Question 1

When more than one operon is under the control of a single regulatory protein, the operons are collectively called a(n)
A) regulon.
B) operator.
C) autoinducer.
D) riboswitch.

Accepted Answer

When a single regulatory protein controls multiple operons, it is known as a regulon. Therefore, the correct answer is A. An operator is a DNA sequence that acts as a binding site for a regulatory protein, and an autoinducer is a small signaling molecule that regulates gene expression. A riboswitch is a specialized RNA molecule that can bind to a small molecule and alter gene expression. None of these terms describe a situation where multiple operons are controlled by a single regulatory protein.

Question 2

Most riboswitches control
A) transcription.
B) translation.
C) ribosome synthesis.
D) tRNA synthesis.

Accepted Answer

Riboswitches are regulatory sequences that control gene expression at the level of translation. They are located in the 5' untranslated region (UTR) of mRNAs and bind to specific ligands, which can be metabolites, ions, or small molecules. When a riboswitch binds to its ligand, it undergoes a conformational change that either blocks or promotes the binding of the ribosome to the mRNA, thereby regulating translation.

Question 3

Global regulatory systems include all of the following EXCEPT
A) amino acid synthesis.
B) transformation.
C) heat shock response.
D) anaerobic respiration.

Accepted Answer

Amino acid synthesis is not typically controlled by global regulatory systems, which regulate gene expression in response to various environmental or physiological signals. Transformation, heat shock response, and anaerobic respiration are all examples of global regulatory systems that are found in many organisms.

Question 4

A common structure for proteins that bind DNA is helix-turn-helix.

Accepted Answer

The helix-turn-helix structure is a common motif in proteins that interact with DNA. It consists of two alpha helices connected by a short loop, with the first helix often involved in recognizing a specific DNA sequence and the second helix facilitating binding to the DNA.

Question 5

Proteins required at approximately the same level throughout a cellʹs growth cycle are often not subject to regulatory mechanisms and are constitutively synthesized.

Accepted Answer

Constitutively synthesized proteins are not subject to regulatory mechanisms and are required at approximately the same level throughout a cell's growth cycle. This is because their synthesis is needed for basic metabolic processes or cellular functions that are constant.

Question 6

Cyclic AMP (cAMP) is involved in the global regulation of catabolic pathways in Escherichia coli, including the lac operon. A high activity of the enzyme adenylate cyclase which makes cAMP is suggestive of catabolite repression.

Accepted Answer

High activity of adenylate cyclase, leading to high levels of cAMP, is indicative of low glucose levels and thus alleviates catabolite repression, allowing for the activation of catabolic pathways such as the lac operon.

Question 7

All of the following are functions of heat shock proteins in bacteria EXCEPT
A) prevention of inappropriate protein subunit aggregation.
B) degradation of denatured proteins.
C) responding to exposure to high levels of ethanol.
D) stimulation of binary fission.

Accepted Answer

Heat shock proteins in bacteria do not stimulate binary fission. Instead, they perform other functions such as prevention of protein aggregation and degradation of denatured proteins. Some heat shock proteins also respond to environmental stressors such as exposure to high levels of ethanol. However, none of these functions involve stimulation of binary fission.

Question 8

Some proteins that bind to DNA block transcription, whereas other proteins activate transcription.

Accepted Answer

This statement is true. Some proteins, known as repressors, bind to DNA and prevent RNA polymerase from transcribing genes, while other proteins, known as activators, bind to enhance regions and promote transcription.

Question 9

Depending on the type of regulatory mechanism, activators and repressors can bind to operator regions which control transcription.

Accepted Answer

The answer of Depending on the type of regulatory mechanism,...

Question 10

Proteins and RNA molecules that are needed in the cell at about the same level under all growth conditions, require constitutive expression.

Accepted Answer

Constitutive expression refers to genes that are expressed at a relatively constant level under all growth conditions. Proteins and RNA molecules that are needed at a consistent level in the cell would require constitutive expression.

Question 11

The preferential use of glucose over other available carbon substrates for growth is mechanistically explained by catabolite repression.

Accepted Answer

Catabolite repression is a regulatory mechanism in which the presence of a preferred carbon source, such as glucose, inhibits the uptake and metabolism of other carbon sources. This results in the cell utilizing glucose first before any other carbon sources, which is known as the preferential use of glucose.

Question 12

Enzyme repression typically affects catabolic pathways.

Accepted Answer

Enzyme repression typically affects anabolic pathways, where it serves to inhibit the synthesis of enzymes involved in the synthesis of end products when they are already abundant.

Question 13

Short regions at the beginning and end of gene sequences are not translated into proteins.

Accepted Answer

These regions, called untranslated regions (UTRs), play important regulatory roles in controlling gene expression and are transcribed into mRNA along with the protein-coding regions. However, they are not used as templates for protein synthesis.

Question 14

A two-component regulatory system usually involves both the sensor and response proteins being subject to phosphorylation.

Accepted Answer

A two-component regulatory system involves a sensor kinase protein that detects a specific signal or stimulus and phosphorylates a response regulator protein. The phosphorylation of the response regulator allows it to activate or repress gene expression or other cellular processes. Both the sensor and response proteins are typically subject to phosphorylation for proper function of the system.

Question 15

Small molecules usually act directly (rather than indirectly) in regulating transcription.

Accepted Answer

Small molecules often regulate transcription indirectly by affecting the activity of transcription factors rather than binding directly to DNA or RNA.

Question 16

The residues in a DNA-binding protein that interact with DNA usually correspond to each other according to the amino acids encoded by the DNA. For example, a DNA sequence containing AGC-AGA-CAG which encodes for Ser-Arg-Gln would likely have a DNA-binding protein with the sequence Ser-Arg-Gln.

Accepted Answer

The residues in a DNA-binding protein that interact with DNA do not necessarily correspond to the amino acids encoded by the DNA sequence they bind to. The specificity of a DNA-binding protein for its DNA target is determined by the shape and chemical properties of the protein's DNA-binding domain, not by the amino acids encoded by the DNA sequence.

Question 17

A regulon is composed of at least two operons regulated by the same protein.

Accepted Answer

A regulon is a group of operons that are coordinately regulated by a regulatory protein, which can bind to the promoter region of multiple operons to control their expression. Therefore, a regulon must be composed of at least two operons.

Question 18

PII proteins are a family of signal-transducing proteins that regulate ________ during nitrogen metabolism.
A) transcription factors.
B) enzymes.
C) membrane transport proteins.
D) PII proteins regulate each of the above during nitrogen metabolism.

Accepted Answer

PII proteins are involved in regulating various aspects of nitrogen metabolism. They act as signal transducers that sense the cellular nitrogen status and modulate the activity and/or expression of transcription factors, enzymes, and membrane transport proteins accordingly. Therefore, the best choice is D - PII proteins regulate each of the above during nitrogen metabolism.

Question 19

In most cases, the first product of a particular biosynthetic pathway represses the enzymes of the pathway.

Accepted Answer

In most cases, it is the end product of a biosynthetic pathway that represses the enzymes of the pathway, a mechanism known as feedback inhibition.

Question 20

Once cytoplasmic sensor proteins involved in chemotaxis regulation are phosphorylated, a cascade of other phosphate-transferring mechanisms provides ATP to rotate flagella.

Accepted Answer

The phosphorylation of cytoplasmic sensor proteins in chemotaxis regulation does not provide ATP for flagella rotation. Instead, it leads to a signaling cascade that alters the behavior of the flagella (e.g., changes in rotation or direction), but ATP or proton motive force directly powers flagellar rotation, not the phosphorylation events themselves.

Quiz 6: Microbial Regulatory Systems

When more than one operon is under the control of a single regulatory protein, the operons are collectively called a(n)

Most riboswitches control

Global regulatory systems include all of the following EXCEPT