Bacteria Chapter 2: Cell Structure

Question 1

What is the Svedburg unit (S)?

Answer 1

relates to density of molecules and how fast they sediment (during centrifugation)

Question 2

What are bacterial ribosomes composed of?

Answer 2

is a 70S ribosome formed by:

large subunit: 50S
small subunit: 30S

Question 3

What are eukaryotic ribosomes composed of?

Answer 3

is a 80S ribosome formed by:

large subunit: 60S
small subunit: 40S

Question 4

Why do antibiotics targeting bacterial ribosomes not affect eukaryotic ribosomes?

Answer 4

bacterial 30S small subunit has 16S rRNA

eukaryotic 40S small subunit has 18S rRNA

Question 5

What colour do gram-positive cells stain?

Answer 5

purple

Question 6

What colour do gram-negative cells stain?

Answer 6

pink

Question 7

What does the cell wall of Gram-positive bacteria consist of?

Answer 7

thick peptidoglycan

Question 8

What does the cell wall of Gram-negative bacteria consist of?

Answer 8

• thin peptidoglycan

- outer membrane

Question 9

What is peptidoglycan composed of?

Answer 9

• glycan chains

- cross-linking peptides

Question 10

What are glycan chains composed of?

Answer 10

two joined sugars

• N-acetylglucosamine (NAG or G)
• N-acetylmuramic acid (NAM or M)

Question 11

How does the outer membrane (OM) of Gram-negative bacteria differ from cytoplasmic membrane?

Answer 11

has lipopolysaccharide (LPS) – negatively charged

Question 12

What do Gram-positive cell walls have that Gram-negative cell doesn’t?

Answer 12

teichoic acids (sugars)

• if anchored to PG: techoic acid
• if anchored to lipid in cytoplasmic membrane: lipoteichoic acid (LTA)

Question 13

How are polysaccharide capsules anchored to the cell wall in Gram-negative bacteria?

Answer 13

via phospholipid

OR

replacing polysaccharide portion of LPS

Question 14

How are polysaccharide capsules anchored to the cell wall in Gram-positive bacteria?

Answer 14

via NAM and NAG sugars (of peptidoglycan glycan chains)

Question 15

What are the functions of capsules in bacteria?

Answer 15

• protect from being engulfed by phagocytic cells
• protect from phages trying to reach cell wall to infect celll
• mediate attachment to surfaces (ie. to get food)
• mechanism for specific attachment of pathogenic and non-pathogenic bacteria to surfaces (ie. prevent being swept out of body, off rocks, and be more resistant to predation, etc.)

Question 16

What is a phage?

Answer 16

virus that infects bacteria

Question 17

Where can pili be anchored?

Answer 17

cell envelope

• cytoplasmic membrane
• cell wall

Question 18

What are the functions of pili?

Answer 18

• attachment to surfaces

- twitching motility

Question 19

What is a serovar or serotype?

Answer 19

strain differentiated by immunological means

Question 20

What does a bacterial cell wall consist of?

Answer 20

• plasma membrane

- cell wall

Question 21

What are capsules?

Answer 21

outer layer produced by some prokaryotic cells

Question 22

In prokaryotic cells like bacteria, transcription and translation are linked. Why is that?

Answer 22

DNA is not surrounded by a membrane, and mRNA does not need to be transported
out to cytosol

therefore, ribosomes can access mRNA as it is still being synthesized

Question 23

What can antibiotics target?

Answer 23

• ribosomes
• RNA polymerase
• dNA polymerase

Question 24

What structures are only found in some bacteria?

Answer 24

• flagella
• pili
• fimbriae
• capsule