Generic selectors
Exact matches only
Search in title
Search in content
Search in posts
Search in pages
Filter by Categories
nmims post
Objective Type Set
Online MCQ Assignment
Question Solution
Solved Question
Uncategorized

Interview MCQ Set 1

1. _________________ are mathematical problems defined as a set of objects whose state must satisfy a number of constraints or limitations.
a) Constraints Satisfaction Problems
b) Uninformed Search Problems
c) Local Search Problems
d) All of the mentioned

View Answer

Answer: a [Reason:] Refer definition of CSPs.

2. Which of the Following problems can be modeled as CSP?
a) 8-Puzzle problem
b) 8-Queen problem
c) Map coloring problem
d) All of the mentioned

View Answer

Answer: d [Reason:] All of above problems involves constraints to be satisfied.

3. What among the following constitutes to the incremental formulation of CSP?
a) Path cost
b) Goal cost
c) Successor function
d) All of the mentioned

View Answer

Answer: d [Reason:] Initial state: The empty assignment ( ), in which all variables are unassigned. Successor function: A value can be assigned to any unassigned variable, provided it does not conflict with previously assigned variables. Goal test: The current assignment is complete. Path cost: A constant cost (e.g., 1) for every step.

4. The term ___________ is used for a depth-first search that chooses values for one variable at a time and returns when a variable has no legal values left to assign.
a) Forward search
b) Backtrack search
c) Hill algorithm
d) Reverse-Down-Hill search

View Answer

Answer: b [Reason:] Refer definition of backtracking algorithm.

5. To overcome the need to backtrack in constraint satisfaction problem can be eliminated by
a) Forward Searching
b) Constraint Propagation
c) Backtrack after a forward search
d) Omitting the constraints and focusing only on goals

View Answer

Answer: a [Reason:] Forward Searching is technique in which a forward check till k steps is made to analyze that the goal can be achieved satiating all constraints. With constraint propagation, constraints on a variable can be propagated to next level/hierarchy and satisfied at that level, eliminating need to backtrack.

6. The BACKTRACKING-SEARCH algorithm in Figure 5.3 has a very simple policy for what to do when a branch of the search fails: back up to the preceding variable and try a different value for it. This is called chronological-backtracking. It is also possible to go all the way to set of variable that caused failure. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] Intelligent backtracking

7. Consider a problem of preparing a schedule for a class of student. This problem is a type of
a) Search Problem
b) Backtrack Problem
c) CSP
d) Planning Problem

View Answer

Answer: c [Reason:] Schedule developer needs to consider all constraints on teacher as well as students.

8. Constraint satisfaction problems on finite domains are typically solved using a form of ___________
a) Search Algorithms
b) Heuristic Search Algorithms
c) Greedy Search Algorithms
d) All of the mentioned

View Answer

Answer: d [Reason:] Any Search techniques can be used

9. Solving a constraint satisfaction problem on a finite domain is an/a ___________ problem with respect to the domain size.
a) P complete
b) NP complete
c) NP hard
d) Domain dependent

View Answer

Answer: b [Reason:] None.

10. ____________ is/are useful when the original formulation of a problem is altered in some way, typically because the set of constraints to consider evolves because of the environment.
a) Static CSPs
b) Dynamic CSPs
c) Flexible CSPs
d) None of the mentioned

View Answer

Answer: b [Reason:] Refer to the definition of Dynamic CSPs algorithm.

11. Flexible CSPs relax on _______
a) Constraints
b) Current State
c) Initial State
d) Goal State

View Answer

Answer: a [Reason:] Definition of flexible CSPs.

12. Language/Languages used for programming Constraint Programming includes
a) Prolog
b) C#
c) C
d) Fortrun

View Answer

Answer: a [Reason:] None.

13. Backtracking is based on,
a) Last in first out
b) First in first out
c) Recursion
d) Both Last in first out & Recursion

View Answer

Answer: d [Reason:] Recursion uses LIFO.

14. Constraint Propagation technique actually modifies the CSP problem.
a) True
b) False

View Answer

Answer: a [Reason:] Constraints are propagated towards goal node, modifying actual problem.

15. When do we call the states are safely explored?
a) A goal state is unreachable from any state
b) A goal state is denied access
c) A goal state is reachable from every state
d) None of the mentioned

View Answer

Answer: c [Reason:] None.

16. Which of the following algorithm is generally used CSP search algorithm?
a) Breadth-first search algorithm
b) Depth-first search algorithm
c) Hill-climbing search algorithm
d) None of the mentioned

View Answer

Answer: b [Reason:] Provides backtrack facility.

Interview MCQ Set 2

1. The functional unit in which genes are arranged consecutively is known as ___________
a) Induction system
b) An end product repression system
c) A consecutive enzyme system
d) Operon

View Answer

Answer: d [Reason:] An operon is defined as a functionating unit of genomic DNA containing a cluster of genes under the control of a single promoter. Thus the two ends of an operon are marked by the promoter and terminator.

2. The investigation of the lac operon for the metabolism of lactose was done by __________
a) Gilbert
b) Walter Gilbert
c) Francois Jacob and Jacques Monod
d) Walter

View Answer

Answer: c [Reason:] The pioneering studies of gene regulation in E. coli were carried out by Francois Jacob and Jacques Monod in the 1950s. These investigators and their colleagues analyzed the expression of enzymes involved in the metabolism of lactose, which can be used as a source of carbon and energy via cleavage of glucose and galactose.

3. Presence of lactose itself induces the production of β-galactoside transferase.
a) True
b) False

View Answer

Answer: a [Reason:] The enzyme that catalyzes the cleavage of lactose that is β-galactosidase and the other enzymes β-galactoside transferase and β-galactoside permease involved in the lactose metabolism are expressed only when lactose is available for use by the bacteria. Otherwise, the cell is able to economize by not by not investing energy in the synthesis of unnecessary RNAs and proteins. Thus lactose induces the synthesis of enzymes involved in its own metabolism.

4. How many enzymes are produced in the lac operon under the same promoter?
a) 4
b) 3
c) 2
d) 1

View Answer

Answer: b [Reason:] A total of three genes are transcribed thus producing 3 distinct enzymes under the same promoter in the bacterial lac operon. The three enzymes thus produced are β-galactosidase, β-galactoside transferase and β-galactoside.

5. Defects in which regions can affect the activity of the lac operon?
a) Promoter
b) i
c) Terminator
d) i and o

View Answer

Answer: d [Reason:] On the basis of purely genetic experiments, Jacob and Monod deduced the mechanism by which the expression of these genes was regulated. Studies of mutant that were defective in regulation of these genes identified in two distinct loci, called o and i, which control the expression of the operon. Transcription of the operon is controlled by o, which is adjacent to the initiator site. The i gene, which is not physiologically linked to the operon, encodes a repressor protein that regulates transcription by binding to the operator DNA.

6. If the lac operon of the genome of bacteria is always active it has a defect in which region of the operon?
a) i
b) o
c) Promoter
d) Structural gene

View Answer

Answer: a [Reason:] Mutants that fail to make a functional i gene product result in constitutive expression of the operon even when lactose is not available. This result implies that the normal i gene product is a repressor, which blocks transcription when bound to o.

7. Lac operon follows a trans-acting control mechanism.
a) True
b) False

View Answer

Answer: a [Reason:] Regulatory sequences like the operator are called cis-acting elements, because they affect the expression of only linked genes on the same DNA molecule. On the other hand, protein like the repressor can affect the expression of genes located on the other hand; proteins like the repressor can affect the affect the expression of genes located on the other chromosomes within the cell. The lac operon is an example of negative control because binding of the repressor blocks transcription.

8. According to the repressor of lac operon which of the following are false?
a) It is the gene product of the regulatory gene
b) It binds to the promoter region
c) It blocks the transcription of structural genes
d) It combines with allolactose and thus does not bind to the operon

View Answer

Answer: b [Reason:] The repressor of the lac operon does not bind to the promoter region. It binds to the operator region of the lac operon thus repressing the activity of the lac operon.

9. If there is an insertion mutation in the operator of the lac operon, the expression of the lac structural gene will be__________
a) Resistant to catabolic expression
b) Unexpressed
c) Constitutively expressed
d) Permanently disabled

View Answer

Answer: c [Reason:] If there is an insertion mutation in the operator of the lac operon the repressor cannot bind to it. Thus the operon is constitutively expressed.

10. The complete expression of the lac operon requires __________
a) Lactose
b) Allolactose
c) Lactose and cAMP
d) Allolactose and cAMP

View Answer

Answer: d [Reason:] The complete expression of the lac operon requires allolactose and cAMP. They regulate the expression of the lac operon by a positive control system called the catabolite repression.

11. What effect would a loss-of-function mutation have on the expression of the gene encoding the catabolite activator protein of the lac operon?
a) Low expression in the presence of lactose and off in its absence, regardless of the presence or absence of glucose
b) High expression in the presence of lactose and off in its absence, regardless of the presence or absence of glucose
c) Low expression in the presence of glucose and off in its absence, regardless of the presence or absence of lactose
d) High expression in the presence of glucose and off in its absence, regardless of the presence or absence of lactose

View Answer

Answer: a [Reason:] As the mutation occurs in the catabolite activator protein gene occurs which causes loss of its function its protein the activator protein is not synthesized. Thus the operon shows no restrain and is active continuously even when glucose is absent. Even if glucose is present due to the absence of activator the regulation of the operon does not occur resulting in a low expression level.

12. Mutation in the regulatory gene of a positively controlled operon can be identified by __________
a) Operon induction
b) Operon repression
c) High expression
d) Constitutive expression

View Answer

Answer: b [Reason:] In a positively controlled operon the function of the gene is normally active thus no repressor molecules is produced that binds to the operator. Mutation in the regulatory gene leads to the production of repressor molecules that either binds to the operator or the transcription factors thus blocking the function of operon leading to operon repression.

13. In the case of lac operon, the gene expression is inhibited by __________
a) Presence of lactose
b) Interaction of repressor with lactose
c) Interaction of repressor with operator
d) Interaction of lactose with operator

View Answer

Answer: c [Reason:] In the case of lac operon, the gene expression is inhibited by interaction of repressor with operator, as repressor does not bind to lactose. Presence of lactose leads to the interaction of lactose with operator which induces the activity of the operon.

14. Which of the following is false about bacterial tryptophan operon?
a) It has two kinds of regulation system
b) The co-repressor is the catabolite activator protein
c) When tryptophan supply is insufficient the tryptophan operon activates
d) The complex of repressor with co-repressor on binding to the operator blocks transcription

View Answer

Answer: b [Reason:] Trp operon is an example of repressible negative regulated operon. In this the operon’s regulatory sequence, the operator is blocked by the repressor protein in the presence of tryptophan. While in the absence of tryptophan the repressor is liberated thus facilitating operon expression.

15. Attenuator in the tryptophan operon is the __________
a) Operator sequence
b) Non-transcribed region within the operon
c) Leader sequence for the site of RNA polymerase binding
d) Leader sequence in the tryptophan mRNA coding for many tryptophan residues

View Answer

Answer: d [Reason:] The Trp operon has a leader sequence of 14 amino acid long polypeptide. This contains two tryptophan residues at 10th and 11th positions which are very unusual in case of amino acid recruitment. This stretch of mRNA is known as the attenuator sequence.

Interview MCQ Set 3

1. We can specify filenames in command line using perl.
a) True
b) False

View Answer

Answer: a [Reason:] perl provides specific functions to open a file and perform I/O operations on it. The <> (diamond) operator is used for reading lines from a file. For example,

 perl  -e ‘print while (<>)’  dept.lst        // file opening implied

2. Which of the following is referred to as default variable?
a) $0
b) $1
c) $!
d) $_

View Answer

Answer: d [Reason:] perl assigns the line read from input to a special variable $_; often called default variable. This is an extremely important variable, which can make our code compact.

3. ___ operator is used for selecting current line number.
a) $0
b) $1
c) $.
d) $_

View Answer

Answer: a [Reason:] perl stores the current line number in a special variable $. ($ followed by a dot). We can use it to represent a line address and select lines from anywhere:

Perl  -ne  ‘print if {$.  &lt; 4}’ foo        // same as head  -n 3

4. ___ is known as range operator.
a) . .
b) $1
c) $.
d) $_

View Answer

Answer: a [Reason:] perl . . (range operator) is a counterpart of awk’s NR variable. For example,

the following command prints 1,2,3,4,5
for each(1..5) 
{
  print “$_”;
}

5. The command @x=(1. .10) will assign first ten integer values to the array ‘a’.
a) True
b) False

View Answer

Answer: a [Reason:] Lists and arrays lie at the heart of perl. Perl has a large number of functions to manipulate them. For example, in the following we’ve assigned three values to array @month:

@month =  {“jan”, “feb”, “march”} ;        //$month[1] is feb

6. The ___ prefix to an array name signifies the last index of the array.
a) $0
b) $#
c) #$
d) $_

View Answer

Answer: b [Reason:] The $# prefix to an array name signifies the last index of the array. It is always one less than the size of the array. For example,

@month =  {“jan”, “feb”, “march”} ;
$last_index = $#month;        //$last_index is “march”

7. For deleting the elements from the left of the array ___ function is used.
a) pop
b) push
c) queue
d) shift

View Answer

Answer: d [Reason:] perl provides a handful of functions for manipulating the contents of an array. For example, perl uses shift function to delete the left-most element of an array.

@list= (3. .5,9) ;    // this is 3,4,5,9
shift(@list)         // now it is 4,5,9

8. For deleting the elements from the right of the array ___ function is used.
a) pop
b) push
c) queue
d) shift

View Answer

Answer: a [Reason:] perl provides a handful of functions for manipulating the contents of any array. For example, perl uses the pop function to delete the right-most element of an array.

@list= (3. .5,9) ;      // this is 3,4,5,9
pop(@list)             // now it is 3,4,5

9. To add elements to the left side of the array ____ function is used.
a) pop
b) push
c) queue
d) unshift

View Answer

Answer: d [Reason:] Ta add elements to the left side of the array, use the unshift function. For example,

@list= (5,9) ;                // this is 5,9
unshift( @list,1. .3) ;      // now it becomes 1,2,3,5,9

10. To add elements to the right side of the array ____ function is used.
a) pop
b) push
c) queue
d) unshift

View Answer

Answer: b [Reason:] Ta add elements to the right side of the array, use the push function. For example,

@list= (5,9) ;            // this is 5,9
unshift( @list,13) ;     // now it becomes 5,9,13

11. Which function can combine the functionalities of push, pop, unshift and shift?
a) splice
b) add
c) delete
d) split

View Answer

Answer: a [Reason:] The splice function can perform all the four functions performed by these functions. It uses upto four arguments to add or remove elements at any location of the array. The second argument is the offset from where we’ve to perform insertion or deletion, the third argument represents the number of elements to be removed. If it is 0, elements are to be added. The fourth argument specifies the new replaced list. For example,

@list= (1,2,3,4,5,9) ;
splice(@list, 5, 0, 6. . 8);        //adds at 6th location -1,2,3,4,5,6,7,8,9

12. For looping in a list, ____ is used.
a) for
b) fordo
c) foreach
d) while

View Answer

Answer: a [Reason:] perl provides an extremely useful foreach construct to loop through a list. The syntax is,

foreach $var (@arr) 
{
   statements
}

13. perl also supports use of for loop in the following manner.

for($i=0;$i<3;$i++){ }

a) True
b) False

View Answer

Answer: a [Reason:] perl supports both foreach construct and for loop for looping purposes. For example,

for($i=0;$i<3;$i++){print(“hello”) ; }        //print “Hello” three times

14. For splitting a line or expression into fields, __ is used.
a) foreach
b) for
c) split
d) join

View Answer

Answer: c [Reason:] split breaks a particular line or expression into fields. These fields are assigned either to variables or an array. For example,

($var1, $var2, $var3 . . . ) = split(/sep/,stg) ;
@arr= split(/sep/,stg) ;      
// splits string stg on sep (sep can be literal character or regular expression)

15. ___ function is used for joining lists.
a) foreach
b) for
c) split
d) join

View Answer

Answer: d [Reason:] The join function acts in an opposite manner to split. It combines its arguments into a single string and uses the delimiter as the first argument. For example,

$weekstr = join( “ “, @week_arr) ;
@weekstr = join(“ “, “mon”, “tue”, “wed”);
print $weekstr ;            // output will be mon, tue, wed

16. perl is ____ of grep, tr, sed and awk.
a) subset
b) superset
c) child
d) parent

View Answer

Answer: b [Reason:] perl is a superset of grep, sed, awk and the shell. It can perform all the functions performed by all these and that too more efficiently.

17. The following will display :

perl -e ‘print “UNIX” x 10 . “n” ;’

a) UNIX
b) UNIX 10 times
c) error message
d) n

View Answer

Answer: b [Reason:] The perl x operator is used for repeating a string. So the above command will print UNIX 10 times.

Interview MCQ Set 4

1. For the correct addition of amino acid to the growing polypeptide chain which of the following does not play any role?
a) Loading of initiator tRNA to the P site
b) Loading of correct aminoacyl tRNA to the A site
c) Formation of peptide bond between the existing amino acid and the incoming amino acid
d) The formed tRNA with the growing polypeptide is translocated from the A site to the P site

View Answer

Answer: a [Reason:] The correct addition of amino acid involves only three steps: i) Loading of correct aminoacyl tRNA to the A site ii) Formation of peptide bond between the existing amino acid and the incoming amino acid iii) The formed tRNA with the growing polypeptide is translocated from the A site to the P site Loading of the initiator tRNA is the part of initiation of translation process.

2. The events controlling the correct addition of amino acid is controlled by ____________ proteins.
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: b [Reason:] The events controlling the correct addition of amino acid are controlled by 3 proteins known as elongation factors. They are IF1, IF2 and IF3.

3. The auxillary protein required for the elongation of polypeptide is energy independent.
a) True
b) False

View Answer

Answer: b [Reason:] The auxillary protein required for the elongation of polypeptide is energy dependent processes. All these factors use energy of the GTP binding and hydrolysis to enhance the rate and accuracy of ribosome function.

4. Aminoacyl tRNA needs an escort to carry them to the ribosome bound mRNA.
a) True
b) False

View Answer

Answer: a [Reason:] Aminoacyl-tRNAs do not bind to the ribosome on their own. Instead, they are escorted to the ribosome by the elongation factor EF-Tu.

5. Once the tRNA is aminoacylated, EF-Tu binds to the tRNA at the ____________
a) 5’ end of the tRNA
b) 3’ end of the tRNA
c) Amino acid
d) Variable loop of tRNA

View Answer

Answer: b [Reason:] Once the tRNA is aminoacylated, EF-Tu binds to the tRNA at the3’ end of the tRNA, masking the coupled amino acid. This interaction prevents the bound aminoacyl-tRNA from participating in peptide bond formation until it is released from EF-Tu.

6. The activation of GTPase activity of the enzyme EF-Tu occurs after its binding to the aminoacylated tRNA.
a) True
b) False

View Answer

Answer: b [Reason:] The trigger h the factor binding center after the tRNA is loaded into that activates the EF-Tu GTPase id known as factor binding center. EF-Tu only interacts with the factor binding center after the tRNA is loaded into the A site and a correct codon-anticodon match is made. At this point, EF-Tu hydrolyzed its bound GTP and is released from the ribosome.

7. The only fidelity testing of the translation is by observing the energy difference involved in the correct and incorrect base pairing.
a) True
b) False

View Answer

Answer: b [Reason:] The energy difference between a correctly formed codon-anticodon pair and that of a near match is not equal but still cannot account for the high level of accuracy required for the translation process. Thus there are three more mechanisms that contribute to this specificity. In each case, these mechanisms select against incorrect codon-anticodon pairings.

8. How many mechanisms are involved in the maintenance of the fidelity of translation?
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: d [Reason:] A total of 4 mechanisms are involved in the maintenance of the fidelity of translation. In addition to the codon-anticodon interactions, the ribosome exploits minor grove interactions and two phases of proof reading to ensure that a correct aminoacyl-tRNA binds in the A site.

9. Which part of the large subunit helps in the formation of the peptide bond?
a) 5S rRNA
b) Proteins
c) 23S rRNA
d) 18S rRNA

View Answer

Answer: c [Reason:] Once the correctly charged tRNA has been placed in the A site and has rotated into the peptidyl transferase center, peptide bond formation takes place. This reaction is catalyzed by RNA, specifically the 23S rRNA component of the large subunit.

10. Which of the following steps is not required for the process of translocation?
a) Frame shift in hybrid states
b) Movement of P site tRNA to E site
c) Movement of A site tRNA to P site
d) Movement of ribosome by three nucleotides

View Answer

Answer: a [Reason:] For a new round of peptide chain elongation to occur, the P site tRNA must move to the E site and the A site tRNA must move to the P site. At the same time the mRNA must move by 3 nucleotides to expose the next codon. These movements are coordinated within the ribosome and are collectively referred to as translocation.

11. The completion of translocation requires the action of the factor _________________
a) EF-Tu
b) EF-G
c) eIF2
d) eIF4G

View Answer

Answer: b [Reason:] The completion of translocation requires the action of a second elongation factor called EF-G. EF-G can only bind to the ribosome when associated with GTP. After the peptidyl transferase reaction, the shift in the location of the A site tRNA uncovers a binding site for EF-G in the large subunit portion of the A site.

Interview MCQ Set 5

1. In case of transcription which is the rate limiting step?
a) Binding of RNA polymerase
b) Unwinding of DNA duplex
c) Promoter escape
d) Formation of the open complex

View Answer

Answer: a [Reason:] When polymerase binds it spontaneously undergoes a transition to the open complex and initiates transcription. This gives a low level of constitutive expression called the basal level. Thus binding of RNA polymerase is the rate limiting step.

2. The site where repressor binds the DNA is the ______________
a) Promoter
b) Terminator
c) Operator
d) ORF

View Answer

Answer: c [Reason:] Operator is the repressor binding site. Promoter is the polymerase binding site. Terminator is the site for transcription termination. ORF is the open reading frame in the mRNA used by the ribosome for translation.

3. Recruitment of RNA polymerase to the promoter is a ___________
a) Covalent binding
b) Cooperative binding
c) Protein – protein interaction
d) Van der Waals forces

View Answer

Answer: b [Reason:] The activator uses one surface to bind to a site on the DNA near the promoter; with another surface, the activator simultaneously interacts with the RNA polymerase, bringing the enzyme close to the promoter. This mechanism is known as the recruitment of polymerase and is an example of cooperative binding of proteins to DNA.

4. The proteins of which of the following genes are regularly needed for cellular activity?
a) Regular genes
b) Smart genes
c) Structural genes
d) Housekeeping genes

View Answer

Answer: d [Reason:] Housekeeping genes are those genes that are typically constitutive genes. They are generally required for the maintenance of basic cellular functions. They are thus expressed in all cells of an organism under normal conditions.

5. Which of the following are the products of constitutive gene?
i. Involved in the synthesis of structural elements of the cell
ii. Involved in catabolic pathway
iii. Involved in anabolic pathway
iv. Synthesized continuously
a) i and ii
b) ii and iii
c) iii and iv
d) i, ii, iii and iv

View Answer

Answer: d [Reason:] The products of the constitutive genes are generally used all the time for different cellular processes. They include all metabolic, that is, catabolic and anabolic processes and production of structural elements of the cell. Thus they are synthesized continuously within the cell.

6. Which of the following is not an example of allosteric regulation?
a) Inactivation of nitrogenase by ADP ribosylation
b) Catabolite repression by CAP in E. coli
c) Regulation of phosphofructokinase activity
d) Regulation of lac operon by allolactose

View Answer

Answer: a [Reason:] When the nitrogenase product, ammonium, becomes available, the ADP ribosyltransferase covalently links to the ADP-ribose moiety to a specific arginine residue on nitrogenase switching-off nitrogenase activity. Thus as it involves covalent reaction and is not an example of allosteric regulation.

7. Operons are ___________
a) of approximately uniform size
b) found in some eukaryotes
c) not able to bind to proteins
d) smaller in lower eukaryotes and longer in higher eukaryotes

View Answer

Answer: b [Reason:] Operons are generally of varied lengths as the number of genes differs from operon to operon. They are able to bind to different proteins such as activators, repressors, polymerases, etc. their size does not depend on the genetic complexity of the eukaryotes and are generally not found in higher eukaryotes.

8. Which of the following are correct according to operons?
i) Consists of multiple genes organized between a promoter and a terminator
ii) Member genes regulate with coordination
iii) Usually controlled by autogenous transcription
iv) Contains genes for stress tolerance exclusively
a) i and ii
b) ii and iii
c) iii and iv
d) i, ii, iii and iv

View Answer

Answer: a [Reason:] An operon is a functionating unit of genomic DNA containing a cluster of genes under the control of a single promoter. Thus the two ends of an operon are marked by the promoter and terminator on either side. As they are regulated by a single promoter, they work in coordination.

9. Choose the correct pair among the following.
a) The DNA sequence to which stigma factor binds – enhancer
b) The DNA sequence to which RNA polymerase binds – operator
c) The DNA sequence that codes for a protein – structural gene
d) The DNA sequence to which repressors binds – promoter

View Answer

Answer: c [Reason:] The correct pairs are: i) The DNA sequence to which stigma factor binds – promoter ii) The DNA sequence to which RNA polymerase binds – promoter iii) The DNA sequence to which repressors binds – operator.

10. Which of the following is not present in the β-galactosidase structural gene and thus is not transcribed by the same promoter?
a) Lac A
b) Lac I
c) Lac Z
d) Lac Y

View Answer

Answer: b [Reason:] β-galactosidase structural gene consists of three genes, lac A, lac Z and lac Y. They synthesize β-galactoside transacetylase, β-galactosidase and β-galactoside permease respectively.

11. Glucose, as the carbon source, is the first choice by bacteria even if other sugars are available. The mechanism behind this selectivity is ___________
a) Operon repression
b) Glucose utilization
c) Enzyme repression
d) Catabolite repression

View Answer

Answer: d [Reason:] Catabolite repression allows bacteria to adapt quickly to a preference carbon and energy source first. As the primary source of carbon for bacteria is glucose, thus it takes up glucose even if other sugars are present in abundance.

12. The lac operon is regulated by cAMP by ___________
a) Binding to lac repressor
b) Binding to operator
c) Binding to promoter
d) Binding to catabolite activator protein

View Answer

Answer: d [Reason:] The cAMP binds to catabolite activator protein to regulate the activity of the lac operon. This enables the formation of a cAMP-activator complex that turns on transcription after it binds near the promoter.

13. Tryptophan operon in E. coli is a repressible operon.
a) True
b) False

View Answer

Answer: a [Reason:] Tryptophan operon is a repressible negative regulated operon. Within the operon’s regulatory sequence, the operator is blocked by the repressor protein in the presence of tryptophan and is liberated in tryptophan’s absence. The process of attenuation complements this regulatory action.

14. Which of the following is true about tryptophan operon?
a) Tetramer of identical subunits
b) The RNA product is very stable
c) The Trp repressor binds to the tryptophan
d) The Trp repressor is the product of the Trp operon

View Answer

Answer: c [Reason:] The tryptophan operon contains a gene trp R which synthesizes mRNA for a regulatory protein. This protein binds to tryptophan molecule and further interacts with the operator of the trp operon, thus effectively blocking transcription of the gene.

15. The expression of the tryptophan operon is independent of the availability of tryptophan in culture media.
a) True
b) False

View Answer

Answer: b [Reason:] The expression of the tryptophan operon is dependent of the availability of tryptophan in culture media. This type of regulatory process is termed as attenuation that is, the operator is blocked by the repressor protein in the presence of tryptophan and is liberated in the presence of tryptophan.