Prior to mutation, a sequence of DNA reads GAGCCTATGCCAGTA. After the mutation, the sequence reads GAGCGTACGCCATTA. Which of the following best explains the change in DNA that has occurred?
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Solution
Since the total number of bases is the same, either no deletions or insertions occurred, or an equal number of each must have occurred. In this case, however, simply comparing each strand base-for-base shows that the more likely, explanation is that multiple substitutions took place along the sequence.
Which one(s) is / are correct?
1. In prokaryotes single type of RNA polymerase can transcribe mRNA, tRNA and rRNA.
2. In eukaryotes RNA polymerase I transcribes rRNA (28S, 18S and 5.8S) whereas RNA pol III is responsible for transcription of tRNA, 5S rRNA and Sn RNAs.
3. RNA pol II transcribes hn RNA in eukaryotes.
4. Ribosomal large subunit has P and A-sites.
The difference(s) between mRNA and tRNA is / are that –
1. mRNA has more elaborated 3-dimensional structure due to extensive base – pairing.
2. tRNA has more elaborated 3-dimensional structure due to extensive pairing.
3. tRNA is usually smaller than mRNA.
4. mRNA bears anticodon but tRNA has codons.
Select the two correct statements out of the four (a–d) given below about lacoperon.
1. Glucose or galactose may bind with the repressor and inactivate it.
2. In the absence of lactose the repressor binds with the operator region.
3. The z-gene codes for permease.
4. This was elucidated by Francois Jacob and Jacque Monod.
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Solution
Jacob and Monod proposed the lac operon of E. coli.The lac operon contains a promoter, an operator, and three structural genes called Z, Y,and A, coding for the enzyme, β galactosidase, permease and transacetylase respectively. The lac regulator gene, designated as i gene,codes for repressor. In the absence of the inducer, the repressor binds to the lac operator, preventing RNA polymerase from binding to the promoter and thus transcribing the structural gene.
Match Column-I with Column-II
| Column I | Column II |
|---|---|
| A. Operator site | 1. Binding site for RNA polymerase |
| B. Promoter site | 2. Binding site for repressor molecule |
| C. Structural gene | 3. Codes for enyzyme protein |
| D. Regulator gene | 4. Codes for repressor molecules |
Match Column-I with Column-II
| Column I | Column II |
|---|---|
| A. Helicase | 1. Joining of nucleotides |
| B. Gyrase | 2. Opening of DNA |
| C. Primase | 3. Unwinding of DNA |
| D. DNA polymerase | 4. RNA priming |
Identify A, B and C of a nucleosome.
In an inducible operon, the genes are
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Solution
Inducible operons are usually switched off. This is a type of operon which is switched on when a chemical called inducer is present. The inducer is almost always a substrate.
One of the most frequently used techniques in DNA finger printing is
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Solution
The technique of DNA fingerprinting was developed by Dr. Alec Jeffrey in 1984. It is a technique generally using repeated sequences (repetitive DNA) in the human genome that produces a pattern of band that is unique for every individuals. These short nucleotide repeats vary in number from person to person and are called variable number of tandem repeat (VNTR). VNTR belongs to class of satellite DNA referred to as minisatellite.
Which of the following is not a property of the genetic code?
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Solution
Genetic code is the relationship of amino acid sequence in a polypeptide and nucleotide/base sequence in mRNA/antisense strand of DNA.
It is universal, i.e., a codon specifies the same amino acid in all organisms, non-overlapping, i.e., adjacent codons are independent with no base being member of two codons, degeneracy, i.e., some amino acids are coded by more than one codon, hence the code is degenerate, unambiguous, i.e., one codon codes for only one amino acid.