Exam 1 (Lect. Qs 6-10) Flashcards
An active transport uniport uses what sources of energy to bring molecules across the cell membrane?
The voltage potential (electrical charge) across the membrane
a primary active transporter is essentially irreversible (it only transports molecules in one direction) because ..
it uses ATP, which is much more powerful energy source than the PMF and it requires a protein to bind form the outside before the channel can open
double check
Which of the following is NOT true of the PTS (phosphotransferase) transport system?
it involves direct transfer of a phosphate from ATP to glucose
Why are we interested in studying type III secretion systems?
They are often associated with insertion of toxin directly into eukaryotic cells
What type of transport is carried out by the PTS (phosphotransferase system)?
import of sugars
a hallmark of type III secretion systems is …
secretion only once contact has been made with a host cell membrane receptor
why does passive transport require energy?
to open facilitated diffusion channels in the membrane
how does this MFS antiport pump Na+ out of the cell?
it uses the energy of the proton gradient
Which of the following is characteristic of a bacterial type II export system?
use of a leader peptide (signal sequence) to determine which proteins to secrete
why does the PTS (phosphotransferase system) use a phosphorelay mechanism?
to sense the available carbohydrate and regulate cell responses accordingly
Which of the following is NOT a feature of the “gated rocker-switch” mechanism for transporter function?
plug in transport channel moved aside by energy from ATP
Why is a phosphorelay mechanism involved in sugar transport in bacteria?
each protein in the relay can be used to regulate other cell processes based on the presence or absence of sugar in the environment
HIGHLIGHTED
There has been an evolutionary progression from facilitated diffusion carriers to MFS-type transport channels to gated channels to ABC transporters. What selective advantage has driven this evolution in bacteria?
accumulation of solutes from increasingly nutrient-deprived environments
Structurally what does it mean that transport of solute #1 with its gradient allows transport of solute #2 against its gradient?
solute #1 holds the transporter open long enough for solute #2 to bind
which of the following is a unique feature of the PTS transport system?
a relay that allows many opportunities for regulation of the transporter
there is currently much interest in studying efflux pumps that bacteria use to eliminate toxins and antibiotics. What is one characteristic of these efflux pumps?
the toxin is secreted through both bacterial membranes in one step
Which of the following is NOT a feature found in Type II secretion systems (T2SS)?
transport is blocked until the bacterium contacts another cell
If passive transport requires energy, what is the energy used for?
to open facilitated diffusion channels in the membrane
What special feature of ABC import transporters makes them essentially irreversible?
a protein that binds solute before it signals from the periplasm for the transporter to open
What type of transport is carried out by the phosphotransferase system (PTS)?
import of glucose
what makes passive transport “passive”?
it is unable to concentrate a solute against a chemical gradient
some transporters have gates. what is the purpose of the gates in gated transporters?
to increase the accumulation ration by preventing reverse transport
Which of the following is a unique feature of the PTS transport system?
a relay that allows many opportunities for regulation of the transporter
what is the “sec translocon”?
a transporter that inserts proteins with a signal sequence through the inner membrane
the most evolutionary primitive rocker-switch model for transport proteins requires …
a transporter with two alternating conformations
a bacterium is growing is a medium with a [K+] of 1mM. the bacterium uses a uniport to accumulate k+ to 10 mM concentration inside the cell. what is the energy for this transport?
the membrane potential
Which of the following is NOT a characteristic of the bacterial PTS system
It can be used to import and export a wide variety of solutes
what is the purpose of a molecular chaperone during protein secretion in bacteria?
it keeps a protein in a unfolded conformation until transport
a certain bacterium uses proline as an osmoprotectant. what sort of proline transporter serves this purpose best? Why?
an ABC system because of a protein that prevent reverse transport
Which of the following is a similarity between type II and Type III secretion systems?
use of ATP hydrolysis as the energy source for transport
how is the energy of a H+ gradient most directly used by the cell to uptake glucose
binding of a H+ gradient most directly used by the cell to uptake glucose
Which of the following is NOT a feature of facilitated diffusion channels, such as aquaporins?
they transport solutes in only one direction
The drug valinomycin affects the membrane potential, but not the delta pH. which is the following transporters would be the most affected by treatment with valinomycin
a lysine uniport
what is the role of the periplasmic binding protein in ABC uptake systems
is blocks reverse transport of the solute
all the following are advantages of the PTS system, EXCEPT
allows the cell to sense the presence of glucose
It allows regulation of intracellular reactions in response to glucose.
It readies glucose for the metabolic reactions in which it will later be used.
It takes advantage of LeChatelier’s Principle to increase transport efficiency.
IT IS AN EFFICIENT TRANSFER OF PHOSPHATE FROM STP DIRECTLY TO GLUCOSE
Lecture 7
Once they enter and start to live in a eukaryotic host cell, flagellated bacteria often lose their
flagella. Why?
Nutrients are all around, and there is no gradient to move towards.
Pili are involved in all of the following EXCEPT. . .
protein secretion
An organism with carboxysomes would be expected to be a . .
autotroph
Which of the following is NOT a part of the process of endospore formation?
Spore replicates its DNA one last time in case conditions improve
Which of the following is NOT a function of capsules or slime layers?
motility
The large intracellular structures seen inside this cell are likely used for . .
storage of carbon reserves for later metabolism
how are pili involved in bacterial motility?
They are extended and retracted like grappling hooks
the bacterium E. coli exhibits flagellar motility and chemotaxis toward the amino acid alanine. If E. coli is placed in a 100 millimolar solution of alanine, which of the following would best describe its behavior?
random, undirected motion
Why do we consider that the bacterial Type III secretion system is an intermediate in flagellar
evolution?
T3SS and flagella are both hollow filaments with similar membrane proteins.
What is the function of the bright structures seen inside these chemolithoautotrophic cells?
They can provide a source of electrons.
The protein coat of an endospore . .
is deposited between the membranes of the forespore and the mother cell.
The bacterium Streptococcus mutans is well known for its ability to form biofilms. What feature of the bacterium is responsible for this ability?
A sucrose-induced glycocalyx
flagella and pili can both be responsible for bacterial cell motility. How are these two types of motility similar?
Both involve secretion and withdrawal of appendages from the cell.
Volutin (metachromatic) granules are used to store .
phosphate
What is the function of the bacterial structure shown at the right?
to concentrate enzymes used to reduce CO2 in autotrophs
Capsules or slime layers are wholly or partly responsible for all of the following EXCEPT …
motility
The bacterium E. coli exhibits flagellar motility and chemotaxis toward the amino acid alanine.
Assume E. coli is placed in a defined medium, and a crystal of alanine is added. Which of the
following best describes the behavior of the E. coli?
Directed motion with occasional random reorientations
the structures indicated by the arrow in this picture are made of . .
the protein pilin
The presence of carboxysomes in a bacterial cell indicates that the cell . .
is an autotroph
Phosphate that will be used to make cellular structures is stored in . . .
volutin granules
the negative staining procedure must be used to visualize a bacterial capsule in the bright field
microscope. What conclusion can you make from that statement?
Carbohydrates must not be able to bind charged dyes.
How can an E. coli cell move toward a point source of a molecular attractant?
E. coli can tumble less frequently if it is moving towards a continually increasing attractant concentration.
the structure indicated by the arrow is most important for . .
DNA transfer
A bacterium with carboxysomes is most likely . .
an autotroph
Which part of a bacterial endospore contains a special type of peptidoglycan that is responsible for absorbing the water from the core to keep it dry?
D - first center layer
This is a picture of Neisseria gonorrhoeae adhering to cervical epithelial cells. What structure is it using to adhere to the cells?
pili
What happens to a swimming bacterial cell when its flagella reverse their direction of rotation?
The cell re-orients randomly to face a new direction.
Chemolithoautotrophic bacteria can increase their growth rate if they contain inclusions
called_______________ that make the cell’s metabolism more efficient.
carboxysomes
The structure shown here is able to survive boiling water. The arrow is pointing to a layer of this structure. What is the function of this layer?
To soak water from the internal part of the structure, keeping it dry and inert
Structures that transport electrons between bacterial cells in a dense culture are
called_______________.
nanowires
Streptococcus mutans produces this only in the presence of sucrose, leading to the development of dental caries (cavities).
glycocalyx
Why does E. coli reverse the direction of its flagellar rotation periodically?
The cell fails to encounter a higher attractant concentration.
Which of the following would you expect to find in both photolithoautotrophs and
chemoorganoheterotrophs?
volutin granules
Why is a glycocalyx usually viewed by using the negative staining procedure?
The glycocalyx usually has no charge.
E. coli cells are able to chemotax towards a nutrient attractant (ATR). How?
By sensing ATR concentration every few milliseconds and keeping a “memory” of it
What is “Horizontal Gene Transmission”?
The transfer of DNA from one bacterium to another using special pili
What function do bacterial microcompartments carry out?
They concentrate enzymes and their substrates to improve reaction rates.
Which of the following lists of three bacterial structures all contain a substantial
proportion of carbohydrates?
Capsule, Peptidoglycan and LPS
Which of these is important for the function of flagella, but not for Type III secretory systems?
A H+ channel
You’re a microbiologist looking at a biofilm from a lithotrophic bacterium. Some cells have sulfur
granules, but not all do. What other organelles could you expect to find in this culture?
nanowires
Why are Microbiologists so interested in studying bacterial microcompartments (BMCs)?
We can concentrate enzymes whose efficiency we want to increase.
lecture 8
the best way to store an unknown bacterial culture long-term is to . .
freeze it in 15% glycerol
superoxide dismutase is . . .
an enzyme that allows aerobes to survive in oxygen
adding an antibiotic to a microbial growth medium makes the medium . .
selective
an enrichment culture for a psychrophile would involve which of the following steps?
grow a mixed culture at 4 degrees C
The growth temperature profile for a bacterium shows an optimal growth rate at a temperature of 39oC. Which of the following is true?
The organism would probably not grow at 42oC
An organism that does not have a respiratory electron transport chain, but produces some catalase or superoxide dismutase would be called . . .
an aerotolerant anaerobe
One consequence of an acidophilic lifestyle is . .
the need to use ATP to pump H+ out of the cell
You wish to perform an enrichment culture to isolate a chemolithoautotroph from the sludge at the bottom of a bog. Which of the following could be a part of this enrichment culture?
Use of a CO2-enriched atmosphere in a Gas-Pak jar
Adding a pH indicator to a minimal medium makes the medium . . .
differential
A bacterium that is an obligate intracellular parasite of human cells is most likely a/an . . .
mesophile
the organism that grows as shown in an agar shake tube . . .
requires O2 as an electron acceptor
Adding an antibiotic to a microbial growth medium makes the medium . . .
selective
The purpose of an enrichment culture is to . . .
allow better growth of one type of bacteria than others from an environmental sample
What does it mean to say that a bacterial colony is “clonal”?
All the cells in the colony arose by binary fission from a single cell.
What must be true of a bacterium growing as shown in a thioglycollate tube?
It produces the enzyme catalase.
A bacterial growth medium is prepared with Na3PO4, K2SO4, NH4Cl, C6H12O6 and yeast extract. What is the purpose of the yeast extract?
It allows the growth of nutritionally fastidious organisms.
You have a mixed mesophilic culture of halophilic Bacteria and halophilic Archaea, and you want to set up an enrichment culture for the Archaea. How would you do it?
Add penicillin and vancomycin to the growth media.
Microaerophiles . . .
usually have a metabolism that depends on a respiratory chain
A chemolithoheterotroph might get its ________ from _________.
energy from glucose
What significant information did we discover from our realizing in the last 15 years or so that
bacteria can form biofilms?
Bacterial populations can become specialized and behave like a multicellular organism.
Given their particular lifestyle, thermophilic bacteria must have evolved specialized mechanisms to guard against . . .
denaturation of their enzymes
In the diagram of a shake tube at the right, dots represent bacterial growth. A bacterial culture that grows as shown . . .
has no respiratory chain, but can detoxify oxygen
A photoorganoautotroph gets its ___________ from ___________
gets its carbon from CO2
Complex growth factors are most likely to be required . . .
for growth of fastidious organisms
Why is a freezer culture of bacteria stored in a solution of glycerol?
Glycerol disrupts the hydrogen bonding structure of frozen water.
A bacterium that can grow within the temperature range of 70oC to 110oC typically has an optimum growth temperature of_____________.
105oC
Microaerophilic bacteria . . .
require small amounts of O2 to grow
A growth medium with the recipe shown at the
right would be considered a ________ medium
defined
How should you try to grow a bacterium that cannot make its own ATP?
It should be grown on a layer of eukaryotic cells in tissue culture.
You have isolated a new bacterium, and you would like to store a culture of it for future use. What is the best way to do that?
Add glycerol to 25% concentration and store the liquid culture at -70oC.
Look at the table below. Which row of the table represents aerotolerant anaerobes?
ability to detoxify oxygen - yes
metabolic style - fermentative
Which of the following evolutionary adaptations would alkalophilic bacteria need in order to live
in the environment where they are found?
A Na+ transport channel between their flagellar rotor and stator
What must be provided in a growth medium in order to grow auxotrophs?
growth factors
A human pathogen whose optimal growth temperature is 37oC is LEAST likely to also be able to grow . . .
at 45oC
Which of the following is true about microaerophiles?
they have a respiratory chain
Addition of yeast extract to a bacteriological growth medium would be most important for the
growth of . . .
auxotrophs
You have just incubated a steak plate, and you see that it has two distinct colony types growing on it. You want to save both colony types long term? How?
pick each colony to a small tube containing 20% glycerol
A psychrotroph growing at 30oC has a membrane with 60% saturated lipids. The same organism incubated at 40oC would most likely . . .
not grow at all
What is the purpose of an osmoprotectant during growth in a hypertonic environment?
To balance solute concentrations on both sides of a membrane
in the medium used to grow a lithotroph, you would most likely require which of the following?
NH4+ as a source of electrons
Which of the following makes a bacterial culture selective?
incubation at 55oC
addition of methylene blue
lecture 9
Which of the following equations would be used to solve this problem? (You do not need a
calculator for this.)
“How many bacteria would you need to start with in order to have as many cells as the
Earth’s population (6 billion) within 12 hours? The bacterium divides in 30 minutes.”
(6 X 10^9) = x e^(0.5)(12)
A pharmaceutical technician wished to produce large quantities of a bacterial secondary metabolite from a chemolithoheterotroph. She grew the organism in a chemostat with glucose, H2S and oxygen, plus trace elements and growth factors. But she got very low yields of the secondary metabolite. What was her mistake?
she shouldnt have used. a chemostat
Cells in a biofilm are very tightly adherent to one another, have variable metabolic activity, and many are dead. What technique would be best to enumerate (count) the cells in a biofilm?
most probable number method
More than 99% of the organisms present in a soil sample do not grow in laboratory media. What would be the most appropriate way to count the organisms present in a soil sample?
Petroff-Hausser chamber
One major difference between batch culture and continuous culture is that . . .
Continuous culture allows the researcher to change the bacterial growth rate
the Most Probable Number (MPN) method . . .
requires multiple culture tubes, but no petri dishes
A colony (100,000 cells) is inoculated into a liter of broth. It takes 24 hours to reach stationary
phase (10^9 cells/ml). How would you find the growth rate ()?
10^12 = 10^5 e^24
A new bacterial enumeration method has been developed that moves bacteria physically from one chamber of a microchip to another with a micromanipulator (sort of like an atomic force microscope probe tip). This would be an example of . . .
a direct cell count
Compare the two cultures represented by the growth curves at right. Which of the following conclusions can you make?
Culture B has the higher growth rate.
One advantage of growing cells in continuous culture is that . . .
you can make the cells grow as fast or as slowly as you want.
Which of the following methods would give the lowest count for a population of bacteria in
stationary phase?
Counting colonies on a pour plate
At the right is a bacterial growth curve. What can you conclude about the culture from which the growth curve was measured?
It did not have to adapt to new growth conditions.
You have a bacterial culture with high turbidity. Which of the following would NOT be a
reasonable way to quantify the number of bacteria in this sample?
membrane filtration and plating the filter
Which of the following methods of enumerating bacterial growth could be most easily adapted to counting only motile bacterial cells in a culture?
luciferase reaction
Two bacterial cultures, A and B, were inoculated into “medium M,” and produced the growth curves shown at the right. What can you conclude about these cultures?
Culture A had been growing in a medium
similar to “medium M” before it was inoculated.
Which of the following would typically be done in a chemostat?
Measuring the growth rate, , under a variety of nutrient concentrations
You are using a fluorescence microscope and an antibody-based stain to examine a mixed culture from a patient’s blood for the titer of Treponema pallidum, the bacterium that causes syphilis. What would be the best method to make this titer determination?
Petroff-Hausser chamber
Which equation would you use to solve the following problem:
You inoculate a single cell with a doubling time of 30 minutes into 50 ml of culture medium and allow it to grow for 7 days. How many cells will be in the culture after 7 days.
N= e^(0.5)(7*24)
the bacterium Streptomyces does not undergo binary fission, but rather each cell elongates and then divides to become from 6 to 10 identical daughter cells. What would be the best way to
enumerate the cells in this culture?
viable cell count
Which equation could be used to solve the following problem?
A sample of milk has been pasteurized (bacterial count reduced by 5 logs). If the bacteria are growing at the rate of 0.1 per hour, how long will it take until there are as many bacteria in the
milk as there were before the pasteurization?
ln(100,000) = (0.1)(t)
Why would a scientist want to grow a bacterial culture in a chemostat?
So she can adjust the bacterial growth rate
Based on what you know about how the following methods for bacterial growth enumeration work, you should be able to classify one of them as a direct method. Which one?
measurement of bacterial turbidity with a spectrophotometer
In the United States, swimming beaches are periodically tested for bacterial counts. In Indiana, a beach is closed if the bacterial titer exceeds 125 bacteria per 100 ml. Which of the following would be the best way to determine this titer?
membrane filtration and plating
Which of the following is NOT an example of a direct cell count?
Detecting acid production in the well of a biochip
Salmonella is one of the important bacteria responsible for causing human diarrhea. It generally takes a million to ten million cells of Salmonella to make a person sick. You’re running a medical clinic, and a patient comes to you with diarrhea. You want to count the titer of Salmonella in the fecal sample accurately, but as quickly as possible. Which of the following would be the best way to do it?
Dilute the fecal sample and plate it on selective media
You are measuring turbidity as a surrogate for cell number to make a growth curve. What will
happen during the death / decline phase?
turbidity will remain the same, since dead cells still reflect light
Secondary metabolites, such as antibiotics, are produced most effectively . . .
by cells in crowded growth conditions
You suspect a patient has a blood infection caused by a bacterium, and you need to get a titer of bacteria from the patient’s blood. How would you do that most effectively?
Use a Petroff-Hausser chamber to estimate the titer
You have developed a new way to enumerate the bacteria in a culture. It involves covalently
adding a fluorescent label to peptidoglycan monomers so that newly synthesized peptidoglycan becomes fluorescent. Then a special device counts only fluorescent cells. This method . . .
is a type of viable cell count
The Luciferase reaction is not routinely used to obtain an accurate bacterial titer. Why not?
The amount of ATP produced per cell is not constant
lecture 10
A non-competitive (allosteric) enzyme inhibitor . . .
induces a shape change in the active site
Oxidative decarboxylation occurs during three separate reactions in central catabolism. The main purpose of these reactions is to . . .
produce reducing power
Amino acids are NOT synthesized from
fermentation products
A competitive inhibitor of an enzyme . . .
must structurally resemble the substrate of the enzyme it inhibits
Based on the graph at right,
SO4 could be reduced by electrons from glucose.
The main purpose of the TCA cycle in central catabolism is . . .
to produce additional reducing power
This molecule is one of the most versatile in central catabolism. It can be oxidized or reduced. It is a point at which side reactions feed into central catabolism, and is also a starting material for anabolic reactions
pyruvate
What form of energy is directly generated by the oxidative decarboxylation of pyruvate?
NADH
Some bacteria can catabolize lipids as carbon and energy sources. How do lipids enter central
metabolic pathways?
They are first hydrolyzed, then oxidized, and enter glycolysis and the TCA cycle.
In a chemotrophic bacterial reaction, electrons are donated from glucose to NAD+, forming 2
molecules of pyruvate plus NADH. Which of the following must also be true?
Glucose is at a higher energy level than NADH.
Which of the following statements about enzyme inhibitors is correct?
An allosteric inhibitor functions even at a much lower concentration than the substrate
The main purpose of fermentation reactions in a typical bacterial cell is . . .
NADH
Why is pyruvate an especially important molecule in central catabolism?
It can either accept electrons from NADH or donate electrons to NAD+.
Bacterial central catabolism includes all of the following EXCEPT . . .
respiratory electron transport
The main purpose of fermentation in bacterial metabolism is to . . .
oxidize NADH to NAD+
Much of the bacterial cell membrane is made of lipids. Where do lipids come from during
bacterial metabolism?
They are built up from glycerol and acetyl-CoA
Molecule A donates electrons to molecule B. Which of the following is true?
During the reaction, molecule A loses more energy than molecule B gains.
The main product of the TCA cycle is . . .
NADH
From which central metabolic pathway(s) is DNA synthesized by the cell?
from the pentose phosphate pathway
Which of the following is the most highly oxidized molecule?
CO2
How many oxidation reactions occur in the biochemical pathway shown at the right?
3
Bacteria that can use lipids as a carbon source typically have what type of metabolism?
Strictly respiratory since oxidation of fatty acids generates lots of NADH
A pharmacist wants to develop a drug that inhibits a bacterial enzyme. He has an option to develop either a competitive inhibitor (CI) or a non-competitive inhibitor (NCI). All other things (toxicity, cost, etc.) being equal, which one would he prefer to develop? Why?
The NCI, because it does not have to be present in large concentration excess
The reaction NADH → NAD+ + H+ occurs in BOTH . . .
respiration and fermentation
We said, but didn’t explain, that oxygen inhibits nitrogenase, the enzyme that catalyzes the reaction ½ N2 + 4 H+ → NH4+. Deduce how oxygen likely inhibits nitrogenase.
it alters an allosteric site, which prevents N2 from binding to the active site
Glucose is “broken down” in glycolysis. What does “broken down” mean in this case?
Glucose is first hydrolyzed, and then oxidized
What is the purpose of lactic acid fermentation in bacterial metabolism?
to oxidize NADH
What is the metabolic purpose of beta oxidation?
It is a way to turn fatty acids into TCA cycle precursors
n the following spontaneous reaction . . . : Aox + Bred → Ared + Box
B loses energy
Which of the following is true about an allosteric inhibitor?
The inhibitor alters the active site without binding to it.
Whether a eukaryotic cell will use the TCA cycle depends on how much O2 is present in the
environment. What determines whether a bacterium will use its TCA cycle or not?
An excess of NADH in the cell
All of the following reactions release energy EXCEPT . . .
pyruvate → lactate
Which biochemical pathway is correctly matched with a macromolecular product it produces?
Proteins come from TCA cycle intermediates
