biology : class12 Restriction Endonuclease Recognition : DNA Isolation, Restriction Enzymes, Vector, Ligation, Host Cell : Recombinant DNA Technology MCQ Questions and Answers
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Restriction Endonuclease Recognition
MCQ questions and answers.
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MCQ Questions
1. Which cleavage pattern correctly represents EcoRI action on its recognition site?
A.
5'-G^AATTC-3' and 3'-CTTAA^G-5'
B.
5'-GA^ATTC-3' and 3'-CTTAA^G-5'
C.
5'-GAA^TTC-3' and 3'-CTTAA^G-5'
D.
5'-GAAT^TC-3' and 3'-CTTAA^G-5'
Correct Answer:
5'-G^AATTC-3' and 3'-CTTAA^G-5'
Explanation:
EcoRI recognizes the palindromic sequence 5'-GAATTC-3' and cleaves between G and A on both strands, producing staggered cuts with 5' AATT overhangs.
2. A linear DNA molecule has the sequence 5'-GGAATTCCGAATTCG-3' on one strand. How many EcoRI recognition sites are present in this strand, and how many EcoRI cleavage events will occur in the double-stranded molecule?
A.
One recognition site and one cleavage event
B.
Two recognition sites and two cleavage events
C.
Two recognition sites and four cleavage events
D.
Three recognition sites and two cleavage events
Correct Answer:
Two recognition sites and two cleavage events
Explanation:
The sequence contains two GAATTC sites. Each double-stranded recognition site is cleaved at one corresponding position on each strand, which is counted as one restriction cleavage event per site.
3. Which single-base substitution would abolish recognition of a DNA site by EcoRI while leaving the remaining bases unchanged?
A.
5'-GAATTC-3' changed to 5'-GACTTC-3'
B.
5'-GAATTC-3' changed to 5'-GAATTT-3'
C.
5'-GAATTC-3' changed to 5'-GAAGTC-3'
D.
Any of the substitutions listed above
Correct Answer:
Any of the substitutions listed above
Explanation:
EcoRI requires the complete GAATTC recognition sequence. A single-base change at any of the six positions disrupts the recognition sequence and prevents normal EcoRI recognition.
4. Which pair of restriction enzymes recognizes different DNA sequences but produces the same type of cohesive end with the same four-nucleotide 5' overhang?
A.
EcoRI and MfeI
B.
HindIII and BamHI
C.
HaeIII and SmaI
D.
AluI and HaeIII
Correct Answer:
EcoRI and MfeI
Explanation:
EcoRI recognizes GAATTC and generates a 5' AATT overhang. MfeI recognizes CAATTG and also generates a 5' AATT overhang, making their cohesive ends compatible.
5. Which recognition site is cleaved to produce blunt-ended DNA fragments rather than staggered cohesive ends?
A.
5'-G^AATTC-3' by EcoRI
B.
5'-A^AGCTT-3' by HindIII
C.
5'-GG^CC-3' by HaeIII
D.
5'-C^TGCAG-3' by PstI
Correct Answer:
5'-GG^CC-3' by HaeIII
Explanation:
HaeIII recognizes GGCC and cuts between the central G and C on both strands at corresponding positions, producing blunt ends without single-stranded overhangs.
6. A DNA segment contains the sequence 5'-CTGCAG-3'. Which enzyme and cleavage pattern correctly identifies this site?
A.
PstI; 5'-CTGCA^G-3'
B.
PstI; 5'-C^TGCAG-3'
C.
SmaI; 5'-CCC^GGG-3'
D.
BamHI; 5'-G^GATCC-3'
Correct Answer:
PstI; 5'-CTGCA^G-3'
Explanation:
PstI recognizes the palindromic sequence CTGCAG and cleaves between A and G, producing a staggered end with a 3' overhang.
7. Which recognition sequence is most likely to be cleaved by a restriction enzyme at the same position when read in either 5' to 3' direction because it is palindromic?
A.
5'-GAATTC-3'
B.
5'-GAATCC-3'
C.
5'-GATTAC-3'
D.
5'-GACCTA-3'
Correct Answer:
5'-GAATTC-3'
Explanation:
GAATTC is the EcoRI recognition sequence. Its complementary strand, read 5' to 3', is also GAATTC, so the sequence is palindromic and forms a symmetric recognition site.
8. A DNA sequence contains five occurrences of the tetranucleotide GGCC, with no overlapping occurrences. If the DNA is completely digested with HaeIII, how many fragments will be produced from a linear molecule?
A.
Four
B.
Five
C.
Six
D.
Ten
Correct Answer:
Six
Explanation:
HaeIII recognizes and cleaves at each GGCC site. Complete digestion of a linear DNA molecule at five distinct sites produces five plus one, or six, fragments.
9. Which enzyme-recognition-site pair correctly predicts a 3' cohesive overhang after cleavage?
A.
EcoRI; 5'-G^AATTC-3'
B.
PstI; 5'-CTGCA^G-3'
C.
HindIII; 5'-A^AGCTT-3'
D.
BamHI; 5'-G^GATCC-3'
Correct Answer:
PstI; 5'-CTGCA^G-3'
Explanation:
PstI cleaves CTGCAG between A and G on one strand and the corresponding position on the opposite strand, leaving a single-stranded 3' overhang. EcoRI, HindIII, and BamHI produce 5' overhangs.
10. A circular DNA molecule contains three non-overlapping EcoRI recognition sites. After complete digestion with EcoRI, how many DNA fragments will be generated?
A.
Two
B.
Three
C.
Four
D.
Six
Correct Answer:
Three
Explanation:
For circular DNA, the number of fragments produced by complete digestion equals the number of distinct cleavage sites. Three EcoRI sites therefore produce three fragments.
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