outer wall (outer leaflet)
- Porins = outer membrane
- Asymetric = outer membrane
What three main sections does a Lipopolysaccharide consist of?
Hydrophobic Lipid A; Variable Core Oligosaccharide; O-specific polysaccharide (O antigen)
Describe the variety of sugars found in the core oligosaccharide in LPS
Unusual sugars like KDO and heptoses (as well as more common ones such as glucose/galactose)
3 Key Facts about Lipid A in LPS (“known as…”, “contains a…”, “can be…”)
It is also known as endotoxin, it contains a disaccharide, it can be phosphorylated
What 3 things is an Archaeal cell surface characterised by?
Single membrane; S-layers; Ether-linked lipids
What is an S-layer?
A surface-located, self arranging, paracrystalline protein layer
Why is Archaeal pseudomurein resistant to lysozyme, while peptidoglycan in bacteria is susceptible to it?
Glycan backbone sugars (NAG/NAM) are connected by ß-1,3 Glycosidic bonds rather than 1,4
5 roles of pili + fimbriae
- Transformation
- Conjugation
- Biofilm formation
- Adherence
- Motility
Order of the 4 “rings” in flagellum structure (top/distal to bottom/proximal)
L ring, P ring, MS ring, C ring
Name and define the four groups of microbes in terms of flagella arrangement
Monotrichous = 1 flagellum
Amphitrichous = 2 opposite flagella
Peritrichous = Flagella all over
Lophotrichous = All on one side
What are the three main weaknesses of peptidoglycan?
Lysozymes, antibiotics, bacteriophage lysins
Are there any bacteria which do not have peptidoglycan?
Yes - they have no rigid cell walls, so are pleiomorphic, and insensitive to antibiotics that target peptidoglycan; sterols in cell membrane provide stability
How variable is the peptide side chain in peptidoglycan?
There are over 100 different types of peptidoglycan due to diversity in side chains and cross links
Are peptide groups in peptidoglycan attached to NAG or NAM?
ALWAYS NAM
How is one side chain attached to the other in the Staphylococcus aureus example of Peptidoglycan?
Indirectly via a Pentaglycine Interbridge
What are the components of the cell wall in Gram-Positive bacteria?
Peptidoglycan and Teichoic acid (Wall Teichoic acid and Lipoteichoic acid)
Describe the structure of Teichoic acid and how it is incorporated into Gram positive cell walls
It is a polymer of glycerol or ribitol (5C) phosphate
Wall TA is covalently bonded to NAM in peptidoglycan
Lipoteichoic Acid is embedded in the membrane via a lipid component
Name the layers of the cell wall in Gram-negative bacteria
Outer membrane (LPS, proteins + lipids)
Thin Peptidoglycan layer
Periplasmic space (both sides of PG)
Cytoplasmic Membrane
What is the significance of the Lipid A (endotoxin) part of LPSs in outer leaflet of outer membrane of GN bacteria
It is the only part of LPS recognised by the innate immune system
It stimulates Toll Like Receptor 4 to trigger an inflammatory response
What can be the consequence of Lipid A in the bloodstream?
Toxic shock, eventually resulting in multi-organ failure and death
What is the extra component of SOME Archaean cell walls (e.g. in methanogens)?
Pseudomurein (between cytoplasmic membrane and S-layer)
What is different about the amino acids in an Archaean cell wall compared to a bacterial one?
ALL Amino Acids are L-amino acids (no D)
Name the three main parts of the Flagella Ultrastructure
Filament, Hook and Basal Body
Name the 6 ““stuctural”” components of the Basal Body of Flagella, plus the 2 ““other?”” components
L ring, Distal Rod, P ring, Proximal Rod, MS Ring, C ring
MotB and Mot A
How are flagellae powered?
By protons moving down a proton gradient through MotA (rather than ATP)
Describe the overall structure and function of flagellae
Protein subunit is FLAGELLIN - they are helical in structure (essential for their function)
Can be polar or peritrichous
Rotate in CW AND CCW directions during chemotaxis
Name the type of movement seen in peritrichous bacteria (and the two types of this)
Taxis - moving towards/away from chemical or physical clues (chemotaxis/phototaxis)
Describe the process of chemotaxis in peritrichous E. coli
Two “modes” - a run is when the flagella are bundled and rotate CCW; a tumble is when flagella are pushed apart and rotate CW, randomising the direction of the next run
Runs are elongated up a gradient chemical attractant + vice versa -> biased random walk
Name the two main functions of fimbriae
Adherence to surfaces/tissues + Biofilm formation
Name the four main functions of pili
- Adherence to host tissues
- Conjugation
- Transformation
- Motility (twitching)
Which two functions only apply to TYPE IV pili?
Transformation and Motility
Name 4 things that bacteria need in order to grow
- Carbon source
- Nitrogen source
- S/P/Mg and trace elements
- Growth factors (e.g., vitamins)
Describe briefly the process of binary fission
A cell grows to 2x length, DNA and ribosomes are partitioned, septum forms while DNA remains attached to membrane
What is the function of the FtsZ protein?
Once all nucleoids have replicated, polymerisation of FtsZ forms a ring structure which then attracts other proteins involved in cell division, and forms a division plane between the nucleoids (the FtsZ ring DEpolymerises after division)
What is the function of the MreB protein?
MreB forms patch-like filaments around the cell below the cytoplasmic membrane - these filaments move from one side to the other; MreB recruits enzymes involved in peptidoglycan biosynthesis
In what types of bacteria is MreB present?
ONLY ROD SHAPED; NOT COCCI (therefore in cocci, peptidoglycan biosynthesis happens only at the septum)
What two enzymes are required for MreB (and its recruited peptidoglycan synthesis enzymes) to function?
AUTOLYSIN - breaks the ß1-4 linkage between NAM and NAG
TRANSGLYCOSYLASE - adds new peptidoglycan unit
Describe what happens during Log Phase
Cells double in each unit of time - plotted logarithmically this gives a straight line
What is the mean doubling time for E. coli?
(In optimal conditions) 20 minutes
Why do cells stop dividing in Stationary Phase?
Nutrient limitation (e.g. glucose, O2)
or Accumulation of Toxic Waste (e.g. lactic acid in streptococci)
What are the four main temperature classes of microorganisms?
Psychrophiles: LOW T(opt) <15C
Mesophiles: MIDRANGE Topt 15-45C
Thermophiles: HIGH Topt 45-80C
Hyperthermophiles: VERY HIGH Topt 80-100C
Where are the four main temperature classes of microbes generally found?
Psychrophiles: Oceans
Mesophiles: Animals
Thermophiles: Soil
Hyperthermophiles: Hot springs, geysers, vents etc
What are the 3 main adaptations of Psychrophiles?
- Semi-fluid membranes at low temperatures
- Altered proteins (more alpha-helices)
- Anti-freeze molecules (only eukaryotes)
What are the 2 main adaptations of Thermophiles?
Semi-fluid membranes at high temperatures AND Altered Proteins
What are the 2 main adaptations of Hyperthermophiles?
No fatty acids in membrane AND lipid monolayer rather than bilayer
What is the general pattern of microbial death upon heating?
Cells lose viability first; then more and more start to die; population death is exponential/logarithmic
What is the (mentioned) parameter to measure heat killing of bacteria?
D VALUE - time required to kill 90% of cells (time to drop cell numbers by one log cycle)
State the conditions required for Autoclaving (and what this achieves)
Temp 121C
Time 20 mins
Pressure 138 kPa
“Kills all known germs”
