Bacterial Structure and Function

Question 1

Name the eukaryotic homologs and action of the following bacterial cytoskeleton elements:

1. ) FtsZ
2. )MreB
3. )CreS

Answer 1

1. ) Homolog = tubulin. Used in division.
2. ) Homolog = actin. Used in shape, polarity, and chromosome segregation. Dynamic shape. Bacillus vs. Coccus.
3. ) Homolog = intermediate filament. Maintains shape. Curving of spirillum vs. bacillus

Question 2

What is the peptidoglycan layer composed of?

Answer 2

Polymer of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MucNAc.) MucNAc linked to tetrapeptide chains.

Question 3

How are gram neg and gram pos bacteria in respect to their peptidoglycan layer?

Answer 3

Gram neg - Sugar polymer + tetrapeptide chains w/ crosslinking via DAP to D-ala on another chain.

Gram pos - Sugar polymer + tetrapeptide chains, crosslinking via L-lys. Links via intermediate element. MUCH MORE CROSSLINKING than gram neg. (can sustain a much higher osmotic pressure too)

Question 4

What do lysozymes do (specific to their effect on peptidoglycan layer)?

Answer 4

Cleave glycoside bond between MurNAc and GlcNAc. Part of innate immune system.

Question 5

Name components of gram neg bacterial outer membrane

Answer 5

((lipopolysaccharides - outer membrane)), lipoproteins and ((porins - inner membrane, transport.))
Barrier to detergents and toxins.

Question 6

What is Lipid A and where is it located?

Answer 6

Toxic part of endotoxin. located in inner leaflet of outer membrane on gram neg bacteria.

Question 7

What is O-antigen and where is it located?

Answer 7

Oligosaccharide that functions as a somatic antigen in inner leaflet of outer membrane of gram neg bacteria.

Question 8

Name components of gram pos bacterial outer membrane

Answer 8

thick, extensively cross-linked peptidoglycan layer with teichoic acids

Question 9

What are teichoic acids and where are they located?

Answer 9

Gram pos bacteria
Teichoic acids = repeating polyglycerol-P or polyribitol-P backbone, covalently attached to the peptidoglycan layer.

Lipoteichoic acids attached to cytoplasmic membrane, anchor the cell wall to the membrane.

Question 10

What are bacterial capsules?
What do they do for the bacteria?
When are they used in humans?

Answer 10

loose, gelatinous, consist of complex polysaccharides

(exception: capsule of Bacillus anthracis is a polymer of D- glutamic acid.)

Enhance resistance to phagocytosis. Most are antigenic. (some used as components of vaccines)

Question 11

What are flagella?

What are directions/names of flagellar rotations?

Answer 11

Motility.

All over the surface = peritrichous
one or several flagella on either end of the cell=polar

Flagellar rotation:
(clockwise=swimming, counterclockwise=tumbling)

Most flagella are antigenic.

H-antigents used for classification of enteric bacteria are flagellar antigens.

Question 12

What are pili (fimbriae)?

Answer 12

hair like structures, play role in bacterial adherence to surfaces and tissues.

Sex pili play role in bacterial conjugation.

Question 13

Cytoplasmic membrane of bacteria - composition? What does it let through?

Answer 13

physiological barrier
No sterols, higher content of protein (60-70%)

Home of electron transport system!

Impermeable to ALL charged substances.
Only hydrophobic molecules/uncharged molecules no larger than glycerol can diffuse through it.

Also transports metabolites into the cytoplasm, biosynthesis of lipids, certain aspects of DNA replication and flagellar rotation.

Question 14

What occurs in ribosomes?

How are polyribosomes formed?

Answer 14

closely related to mitochondrial ribosomes.

Protein synthesis occurs here.

Polyribosomes are formed by the interaction of several ribosomes with a single messenger RNA. (bacterial mRNA’s may be polycistronic - aka code for more than one protein)

Question 15

What is the nucleoid? What occurs here?

Answer 15

No nuclear membrane lol

DNA of the bacteria is located here.

DNA is tightly packed and supercoiled.

Transcription and translation can occur as coupled processes.

Question 16

What are bacterial chromosomes? Do bacteria have more than one?

Answer 16

-Chromosome – single, double stranded, circular DNA molecule.

Some bacteria have more than one chromosome.

Contains cytoskeletal components which function as primitive mitotic apparatus during bacterial cell division.

Question 17

What are plasmids?

What are R-factors?

Answer 17

extra-chromosomal, self-replicating DNA molecules

In pathogenic bacteria, encode virulence factors.

R factors are plasmids that carry genes that determine resistance to antibiotics in many pathogenic bacteria.

Question 18

What are bacteriophages?

What is phage conversion?

Answer 18

viruses that infect bacteria

DNA genomes of bacteriophages can integrate into bacterial chromosomes, then replicate as part of the chromosome.

Often carry genes that encode bacterial toxins, resistance to antibiotics.

Phage conversion – change in the phenotype of a host bacterium as a consequence of expression of a gene that is encoded by a bacteriophage within the host bacterium.

Question 19

Describe lag phase of bacterial growth

Answer 19

period of physiologic adjustment for starting cells (inoculum)

induction of new enzymes and the establishment of proper intracellular environment for optimal growth in the new medium.

Question 20

Describe exponential phase of bacterial growth

What is generation time?

Answer 20

Rt of increase in cell number that is proportional to the mass already present.

Generation time = Constant interval of time required for doubling

Rt of growth is maximal for available nutritional conditions.

Question 21

Describe stationary phase of bacterial growth

Answer 21

essential nutrients are consumed, toxic products of metabolism accumulate

Cell growth slows or stops, cell death balances cell growth

Increased resistance to antibiotics (like penicillin or beta-actam antibiotics that act on growing cells)

MOST TIME SPENT HERE

Question 22

Describe death phase of bacterial growth

Answer 22

They die

number of viable bacteria decrease. Autolysis may occur.

Question 23

What are heterophilic bacteria?

Answer 23

Bacteria that require organic carbon source (most bacterial pathogens.)

Question 24

What are autotrophic bacteria?

Answer 24

Bacteria that obtain their carbon exclusively from CO2

Question 25

What are fastidious bacteria?

Answer 25

Deficient in biosynthetic pathways. Require amino acids, vitamins, etc etc.

Question 26

What are obligate intracellular bacteria?

Answer 26

grow within eukaryotic cells, cannot be cultivated in artificial media.

Question 27

What types of bacteria produce oxygen? What do these bacteria produce that protects them against ROS in immune system?

Answer 27

Aerobe, Indifferent + Facultative – produce toxic oxygen metabolites (hydrogen peroxide and superoxide.)

Usually produce catalase or peroxidase and superoxide dismutase (SOD) that protects them against toxic reactive oxygen species.

Question 28

What is “energy currency” in bacteria?

Answer 28

Currency : ATP and electrochemical gradients (proton motive force.)

Interconvertible by the membrane ATPase.

Need NADPH -> NADP reducing pover to interconvert.

Question 29

What is bacterial respiration? Which types of bacteria do this?

Answer 29

generation of ATP through electron transport and use molecular oxygen as final electron acceptor.

Aerobe, indifferent (aerotolerant aerobe) facultative and microaerophilic.

In anaerobic respiration, bacteria may use inorganic substrates (nitrate or nitrite) as terminal electron acceptors.

Question 30

What is bacterial fermentation? Which types of bacteria do this?

Answer 30

Organic compounds serve as both electron donors and electron acceptors -> no net oxidation of substrates occurs.

Done by anaerobic, facultative bacteria and indifferent bacteria

Question 31

What is sporulation? What are spores? When are they produced?

Answer 31

Sporulation is the process of forming a highly resistant, dehydrated form of the bacteria with no metabolic activity, adapted for long survival.

When back in good environment, may convert back to vegetative cells through the process of germination.

Produced when nutritional supply of carbon, nitrogen or phosphorus is limited.

Question 32

Cell-wall active antimicrobials

Answer 32

Bacteria require cell wall for resistance to osmotic pressure– if peptidoglycan synthesis is interfered with, the bacterial cells will lyse.

a. β-lactams (penicillins, cepalosporins, etc)
b. Vancomycin
c. Cycloserine

Question 33

Outer and cytoplasmic membrane-active antimicrobials

Answer 33

Polymyxins are cationic surfactants that disrupt bacterial outer and cytoplasmic membranes. They are less active on mammalian cell membranes.

Question 34

Inhibitors of protein synthesis at the ribosomal level

Answer 34

Bacteria - 70S, different from 80S, so can selectivily inhibit. Make sure not to hurt mitochondrial ribosomes tho!

a. Aminoglycosides (including streptomycin, kanamycin, gentamicin, neomycin, tobramycin, amikacin, etc)
b. Tetracyclines
c. Chloramphenicol
d. Macrolides (such as erythromycin) and lincomycins (such as lincomycin and clindamycin)

Question 35

Inhibitors of nucleic acid synthesis.

Answer 35

a. Quinolones (inhibit DNA gyrase +topoisomerase)

b. Rifampicin (inhibits RNA polymerase)

Question 36

Metabolic inhibitory antimicrobials

Answer 36

Can target metabolic pathways that are not duplicated in humans, like the pathway to produce folic acid (humans must consume it in their diet)

a. Sulfonamides (folic acid pathways)
b. Trimethoprim (interfere w/ folate metabolism)
c. Isoniazid (inhibits lipid synthesis)
d. Metronidazole (anaerobic bacteria)