Exam 1 - Lecture 3

Question 1

what are the three types of peptidoglycan variations?

Answer 1

• composition of linkage (direct or bridges)
• amino acid at #3 position
• linkage type (2 to 4, 3 to 4)

Question 2

which type of amino acid is usually only found in bacterial cell walls, L- or D-?

Answer 2

D- amino acids

Question 3

what kind of linkage connects NAM and NAG sugars?

Answer 3

beta-(1,4) glycosidic bonds

Question 4

how thick is the peptidoglycan layer in Gram-positive cell walls?

Answer 4

20-80 nm thick

Question 5

what are teichoic acids?

are they found in Gram-positive or Gram negative cell walls?

Answer 5

• negatively charged acids that help maintain the cell envelope, protect from environmental substances, and may bind to host cells
• only found in Gram-positive walls

Question 6

what are teichoic acids composed of?

Answer 6

alternating phosphate and glycerol groups

Question 7

where can you find teichoic acids? what about lipoteichoic acids?

Answer 7

teichoic: covalently attached to peptidoglycan

lipoteichoic: covalently attached to lipids in plasma membrane

Question 8

what is the cell wall protein sequence in Gram-positive cell walls?

which residue of the sequence is covalently linked to peptidoglycan via what enzyme?

Answer 8

• LPXTG
• T residue, Sortase

Question 9

what is an LPS?

Answer 9

lipopolysaccharide

Question 10

how many membranes does a Gram-negative cell wall have?

what are they called?

Answer 10

• two
• outer membrane and inner/plasma membrane

Question 11

do Gram-negative cells have teichoic acids?

Answer 11

nope

Question 12

what connects the outer membrane to the peptidoglycan in Gram-negative bacteria?

Answer 12

Braun’s lipoprotein

Question 13

what is the inner leaflet of the outer membrane composed of in Gram-negative bacteria?

Answer 13

phospholipids

Question 14

what is the outer leaflet of the outer membrane composed of in Gram-negative bacteria?

Answer 14

lipopolysaccharide (LPS)

Question 15

where is LPS found?

Answer 15

only in Gram-negative bacteria

Question 16

what are the three parts of LPS?

Answer 16

• O antigen
• core polysaccharide
• Lipid A

Question 17

what parts of LPS are embedded in the outer membrane, and which extend out from the cell?

Answer 17

Lipid A is embedded in the outer membrane

O antigens and the core polysaccharide extend from the cell

Question 18

what is the importance of LPS?

Answer 18

• contributes to negative charge on cell surface (core polysaccharide)
• stabilizes the outer membrane (Lipid A)
• protects from host defenses (O antigen)
• creates permeability barrier
• can act as a toxin (lipid A)

Question 19

how many endotoxins do we have?

Answer 19

one! (LPS’s Lipid A)

Question 20

what makes the outer membrane permeable?

Answer 20

the presence of porin proteins: channels that let small molecules pass through

Question 21

what is the mechanism of Gram-staining in Gram-positive cells?

Answer 21

the constriction/shrinkage of the thick peptidoglycan layer prevents loss of crystal violet during decolorization

Question 22

why doesn’t the peptidoglycan layer in Gram-negative cells retain crystal violet?

Answer 22

the peptidoglycan layer is thinner and more porous

Question 23

can you explain the steps of Gram-staining?

Answer 23

• crystal violet dye is added
• iodine is added
• complex forms between CV and iodine
• the sample is decolorized (with ethanol)
• the thinner Gram-negative cells lose their color, Gram-positive stays purple
• a counterstain, safranin, is added
• Gram-positive cells are now pink

Question 24

what protects bacterial cells from osmotic stress?

Answer 24

the cell wall

Question 25

what is a hypotonic environment?

Answer 25

- the solute concentration is higher inside the cell - water moves into the cell and cell swells - cell wall protects from lysis

Question 26

what is a hypertonic environment?

Answer 26

- the solute concentration is higher outside the cell - water leaves the cell - plasmolysis occurs (shrinking of the cytoplasm)

Question 27

what do we call Gram-positive bacteria without the peptidoglycan?

Answer 27

protoplasts

Question 28

what do we call Gram-negative bacteria without the peptidoglycan?

Answer 28

spheroplasts

Question 29

if the peptidoglycan cell wall is removed, the cells will lyse in _____tonic solution and survive in _____tonic solution

Answer 29

hypotonic; isotonic

Question 30

what are the three most common types of external layers found in bacteria?

Answer 30

- capsules - slime layers - S-layers

Question 31

what is the role of the external layer in bacteria?

Answer 31

plays a role in interaction of the bacterial cell and its environment

Question 32

what are capsules composed of?

Answer 32

polysaccharides (sugars)

Question 33

true of false: capsules are well organized and not easily removed from the cell.

Answer 33

true

Question 34

what are the protective advantages of capsules?

Answer 34

- resistant to phagocytosis - protect from desiccation - exclude viruses and detergents

Question 35

true of false: slime layers are well organized and not easily removed from the cell.

Answer 35

false; slime layers diffuse, are unorganized, and are removed easily

Question 36

what might slime layers aid in?

Answer 36

motility

Question 37

what are S-layers?

Answer 37

regularly structured layers of protein or glycoproteins that self-assemble

Question 38

where does the S-layer adhere to in Gram-negative bacteria? Gram-positive bacteria?

Answer 38

- the outer membrane - the peptidoglycan surface

Question 39

what is the cytoplasm?

Answer 39

material bound by the plasmid membrane

Question 40

what are the five bacterial cytoplasmic structures?

Answer 40

- cytoskeleton - intracytoplasmic structures - ribosomes - nucleiod and plasmids - inclusions

Question 41

what are the three eukaryotic cytoskeletal elements?

Answer 41

- actin - tubulin - intermediate filaments (homologues of all three have been found in bacteria)

Question 42

what is FstZ? where is it found?

Answer 42

- a tubulin homologue that aids in septum formation during cell division - found in many bacteria

Question 43

what is MreB? where is it found?

Answer 43

- an actin homologue that maintains shapes by positioning peptidoglycan synthesis machinery - found in rods

Question 44

what is CreS and where is it found?

Answer 44

a rare intermediate filament homologue that maintains the shape of curve shaped bacteria

Question 45

what does the S in 16S, 80S, etc., stand for?

Answer 45

Svedberg unit

Question 46

what are ribosomes?

Answer 46

sites for protein synthesis

Question 47

how big is the eukaryotic ribosome? prokaryotic (archaeal and bacterial)?

Answer 47

- 80S - 70S

Question 48

what ribosomal RNA is found in bacteria (large and small subunits)?

Answer 48

- small subunit: 16S - large subunit: 23S and 5S

Question 49

what is in the nucleoid of a cell?

Answer 49

the genetic material

Question 50

what are plasmids?

Answer 50

extrachromosomal DNA (like extra DNA)

Question 51

what does it mean when a cell is "cured"?

Answer 51

it has "lost" its plasmids

Question 52

true or false: plasmids exist and replicate independently of the chromosome and can be inherited during cell division?

Answer 52

true

Question 53

true of false: there can only be one copy of plasmid in a cell

Answer 53

false; there can be multiple

Question 54

plasmid genes are (essential or non-essential)?

Answer 54

non-essential

Question 55

what are inclusions? what is another name for them?

Answer 55

- granules of organic or inorganic material stockpiled by the cell for future use - sometimes called microcompartments

Question 56

what are the three best known examples of external structures in bacteria?

Answer 56

pili, fimbriae, and flagella

Question 57

what are the four functions of external structures in bacteria?

Answer 57

- attachment to surfaces - cell movement - protection - horizontal gene transfer

Question 58

what is conjugation in bacteria?

Answer 58

transfer of plasmid from one cell to another

Question 59

what is the main function of flagella?

Answer 59

motility

Question 60

what does it mean when a bacteria is monotrichous?

Answer 60

it has one flagella

Question 61

what does it mean when a bacteria is amphitrichous?

Answer 61

it has one flagella at each end

Question 62

what does it mean when a bacteria is lophotrichous?

Answer 62

it has a cluster of flagella at one or both ends

Question 63

what does it mean when a bacteria is peritrichous?

Answer 63

it has flagella spread over the entire surface of the cell

Question 64

what are the three parts of flagella?

Answer 64

- filament - hook - basal body

Question 65

filament subunits self-assemble with the help of filament caps at the (tip or base).

Answer 65

tip, NOT base

Question 66

what is chemotaxis?

Answer 66

moving towards chemical attractants such as nutrients, and away from harmful substances

Question 67

what are the four common types of motility?

Answer 67

- flagellar movement - spirochete motility - twitching motility - gliding motility

Question 68

match the following flagellar movements: a.) clockwise b.) counterclockwise 1.) run (forward motion) 2.) tumble (turning)

Answer 68

b1.) counterclockwise is run a2.) clockwise is tumbling

Question 69

in spirochetes, where do the flagella remain?

Answer 69

the periplasmic space inside the outer membrane

Question 70

which describes short, intermittent, jerky motions: gliding or twitching?

Answer 70

twitching

Question 71

in the presence of a chemical attractant, does CW rotation of flagella increase or decrease? why?

Answer 71

CW (tumbling) decreases so that the run (CCW) in the direction of the attractant is longer

Question 72

when concentration of a chemical attractant decreases, does CW rotation of flagella increase or decrease? why?

Answer 72

CW (tumbling) increases so that the cell can redirect until it is moving toward the attractant again

Question 73

what is sporulation? what is its purpose?

Answer 73

- endospore formation by bacteria - survival and preservation of the genetic material (NOT reproduction)

Question 74

what are the three steps of formation of vegetative cells?

Answer 74

- activation (of spores) - germination - outgrowth