Cell Structure

Question 1

What are polyphosphate globules? Why are they important?

Answer 1

Polyphosphate globules are long chains of phosphate ( volutin). They are important because are a reservoir of phosphate ( limiting nutrient), are used in place of ATP for sugar phosphorylation.

Question 2

How is Fe3+ taken up to make magnetosomes?

Answer 2

Fe3+ is taken up by active transport, reduced to Fe2+ and reoxidized to form magnetite within the vesicle.

Question 3

In which microorganism do you find magnetosomes?

Answer 3

In acquatic bacteria and unicellular algae ( eukaryotes)

Question 4

What’s the structure of gas vesicle ? What is their function?

Answer 4

Structure: aggregates of hollow cylinders composed of rigid proteins impermeable to water, but permeable to gas
Function: allow buoyant motility of acquatic microbes, change position in water column according to amount of gas within the vesicle, in order to get light and nutrients

Question 5

What’s the chemical structure of flagella?

Answer 5

Flagella are made of flagellin subunits bound in long chains wrapped in a left handed helix

Question 6

What are the surface structures of bacteria?

Answer 6

Flagella, fimbriae, pili ( pili IV and sex pilus ) and the glycocalix ( capsule and slime layer)

Question 7

How does flagellar synthesis occur? How is the final filament ?

Answer 7

Flagellum regenerates starting not from base but growing from the tip up to maximum length. The filament is hollow and self assemble at the end

Question 8

Methods to look for indirect detection of motility

Answer 8

-Flagellar stains ( basic fuchsin, pararosalin)
- antibody stains
- electron microscopy

Question 9

Methods for direct detection of motility ( flagellar movement )

Answer 9

• phase contrast microscopy
• motility medium ( semisolid, motile bacteria can swim through and cause turbidity )

Question 10

Type of directed motility in bacteria ?

Answer 10

Chemotaxis, aerotaxis, phototaxis, magnetotaxis

Question 11

What is the glycocalyx composition ?

Answer 11

It is made of a network of polysaccharides or/ and glycoproteins

Question 12

How is the glycocalix stained ?

Answer 12

Via India ink. Dark cells, visible outline that can be either slime layers or capsule

Question 13

What’s the function of pili?

Answer 13

Gene transfer and attachment

Question 14

What is gliding motility? What is it caused by?

Answer 14

It’s a glide movement of the bacterium when it comes in contact with a solid surface. Caused by circular motors underneath bacterium

Question 15

Difference between flagella and fimbriae

Answer 15

Fimbriae are shorter and more numerous than flagella. They are not involved in motility, but mainly in cells sticking and attachment to surfaces

Question 16

What’s a compound found in bacterial cell wall and nowhere else ?

Answer 16

NAM

Question 17

How do bacteria convert btw L and D forms of aminoacids?

Answer 17

By enzyme racemases

Question 18

On what does it depend the exact molecular makeup of peptidoglycan layers?

Answer 18

It depends on bacterial species. It’s species specific

Question 19

How does lysozyme harm bacteria?

Answer 19

It attacks peptidoglycan hydrolysing the NAM-NAG B-1,4 glycosidic bond

Question 20

How does antibiotic penicillin act?

Answer 20

It inhibits cell wall synthesis by blocking the enzyme transpeptidase ( responsible of cross links formation btw aminoacids )

Question 21

What is the main target of many antibiotics and lysozyme ?

Answer 21

The bacterial cell wall

Question 22

What’s the reason of forming cross linking between peptidoglycan chains?

Answer 22

To strengthen the cell wall structure

Question 23

What’s a main risk for bacterial cells lacking a cell wall, beside a lost defined shape?

Answer 23

Osmotic lysis

Question 24

What’s the bond between 2 peptidoglycan units?

Answer 24

Covalent bond

Question 25

What’s the difference in the cross linking between G- and G+ bacteria?

Answer 25

-G+ the cross linking between 3 and 4 aminoacids of two strands occur with a pentaglycine inter bridge.
- G- the cross links occur directly between aa via covalent bond

Question 26

Where is the Braun’a lipoprotein?

Answer 26

It is in the G- cell wall, covalently bound in the peptidoglycan layer and with an anchor in the OM

Question 27

What is the lipid A ? (2 def)

Answer 27

It is a hydrophobic domain in the LPS, inserted in the OM bilayer
It’s a derivative of NAG with up to 7 fatty acids chains

Question 28

What does the core polysaccharide contain?

Answer 28

KDO (2-keto-3-deoxyoctanoate), heptose, glucose, glucosamine sugars

Question 29

What’s the reason of the name O-antigen? What is it ?

Answer 29

The reason is the fact it is exposed to the outer environment. It is made of repeating sugars and it’s the structure against which the host makes antibodies

Question 30

What’s the lipid A in free LPS for humans?

Answer 30

An endotoxin

Question 31

What class of proteins is inserted in the OM?

Answer 31

Porins

Question 32

What’s present in the periplasmic space of G-?

Answer 32

Enzymes ( phdophatases, detoxifying enzymes like b-lactamase, binding proteins, osmotic protection)

Question 33

Class of microbes lacking cell wall

Answer 33

Mycoplasma

Question 34

How are the G- cell walls from a chemical point of view?

Answer 34

Hydrophilic due to the LPS presence

Question 35

What are extra cellular vesicles ?

Answer 35

Small membrane bound particles budding off from membranes (G+: cell memb, G-: OM)

Question 36

Functions of EV? (4)

Answer 36

1)Carry ATP,
2)influence cell-cell interaction,
3)deliver their content to euk cells,
4) increase in response to cell stress