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Genetic Engineering [ Question No: 1 To 9 ] :
Ti plasmid used in genetic engineering is obtained from :
Root Inducing (RI) plasmid was derived from :
Which of the following is a phagemid vector ?
Two micron plasmid can be obtained from the following yeast :
What is the normal role of restriction enzyme in bacterial cells ?
Methyl transferases of restriction modification systems seem to have evolved by :
Which one of the following could be a correct sequence for a restriction enzyme ?
A circular plasmid was digested with restriction enzymes to generate a map. Digestion with Bam H1 enzyme gave a single band of 11kb, while digestion with Not I gave two bands corresponding to 7kb and 8 kb. What is the minimal size of the circular plasmid that will be consistent with above observation ?
Which one of the following vector types is suitable to clone 2000 kb DNA insert?
Total number of questions : 9
Number of answered questions : 0
Number of unanswered questions : 9
Genetic Engineering [ Question No: 1 To 9 ] :
Ti plasmid used in genetic engineering is obtained from :
Your Answer : (Not Answered)
Correct Answer : D
The Ti plasmid is obtained from Agrobacterium tumifaciens (A. tumefaciens).
The tumour-inducing (Ti) plasmid of this soil bacterium carries a segment, the T-DNA, that is transferred into the plant genome and causes crown gall. In engineered vectors the tumour genes are removed and the gene of interest is placed between the T-DNA borders, so the bacterium delivers it into plant cells.
Agrobacterium rhizogenes carries the related Ri (root-inducing) plasmid that causes hairy root. Bacillus thuringiensis is the source of Bt toxin genes, and Thermus aquaticus the source of Taq polymerase.
Root Inducing (RI) plasmid was derived from :
Your Answer : (Not Answered)
Correct Answer : B
The Ri plasmid comes from Agrobacterium rhizogenes.
A. rhizogenes causes hairy root disease. Its root-inducing (Ri) plasmid transfers T-DNA carrying the rol genes into plant cells, which then proliferate as masses of fast-growing roots; hairy root cultures are used to produce plant metabolites.
A. tumefaciens carries the tumour-inducing (Ti) plasmid and causes crown gall. Azotobacter and Azospirillum are free-living and associative nitrogen-fixing bacteria with no such plasmid.
Which of the following is a phagemid vector ?
Your Answer : (Not Answered)
Correct Answer : D
The phagemid vector is pBluescript.
A phagemid is a plasmid that also carries the origin of replication of a filamentous phage such as f1 or M13. pBluescript has the f1 origin, so in cells infected with a helper phage it can be packaged as single-stranded DNA, useful for sequencing and mutagenesis, while it otherwise replicates as an ordinary plasmid.
pUC19 and pBR322 are plain plasmid vectors with no phage origin, and λEMBL3 is a lambda replacement vector, a phage rather than a phagemid.
Two micron plasmid can be obtained from the following yeast :
Your Answer : (Not Answered)
Correct Answer : D
The two micron plasmid is obtained from Saccharomyces cerevisiae.
The 2-micron (2 µm) plasmid is a circular DNA of about 6.3 kb, named for its contour length, present in some 40-60 copies per cell in most strains of baker's yeast. Its origin of replication is used to build high-copy yeast episomal plasmid vectors (YEp).
Candida shehatae, Pichia pastoris and the fission yeast Schizosaccharomyces pombe do not carry the 2-micron plasmid.
What is the normal role of restriction enzyme in bacterial cells ?
Your Answer : (Not Answered)
Correct Answer : B
Their normal role is to degrade invading phage DNA.
Restriction enzymes are part of the bacterial restriction-modification system. The cell's own DNA is protected by a matching methylase, which methylates the enzyme's recognition sites. Foreign DNA, such as that of an infecting bacteriophage, lacks those methyl groups and is cut, which 'restricts' the phage's growth.
The enzymes do not break up the cell's own chromosome, make RNA primers (that is primase) or restrict the growth of the bacterium itself; the word 'restriction' refers to the phage.
Methyl transferases of restriction modification systems seem to have evolved by :
Your Answer : (Not Answered)
Correct Answer : B
The key's answer is divergent evolution.
DNA methyltransferases of restriction-modification systems share a common catalytic fold and a set of conserved sequence motifs for binding S-adenosylmethionine and the target base. Within the amino-methyltransferases the same motifs appear in different orders, explained by circular permutation of the genes during their history. That pattern points to descent from a common ancestral enzyme followed by divergence, rather than separate origins.
Convergent evolution would mean unrelated enzymes arriving at similar structures independently, which the shared motifs argue against, and 'natural evolution' is not a mode of evolution.
Which one of the following could be a correct sequence for a restriction enzyme ?
Your Answer : (Not Answered)
Correct Answer : B
The possible restriction site is AAGCTT / TTCGAA.
Type II restriction enzymes recognise palindromic sequences, which read the same 5' to 3' on both strands. Reading the lower strand of AAGCTT/TTCGAA from its own 5' end (right to left) gives AAGCTT again, so the site is a palindrome. It is in fact the site of HindIII, which cuts between the two A's.
The others are not palindromes. The lower strands of GAGAGA, GAGTCG and AAAAAA, read 5' to 3', give TCTCTC, CGACTC and TTTTTT, none of which matches its upper strand.
A circular plasmid was digested with restriction enzymes to generate a map. Digestion with Bam H1 enzyme gave a single band of 11kb, while digestion with Not I gave two bands corresponding to 7kb and 8 kb. What is the minimal size of the circular plasmid that will be consistent with above observation ?
Your Answer : (Not Answered)
Correct Answer : D
The minimal size consistent with both digests is 22 kb.
A circular plasmid cut at n sites gives n fragments whose sizes add up to the plasmid. Fragments of the same size run together as one band, so a single band can hide several copies.
\[ \begin{aligned} \text{BamHI: } N &= 11n \\ \text{NotI: } N &= 7a + 8b,\ a, b \ge 1 \end{aligned} \]
For n = 1, N = 11 kb, but the NotI fragments alone add up to at least 7 + 8 = 15 kb, so that fails. For n = 2, N = 22 kb, and 22 = 7 + 7 + 8, so NotI cuts three times, giving two 7 kb fragments in one band and one 8 kb fragment. BamHI cuts twice, giving two 11 kb fragments in one band.
15 kb fits NotI but cannot give a single 11 kb band, 11 kb is too small for NotI, and 26 kb is not a multiple of 11.
Which one of the following vector types is suitable to clone 2000 kb DNA insert?
Your Answer : (Not Answered)
Correct Answer : D
A 2000 kb insert needs a yeast artificial chromosome (YAC).
2000 kb is 2 Mb. YACs carry a centromere, telomeres and an origin of replication, so they are maintained like natural yeast chromosomes and can hold inserts from about 100 kb up to the megabase range, which made them the vector of choice for early genome mapping.
The other vectors are far too small: a bacterial plasmid carries up to roughly 10-15 kb, a lambda bacteriophage vector about 20-25 kb, and a cosmid about 35-45 kb, since it must still be packaged into a phage head.
Marks
Total number of questions : 9
Number of answered questions : 0
Number of unanswered questions : 9