Chapter 3: Cell Structure - External

Question 1

Why do both gram positive and negative bacteria have flagella and fimbriae?

Answer 1

• help bacteria to move and attach to microorganisms

Question 2

What is the genome size of bacteria?

Answer 2

• 4-5 million base pairs
• size of a bacteria gene is 1 kb

Question 3

What are the 3 external structures of bacteria that we will cover in this deck?

Answer 3

• capsule and slime layers
• flagella
• Fimbriae and Pili

Question 4

What are capsules and slime layers?

Answer 4

• Sticky, gelatinous layer external to the cell

Question 5

What are capsules and slime layers made of?

Answer 5

• polysaccharide, proteins, or both

Question 6

How can we tell if the layer is a capsule?

Answer 6

• If the layer is organized and firmly attached to the cell wall

Question 7

How can we tell if the layer is a slime layer?

Answer 7

• if the layer is unorganized and loosely attached to the cell wall

Question 8

What is the purpose of capsules? (2)

Answer 8

• in some bacteria capsules, they play a role in virulence
• protection against phagocytosis
  ex. S. pneumoniae, with capsule causes disease, without does not

Question 9

What is the purpose of slime layers? (2)

Answer 9

• allow bacteria to attach to surfaces
• medical implants, water pipes teeth
  ex. S. mutans makes polysaccharide slime from sucrose that attaches to teeth to form cavities

Question 10

What are flagella? (2)

Answer 10

• long protein appendages
• present in both gram pos and neg

Question 11

What is the structure of flagella? (3)

Answer 11

• semi-rigid
• helical
• turns like a propeller

Question 12

What is flagella used for?

Answer 12

motility

Question 13

Bacterial cells have four typical arrangements of flagella. What are they?

Answer 13

• monotrichous
• lophotrichous
• amphitrichous
• peritrichous

Question 14

What are monotrichous flagella?

Answer 14

• a single polar flagellum

Question 15

What are lophotrichous flagella?

Answer 15

two or more flagella originating from one pole

Question 16

What are amphitrichous flagella?

Answer 16

• tuffs of flagella originating from opposite poles

Question 17

What are peritrichous flagella?

Answer 17

• flagella distributed all over the cell

Question 18

What are steps in how flagella aid in cell motility? (2)

Answer 18

1. flagella turn, causing the cell to move in one direction “run”
2. Periodically, flagella reverse direction, causing a random change in direction “tumble”

Question 19

How does flagella allow for chemotaxis?

Answer 19

• movement toward or away from a stimulant
• toward a nutrient (attractant)
• away from a toxin (stimulant)
  ex. E. Coli will move toward glucose

Question 20

How can flagellar protein be used to distinguish bacteria?

Answer 20

• can be used to distinguish among strains of a species
  ex. E. Coli O157:H7

Question 21

What will a cell do if there is no concentration gradient, speaking in terms of the flagella?

Answer 21

• the cell will move randomly when no CG of attractant or repellant

Question 22

What will a cell do when it senses an attractant, in terms of flagella?

Answer 22

• When a cell senses it is moving towards an attractant, it tumbles less frequently so the runs in the direction of the attractant are longer

Question 23

What are the structures of fimbriae and Pili? (2)

Answer 23

• short, hair-like appendages
• hollow

Question 24

What is the function of fimbriae? (2)

Answer 24

• allow the cell to adhere to surfaces
• contribute to pathogenicity
  Ex. some strains of E. coli have fimbriae that allow them to attach to the intestinal wall

Question 25

What is the function of pili? (2)

Answer 25

- allows attachment of two bacteria to each other - involved in the transfer of genetic material between bacteria ex. E. coli's sex pilus