Bacterial Structure and Physiology

Question 1

What is the basic structure of peptidoglycan?

Answer 1

Long polymers of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) w/ alternating L-and D- amino acids

The polymers are crosslinked to each other to form 3D sheets

Question 2

What kinds of bacteria contain teichoic acid in their cell walls?

Answer 2

Gram positive

Question 3

Which enzymes are responsible for proper crosslinking of NAG/NAM chains?

Answer 3

Penicillin-binding proteins (PBPs)

Question 4

Which types bacteria are poorly visualized by Gram staining?

Answer 4

Mycobacteria, some spirochetes, and mycoplasma

Mycobacteria: cause TB, leprosy, other diseases

Spirochetes: Treponema pallidum causes syphilis

Question 5

How do capsules prevent engulfment by phagocytes?

Answer 5

Prevent complement activation via the alternate pathway on the cell surface

Question 6

What diseases are encapsulated bacteria important in causing?

Answer 6

• Meningitis
• Bacteremia in people without a functional spleen

Question 7

What are K antigens?

Answer 7

Capsules of certain bacteria used for serological typing

Question 8

What are flagella designated for serotyping?

Answer 8

H antigens

Question 9

The presence of flagella can be used to serologically distinguish and classify which bacteria?

Answer 9

Gram-negative enteric bacteria

Ex: Escherichia coli O157:H7 has type 7 flagella and type 157 O antigen

Question 10

What causes bacterial running?

Answer 10

Counterclockwise rotation of flagella

Question 11

What causes tumbling of bacteria?

Answer 11

Clockwise rotation of flagella

Question 12

Describe bacterial ribosomes

What subunits do they include?

Answer 12

70S ribonucleoprotein structures

50S subunit (includes 23S, 5S, 34 proteins)

30S subunit (includes 16S and 21 proteins)

Question 13

The gene sequence of which portion of bacterial ribosomes can be used to identify bacteria?

Which subunit is it found in?

Why can this be done?

Answer 13

16s rRNA gene sequence

Found in 30S subunit

The sequences of some regions of 16S rRNA gene are unique to various bacterial genera and species

Question 14

In what ways does bacterial transcription differ from eukaryotic transcription?

Answer 14

• Bacterial RNA polymerase is different
• Genes may be organized into operons (clusters of genes all transcribed from a single promoter onto a single mRNA molecule)
• Occurs in cytoplasm
• Performed concurrently w/ translation

Question 15

What is an operon?

Answer 15

A cluster of genes that are all transcribed from a single promoter onto a single mRNA molecule

Question 16

What stage do the Gram-positive bacilli have to be in for spores to develop?

Answer 16

Vegetative (dividing cells)

Question 17

Which sorts of bacteria can form spores?

Which bacteria specifically?

Answer 17

Some Gram-positive bacilli

Clostridium and Bacillus

Question 18

How do many bacteria acquire iron from host molecules?

Answer 18

Secrete siderophopres (low molecular weight molecules) that remove iron from host molecules and allow it to be taken up by bacterial cells

(Exceptions: Neisseria meningitidis and Neisseria gonorrhoeae produce surface receptors that bind to lactoferrin and transferrin, then remove and internalize iron)

Question 19

Which bacteria contain cytochrome c?

What test can detect cytochrome c? What does it measure?

Answer 19

Pseudomonas aueroginosa and Neisseria spp.

Oxidase test: measures ability of bacteria to oxidize and change color of N,N-dimethyl-p-phenylenediamine

Question 20

What are oxidase positive bacteria?

Answer 20

Bacteria containing cytochrome C

Question 21

Why would you use MacConkey agar?

Answer 21

MacConkey agar is selective for gram (-) rods

It is also differential for lactose fermentation

Question 22

What is the difference between an insertion sequence and a transposon?

Answer 22

Insertion sequences (IS) only contain genes for tranposases

Transposons contain genes for transposase AND other genes that may encode antibiotic resistance or virulence determinants.

Note: Transposons may contain IS at each end

Question 23

What virulence determinants of Escherichia coli are encoded by plasmids?

Answer 23

Enterotoxins (LT and ST)

Question 24

What virulence determinants of Clostridium tetani are encoded by plasmids?

Answer 24

Tetanus toxin

Question 25

What is transformation?

Answer 25

Pieces of naked DNA from lysed bacterial cells are taken up by other bacterial cells and incorporated into their chromosomes

Question 26

What are “naturally competent bacteria?”

Answer 26

Bacteria that are naturally able to take up DNA in transformation

Question 27

What is transduction?

Answer 27

The mechanism that bacteriophages use for DNA transfer

2 types of transduction:

• Generalized
• Specialized

Question 28

Can lytic bacteriophages every be useful to humans? How?

Answer 28

Lytic phages can be useful in treating certain bacterial infections in humans

The lytic phage infects the bacterium and causes it to lyse, thus killing the bacteria and potentially eradicating the bacterial infection

Question 29

Would a beta-lactam antibiotic be useful against gram-positive or gram-negative bacteria?

Answer 29

Both; Both types of bacteria can be treated by beta-lactam antibiotics because both have peptidoglycan in their cell walls (although the layer is thinner in gram (-) bacteria)

Question 30

What kinds of bacteria contain superoxide dismutase and catalase?

Answer 30

Obligate aerobes, facultative anerobes, aerotolerant anaerobe

Question 31

What kinds of bacteria (in general) would not contain superoxide dismutase and catalase?

Answer 31

Obligate anaerobes

Question 32

Which genetic exchange mechanism utilizes a sex pilus?

Answer 32

Conjugation