Bacterial shape, size, appendages and lifestyles

Question 1

What is the resolution limit of light microscopy

Answer 1

200nm (but can be stretched to 10nm by super resolution methods)

Question 2

Which two types of microscope use tissue sections of specimen

Answer 2

Light and transmission electron

Question 3

Which type of microscope uses 3D specimen

Answer 3

Scanning electron

Question 4

Which type of microscope contains a scanning coil (beam deflector)

Answer 4

Scanning electron

Question 5

Which type of microscope contains a projection lens

Answer 5

Transmission electron

Question 6

Which type of microscope contains an eyepiece lens

Answer 6

Light microscope

Question 7

Which type of microscope views the image directly and in colour

Answer 7

Light microscope

Question 8

Which type of microscope contains views the image on a monitor

Answer 8

Scanning electron

Question 9

Which type of microscope views the image on a fluorescent screen

Answer 9

Transmission electron

Question 10

What is the magnification of light microscopes

Answer 10

Up to about 1000x

Question 11

What are the 7 types of light microscope

Answer 11

Brightfield, darkfield, phase contrast, Differential Interference Contrast (DIC), fluorescence, confocal and two-photon

Question 12

Describe the Brightfield light microscope

Answer 12

Commonly used in laboratory applications as the standard microscope, produces an image on a bright background

Question 13

Describe the Darkfield light microscope

Answer 13

Increases contrast without staining by producing a bright image on a darker background, making it useful for viewing live specimen

Question 14

Describe the phase contrast light microscope

Answer 14

Uses refraction and inference caused by structures in the specimen to create high contrast and high resolution images without staining making it useful for viewing live specimens and structures

Question 15

Describe the Differential Interference contrast (DIC) microscope

Answer 15

Uses interference patterns to enhance contrast between different features of a specimen to produce high contrast images of living organism with 3D appearance making it useful in distinguishing structures within live and unstained specimen

Question 16

Describe the fluorescence light microscope

Answer 16

Uses fluorescent stains to produce an image, useful for identifying pathogens, species, locations of particular molecules distinguishing dead from live cells and immunofluorescence

Question 17

Describe confocal light microscopes

Answer 17

Uses a laser to scan multiple z-planes successively to produce numerous 2D high resolution images at various depths that are constructed into 3D images by a computer so it is useful for examining thick specimen e.g. biofilms

Question 18

Describe the two-photon light microscope

Answer 18

Uses a scanning technique, fluorochromes and long wavelength light e.g. infrared to penetrate deep into thick specimens

Question 19

Describe the 4 steps of gram staining

Answer 19

1) application of the primary stain (the crystal violet)
2) application of iodine (the mordant)
3) wash with alcohol (the decolouriser)
4) application of the safranin (the couterstain)

Question 20

What colour do gram positive bacteria appear after gram staining

Answer 20

Purple

Question 21

What colour do gram negative bacteria appear after staining

Answer 21

Red

Question 22

What is the difference between gram positive and gram negative bacteria

Answer 22

Gram negative bacteria have an outer membrane

Question 23

What are the functions of the bacterial cell wall

Answer 23

• protection against osmotic and environmental stress
• defines shape and helps with uniform cell division

Question 24

What component of bacteria is the target for immune defence and antibiotics

Answer 24

Bacterial cell wall

Question 25

What is the green fluorescent protein method

Answer 25

Genetic manipulation to make a protein-GFP fusion to enable live cell time lapse imaging

Question 26

What are the advantages of the GFP method

Answer 26

Many colour variants so simultaneous visualisation of different proteins

Question 27

What are the disadvantages of the GFP method

Answer 27

Many fusion proteins malfunction and localisation may be misleading

Question 28

What did fluorescence microscopy reveal

Answer 28

The complexity of the bacterial cell e.g. the bacterial cell contains FtsZ which is the equivalent of eukaryotic tub,in and MreB which is the equivalent of eukaryotic actin

Question 29

What is the proteinaceous S-layer of bacteria

Answer 29

Outermost layer of cell envelope that is a crystalline lattice of a single protein and acts as a protective, selective sieve that is often lost in lab strains

Question 30

What are capsules

Answer 30

Usually polysaccharides that are sometimes covalently attached to the wall that can be immunogenic and help in avoidance of immune responses

Question 31

What are pili and fimbriae

Answer 31

Immunogenic surface appendages that are protein polymers that attach/ adhere to organisms and provide a ‘twitching’ motility and support gene transfer by conjugation. They are also important in pathogenesis

Question 32

What is the difference between pili and fimbriae

Answer 32

Pili are longer and there are fewer of them

Question 33

What is the flagella

Answer 33

Rotatory motor that acts as a biological nanomachine with a rotation and helical structure to generate movement for chemotaxis (directionality)

Question 34

What is the flagella

Answer 34

Rotators motor that acts as a biological nanomachine with a rotation and helical structure to generate movement for chemotaxis (directionality)

Question 35

What are endospores

Answer 35

Survival mechanism that remain dormant for centuries and are triggered by starvation and are incredibly resistant to heat, solvents, lysozymes etc. They germinate when favourable conditions recur

Question 36

What are Biofilms

Answer 36

Communities of often multiple species held togteher by a matrix and differentiate to promote adhesion and resistance

Question 37

What forms the matrix holding biofilms together

Answer 37

Mainly polysaccharide also proteins and nucleic acids