Formative Quiz #4 - Topic 7, 8, 9, 10

Question 1

A regulon refers to…

a) A set of sigma factors that coordinate gene expression
b) A set of genes that respond to the same regulatory system
c) A region of a bacterial genome that contains an operator, promoter, and genes
d) A system that suppresses translation

Answer 1

b) A set of genes that respond to the same regulatory system

Explanation: A regulon consists of genes or operons that are controlled by the same regulatory protein, allowing a coordinated response.

Question 2

Describes a cell that can take up free DNA from its surroundings:

1) Transformed
2) Competent
3) Promiscuous
4) Accepting

Answer 2

2) Competent

Explanation: Competent cells have the ability to take up extracellular DNA through natural competence or artificial induction.

Question 3

Which of these is typically involved in a two-component regulatory system?

a) Activator protein and coactivator
b) Histidine kinase and response regulator
c) Repressor protein and activator protein
d) Repressor protein and inducer
e) Repressor protein and corepressor

Answer 3

b) Histidine kinase and response regulator

Explanation: Two-component systems regulate cellular processes in bacteria. The histidine kinase senses environmental signals, and the response regulator mediates changes in gene expression.

Question 4

You are a scientist studying mutations. You put your cells under UV light, grow your cells on regular agar, and observe no changes in phenotype. What happened?

a) Any of the below
b) A frameshift mutation occurred
c) No mutation occurred
d) A silent mutation occurred
e) A nonsense mutation occurred
f) Two of the answers

Answer 4

d) A silent mutation occurred; c) no mutation occurred

Therefore: f) two of these answers

Explanation: A silent mutation may have occurred that had no effect on your phenotype, or no mutation may have occurred at all. Frameshift mutations and nonsense mutations are most likely to have much larger effects on phenotype.

Question 5

The lac operon:

a) Is constitutively expressed so lactose can be readily utilized if encountered
b) Has a LacI activator protein that binds the DNA and activates expression through positive control
c) Is positively regulated by cyclic AMP
d) Is activated in the presence of lactic acid

Answer 5

c) Is positively regulated by cyclic AMP

Explanation: The lac operon acts through negative control. It is normally repressed and requires an inducer (negative control) to de-repress and allow expression.

Question 6

Which of these is required for transcription that is regulated by positive control?

a) Activator protein
b) Repressor protein
c) DNA polymerase
d) Attenuator protein
e) Inducer protein

Answer 6

a) Activator protein

Explanation: In positive control, activator proteins bind to the promoter or enhancer regions to increase transcription levels of the target gene.

Question 7

You are selecting for mutants that contain streptomycin resistance. Which method would be best?

a) Grow the cells in liquid media containing streptomycin, then plate on regular agar and pick the colonies
b) Plate the cells on a non-selective agar, pick all the colonies, and sequence their genome to identify which contain mutated sequences
c) Screen for mutants by making replicate plates, treating one with streptomycin, and taking the colonies from the support plate if they are missing from the streptomycin plate
d) Select for mutants by plating them on a streptomycin plate and picking the colonies that grow

Answer 7

d) Select for mutants by plating them on a streptomycin plate and picking the colonies that grow

Explanation: This method ensures that only the mutants resistant to streptomycin survive, making it the most efficient selection process.

Question 8

Restriction enzymes:

a) Are relatively rare in nature
b) Recognize specific sites in bacterial DNA
c) Are recognized by their repeating non-palindromic sequences

Answer 8

b) Recognize specific sites in bacterial DNA

Explanation: Restriction enzymes are used in molecular biology to cut DNA at specific recognition sequences, often palindromic.

Question 9

What is an auxotroph?

1) A mutant that uses inorganic carbon for a carbon source
2) A mutant that has gained the ability to synthesize all substances required for growth
3) A mutant that has lost the ability to synthesize certain substances required for growth and metabolism
4) A revertant

Answer 9

3) A mutant that has lost the ability to synthesize certain substances required for growth and metabolism

Explanation: Auxotrophs require specific supplements in the media to grow because they cannot produce these substances themselves.

Question 10

Which one of the following is NOT an advantage to studying genetics in bacteria?

1) Cell differentiation and specialization is a comparatively simple process
2) More than one copy of each gene on the chromosome
3) Each cell is a complete organism
4) Short division time

Answer 10

2) More than one copy of each gene on the chromosome

Explanation: Bacteria typically have a single copy of each gene on their chromosome, making genetic studies straightforward.

Question 11

What is a cloning vector?

1) A DNA molecule that can be cut by restriction enzymes
2) A DNA molecule that can be genetically manipulated and replicates in cells
3) A plasmid used to carry antibiotic resistance to a new strain
4) A DNA molecule used to make novel organisms

Answer 11

2) A DNA molecule that can be genetically manipulated and replicates in cells

Explanation: Cloning vectors are used to insert foreign DNA into host cells, where it can replicate and be expressed.

Question 12

If a cell has an F plasmid, it can:

1) become antibiotic resistant
2) be used to clone new fragments of DNA
3) conjugate and transfer DNA to a recipient cell
4) be used in conjugation experiments

Answer 12

3) Conjugate and transfer DNA to a recipient cell

Explanation: The F plasmid enables bacterial cells to transfer DNA through conjugation, a process of horizontal gene transfer.

Question 13

How does attenuation work to control the trp operon?

1) If translation of the region occurs quickly during high levels of trp, an RNA secondary structure forms which prevents transcription of the operon
2) If translation of the region occurs quickly during high levels of trp, an RNA secondary structure forms which allows transcription of the operon
3) In the presence of high levels of trp, trp binds to the RNA and causes transcription to cease
4) In the presence of low amounts of trp, no trp binds to the RNA which allows transcription to occur

Answer 13

1) If translation of the region occurs quickly during high levels of trp, an RNA secondary structure forms which prevents transcription of the operon

Explanation: Attenuation relies on the formation of specific secondary structures in the mRNA that act as terminators or anti-terminators, regulating transcription based on trp levels.

Question 14

Plasmid that can replicate in more than one host, typically containing more than one origin of replication:

1) F plasmid
2) Cosmid vector
3) Shuttle vector
4) Transposon

Answer 14

3) Shuttle vector

Explanation: Shuttle vectors can replicate in multiple hosts as they contain more than one origin of replication, making them versatile tools in genetic engineering.

Question 15

Signal molecule used in quorum sensing that increases in concentration as the density of the population increases:

1) Autoregulators
2) Autoinducers
3) Autopromotors
4) Autorepressors

Answer 15

2) Autoinducers

Explanation: Autoinducers are signaling molecules that accumulate as cell density increases and regulate gene expression in quorum sensing.

Question 16

The effects of quorum sensing include:

1) Changes in motility and biofilm formation
2) Pathogenesis
3) Competitive interactions between other organisms
4) All of these can be controlled by quorum sensing

Answer 16

4) All of these can be controlled by quorum sensing

Explanation: Quorum sensing regulates diverse behaviors such as biofilm formation, motility, and pathogenesis, depending on cell density.

Question 17

The mRNA of bacterial cells is often polycistronic. What does this term mean?

1) It can be translated more than once.
2) It contains the code for multiple peptides.
3) The translated protein may be modified in different ways.
4) It can be translated from either end.
5) It is transcribed from multiple sites on the chromosome.

Answer 17

2) It contains the code for multiple peptides

Explanation: Polycistronic mRNA contains multiple coding regions, each corresponding to a different peptide, typical in bacterial gene expression.

This is because polycistronic mRNA specifically refers to a single mRNA molecule that includes multiple coding regions (cistrons), each of which can be translated into a different protein. This is a hallmark of bacterial gene expression, often seen in operons like the lac operon.

Question 18

Which of the following is NOT part of an operon?

1) A promoter
2) An operator
3) A gene sequence
4) An allosteric binding site

Answer 18

4) An allosteric binding site

Explanation: An operon includes a promoter, operator, and structural genes. Allosteric binding sites are not part of the operon but can influence regulatory proteins.

Question 19

Chemotaxis is regulated by:

1) Increased gene expression
2) A series of signal transduction events
3) Decreased gene expression
4) Allosteric enzymes
5) An induction-type mechanism

Answer 19

2) A series of signal transduction events

Explanation: Chemotaxis involves a complex series of signal transduction pathways that detect chemical gradients and adjust cellular movement accordingly.

Question 20

How does an activator increase transcription of a gene?

1) By blocking a repressor
2) By increasing the rate of transcription
3) By increasing the affinity of RNA polymerase for the promoter
4) By changing the conformation of the sigma factor

Answer 20

3) By increasing the affinity of RNA polymerase for the promoter

Explanation: Activators bind to DNA near the promoter, enhancing RNA polymerase binding and increasing transcription.

Question 21

A strain of bacteria that was missing RecA would be unable to:

1) Unwind invading DNA
2) Line up homologous sequences
3) Find a place to integrate two blunt ends of broken DNA
4) Do non-homologous recombination

Answer 21

2) Line up homologous sequences

Explanation: RecA is essential for homologous recombination, helping align homologous DNA sequences for strand exchange.

Question 22

Methyl-accepting chemotaxis proteins are found:

1) As part of the sensor complex and modulates CheA/CheY interactions
2) At the ‘end’ of the chemotaxis pathway and responsible for controlling the flagellum
3) As part of the sensor complex and is the receptor for attractants
4) External to the cell and act as binding molecules to identify attractant/repellents

Answer 22

3) As part of the sensor complex and is the receptor for attractants

Explanation: Methyl-accepting chemotaxis proteins are part of bacterial sensor complexes that detect attractants and repellents.

Question 23

Which of these is a term for a point mutation that results in a change in the amino acid specificity of the codon but does not change the length of the protein?

1) Silent
2) Nonsense
3) Frameshift
4) Missense
5) Deletion

Answer 23

4) Missense

Explanation: A missense mutation changes the amino acid sequence without altering the length of the protein, potentially affecting its function.

Question 24

You are a scientist growing a histidine auxotroph. You would:

1) Grow it on a medium containing histidine
2) It doesn’t matter, it will grow on either medium
3) Grow it on a medium containing no histidine

Answer 24

1) Grow it on a medium containing histidine

Explanation: Histidine auxotrophs cannot synthesize histidine and require it to be supplied in the growth medium.

Question 25

What is the principle behind plasmid incompatibility? 1) The cell maintains a certain copy number of plasmids with the same control mechanism and origin of replication 2) Two plasmids with similar functions are toxic to the cell 3) The cell cannot maintain more than one type of plasmid 4) Too much extrachromosomal DNA is toxic to the bacteria

Answer 25

1) The cell maintains a certain copy number of plasmids with the same control mechanism and origin of replication Explanation: Plasmid incompatibility arises when two plasmids with the same replication system cannot coexist in the same cell due to competition for replication machinery. Plasmid incompatibility occurs when two plasmids with the same replication control system are present in a bacterial cell. These plasmids compete for replication machinery, often leading to the loss of one plasmid. Each plasmid type is maintained at a specific copy number, which depends on its control mechanism. For example, low-copy-number plasmids might only replicate once per cell cycle, resulting in one or two copies per cell, while high-copy-number plasmids may replicate multiple times, leading to several copies. If two incompatible plasmids are present, the cell’s replication machinery cannot regulate both simultaneously, leading to uneven distribution during cell division and, eventually, the loss of one plasmid type.

Question 26

The _____ facilitates initiation of translation in bacteria: 1) TATA binding box 2) Monte-Carlo sequence 3) Open reading frame start codon 4) Shine-Dalgarno sequence

Answer 26

4) Shine-Dalgarno sequence Explanation: The Shine-Dalgarno sequence in bacterial mRNA aligns the ribosome with the start codon, facilitating translation initiation.

Question 27

Expression of genes that are constitutive is: 1) Unregulated 2) Regulated by activation 3) Regulated by repression 4) Regulated by attenuation 5) Regulated by induction

Answer 27

1) Unregulated Explanation: Constitutive gene expression is unregulated, meaning that the gene is continuously transcribed and expressed regardless of environmental conditions.

Question 28

A shuttle vector expands the range of host cell types because: 1) They contain multiple types of origins of replication 2) They enter the cell quickly before the host CRISPR system can degrade the plasmid 3) They are comparatively small and so integrate quickly into the host genome 4) They contain the same origin of replication as the host cell

Answer 28

1) They contain multiple types of origins of replication Explanation: Shuttle vectors can replicate in different host systems due to the presence of multiple origins of replication, enabling versatility in genetic engineering.

Question 29

A key enzyme for critical processes required by the cell is likely to be: 1) Carefully regulated by the cell 2) Constitutively expressed

Answer 29

2) Constitutively expressed Explanation: Key enzymes essential for cellular survival are constitutively expressed to ensure their availability at all times.

Question 30

How is quorum sensing, a type of cell-to-cell communication, mediated? 1) By direct cell contact 2) By two-component regulation 3) By chemical signalling 4) By an induction mechanism 5) By transfer of genetic information

Answer 30

3) By chemical signalling Explanation: Quorum sensing is mediated by chemical signals that bacteria produce and detect to coordinate group behaviors based on cell density.

Question 31

What does Rho-independent termination of transcription in bacteria involve? 1) The formation of a hairpin loop followed by a poly U sequence 2) A poly U sequence followed by a poly A sequence 3) A poly A sequence followed by a hairpin loop 4) The formation of a hairpin loop only 5) The formation of a hairpin loop followed by a poly A sequence

Answer 31

1) The formation of a hairpin loop followed by a poly U sequence Explanation: Rho-independent termination involves a GC-rich hairpin loop followed by a series of uracil residues, which destabilizes the RNA-DNA interaction and terminates transcription. In bacterial transcription, a poly A tail is not involved in termination. Instead, **Rho-independent termination relies on the formation of a GC-rich hairpin loop followed by a poly U sequence.** The hairpin loop causes physical tension, and the subsequent poly U sequence creates weak RNA-DNA interactions due to the weak hydrogen bonding between adenine and uracil, leading to dissociation of the RNA transcript from the DNA. The poly A tail is a feature specific to eukaryotic mRNA, where it is added post-transcriptionally to stabilize the mRNA and regulate its lifespan, but it does not play a role in bacterial transcription termination.

Question 32

What is the term used to describe movement of DNA between microbes; also called 'lateral gene transfer'? 1) Interspecies gene transfer 2) Homologous recombination 3) Horizontal gene transfer 4) Conjugation

Answer 32

3) Horizontal gene transfer Explanation: Horizontal gene transfer refers to the movement of genetic material between organisms that is not through traditional reproduction.

Question 33

Negative control of transcription: 1) Only acts to prevent gene expression 2) Is energy intensive and so used sparingly 3) May activate enzyme production by removing repressors in response to a signal 4) Includes repression, a type of negative control that regulates most enzymes, particularly anabolic enzymes

Answer 33

3) May activate enzyme production by removing repressors in response to a signal Explanation: Negative control regulates transcription by repressors but can also activate enzyme production if repressors are removed in response to specific signals.

Question 34

During negative regulation of gene expression, the repressor protein binds to the operator to inhibit transcription. What is the effector molecule that controls the activity of the repressor protein called? 1) Co-repressor 2) Inhibitor or activator 3) Co-repressor or inducer 4) Inducer 5) Activator

Answer 34

3) Co-repressor or inducer Explanation: Co-repressors and inducers modulate the activity of the repressor protein, controlling gene expression through negative regulation. The repressor’s behavior depends on the type of system and the role of the effector molecule (e.g., co-repressor or inducer). In **negative regulation**, the following applies: 1. Co-repressor systems: The repressor protein requires the binding of a co-repressor (effector molecule) to assume its active form and bind the operator. This binding blocks transcription by preventing RNA polymerase from accessing the promoter. For example, in the trp operon, tryptophan acts as a co-repressor. 2. Inducer systems: The repressor is initially bound to the operator, preventing transcription. The binding of an inducer (effector molecule) to the repressor causes a conformational change, releasing the repressor from the operator. This derepression allows transcription to proceed. The lac operon is an example where lactose (or allolactose) acts as an inducer. In summary, the effector molecule determines whether the repressor can bind to the operator or not, depending on the regulatory mechanism in place. Example of **Co-repressor System**: •Tryptophan (trp) operon in E. coli: When tryptophan levels are high, tryptophan acts as a co-repressor by binding to the trp repressor protein. This tryptophan-repressor complex then binds to the operator, preventing transcription of the genes involved in tryptophan synthesis. Example of **Inducer System**: •Lactose (lac) operon in E. coli: When lactose is present, allolactose (a derivative of lactose) acts as an inducer by binding to the lac repressor protein. This causes the repressor to release from the operator, allowing RNA polymerase to transcribe the genes needed for lactose metabolism.

Question 35

Transfer of DNA from one cell to another via direct cell-to-cell contact; type of horizontal gene transfer: 1) Clones 2) Conjugation 3) Hfr strains 4) Transposition

Answer 35

2) Conjugation Explanation: Conjugation involves the direct transfer of DNA between bacterial cells via sex pili helping to form a bridge between the two cells.

Question 36

Attenuation is a regulatory mechanism in bacteria that relies on: 1) Transcription and translation occurring simultaneously 2) Transcription termination occurring by a rho-dependent mechanism 3) Translation termination occurring at a stop codon 4) The inactivation of a repressor protein 5) The activation of an activator protein

Answer 36

1) Transcription and translation occurring simultaneously Explanation: Attenuation is a regulatory process in bacteria where the coupling of transcription and translation modulates gene expression based on environmental conditions. Attenuation relies on the simultaneous process of **transcription and translation**, which is unique to bacteria due to the lack of a nuclear envelope. This allows the ribosome to interact with the nascent mRNA transcript while it is being synthesized. The mechanism does not primarily depend on the inactivation of a repressor protein (choice 4), which is a different regulatory process used in systems like the **trp operon** for repression. While repressor proteins are significant in some forms of gene regulation, attenuation is specifically tied to transcription-translation coupling.

Question 37

Which statement is true about F plasmids? 1) F plasmids are transferred during conjugation between two F+ cells 2) An F plasmid may exist autonomously or integrate into chromosome 3) Hfr cells have F plasmids integrated into their DNA but require specific host proteins to excise themselves from the chromosome 4) For transfer, the cells merge their membranes and swap replicated plasmids

Answer 37

2) An F plasmid may exist autonomously or integrate into chromosome Explanation: F plasmids can either replicate independently or integrate into the host chromosome, enabling horizontal gene transfer through conjugation.

Question 38

How does blue/white selection work? 1) The DNA fragment of interest is cloned into a cloning vector and the colonies turn blue 2) The DNA fragment of interest is cloned into the lacZ gene in a cloning vector resulting in loss of lacZ function and white colonies 3) The DNA fragment of interest is cloned into the lacZ gene in a cloning vector resulting in loss of lacZ function and blue colonies 4) The DNA fragment of interest is cloned into the chromosomal lacZ gene resulting in loss of lacZ function and white colonies

Answer 38

2) The DNA fragment of interest is cloned into the lacZ gene in a cloning vector resulting in loss of lacZ function and white colonies Explanation: In blue/white selection, disruption of the lacZ gene by the inserted DNA fragment prevents beta-galactosidase production, leading to white colonies. Option 4 is incorrect because the described process occurs in a cloning vector, not the chromosome. In blue/white selection, the DNA fragment of interest is inserted into the lacZ gene of a plasmid vector, disrupting its function. The disruption prevents the production of beta-galactosidase, which leads to white colonies on media containing X-gal.

Question 39

What role does reversion play in studying auxotrophs? 1) Reversion is a confounding factor in interpreting results 2) Reversion changes the auxotroph so that it has multiple mutations 3) Reversion changes the auxotroph so it can grow in a similar manner to wild type 4) Reversion is a very low probability event so it is not necessary to consider in studying auxotrophs

Answer 39

3) Reversion changes the auxotroph so it can grow in a similar manner to wild type Explanation: Reversion mutations restore the original phenotype, enabling the auxotroph to grow similarly to the wild type organism.

Question 40

The formation of a hairpin loop during rho-dependent transcription signals: 1) A transition point between genes on polycistronic DNA 2) Termination of transcription 3) None of the above 4) The binding site for RNA polymerase holoenzyme

Answer 40

3) None of the above Explanation: Hairpin loop formation is associated with rho-independent transcription termination, not rho-dependent processes.

Question 41

What is the difference between phenotypic selection and screening? 1) Selection is the only way to detect mutants because both wild-type and mutant cell survive in screening 2) Screening is more efficient than selection 3) Phenotypic selection only allows mutants with a particular phenotype to survive, in screening, everything survives but mutants have a different phenotype 4) In both, all mutants survive but they have a different phenotype in selection vs. screening

Answer 41

3) Phenotypic selection only allows mutants with a particular phenotype to survive, in screening, everything survives but mutants have a different phenotype Explanation: Selection isolates specific mutants by allowing their survival, while screening identifies mutants based on observable phenotypic differences.

Question 42

Enzyme that recognizes inverted repeat sequences on a transposon: 1) Restriction endonucleases 2) Reverse DNA transcriptase 3) Restriction enzymes 4) Transposase

Answer 42

4) Transposase Explanation: Transposase is the enzyme responsible for recognizing inverted repeat sequences and catalyzing the movement of transposable elements within the genome.

Question 43

What is quorum sensing? a) The ability of bacteria to detect the **types** of bacteria present in the environment b) The ability of bacteria to detect the **number** of bacteria present in the environment c) Both a and b d) None of these choices

Answer 43

c) Both a and b Explanation: Quorum sensing **allows bacteria to detect both the type and number** of bacteria present in their environment, enabling them to coordinate group behaviors.

Question 44

Technique to screen colonies for phenotypes that cannot be identified by phenotypic selection: a) Homologous recombination b) Non-homologous recombination c) Replica plating d) Patching e) c and d

Answer 44

e) c and d Explanation: Techniques such as replica plating and patching are used to identify phenotypes that cannot be isolated through phenotypic selection.

Question 45

What part of an operon does a repressor bind to? 1) A promoter 2) An operator 3) The gene sequence 4) The enzyme(s) produced

Answer 45

2) An operator Explanation: The operator is the part of an operon where repressor proteins bind to block transcription.

Question 46

What proteins are used in detection of a chemical gradient? 1) Chemotaxis proteins 2) CheW 3) Methyl-accepting chemotaxis proteins 4) CheY

Answer 46

3) Methyl-accepting chemotaxis proteins Explanation: Methyl-accepting chemotaxis proteins detect chemical gradients and help bacteria move toward or away from chemical signals.

Question 47

Escherichia coli regularly uses glucose to generate energy but will also use lactose when it is available (using a galactosidase enzyme). In an environment containing only lactose, which is most likely to happen with respect to regulation? 1) Existing galactosidase enzyme will be post-translationally modified to 'activate' the enzyme 2) The genes encoding for galactosidase will be activated to produce more mRNA 3) All genes will be downregulated until glucose levels increase 4) Glucose-related genes will be upregulated

Answer 47

2) The genes encoding for galactosidase will be activated to produce more mRNA Explanation: In the absence of glucose and the presence of lactose, the lac operon is induced, leading to the production of enzymes needed for lactose metabolism.

Question 48

A blue cell on an X-gal system indicates… 1) The cell has been unsuccessfully transformed: functional LacZ is produced 2) The cell has been successfully transformed: no functional LacZ is produced 3) The cell has been unsuccessfully transformed: no functional LacZ is produced 4) The cell has been successfully transformed: functional LacZ is produced

Answer 48

1) The cell has been unsuccessfully transformed: functional LacZ is produced Explanation: A blue cell indicates the presence of functional LacZ, which cleaves X-gal and produces a blue product, showing that transformation did not disrupt the gene.

Question 49

What is a wild-type strain? 1) A strain without any mutations 2) The original or laboratory strain 3) The most important strain to study 4) The most common strain in nature

Answer 49

2) The original or laboratory strain Explanation: Wild-type refers to the reference strain used in experiments, typically representing the original, non-mutated state of an organism.

Question 50

An effector molecule 1) Binds to the active site of an enzyme to regulate activity 2) Is not normally a product of a multi-step pathway 3) Can activate or inhibit an enzyme 4) Binds to the substrate to catalyze enzyme activity

Answer 50

3) Can activate or inhibit an enzyme Explanation: Effector molecules regulate enzyme activity by either activating or inhibiting them, often binding at sites distinct from the active site.

Question 51

Regulatory mechanism that occurs after the initiation of transcription but before transcription of the operon is complete: 1) Activator molecule 2) SRNA 3) Inducible expression 4) Attenuation

Answer 51

4) Attenuation Explanation: Attenuation is a regulatory mechanism in bacteria where transcription is halted prematurely based on environmental or metabolic conditions.

Question 52

A two-component regulatory system… 1) Uses one protein that acts as both a sensor and activator for gene expression 2) Relies on signal transduction and conformational changes to communicate between the external and internal environment 3) Is composed of two proteins that operate only in the cytoplasm 4) Is specialized and absent from many bacteria

Answer 52

2) Relies on signal transduction and conformational changes to communicate between the external and internal environment Explanation: Two-component systems use signal transduction pathways to detect and respond to environmental changes.

Question 53

The ability for a population of bacteria to communicate via chemical signaling is best termed: 1) Chemotaxis 2) Chemical consensus 3) Quorum sensing 4) Cooperative chemotaxis

Answer 53

3) Quorum sensing Explanation: Quorum sensing allows bacterial populations to coordinate behaviors such as biofilm formation and virulence through chemical signaling.

Question 54

Positive control of transcription: 1) Involves deactivating repressor molecules 2) Requires that the activator site be adjacent to the promotor (i.e., a few bases away) 3) Can cause structural changes in the DNA to improve RNA polymerase binding 4) Is energy intensive and so used sparingly

Answer 54

3) Can cause structural changes in the DNA to improve RNA polymerase binding Explanation: Positive control mechanisms involve activators that enhance RNA polymerase binding, this interaction often leads to structural changes in the DNA, such as bending or unwinding, which make the promoter more accessible and improve the ability of RNA polymerase to bind and initiate transcription, increasing transcription efficiency. Positive control of transcription is a regulatory mechanism where activator proteins enhance the interaction between RNA polymerase and the promoter region of a gene. This interaction often leads to structural changes in the DNA, such as bending or unwinding, which make the promoter more accessible and improve the ability of RNA polymerase to bind and initiate transcription. These structural changes can include alterations in the supercoiling of DNA or the positioning of nucleosomes, especially in eukaryotes. For example, in bacteria, the catabolite activator protein (CAP) binds to a specific DNA site near the promoter when complexed with cyclic AMP (cAMP). This binding enhances the recruitment of RNA polymerase to the promoter, facilitating transcription of genes required for lactose metabolism in the absence of glucose. The activator binding site does not necessarily have to be adjacent to the promoter. It can be located upstream or even farther away, as seen in eukaryotic enhancers, which loop the DNA to bring the activator into proximity with the RNA polymerase complex. This flexibility allows fine-tuned regulation of gene expression based on environmental or cellular signals.

Question 55

What does the phrase 'bacterial genomes are genetically compact' mean? 1) Bacterial genomes are small and contain very few genes 2) Bacterial genomes are easily transferable from one bacterium to another 3) Bacterial genomes do not contain introns 4) Most of the bacterial genome codes for proteins

Answer 55

4) Most of the bacterial genome codes for proteins Explanation: Bacterial genomes are considered genetically compact because they lack large noncoding regions, and a majority of the genome is dedicated to coding for proteins.

Question 56

N-acyl-homoserine 1) Is a quorum sensing molecule that is conserved and has only a few variants 2) Is involved in regulating the expression of luciferase and bioluminescence 3) Is found in the parasitic Aliivibrio fischeri bacterium associated with Hawaiian bobtail squid 4) Is produced in large amounts when cell densities are low

Answer 56

2) Is involved in regulating the expression of luciferase and bioluminescence Explanation: N-acyl-homoserine lactones are quorum sensing molecules that regulate bioluminescence in symbiotic bacteria such as Aliivibrio fischeri, which interact with the Hawaiian bobtail squid. Bacterium and animal host relationship is symbiotic, not parasitic.