1. Bacterial cell structure

Question 1

how is bacterial DNA structured

Answer 1

in two forms:
- nucleoid = region where chromosomes are found

• plasmids = small, circular closed DNA molecules, carry non essential genes

Question 2

how many nucleoids per cell

Answer 2

1

Question 3

what is the nucleoid responsible for

Answer 3

basic cell needs: reproduction, division, feeding

Question 4

what are plasmids responsible for

Answer 4

carry non essential genes: e.g. antibiotic resistant genes

Question 5

how are plasmids swapped between cells? what does this allow?

Answer 5

via a sex pili that facilitates conjugation

allows transfer of genes, e.g. antibiotic resistance

Question 6

what are inclusions, what are they used for

Answer 6

granules of organic or inorganic material reserved for future use (e.g. when a bacterium exits a growth cycle and runs out of nutrients)

Question 7

name 2 components of inclusions

Answer 7

glycogen, sulphur granules

Question 8

true or false: bacteria have a phospholipid bilayer

Answer 8

true:

- permeable barrier containing integral proteins

Question 9

what structure is used to classify bacteria

Answer 9

the cell wall

Question 10

what colour Gram stain is a Gram-positive bacteria

Answer 10

purple

Question 11

what colour Gram stain is a Gram-negative bacteria

Answer 11

pink

Question 12

what does crystal violet bind to

Answer 12

peptidoglycan in the cell wall

Question 13

what happens to the crystal violet in a Gram-negative species

Answer 13

binding is weak, following ethanol wash crystal violet dissociates

Question 14

how can we identify the cells with no peptidoglycan

Answer 14

counter-staining with safranin

Question 15

what two sugars is peptidoglycan composed of

Answer 15

G = NAG = n-acetylglucosamine 
M = NAM = n-acetylmuramic acid

Question 16

what is the peptidoglycan structure

Answer 16

M-G polymer chains linked via peptide bridges holding the molecule together

Question 17

what two acids are found in gram-positive cell walls

Answer 17

teichoic acid

lipoteichoic acid

Question 18

what is teichoic acid used for

Answer 18

carbohydrate used by phagocyte for recognition of bacterial prey

Question 19

what is the function of lipoteichoic acid

Answer 19

a adhesion molecule that can travel through the plasma membrane

Question 20

Gram-negative bacteria has periplasm, what is this?

Answer 20

an inter-membrane space, prevents crystal violet binding

Question 21

what is the role of porin? (Gram-neg)

Answer 21

allows soluble nutrients to be transported into the cell. the pore is filled with water and is mostly non-selective

Question 22

Gram negative bacteria have lipopolysaccharide, what are its three components?

Answer 22

1. lipid A = sits in the membrane anchoring the LPS
2. Sugar chain = core polysaccharide
3. O-polysaccharide = O antigen recognised by phagocytes (facilitating phagocytosis)

Question 23

what does the capsule contain

Answer 23

thick layer of sugars and water

Question 24

what is the function of the capsule

Answer 24

• protect host from phagocytosis: this thick layer is difficult to digest
• protect from harsh environment conditions
• overproduction - allows attachment to surfaces

Question 25

S-layer:

• function?
• structure?

Answer 25

function = site for adhesion, anti-phagocytic
structure = monolayer of identical proteins or glycoproteins

Question 26

flagella:

• what protein is the motor for flagellum?
• use?
• arrangement?
• two types:

Answer 26

• dynein
• swimming, motility, attachment to surfaces
• 9 +2
• polar flagellum (at end of the cell), amphitrichous (one flagella at each end of the cell)

Question 27

what are fimbrae

Answer 27

short hairs that cover the cell, used for recognition and attachment to surfaces

Question 28

define population of bacteria

Answer 28

single species

Question 29

define communities of bacteria

Answer 29

more than one species

Question 30

why do we catalogue bacteria

Answer 30

• to bring a sense of order to the huge diversity

- enhance communication between scientists

Question 31

how can we catalogue bacteria

Answer 31

by 16S rRNA comparison

Question 32

describe the nature of the prokaryotic ribosome

Answer 32

two subunits:
50S = stable no subject to much variation
30S = variable, unconserved (we sequence this)

Question 33

what does 16S rRNA sequencing allow

Answer 33

phylogenetic trees to be established - visualise evolutionary distance

Question 34

what are the 3 domains of life

Answer 34

1. bacteria
2. archaea -> divides into Asgard archaea
3. eukarya