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Microbes > Module 2 - Bacterial Structure and Function > Flashcards

Module 2 - Bacterial Structure and Function Flashcards

1
Q

What is the “simplest” bacterial cell shape?

A

Coccus (spherical)

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2
Q

What is the typical scale of a bacterial cell?

A

A few micrometres across

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3
Q

What is the name of the star-shaped genus?

A

Stella

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4
Q

Name the three “arrangements” of cells described in the lecture

A

Streptococcus (chains); Staphylococcus (clusters); Pairs of Rods (e.g., E. coli)

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5
Q

What are the two main architectural differences between Gram-positive and Gram negative bacteria?

A

GP - thicker layer of peptidoglycan which forms the outer layer
GN - less peptidoglycan, outer layer is lipopolysaccharides and proteins

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6
Q

Name the 5 steps of the Gram Staining process

A
  1. Heat fixing
  2. Crystal Violet
  3. Fix with Gram’s Iodine
  4. Decolourise with ethanol/acetone
  5. Counterstain
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7
Q

Why are bacteria gently heated at the start of the Gram Staining process?

A

To fix them to the surface of the microscope slide

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8
Q

Why is iodine added during the Gram Staining process?

A

To form a larger iodine-crystal violet complex within the cell walls of the bacteria (fixing)

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9
Q

Why do ethanol/acetone decolourise GN cells but not GP?

A

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

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10
Q

What is the main role of peptidoglycan?

A

To prevent cells from osmotic lysis (high internal osmotic pressure)

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11
Q

Which two amino sugars form the glycan backbone of Peptidoglycan?

A

N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM)

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12
Q

Which elements of peptidoglycan are more and less conserved across species?

A

Glycan backbone is very conserved, peptides are more variable

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13
Q

What is unusual about the forms of amino acids found in peptidoglycan?

A

It can contain both L- and D-form amino acids

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14
Q

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

A
  • Less fluid = outer wall (due to LPS)
  • Contains LPS = outer wall (outer leaflet)
  • Porins = outer membrane
  • Asymetric = outer membrane
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15
Q

What three main sections does a Lipopolysaccharide consist of?

A

Hydrophobic Lipid A; Variable Core Oligosaccharide; O-specific polysaccharide (O antigen)

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16
Q

Describe the variety of sugars found in the core oligosaccharide in LPS

A

Unusual sugars like KDO and heptoses (as well as more common ones such as glucose/galactose)

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17
Q

3 Key Facts about Lipid A in LPS (“known as…”, “contains a…”, “can be…”)

A

It is also known as endotoxin, it contains a disaccharide, it can be phosphorylated

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18
Q

What 3 things is an Archaeal cell surface characterised by?

A

Single membrane; S-layers; Ether-linked lipids

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19
Q

What is an S-layer?

A

A surface-located, self arranging, paracrystalline protein layer

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20
Q

Why is Archaeal pseudomurein resistant to lysozyme, while peptidoglycan in bacteria is susceptible to it?

A

Glycan backbone sugars (NAG/NAM) are connected by ß-1,3 Glycosidic bonds rather than 1,4

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21
Q

5 roles of pili + fimbriae

A
  1. Transformation
  2. Conjugation
  3. Biofilm formation
  4. Adherence
  5. Motility
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22
Q

Order of the 4 “rings” in flagellum structure (top/distal to bottom/proximal)

A

L ring, P ring, MS ring, C ring

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23
Q

Name and define the four groups of microbes in terms of flagella arrangement

A

Monotrichous = 1 flagellum
Amphitrichous = 2 opposite flagella
Peritrichous = Flagella all over
Lophotrichous = All on one side

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24
Q

What are the three main weaknesses of peptidoglycan?

A

Lysozymes, antibiotics, bacteriophage lysins

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25
Q

Are there any bacteria which do not have peptidoglycan?

A

Yes - they have no rigid cell walls, so are pleiomorphic, and insensitive to antibiotics that target peptidoglycan; sterols in cell membrane provide stability

26
Q

How variable is the peptide side chain in peptidoglycan?

A

There are over 100 different types of peptidoglycan due to diversity in side chains and cross links

27
Q

Are peptide groups in peptidoglycan attached to NAG or NAM?

A

ALWAYS NAM

28
Q

How is one side chain attached to the other in the Staphylococcus aureus example of Peptidoglycan?

A

Indirectly via a Pentaglycine Interbridge

29
Q

What are the components of the cell wall in Gram-Positive bacteria?

A

Peptidoglycan and Teichoic acid (Wall Teichoic acid and Lipoteichoic acid)

30
Q

Describe the structure of Teichoic acid and how it is incorporated into Gram positive cell walls

A

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

31
Q

Name the layers of the cell wall in Gram-negative bacteria

A

Outer membrane (LPS, proteins + lipids)
Thin Peptidoglycan layer
Periplasmic space (both sides of PG)
Cytoplasmic Membrane

32
Q

What is the significance of the Lipid A (endotoxin) part of LPSs in outer leaflet of outer membrane of GN bacteria

A

It is the only part of LPS recognised by the innate immune system

It stimulates Toll Like Receptor 4 to trigger an inflammatory response

33
Q

What can be the consequence of Lipid A in the bloodstream?

A

Toxic shock, eventually resulting in multi-organ failure and death

34
Q

What is the extra component of SOME Archaean cell walls (e.g. in methanogens)?

A

Pseudomurein (between cytoplasmic membrane and S-layer)

35
Q

What is different about the amino acids in an Archaean cell wall compared to a bacterial one?

A

ALL Amino Acids are L-amino acids (no D)

36
Q

Name the three main parts of the Flagella Ultrastructure

A

Filament, Hook and Basal Body

37
Q

Name the 6 ““stuctural”” components of the Basal Body of Flagella, plus the 2 ““other?”” components

A

L ring, Distal Rod, P ring, Proximal Rod, MS Ring, C ring

MotB and Mot A

38
Q

How are flagellae powered?

A

By protons moving down a proton gradient through MotA (rather than ATP)

39
Q

Describe the overall structure and function of flagellae

A

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

40
Q

Name the type of movement seen in peritrichous bacteria (and the two types of this)

A

Taxis - moving towards/away from chemical or physical clues (chemotaxis/phototaxis)

41
Q

Describe the process of chemotaxis in peritrichous E. coli

A

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

42
Q

Name the two main functions of fimbriae

A

Adherence to surfaces/tissues + Biofilm formation

43
Q

Name the four main functions of pili

A
  • Adherence to host tissues
  • Conjugation
  • Transformation
  • Motility (twitching)
44
Q

Which two functions only apply to TYPE IV pili?

A

Transformation and Motility

45
Q

Name 4 things that bacteria need in order to grow

A
  1. Carbon source
  2. Nitrogen source
  3. S/P/Mg and trace elements
  4. Growth factors (e.g., vitamins)
46
Q

Describe briefly the process of binary fission

A

A cell grows to 2x length, DNA and ribosomes are partitioned, septum forms while DNA remains attached to membrane

47
Q

What is the function of the FtsZ protein?

A

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)

48
Q

What is the function of the MreB protein?

A

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

49
Q

In what types of bacteria is MreB present?

A

ONLY ROD SHAPED; NOT COCCI (therefore in cocci, peptidoglycan biosynthesis happens only at the septum)

50
Q

What two enzymes are required for MreB (and its recruited peptidoglycan synthesis enzymes) to function?

A

AUTOLYSIN - breaks the ß1-4 linkage between NAM and NAG

TRANSGLYCOSYLASE - adds new peptidoglycan unit

51
Q

Describe what happens during Log Phase

A

Cells double in each unit of time - plotted logarithmically this gives a straight line

52
Q

What is the mean doubling time for E. coli?

A

(In optimal conditions) 20 minutes

53
Q

Why do cells stop dividing in Stationary Phase?

A

Nutrient limitation (e.g. glucose, O2)
or Accumulation of Toxic Waste (e.g. lactic acid in streptococci)

54
Q

What are the four main temperature classes of microorganisms?

A

Psychrophiles: LOW T(opt) <15C
Mesophiles: MIDRANGE Topt 15-45C
Thermophiles: HIGH Topt 45-80C
Hyperthermophiles: VERY HIGH Topt 80-100C

55
Q

Where are the four main temperature classes of microbes generally found?

A

Psychrophiles: Oceans
Mesophiles: Animals
Thermophiles: Soil
Hyperthermophiles: Hot springs, geysers, vents etc

56
Q

What are the 3 main adaptations of Psychrophiles?

A
  1. Semi-fluid membranes at low temperatures
  2. Altered proteins (more alpha-helices)
  3. Anti-freeze molecules (only eukaryotes)
57
Q

What are the 2 main adaptations of Thermophiles?

A

Semi-fluid membranes at high temperatures AND Altered Proteins

58
Q

What are the 2 main adaptations of Hyperthermophiles?

A

No fatty acids in membrane AND lipid monolayer rather than bilayer

59
Q

What is the general pattern of microbial death upon heating?

A

Cells lose viability first; then more and more start to die; population death is exponential/logarithmic

60
Q

What is the (mentioned) parameter to measure heat killing of bacteria?

A

D VALUE - time required to kill 90% of cells (time to drop cell numbers by one log cycle)

61
Q

State the conditions required for Autoclaving (and what this achieves)

A

Temp 121C
Time 20 mins
Pressure 138 kPa
“Kills all known germs”

Microbes (7 decks)

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