MBI final

All of the following are components of bacterial cell wall EXCEPT
amino acids.
lipopolysaccharide.
N-acetylmuramic acid.
N-acetylglucosamine.

lipopolysaccharide

Which of the following statements about membrane lipids is true?

Lipids of bacteria have ester linkages, while those of archaea have ether linkages.
Lipids of bacteria and archaea have ether linkages.
Lipids of bacteria have ether linkages, while those of archaea have ester linkages.
Lipids of bacteria and archaea have ester linkages.

Lipids of bacteria have ester linkages, while those of archaea have ether linkages.

Directed movements of bacteria toward or away from a chemical signal are known as
locomotion
flagellation
gliding
chemotaxis

chemotaxis

All of the following are true about prokaryotic outer membranes EXCEPT that they
contain endotoxin.
are the target for the antibiotic penicillin.
are lipid bilayers containing lipopolysaccharides.
are found only in Gram-negative bacteria.

are the target for the antibiotic penicillin.

In bacteria, the macronutrients ___ are commonly found in nucleic acids and proteins.
C, O, N, H
C, O, K, H
N, S, Ca, H
C, O, P, S

C, O, N, H

The proteins embedded in a membrane require that region to be
hydrophilic.
negatively charged.
positively charged.
crystalline.
hydrophobic.

hydrophobic

Which one of the following is FALSE regarding the proton motive force (PMF)?
PMF is an electrochemical potential across the bacterial cell membrane.
PMF is the only force that can be used for flagella movement.
PMF is a major force for ATP generation in microbes.
PMF sometimes can be used for nutrient uptake.

PMF is the only force that can be used for flagella movement.

Which one of the following is NOT correct regarding the roles of membrane proteins?
Membrane proteins determine the fluidity of the cell membrane.
Membrane proteins are involved in transport of ions and nutrients across the membrane.
Membrane proteins are involved in secretion of toxins, proteins, and molecules for communication.
Membrane proteins can sense external signals such as presence of nutrients or toxins.

Membrane proteins determine the fluidity of the cell membrane.

Why can’t bacteria grow in solutions with very high concentrations of sugar?
Sugar lowers the solution’s osmolarity.
Sugar lowers the solution’s pH.
Sugar raises the solution’s pH.
Sugar raises the solution’s osmolarity.
Bacteria cannot digest pure sugar.

Sugar raises the solution’s osmolarity.

Growth of most microorganisms occurs by
budding.
replication.
binary fission.
segregation.

binary fission.

A cafeteria worker who fails to wash his hands thoroughly and fails to wear gloves inoculates a quiche with 4 E. coli cells when he uses his finger to test whether it is done. By the time you purchase the quiche, there are 128 E. coli cells in it. How many generations did the cells go through (assuming cells are in their log phase)?

5

Which of the following represents a coupled transport system where two molecules travel in the same direction?

symport

Which of the following statements is FALSE about the E. coli phosphotransferase system (PTS)?

The phosphate antiport is used to transport glucose or other simple sugars into the cell.

Only less than 1% of microbes in nature are cultured in labs because

it is challenging to identify the growth factor needed for the successful cultivation

Organisms that are adapted to grow at very high pressures (up to 1000 atm) are called

barophiles

Which choice includes only physical methods used to prevent bacterial growth?
Irradiation, probiotics, and filtration
Autoclaving, irradiation, and filtration
Irradiation, autoclaving, and disinfectants
Antibiotics, refrigeration, and pasteurization
Pasteurization, freezing, and phages

Autoclaving, irradiation, and filtration

Endospores are

formed in certain Gram+ bacteria such as Clostridium and Bacillus species to survive harsh environmental conditions.

Alkaliphiles adapt to high pH environment through the following mechanism EXCPET that

the internal pH is more alkaline than the environment to maintain a polarized membrane.

Microbes accumulate ________ in the cell to prevent cell water loss in a hypertonic environment.

compatible solutes

The differentiated cell used for nitrogen fixation in certain cyanobacteria is called

heterocyst

Bacterial shape is determined by

cytoskeleton proteins.

Which of the following is true when comparing microaerophiles with aerotolerant anaerobes?

They both contain enzymes that can neutralize the toxic reactive oxygen species (ROS).

Light is harvested by a special organelle in cyanobacteria called

thylakoid

Microbes use all of the following mechanisms to reduce osmotic stress EXCEPT that

pressure-sensitive channels can allow solutes to escape when cells are in hypertonic environments.

Efflux pumps (ABC transporters) send antibiotics, such as the protein synthesis–inhibitor tetracycline, out of the bacterial cells, enabling them to grow in the presence of antibiotics. Which of the following therapeutic approaches will be LEAST effective?

Increase the concentration of tetracycline.

How do some cyanobacteria fix nitrogen while growing aerobically?

The nitrogenase is sequestered in special cells to protect itself from oxygen damage.

Some microbes are able to survive temporary exposures to elevated temperatures. Which one of the following is FALSE?

Thermophilic proteins are induced during the heat exposure to protect the cell.

The proteins and cell components of halophiles have remarkably high intracellular levels of ________, which helps them survive in high salt conditions.

potassium

A microbe oxidizes sulfur for energy and fixes CO2 as carbon source. This microbe is a ___.

chemoautotroph

Which of the following prokaryotic transport systems does NOT require the use of cellular energy to bring compounds into the cells?

facilitated diffusion

In biofilms, quorum sensing is talking about that cells can 'sense' _____ to elicit cell responses.

population density

Which of the following reinforces and stiffens membranes in bacteria?

hopenes (hopanoids)

Which of the following are prominent members of microbial communities beneath icebergs in the Arctic and Antarctic?

psychrophiles

Filtration of samples to remove microbial cells typically use micropore filters with pore sizes of

0.2 μm.

Psychrophiles favor the cold, since their membranes are more fluid at low temperature as a result of the high proportion of ________ present.

saturated fatty acids

You are measuring growth in a bacterial culture. The number of viable cells remains constant, and when you check the medium, you find that the carbon source has been used up. In which phase of growth is the culture?

stationary

In the EMP pathway, the cofactor ___ serves as a temporary electron carrier when glyceraldehyde 3-phosphate (G3P) is _____ to 1,3-bisphosphoglycerate (1,3PG).

NAD+; oxidized

The enzyme pyruvate kinase catalyzes the conversion of phosphoenolpyruvate to pyruvate; the phosphate group is transferred to ADP to form ATP. This reaction is an example of

ATP synthesis by substrate-level phosphorylation.

In the mitochondrial electron transport chain, the electron transfer process between complex III and complex IV is connected by the mobile electron carrier______.

cytochrome c

The molecule shown below carries energy in the cell but it needs to be stabilized. It is a ________ molecule and is stabilized when it ________.

ATP; complexes with Mg2+

In the EMP pathway, the cofactor ___ serves as a temporary electron carrier when glyceraldehyde 3-phosphate (G3P) is _____ to 1,3-bisphosphoglycerate (1,3PG).

NAD+; oxidized

The enzyme pyruvate kinase catalyzes the conversion of phosphoenolpyruvate to pyruvate; the phosphate group is transferred to ADP to form ATP. This reaction is an example of

ATP synthesis by substrate-level phosphorylation.

In the pentose phosphate shunt, glucose 6-phosphate is oxidized to 6-phosphogluconate, which is then decarboxylated to ribulose 5-phosphate. What is the main metabolic role of this pathway?

production of NADPH and C5 carbohydrate for synthesis of nucleotides

The conversion of glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) in the glycolysis is catalyzed by a ______.

isomerase

A bacterium uses hydrogen as the electron source to fix carbon dioxide into methane. It thus performs a type of metabolism called ________ and, given its sources of electrons, it is performing ________.

methanogenesis; hydrogenotrophy

Fermentation products can include compounds such as lactic acid and ethanol, but many other products like acetic acid and succinic acid are also possible because

these products arise to complete the catabolism of glucose and regenerate NAD+ from NADH

The greatest amount of NADH is produced during which stage of aerobic respiration of glucose molecules?

tricarboxylic acid cycle

The TCA cycle generates all of the following molecules from each acetyl-CoA EXCEPT
two CO2
one FADH2
two ATP or GTP molecules.
three NADH molecules.

two ATP or GTP molecules.

The spontaneity of a reaction is determined by ___________ and the reaction is further accelerated by ___________.

negative Gibbs free energy change; enzymes

What distinguishing feature characterizes aerobic and anaerobic respiration but does not play a role in fermentation pathways?

The presence of an electron transport chain

The six carbons of the glucose molecule that enter the cell respiration pathway are oxidized into CO2 during the process of __________.

pyruvate oxidation and the TCA cycle

E. coli was grown aerobically in batch cultures. Assuming it takes 4 H+ to produce 1 ATP using ATP synthase, _______ ATPs are produced from the breakdown of 1 glucose molecule during aerobic respiration. Out of these ATPs, ____ is from substrate-level phosphorylation.

26; 4

Based on their standard reduction potentials, arrange the following electron carriers in the electron transport chain so electrons flow in the right direction.

Cytochroms a3 (Fe3+) + e- ---> Cytochrome a3 (Fe2+) Eo (volts) = 0.35
Ubiquinone + 2H+ + 2e- ---> Ubiquinol Eo (volts) = 0.10
Cytochrome a (Fe3+) + e- ---> Cytochrome a (Fe2+) Eo (volts) = 0.29
Cytochrome c (Fe3+) + e- ---> Cytochrome c (Fe2+) Eo (volts) = 0.25

ubiquinol - cytochrome c- cytochrome a- cytochrome a3

Bacteriorhodopsin ________.

absorbs light and goes through a photocycle involving excitation and relaxation and ultimately resulting in the pumping of one H+.

Which of the following substrates is an electron donor in organotrophy?

succinate

Which of the following is TRUE regarding microbial metabolism?
Oxygen serves as the terminal electron acceptor during photolysis of water in cyanobacteria.
Electrons can be obtained from inorganic chemicals such as H2S by some lithotrophic bacteria.
Oxygen can serve as an electron donor during chemolithotrophy.
Chemolithotrophy refers to the use of organic molecules as electron sources.
The use of organic compounds as electron donors is known as aerobic respiration.

Electrons can be obtained from inorganic chemicals such as H2S by some lithotrophic bacteria.

The following groups or molecules are components of electron transport systems, EXCEPT
iron-sulfur cluster proteins.
heme b.
quinones.
flavin mononucleotide.
acetyl-CoA.

acetyl-CoA.

What is the chromophore group in bacteriorhodopsin?

retinal

Which of the following is NOT a terminal electron acceptor in anaerobic respirations?
nitrate
hydrogen sulfide
nitrite
sulfate

hydrogen sulfide

Electron donors for anoxygenic photosystem I in green sulfur bacteria include the following, EXCEPT

H2O

Which of the following is NOT correct about fatty acid biosynthesis?
It involves successive condensations of malonyl-ACP.
NADPH is consumed during the fatty acid synthesis.
A dehydratase is used to generate an unsaturated bond.
Many intermediates from glycolysis are involved in the fatty acid synthesis.

Many intermediates from glycolysis are involved in the fatty acid synthesis.

Cyanobacteria are believed to generate the majority of oxygen gas in Earth’s atmosphere. What allows them to produce oxygen?

photosynthesis in which water photolysis produces H+, e-, and O2

Which one of the following molecules from the TCA cycle can be used to synthesize amino acids?

2-oxoglutarate

malonyl-ACP (C3 intermediates) is continuously added to the growing FA chain to yield an even number of carbons.

ATP is produced during fermentation through ___________.

substrate-level phosphorylation

Choose the TRUE statement regarding the difference between mitochondrial and E. coli electron transport chains.

In the mitochondrial electron transport chain, energy released from oxidation reactions is harvested to pump more protons.

In the process of linear electron flow in oxygenic photosynthesis,
All of the choices are correct.
electrons from water flow through electron transport chains resulting in synthesis of ATP and NADPH.
water is split to form oxygen.
photosystems I and II are both required

All of the choices are correct.

Using the same amount of glucose, less energy is produced from fermentation compared to aerobic respiration because

respiration completely oxidizes glucose to CO2, resulting in greater generation of NADH and thus ATP.

Which of the following pathways is NOT a route for CO2 assimilation?

3-hydroxypropionate cycle
reductive pentose phosphate cycle
reductive acetyl-CoA pathway
reductive ED pathway
reverse TCA cycle

reductive ED pathway

What types of bacteria does NOT perform the reductive pentose phosphate cycle to fix CO2?

heterotrophs

Which of the following reactions is catalyzed by Rubisco?

CO2 + ribulose 1,5-bisphosphate mc019-1.jpg 3-phosphoglycerate

In the reductive TCA cycle, three ATPs are used to produce one oxaloacetate. How many molecules of CO2 are fixed in this cycle?

four

The Calvin cycle

involves some intermediates from the EMP pathway

The ________ pathway is utilized for carbon fixation in plant chloroplasts and cyanobacteria.

reductive pentose phosphate cycle

Purines and pyrimidines are precursors for synthesis of _______.

nucleic acids

Which of the following statements is NOT true about Rubisco?

Rubisco also reacts with O2, leading to improved carbon fixation efficiency.

What is the role of reverse electron flow in lithoautotrophic bacteria?

It can be used to generate NADPH by coupling with the PMF.

In oxygenic photosynthesis, the cyclic electron flow

is used to generate more ATP but not NADPH by recycling electrons from ferredoxin back to plastoquinone.

In the mitochondrial electron transport chain, the electron transfer process between complex III and complex IV is connected by the mobile electron carrier______.

cytochrome c

During replication, the lagging strand is synthesized ________, while the leading strand can be synthesized ________.

discontinuously; continuously

RNA differs from DNA in several way. Which one of the following is NOT correct?
Uracil replaces thymine as a base in RNA.
RNA is usually single stranded
RNA adopts intramolecular secondary structures that differ from the predictable helix of DNA.
RNA nucleotides contain deoxyribose instead of ribose.

RNA nucleotides contain deoxyribose instead of ribose.

Which of the following statement is correct regarding DNA replication in E. coli?

DNA is replicated in a semiconservative mode.

If 15% of nucleotides in the DNA of a particular organism contain thymine, estimate the percentage of guanine that is present in the DNA.

35%

Which of the following is NOT correct regarding DNA primase?
During DNA replication, the lagging strand but not the leading strand needs DNA primase to synthesize primers.
DNA primase is a key element in DNA replication because no known DNA polymerases can initiate the synthesis of a DNA strand by themselves.
It is involved in DNA replication to synthesize a primer sequence.
It is a type of RNA polymerase.

During DNA replication, the lagging strand but not the leading strand needs DNA primase to synthesize primers.

Which of the following is a process that involves cell-to-cell contact to move a plasmid from a donor cell to a recipient cell?

conjugation

The natural function of ________ is to cut the DNA of invading plasmids and phages at specific sequences.

restriction endonucleases

Many restriction enzymes recognize palindromic sequences on double-stranded DNA. Among the following, which is a palindromic sequence?

5'-GGATCC-3'
3'-CCTAGG-5'

The process of taking a DNA template and making a complementary RNA molecule is called

transcription

Which of the following is NOT involved in the transcription process?
-10 and -35 sequences
binding of sigma factor to promoter
binding of RNA polymerase
Shine-Dalgarno sequence
separation of the DNA helix

Shine-Dalgarno sequence

Identify the true statement(s) about RNA stem-loop structures.
All of the answers are correct.
They could serve as termination signals during DNA replication.
Transcription termination depends completely on the formation of a stem-loop structure on the mRNA.
They are involved in the attenuation of trp operon.
None of the answers is correct.

They are involved in the attenuation of trp operon.

What does it mean to say that the genetic code is redundant?

More than one codon can specify the same amino acid.

While examining the sequence of bacterial DNA, you noticed a region rich in adenine (A) and thymine (T) base pairs. This leads you to conclude that this particular section of the DNA is likely to be the

oriC site.

A complex consisting of a single mRNA molecule with several ribosomes is called a

polysome

Which of the following is NOT true for the initiation of transcription?
Position +1 marks the start of gene transcription.
The RNA polymerase holoenzyme forms in the promoter region to initiate the transcription.
The promoter contains certain conserved regions for sigma factor binding.
A DNA helicase separates the DNA double strand.

A DNA helicase separates the DNA double strand.

Essential component(s) for termination of translation are a stop codon and ____.

release factor proteins.

Which of the following regarding the fidelity mechanism of DNA replication is NOT correct?

DNA polymerase facilitates correct nucleotide selection and proofreads the newly replicated strand.
Correct base pairing is thermodynamically more favorable.
DNA methylation protects DNA from endonucleases that would cause mutations.
Mismatch repair system can fix post-replicative mutations.

DNA methylation protects DNA from endonucleases that would cause mutations.

Which of the following is a correct comparison between RNA polymerase holoenzyme that functions in transcription and the primase that functions in DNA replication?

Both enzymes synthesize RNA.

tRNA molecules translate the “language of nucleotides” (RNAs) into the “language of amino acids” (proteins). tRNA can recognize the correct amino acid to load onto itself because

each tRNA has an associated amino acyl-tRNA synthase that helps select the correct amino acid.

If a bacterial cell is competent, it means that

the bacterium can import free DNA fragments.

A mutation always results in

a change in DNA sequence