Practice MCQs

Question 1

In a double-stranded nucleic acid, cytosine is typically base-paired with:

a) Adenosine
b) Guanine
c) Inosine
d) Thymine
e) Uracil

Answer 1

b) Guanine

Question 2

A major component of RNA but not DNA is:

a) Adenine
b) Cytosine
c) Guanine
d) Thymine
e) Uracil

Answer 2

e) Uracil

Question 3

The Meselson-Stahl experiment established that:

a) DNA polymerase has a crucial role in DNA synthesis
b) DNA synthesis in E. coli proceeds by a conservative mechanism
c) DNA synthesis in E. coli proceeds in a semiconservative mechanism
d) DNA synthesis requires dATP, dCTP, dGTP, and dTTP
e) Newly synthesised DNA in E. coli has a different base composition that the pre-existing DNA

Answer 3

c) DNA synthesis in E. coli proceeds in a semiconservative mechanism

Question 4

E. coli DNA polymerase III:

a) Can initiate replication without a primer
b) Is efficient at nick translation
c) Is the principal DNA polymerase in chromosomal DNA replication
d) Represents over 90% of the DNA polymerase activity in E. coli cells
e) Requires a free 5’-hydroxyl group as a primer

Answer 4

c) Is the principal DNA polymerase in chromosomal DNA replication

Question 5

RNA polymerase:

a) Binds tightly to a region of DNA thousands of base pairs away from the DNA to be transcribed
b) Can synthesise RNA strands without a primer
c) Has a subunit called lambda, which acts as a proofreading ribonuclease
d) Separates DNA strands

Answer 5

b) Can synthesise RNA strands without a primer

Question 6

Processing of a primary mRNA transcript in a eukaryotic cell does NOT normally involve:

a) Attachment of a long PolyA sequence at the 3’ end
b) Conversion of normal bases to modified bases, such as inosine and pseuouridine
c) Excision of intervening sequences (introns)
d) Joining of exons
e) Methylation of one or more guanine nucleotides at the 5’ end

Answer 6

b) Conversion of normal bases to modified bases, such as inosine and pseuouridine

Question 7

Compared with DNA polymerase, reverse transcriptase:

a) Does not require a primer to initiate synthesis
b) Introduces no errors into genetic material because it synthesises RNA, not DNA
c) Makes fewer errors in synthesising a complementary polynucleotide
d) Makes more errors because it lacks the 3’ to 5’ proofreading exonuclease activity
e) Synthesises complementary strands in the opposite direction from 3’ to 5’

Answer 7

d) Makes more errors because it lacks the 3’ to 5’ proofreading exonuclease activity

Question 8

Which one of the following is true about the genetic code?

a) All codons recognised by a given tRNA encode different amino acids
b) It is absolutely identical in all living things
c) Several different codons may encode the same amino acid
d) The base in the middle position of the tRNA anticodon sometimes permits “wobble” base pairing with two or three different codons
e) The first position of the tRNA anticodon is always adenosine

Answer 8

c) Several different codons may encode the same amino acid

Question 9

Which one of the following is/are true for protein synthesis in eukaryotes?

a) All proteins are initially synthesised with methionine at their C-terminus
b) All proteins are initially synthesised with methionine at their N-terminus
c) All proteins are initially synthesised with tryptophan at their C-terminus
d) All proteins are initially synthesised with a multiple of 3 amino acids in their sequence
e) None of the above

Answer 9

b) All proteins are initially synthesised with methionine at their N-terminus

Question 10

Feedback inhibition is a regulatory mechanism of gene expression that operates at the:

a) Transcriptional level
b) Translational level
c) Transformation level
d) Enzymatic or postranslational level
e) Polycistrionic level

Answer 10

d) Enzymatic or postranslational level

Question 11

Transcription of the lac operon is subject to which of the following regulatory mechanisms?

a) Gene repression
b) Gene induction
c) Gene inhibition
d) Feedback inhibition
e) Attenuation

Answer 11

b) Gene induction

Question 12

Catabolite repression is a regulatory mechanism that controls:

a) A single gene
b) A single operon
c) Multiple genes
d) All genes on the chromosome
e) Various genes and operons

Answer 12

e) Various genes and operons

Question 13

Transformation is:

a) DNA transfer involving direct cell-to-cell contact mediated by pili
b) DNA uptake from the environment
c) DNA transfer from one bacterium to another by a bacteriophage
d) DNA transfer involving attenuation
e) DNA uptake requiring RNA polymerase

Answer 13

b) DNA uptake from the environment

Question 14

Generalised Transduction is carried out by:

a) Lytic bacteriophage
b) F-plasmid containing cells
c) Bacteriphages that are integrated into the host chromosome
d) Bacteria that contain pili
e) Electroporation

Answer 14

a) Lytic bacteriophage

Question 15

The restriction enzyme EcoRI cleaves the 5’-GAATTC-3’ to generate DNA fragments with:

a) A 5’ single stranded overhang
b) A 3’ single stranded overhang
c) Blunt ends
d) Both 5’ and 3’ single stranded overhangs
e) None of the above

Answer 15

a) A 5’ single stranded overhang

Question 16

If a circular plasmid containing 3 EcoRI sites and 2 PvuLL sites is restricted (or cut) using these two enzymes, the number of fragments generated is:

a) 3
b) 2
c) 5
d) 6
e) None of the above

Answer 16

c) 5

Question 17

If a restriction enzyme (of the Type II) recognises a 7 base pair sequence, this sequence is expected to occur once in every:

a) 64 base pairs
b) 256 base pairs
c) 1024 base pairs
d) 4096 base pairs
e) 16384 base pairs

Answer 17

e) 16384 base pairs

Relative frequency = 4^n where n is number of bases

Question 18

Cloning vectors are typically:

a) Small, autonomously replicating, medium to high copy number plasmids that contain restriction sites for cloning
b) Large, autonomously replicating, medium to high copy number plasmids that contain restriction sites for cloning
c) Small, autonomously replicating, low copy number plasmids that contain restriction sites for cloning
d) Large, low copy number plasmids whose replication depends on the bacterial chromosome
e) Small, autonomously replicating, medium to high copy number plasmids that do not contain restriction sites

Answer 18

a) Small, autonomously replicating, medium to high copy number plasmids that contain restriction sites for cloning

Question 19

The scientist and Nobel laureate Frederick Sanger developed:

a) The Polymerase Chain Reaction
b) Southern blotting
c) Gene cloning
d) Dideoxy DNA sequencing
e) Micro arrays

Answer 19

d) Dideoxy DNA sequencing

Question 20

Which one of the following techniques has been used for gene mapping?

a) Southern hybridisation
b) Polymerase chain reaction
c) Conjugation
d) Transformation
e) Attenuation

Answer 20

c) Conjugation

Question 21

The lac operon is subject to two different types of transcriptional control, which are:

a) Attenuation and gene repression
b) Gene repression and feedback inhibition
c) Gene induction and catabolite repression
d) Gene repression and gene induction
e) Gene induction and attenuation

Answer 21

c) Gene induction and catabolite repression

Question 22

The restriction enzyme PvuII generates:

a) 3’ overhanging single stranded DNA
b) 5’ overhanging single stranded DNA
c) 4’ overhanging single stranded DNA
d) No overhanging single strand
e) None of the above

Answer 22

d) No overhanging single strand

Generates BLUNT ENDS

Question 23

The DNA polymerase used in PCR is characterised by its:

a) Heat stability
b) Heat sensitivity
c) Sensitivity to salt
d) Stability at low pH
e) None of the above

Answer 23

a) Heat stability

Question 24

DNA binding proteins typically bind to:

a) Inverted repeats in single stranded DNA
b) Inverted repeats in double stranded DNA
c) Inverted repeats in triple stranded DNA
d) Direct repeats in double stranded DNA
e) Direct repeats in single stranded DNA

Answer 24

b) Inverted repeats in double stranded DNA

Question 25

Gene induction is a regulatory process that involves:

a) An activator protein
b) A leader sequence
c) An operator
d) Isozymes
e) A restriction enzyme

Answer 25

c) An operator

Question 26

The Polymerase Chain Reaction was invented by:

a) Albert Einstein
b) Micheál Martin
c) Donald Trump
d) Kary Mullis
e) Frederick Sanger

Answer 26

d) Kary Mullis

Question 27

The DNA polymerase used for PCR extends primers in a:

a) 5’ to 3’ direction
b) 3’ to 5’ direction
c) Both 5’ to 3’ and 3’ to 5’ directoins
d) No particular direction
e) Any direction

Answer 27

a) 5’ to 3’ direction

Question 28

The temperature-dependent order of a single PCR cycle consists of:

a) DNA denaturation, primer annealing and primer extension
b) DNA denaturation, primer extension and primer annealing
c) Primer annealing, DNA denaturation and primer extension
d) Primer extension, primer annealing and DNA denaturation
e) Primer extension, DNA denaturation and primer annealing

Answer 28

a) DNA denaturation, primer annealing and primer extension

Question 29

The regulatory process of attenuation occurs in:

a) Humans
b) Plants
c) Mammals
d) Yeasts
e) Bacteria

Answer 29

e) Bacteria

Question 30

Catabolite repression is a form of:

a) Positive control
b) Negative control
c) Gene repression
d) Feedback inhibition
e) Post translational regulation

Answer 30

a) Positive control

Question 31

Biosynthesis of tryptophan is regulated by:

a) Gene repression, feedback inhibition and attenuation
b) Gene induction, feedback inhibition and attenuation
c) Catabolite repression, feedback inhibition and attenuation
d) Feedback inhibition, gene repression and gene induction
e) Catabolite repression, attenuation and gene repression

Answer 31

a) Gene repression, feedback inhibition and attenuation