Dmp_712 Bact Exam_1 Robertsons Study Questions

Front 1

1. Briefly define or describe the following:
a. quaternary structure of proteins

Back 1

1. Briefly define or describe the following:
a. quaternary structure of proteins
Describes the number and 3-dimensional structure of the subunits in a protein. The structure is maintained by hydrophobic interactions and disulfide bonds.

Front 2

1. Briefly define or describe the following:
b. two major function(s) of the cell membrane of Gram-positive bacteria

Back 2

1. Briefly define or describe the following:
b. two major function(s) of the cell membrane of Gram-positive bacteria
1) a permeability barrier - determines what enters and leaves the cell
2) the site for the electron transport system and generation of ATP
3) site of active transport (concentrates nutrients in the cytoplasm)

Front 3

1. Briefly define or describe the following:
c. superoxide dismutase

Back 3

1. Briefly define or describe the following:
c. superoxide dismutase
One of two enzymes missing in anaerobes that explains the toxicity of oxygen to anaerobes. The enzyme converts the superoxide anion to hydrogen peroxide and oxygen.

Front 4

1. Briefly define or describe the following:
d. the interpretation of the following results: a TSI tube with a yellow slant,
yellow butt and a black precipitate along the stab line

Back 4

1. Briefly define or describe the following:
d. the interpretation of the following results: a TSI tube with a yellow slant,
yellow butt and a black precipitate along the stab line
These results indicate that the organism fermented glucose and one or both of the sugars lactose and sucrose. The black precipitate indicates that H2S was produced.

Front 5

1. Briefly define or describe the following:
e. molecular events associated with homologous recombination

Back 5

1. Briefly define or describe the following:
e. molecular events associated with homologous recombination
Homologous recombination describes the incorporation of a single strand of DNA into a double stranded (ds) recipient DNA. If ds DNA is internalized, the dsDNA is “nicked” causing it to relax and unwind. The single stranded binding protein (SSB) binds to, and stabilizes the ss donor DNA strand. The recA protein than binds to each end of the SSB-DNA complex and facilitates annealing of the donor strand to the recipient dsDNA. One strand of the recipient DNA is displaced and the donor and recipient sections joined by the enzymes involved in replication of DNA

Front 6

Briefly define or describe the following
generalized transducing phage

Back 6

Briefly define or describe the following
generalized transducing phage
A lytic phage with the capacity to package/stuff host DNA into its protein capsid and infect a new host. The phage can not replicate, but the genotype of the host has changed. A very limited number of phage mediate generalized transduction.

Front 7

Briefly define or describe the following
penicillanic acid and penicilloic acids

Back 7

Briefly define or describe the following
penicillanic acid and penicilloic acids

Penicillanic acid is the precursor of penicillin G and semi-synthetic penicillins. Addition of different functional groups to the amino group of penicillanic acid makes the derivatives either more acid-stable or more resistant to penicillinases.

Penicilloic acids is the term used to described penicillins in which the β-lactam ring has been cleaved. The cleavage product is a good hapten when bound to serum albumins. Antibodies to the B ring can be formed leading to penicillin hypersensitivity.

Front 8

Briefly define or describe the following
phagosome and phagolysosome

Back 8

Briefly define or describe the following
phagosome and phagolysosome
Phagosome is a term used to describe the membrane-bound vacuole containing the ingested particle after being internalized by phagocytic cells.
Phagolysosome is used to describe the fusion of primary and specific lysosomes with the phagosome.

Front 9

Briefly explain the basis/reason(s) for the following observations:
hydrogen bonds are relatively weak, but important in formation of specific base pairs and the structure of DNA

Back 9

Briefly explain the basis/reason(s) for the following observations:
hydrogen bonds are relatively weak, but important in formation of specific base pairs and the structure of DNA
Large numbers of hydrogen bonds are responsible for the stability of DNA. The complementary interaction of hydrogen bonds between adenine - thymine and guanine – cytosine bases of DNA is the basis of the genetic code and determines the helical structure of the two strands, which run in opposite directions.

Front 10

Briefly explain the basis/reason(s) for the following observations:
b. the generation time of Escherichia coli increases in a minimal medium containing salts and glucose compared with a complex medium containing salts, glucose, peptones and yeast extract.

Back 10

Briefly explain the basis/reason(s) for the following observations:
b. the generation time of Escherichia coli increases in a minimal medium containing salts and glucose compared with a complex medium containing salts, glucose, peptones and yeast extract.
Growth is more rapid in a complex medium because most biosynthetic intermediates needed for biosynthesis of macromolecules are supplied to the cell. The cell does not have to expend energy and produce key biosynthetic intermediates during growth and multiplication.

Front 11

Briefly explain the basis/reason(s) for the following observations
c. DNAse inhibits bacterial transformation due to its enzymatic activity

Back 11

Briefly explain the basis/reason(s) for the following observations
c. DNAse inhibits bacterial transformation due to its enzymatic activity
Transformation is mediated by “naked DNA”, which can be destroyed by DNAase.

Front 12

Briefly explain the basis/reason(s) for the following observations
d. most disinfectants exhibit a low amount of selective toxicity

Back 12

Briefly explain the basis/reason(s) for the following observations
d. most disinfectants exhibit a low amount of selective toxicity
Most disinfectants denature either proteins or lipids present in membranes. The differences between membranes of prokaryotes and eucaryotes are not enough to exert any significant amount of selective toxicity.

Front 13

Briefly explain the basis/reason(s) for the following observations
penicillins and cephlasporins are bacteriocidal only to growing cells

Back 13

Briefly explain the basis/reason(s) for the following observations
penicillins and cephlasporins are bacteriocidal only to growing cells
Both block the formation of the final cross-link between either the terminal 5th glycine in Gram-positive bacteria or DAP (diaminopimelic acid) in Gram-negative bacteria and the 4th D-alanine linked to NAMA. In the stationary phase, all of the cross-links are formed and these drugs have no effect.

Front 14

Briefly explain the basis/reason(s) for the following observations
e. AB exotoxins exhibit a specific mechanism of action and specific association with susceptible cells

Back 14

Briefly explain the basis/reason(s) for the following observations
e. AB exotoxins exhibit a specific mechanism of action and specific association with susceptible cells
The binding (B) subunit(s) interacts with a specific receptor on cell surfaces and facilitate the entry of the A subunit, which has a specific intracellular target.

Front 15

Briefly explain the basis/reason(s) for the following observations
f. f. convalescent sera from a patient who survived a septicemia due to Salmonella typhimurium will not neutralize the LPS in the outer membrane of the microbe

Back 15

Briefly explain the basis/reason(s) for the following observations
f. f. convalescent sera from a patient who survived a septicemia due to Salmonella typhimurium will not neutralize the LPS in the outer membrane of the microbe
LPSs are not neutralized by homologous antibodies due to the toxicity of lipid A, which is a poor antigen. Most of the antibodies in serum of patients are directed against the O-antigen of LPS.

Front 16

Briefly explain why the following statements are true
detergents that disrupt membranes are lethal for most Gram-negative bacteria

Back 16

Briefly explain why the following statements are true
detergents that disrupt membranes are lethal for most Gram-negative bacteria
The outer membrane which provides stability to the inner membrane in the absence of a thick peptidoglycan found in Gram-positive bacteria consists of LPS, phospholipids and a limited number of proteins. Detergents that disrupt lipid-protein interactions in membranes disrupt the OM, which leaves the inner membrane more susceptible.

Front 17

Briefly explain why the following statements are true
the shape of a bacteria killing curve is much different compared with a growth curve

Back 17

Briefly explain why the following statements are true
the shape of a bacteria killing curve is much different compared with a growth curve
The shape of a bacterial growth curve is due to binary fission and physiological changes in each stage:
Lag phase – the cell is “tooling up for catabolic and anabolic reactions
Log phase – optimal growth due to adequate supply of nutrients
Stationary phase – nutrients have been exhausted
Death phase – cells are dying faster than new cells are formed
A killing curve is a straight line based on the probability that a percentage/fraction of the cells will die per unit of time

Front 18

Briefly explain why the following statements are true
d. plasmids do not usually encode essential genes, but can provide a selective advantage for bacterial pathogens

Back 18

Briefly explain why the following statements are true
d. plasmids do not usually encode essential genes, but can provide a selective advantage for bacterial pathogens
Plasmids provide a selective/competitive advantage by encoding for one or more of the following: 1) antibiotic resistance, 2) virulence factors such as fimbriae and exotoxins, and 3) the sex pilus needed for conjugation. In addition, plasmids may encode for resistance against heavy metals present in disinfectants.

Front 19

Briefly explain why the following statements are true
e. a pathogen such as Staphylococcus aureus can be resistant to tetracyclines, but sensitive to erythromycin

Back 19

Briefly explain why the following statements are true
e. a pathogen such as Staphylococcus aureus can be resistant to tetracyclines, but sensitive to erythromycin
Tetracyclines act at the 30S ribosome by blocking binding of AA-tRNAs, whereas erythromycin acts at the 50 S ribosome and inhibits peptidyl transfer and translocation.

Front 20

Briefly explain why the following statements are true
pathogens on mucosal surfaces in the early stages of an infection face several
challenges in order to survive and multiply

Back 20

Briefly explain why the following statements are true
pathogens on mucosal surfaces in the early stages of an infection face several
challenges in order to survive and multiply
Pathogens must compete with normal flora for space and nutrients. In addition they must avoid or block the effects of sIgA, PMNs, lysozyme, complement components and mucous that lines mucosal surfaces. The peristalisis of the GI tract and shear forces in the urinary tract also limit growth and multiplication.

Front 21

Briefly explain why the following statements are true
the lipopolysaccharide binding protein in serum plays a key role in the biological activity of LPSs

Back 21

Briefly explain why the following statements are true
the lipopolysaccharide binding protein in serum plays a key role in the biological activity of LPSs
LPS specifically binds to the LPS-binding protein in serum and the LPS-LPS binding protein complex binds to CD14 on surfaces of macrophages, which transmits a transmembane signal for macrophages to produce and release large amounts of cytokines.

Front 22

Briefly explain why the following statements are true
the prognosis for a patient in shock due to a Gram-negative septicemia is
not good

Back 22

Briefly explain why the following statements are true
the prognosis for a patient in shock due to a Gram-negative septicemia is
not good
Shock is due to insufficient volume of blood in relation to the total capacity of the circulatory system. In the case of shock due to LPS, there has been a massive amount of damage done to the circulatory system coupled with the presence of clots in capillary beds, which is almost impossible to reverse.

Front 23

An acidic substance found only in Gram-positive bacteria and covalently linked to the peptidoglycan layer is:
1. lipopolysaccharide
2. ribitol teichoic acids
3. phoshatidyl ethanolamine
4. palmitic acid

Back 23

2
An acidic substance found only in Gram-positive bacteria and covalently linked to the peptidoglycan layer is:
1. lipopolysaccharide
2. ribitol teichoic acids
3. phoshatidyl ethanolamine
4. palmitic acid
2

Front 24

The primary function of the pentose phosphate pathway (also called the
hexose mononphosphate pathgeays during catabolism of glucose and cell growth is:
1. production of NADPH and pentose phosphates for synthesis of DNA and RNA
2. production of ATP
3. production of GTP
4. production of NADH

Back 24

1
The primary function of the pentose phosphate pathway (also called the
hexose mononphosphate pathgeays during catabolism of glucose and cell growth is:
1. production of NADPH and pentose phosphates for synthesis of DNA and RNA
2. production of ATP
3. production of GTP
4. production of NADH
1

Front 25

The increased growth rate of facultative anaerobes using glucose as a
carbon source in the presence of oxygen compared with the absence of oxygen (fermentation) is due to:
1. the presence of the EMP pathway
2. the capacity to convert pyruvic acid to metabolic end products
3. the presence of the electron transport system and capacity to use oxygen as a terminal electron acceptor
4. the absence of acidic end products

Back 25

3
The increased growth rate of facultative anaerobes using glucose as a
carbon source in the presence of oxygen compared with the absence of oxygen (fermentation) is due to:
1. the presence of the EMP pathway
2. the capacity to convert pyruvic acid to metabolic end products
3. the presence of the electron transport system and capacity to use oxygen as a terminal electron acceptor
4. the absence of acidic end products
3

Front 26

Mating experiments between F+ donor/male bacterial cells and F-
cells/female cells results in the entire culture becoming:
1. F+
2. F-
3. part F+ and part F-
4. Hfr

Back 26

1
Mating experiments between F+ donor/male bacterial cells and F-
cells/female cells results in the entire culture becoming:
1. F+
2. F-
3. part F+ and part F-
4. Hfr
1

Front 27

Fimbriae are surface structures on bacterial surfaces that can be described
as:
1. being composed of a protein called flagelin
2. attached as a tuft (group) at the end of rod-shaped bacteria
3. being involved in transfer of DNA
4. numerous “hair-like projections” made of protein subunits

Back 27

4
Fimbriae are surface structures on bacterial surfaces that can be described
as:
1. being composed of a protein called flagelin
2. attached as a tuft (group) at the end of rod-shaped bacteria
3. being involved in transfer of DNA
4. numerous “hair-like projections” made of protein subunits
4

Front 28

The enterotoxic activity of the heat-labile E. coli enterotoxin (LT)
and cholera toxin (CT) is due to:
1. inactivation of 28S RNA associated with 60S ribosomes
2. ADP-ribosylation and inactivation of EF-2
3. ADP-ribosylation and inactivation of the Gs protein subunit
4. production of prostaglandins

Back 28

3
The enterotoxic activity of the heat-labile E. coli enterotoxin (LT)
and cholera toxin (CT) is due to:
1. inactivation of 28S RNA associated with 60S ribosomes
2. ADP-ribosylation and inactivation of EF-2
3. ADP-ribosylation and inactivation of the Gs protein subunit
4. production of prostaglandins
3

Front 29

The primary non-oxidative killing system(s) in PMNs include the
following:
1. myeloperoxidase
2. lysozyme and defensins
3. phospholipase C
4. trypsin

Back 29

2
The primary non-oxidative killing system(s) in PMNs include the
following:
1. myeloperoxidase
2. lysozyme and defensins
3. phospholipase C
4. trypsin
2