Molecular Biology Questions and Answers –
General Principles for Chain Termination
Sequencing
1. Which of the following is not required for DNA sequencing?
a) Restriction digestion
b) Electrophoresis
c) Cloning
d) Polymerase chain reaction
Answer: c
Explanation: DNA sequencing is the process of determining the precise order of
nucleotides within a DNA molecule. It includes the methods and technologies of
restriction endonuclease, electrophoretic techniques and Polymerase Chain
Reaction.
2. End labeled DNA sequencing is known as dideoxy method of sequencing
a) True
b) False
Answer: b
Explanation: The end labeled DNA sequencing is known as Maxem and Gilbert
method. This procedure involves either 3’ or 5’ end labeling thus is also known as
end labeled DNA sequencing.
3. The 32P is added at the 3’ end by polynucleotidyl kinase
a) True
b) False
Answer: b
Explanation: The 32P dNTP is added at the 5’ end by polynucleotidyl kinase. The
32P dNTP is added at the 3’ end by deoxynucleotydil transferase. The end labeling
is done in either one of the two ends.
4. The end labeled fragment is cleaved in how many pieces?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The end labeled fragment is digested with a restriction
, endonuclease which cleaves it into two unequal lengths of fragments. As a result,
only one end of each of the two fragments thus produced will be labeled.
5. Restriction digestion is the only process to achieve sequencing by the Maxem
and Gilbert method.
a) True
b) False
Answer: b
Explanation: Restriction digestion is the one of the two processes to achieve
sequencing by the Maxem and Gilbert method. The alternative method includes
denaturation of its two complementary strands separated by gel electrophoresis.
6. The denatured strands cannot be separated.
a) True
b) False
Answer: b
Explanation: The two complementary strands of DNA generally show different mobility
during electrophoresis. This is because of their different molecular weight as one of the
strands has a higher number of purines and the other pyrimidines.
7. What are the basic base – specific cleavage sites used in Maxem and Gilbert
method?
a) A, T, G, C
b) C, T, A+G, T+C
c) A, G, A+T, G+C
d) G, C, A+G, C+T
Answer: d
Explanation: The single end labeled double or single stranded DNA samples
produced is subjected to base – specific cleavage. The bases – specific cutters are
used to cut at one of the four sites G, C, A+G and C+T.
8. Which step is not involved in base – specific cleavage of DNA fragment?
a) Modification of concerned base
b) Removal of modified base from DNA strand
c) Induction of random strand break
d) End labeled DNA fragments of variable lengths produced
Answer: c
Explanation: The strand breaks is induced in a specific position. This type of break is
induced in the position from which a modified base is removed.
General Principles for Chain Termination
Sequencing
1. Which of the following is not required for DNA sequencing?
a) Restriction digestion
b) Electrophoresis
c) Cloning
d) Polymerase chain reaction
Answer: c
Explanation: DNA sequencing is the process of determining the precise order of
nucleotides within a DNA molecule. It includes the methods and technologies of
restriction endonuclease, electrophoretic techniques and Polymerase Chain
Reaction.
2. End labeled DNA sequencing is known as dideoxy method of sequencing
a) True
b) False
Answer: b
Explanation: The end labeled DNA sequencing is known as Maxem and Gilbert
method. This procedure involves either 3’ or 5’ end labeling thus is also known as
end labeled DNA sequencing.
3. The 32P is added at the 3’ end by polynucleotidyl kinase
a) True
b) False
Answer: b
Explanation: The 32P dNTP is added at the 5’ end by polynucleotidyl kinase. The
32P dNTP is added at the 3’ end by deoxynucleotydil transferase. The end labeling
is done in either one of the two ends.
4. The end labeled fragment is cleaved in how many pieces?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The end labeled fragment is digested with a restriction
, endonuclease which cleaves it into two unequal lengths of fragments. As a result,
only one end of each of the two fragments thus produced will be labeled.
5. Restriction digestion is the only process to achieve sequencing by the Maxem
and Gilbert method.
a) True
b) False
Answer: b
Explanation: Restriction digestion is the one of the two processes to achieve
sequencing by the Maxem and Gilbert method. The alternative method includes
denaturation of its two complementary strands separated by gel electrophoresis.
6. The denatured strands cannot be separated.
a) True
b) False
Answer: b
Explanation: The two complementary strands of DNA generally show different mobility
during electrophoresis. This is because of their different molecular weight as one of the
strands has a higher number of purines and the other pyrimidines.
7. What are the basic base – specific cleavage sites used in Maxem and Gilbert
method?
a) A, T, G, C
b) C, T, A+G, T+C
c) A, G, A+T, G+C
d) G, C, A+G, C+T
Answer: d
Explanation: The single end labeled double or single stranded DNA samples
produced is subjected to base – specific cleavage. The bases – specific cutters are
used to cut at one of the four sites G, C, A+G and C+T.
8. Which step is not involved in base – specific cleavage of DNA fragment?
a) Modification of concerned base
b) Removal of modified base from DNA strand
c) Induction of random strand break
d) End labeled DNA fragments of variable lengths produced
Answer: c
Explanation: The strand breaks is induced in a specific position. This type of break is
induced in the position from which a modified base is removed.
