Practice MCQs

Question 1

TRUE OR FALSE:
EcoR1 is classified as an exonuclease that randomly cleaves single-stranded DNA producing sticky ends with short single-stranded overhangs.

Answer 1

False

EcoRI is an endonuclease (restriction enzyme), cleaving specific sites

Question 2

TRUE OR FALSE:
A linear DNA fragment that is fully digested by a restriction enzyme that cuts at two different positions will generate three DNA fragments, while a plasmid cut at two different positions by a restriction enzyme will generate two fragments of DNA

Answer 2

True

Question 3

TRUE OR FALSE:
DNA ligase is an enzymes that catalyses the formation of a 5’-3’ phosphodiester bond during DNA replication

Answer 3

False

It catalyses the formation of 3’-5’ phosphodiester bonds

Question 4

TRUE OR FALSE:
An EcoR1 DNA fragment can be directionally cloned into an EcoR1 digested vector

Answer 4

False

Question 5

TRUE OR FALSE:
Terminal transferase is an enzyme that adds a nucleotide to the 5’ end of DNA strands

Answer 5

False

Terminal transferase adds nucleotides to the 3’ end of DNA strands

Question 6

TRUE OR FALSE:
Taq Pol has a terminal transferase activity and its optimal polymerisation temperature is 55°C

Answer 6

False

Taq Pol optimal polymerisation temperature is 72°C

Question 7

TRUE OR FALSE:
The ampicillin resistance gene (amp r) codes for an enzyme (β-lactamase) which catalyses the hydrolysis of the antibiotic ampicillin

Answer 7

True

Question 8

TRUE OR FALSE:
In the laboratory, recombinant plasmids are commonly introduced into bacterial cells by electrophoresis as a gentle low-voltage gradient draws the DNA into the cells

Answer 8

False

The technique is called electroporation

Question 9

TRUE OR FALSE:
During a transformation reaction, every competent E.coli cell will be transformed and receive a plasmid

Answer 9

False

Only a subset of cells will take up the plasmid

Question 10

TRUE OR FALSE:
Plasmid DNA can be inserted into a bacterial cell by a technique called calcium chloride transformation where cells and DNA are mixed, then chilled on ice, and finally heated to 100°C for a short time.

Answer 10

False

Heat shock is at 42°C

Question 11

Both the lacI and lacZ gene of the lac operon are constitutively expressed

Answer 11

False

Only lacI is constitutively expressed

Question 12

TRUE OR FALSE:
The start site for transcription of a gene is always found before the RBS

Answer 12

True

Question 13

TRUE OR FALSE:
The enzyme β-galactosidase is only produced in large quantities in E.coli when the lac repressor is bound to the operator site

Answer 13

False

Binding of the repressor prevents transcription of the lac operon

Question 13

TRUE OR FALSE:
The operator site is found 3’ of the promotor site of the structural genes in the lac operon

Answer 13

True

Question 14

TRUE OR FALSE:
The termination sequence for transcription is always positioned 5’ of the stop codon

Answer 14

False

The termination sequence is positioned 3’ of the stop codon

Question 15

TRUE OR FALSE:
In a prokaryotic cell, transcription commences in the -10 consensus sequence of the promotor and occurs in the 5’ to 3’ direction.

Answer 15

False

Transcription commences at the +1 site

Question 16

TRUE OR FALSE:
The alpha subunit of RNA polymerase holoenzyme bind to the RBS to commence translation

Answer 16

False

The α subunit of RNA polymerase holoenzyme binds to the promoter

Question 17

TRUE OR FALSE:
SDS-PAGE is used to separate proteins according to their structure

Answer 17

False

SDS-PAGE separates proteins based on their molecular weight

Question 18

TRUE OR FALSE:
Beta-mercaptoethanol can be used to remove the disulfide bridges in proteins before separation

Answer 18

True

Question 19

TRUE OR FALSE:
Proteins treated with SDS have an overall negative charge

Answer 19

True

Question 20

TRUE OR FALSE:
Affinity chromatography separates proteins according to their shape

Answer 20

False

Separates proteins based on interactions with an immobilised ligand

Question 21

TRUE OR FALSE:
An intron is a section of RNA that is spliced out of the cDNA molecule to allow expression of a eukaryotic protein in a prokaryotic cell

Answer 21

False

cDNA does not contain introns

Question 22

TRUE OR FALSE:
To prepare a cDNA library, the first step is to isolate the total primary RNA from the cell type of interest

Answer 22

False

The first step is to isolate mature mRNA

Question 23

TRUE OR FALSE:
A cDNA library cannot be used to isolate the promoter region of a gene

Answer 23

True

Question 24

TRUE OR FALSE: The principal steps in the construction of a double stranded cDNA molecule is: extraction of mRNA, binding of oligo-dT, treat with reverse transcriptase, removal of single-stranded RNA and synthesis of the second strand of cDNA

Answer 24

True

Question 25

TRUE OR FALSE: In agarose gel electrophoresis, DNA molecules migrate from the negative to the positive electrode

Answer 25

True

Question 26

TRUE OR FALSE: The mRNA molecule transcribed from a segment of a gene with the following DNA coding strand TACGATCGATTTATT has the sequence AUGCUAGCUAAAUAA

Answer 26

False | The **template** strand is transcribed from

Question 27

TRUE OR FALSE: The RBS present in the mRNA molecule is essential as it allows the tRNA molecule to recognise the mRNA during translation

Answer 27

False | The RBS is essential for **ribosome binding** and alignment on the mRNA

Question 28

TRUE OR FALSE: The diagram below depicts a eukaryotic gene. The insertion of a single base pair at position E will alter the sequence of the protein encoded by this gene. ATG is the start codon. TGA is the stop codon

Answer 28

False | Proteins are translated between the **START** and **STOP** codons

Question 29

TRUE OR FALSE: In a cloning experiment when you are using the blue-white β-galactosidase screening system it is important that you transform the ligation reaction into wild type *E.coli* cells

Answer 29

False | **Mutant strains** that lacks functional β-galactosidase are used

Question 30

TRUE OR FALSE: A gene of 500bp was successfully cloned into the *Pvu II* site of the vector pPD2 shown below. This clone was then digested with *Pvu II* and digests analysed by agarose gel electrophoresis. If the *Pvu II* enzyme had completely cut the clone, you would expect to see one fragment at 4.5Kb

Answer 30

False | 2 fragments: 1 at 4.0Kb and 1 at 500bp

Question 31

TRUE OR FALSE: A gene of 500bp was successfully cloned into the *Pvu II* site of the vector pPD2 shown below. The recombinant molecule constructed was digested with *Hind III*. The gene does not contain a site for *Hind III*. If the *Hind III* enzyme had completely cut the recombinant molecule, you would expect to see one fragment at ~4.5Kb.

Answer 31

True

Question 32

TRUE OR FALSE: A experiment was performed to insert a 500bp gene into the *BamH1* site of pBR322. Selection of transformed cells was done on agar media containing Amp (ApR). Plasmid was extracted from the transformed cells and restricted using *Pst1*. Following agarose gel electrophoresis, you would expect to see two fragments, one at 4.36Kb and the other at 500bp.

Answer 32

False | Gene does not have a site for *Pst1*

Question 33

TRUE OR FALSE: Acc651 and Kpn1 both recognise the same 6 base pair sequence, as follows. When Gene X is fully digested with Kpn1, it can be cloned into a plasmid fully digested with Acc651.

Answer 33

False | Don't produce compatible overhangs

Question 34

TRUE OR FALSE: The DNA polymerase used in PCR is a special mutant form of *E.coli* DNA polymerase that is thermostable

Answer 34

False | Taq Pol is a thermostable enzyme derived from thermophilic bacteria

Question 35

TRUE OR FALSE: It is critical that RNA be used as primers for PCR because DNA polymerases require RNA primers to initiate DNA synthesis

Answer 35

False | DNA primers are used in PCR

Question 36

TRUE OR FALSE: Translocation involves moving the ribosome along the mRNA molecule 3 codons at a time

Answer 36

False | Ribosome moves along the mRNA **one codon** (3 nucleotides) at a time

Question 37

TRUE OR FALSE: The mRNA molecule must contain a 5' untranslated region and it is within this area that the Shine-Delgarno sequence is found

Answer 37

True

Question 38

TRUE OR FALSE: The lac operon is induced in the presence of either lactose or IPTG (isopropyl thiogalactoside) and IPTG is not hydrolysed by β-galactosidase, while lactose is hydrolysed

Answer 38

True

Question 39

TRUE OR FALSE: The following vector pXX can be used to produce a recombinant protein, once a gene of interest is cloned in-frame into a restriction enzyme site in the polylinker. P indicates promoter and O indicates operator site

Answer 39

False

Question 40

TRUE OR FALSE: The following represents how a tRNA molecule and mRNA molecule bind during protein synthesis

Answer 40

False

Question 41

TRUE OR FALSE: A higher agarose percentage enhances resolution of smaller bands and a 1.2% agarose gel is suitable for separating fragment sizes of 100 bp from 500 bp

Answer 41

True

Question 42

TRUE OR FALSE: The fusion protein GST-FKBP12 can be purified by affinity chromatography when nickel resin is used in the column

Answer 42

False | Nickel resin requires a **His-tag**

Question 43

TRUE OR FALSE: A histidine tag can be at either the N or C terminus of the protein of interest

Answer 43

True

Question 44

TRUE OR FALSE: The basic components/reagents of a PCR are a single stranded DNA molecule, 2 primers, dNTPs, a heat stable DNA polymerase such as Taq polymerase, and a buffer

Answer 44

False | PCR requires a **Double-Stranded** DNA molecule

Question 45

TRUE OR FALSE: The sigma factor of RNA polymerase catalyses the formation of the phosphodiester bonds that link the nucleotides together

Answer 45

False | It helps the RNA polymerase recognise and **bind the promoter sequence**

Question 46

TRUE OR FALSE: The 5S rRNA of eukaryotes is made by a different RNA polymerase that the 18S, 28S, and 5.8S rRNA's and is also required as a component of the eukaryotic ribosome

Answer 46

True

Question 47

TRUE OR FALSE: In the plasmid DNA extraction method devised by Doly, both NaOH and SDS play a role with SDS required to lyse the cells and the NaOH required to denature both the genomic and plasmid DNA

Answer 47

True

Question 48

TRUE OR FALSE: During the translocation step in the elongation stage of protein synthesis (translation) the release factor binds to the A site of the ribosome

Answer 48

False | Release factors only bind to the A site during the **termination** step

Question 49

TRUE OR FALSE: Codon/anticodon interactions between mRNA and tRNA determines the amino acid that is incorporated into the polysaccharide chain

Answer 49

False | Amino acids are incorporated into the **polypeptide chain**