1. The recognition sequence is at times palindromic in nature. Which of the following statements is correct with respect to it?
a) The molecules which are cut by the same enzyme, anneal only if the sequence is palindromic in nature
b) When the molecules are cleaved by the same enzyme and the recognition sequence is palindromic in nature, there is no effect on annealing
c) There are increased chances of annealing if the recognition sequence is palindromic in nature
d) The term ‘palindromic’ can be used whether the sequence is read from 5’ to 3’ or 3’ to 5’
Explanation: The term palindromic can be used only when a sequence is read along the same polarity ie either 5’ to 3’ or 3’ to 5’. When the recognition sequence is palindromic in nature, there are increased chances of annealing because now there are increased orientations. If the sequence is non-palindromic in nature, then also annealing would take place but in fewer orientations
2. If all the nucleotides are present with equal frequencies and at random, what are the chances of having a particular four nucleotide long motif?
a) 1/256
b) 1/64
c) 1/16
d) 1/8
Explanation: There are four nucleotide bases present in a DNA sequence A, T, C and G. If the bases are present with equal frequency and at random the chances of having a particular 4 nucleotide long motif is 1/ (4*4)= 1/256.
3. Isoschizomers are defined as ___________
a) enzymes having same recognition sequence and always cutting at the same site
b) enzymes having same recognition sequence and always cutting at different site
c) enzymes having different recognition site and cutting at the same site
d) enzymes having same recognition site and they may or may not cut at the same site
Explanation: Isoschizomers are the enzymes which are having same recognition sequence but they necessarily don’t cut at the same site. DraI and AhaIII both recognize and cleave at TTT|AAA, whereas on the other hand, ApaI cuts at GGGCC|C and Bspl20I cuts at G|GGCCC
4. Isocaudomers are defined as the enzymes which recognize different sequence but generate same ends. Which of the following pairs of enzymes can be termed as isocuadomers?
a) DpnI (GA|TC) and Sau3A (|GATC)
b) BamHI (G|GATCC) and Sau3A (|GATC)
c) DpnI (GA|TC) and BglII (A|GATCT)
d) XbaI (T|CTAGA) and BamHI (G|GATCC)
Explanation: BamHI on cleavage leaves GATC as the single stranded end and the same end is left by Sau3A as double stranded, though there recognition sequences are different. The other options don’t satisfy the condition.
5. The specificity of an enzyme is affected by the concentration of buffer used. This phenomenon is termed as:
a) star activity
b) specificity elevation
c) concentration gradient effects
d) diamond activity
Explanation: As concentration of buffer is varied, the specificity of an enzyme is lost and this phenomenon is termed as star activity. By loss of specificity we mean that, instead of a particular sequence, a particular set of sequences can be identified.
6. Which of the following statements is correct with respect to a unit of an enzyme?
a) One unit of enzyme is defined as the amount of enzyme required to digest 1miligram of standard DNA in a specific time of 1hr and under given temperature conditions
b) The amount of enzyme required doesn’t vary with the number of sites present in the DNA
c) If more number of sites is there in the DNA more units of enzyme are required in comparison to same amount of DNA with fewer sites
d) The amount of enzyme required for digestion of DNA with less number of sites is more than that of more number of sites in the same amount of DNA
Explanation: One unit of enzyme is the quantity required for digestion of 1 microgram of DNA in 1hr and under given temperature conditions. The amount of enzyme required is more if more number of sites is there in the same amount of DNA in comparison to less number of sites.
7. Which of the following statement is correct regarding partial digestion?
a) It is defined as the conditions where all the sites in the DNA sequence are not recognized
b) The number of fragments created by partial digestion are same as that of complete digestion
c) It is not useful in representation of genomic library
d) Exactly half of the sites in the DNA are recognized
Explanation: Partial digestion is the condition where all the sites aren’t recognized and thus the number of fragments created are not same as that of complete digestion. It is very useful in genomic library representation because nearly each and every segment is represented.
8. Which of the following is the correct nomenclature of a restriction enzyme obtained from the first activity of strain R of Escherichia coli?
a) EcoR1
b) EscRI
c) EcorI
d) EcoRI
Explanation: The first letter is the first letter of the genus and the next two letters are the first two letters of the species. They are then followed by the strain and the activity from which they are isolated. The activity is represented in Roman numerals.
9. Why is DNase preferred over restriction endonuclease in some cases?
a) DNase is preferred over restriction endonuclease in some cases because the latter are not able to recognize some of the restriction sites
b) DNase is more specific as restriction endonuclease, so the required fragment is obtained
c) DNase is less specific as compared to restriction endonuclease, hence there are more chances of representation of all the possible fragments
d) DNase is abundant in comparison the restriction endonuclease
Explanation: As the DNase is less specific than restriction endonuclease, thus it cuts more randomly. It further leads to the representation of more fragments and hence they can be very useful in genomic library construction.
10. The ends created by use of DNase have unique single stranded sequences.
a) True
b) False
Explanation: The ends created by DNase don’t have unique single stranded sequences. It is so because DNase is not specific in nature