AIIMS Molecular basis of Inheritance Assertion and Reason

1. Assertion (A) : RNA mutates at a much faster rate than DNA.
Reason (R) : 3-OH group present in ribose sugar of RNA is a reactive group.
2. Assertion (A): No lac mRNA is made in the presence of glucose.
Reason (R) : In the presence of glucose and lactose, activity of lac operon is not required.
3. Assertion (A) : In a repressible operon system, the operator gene is switched off when a corepressor is available along with aporepressor.
Reason (R): Aporepressor produced by regulator gene can block the operator gene completely.
4. Assertion (A) : Repetitive DNA sequences are the nucleotide sequences that are repeated many times in human genome.
Reason (R): Repetitive DNA sequences have no direct role in coding.

5. Assertion (A) : The DNA strand which functions as template for RNA synthesis is sense strand and its complementary strand is antisense strand.
Reason (R) : Both strands of DNA are transcribed simultaneously to produce two complementary RNAs.
6. Assertion (A): RFLPs are used in fingerprinting of DNA for identification of different individuals.
Reason (R) : Short nucleotide repeats in DNA which are very specific in each individual and vary in number from person to person are called VNTRs.
7. Assertion (A): In backbone of DNA chain, phosphate group is connected to carbon 3′ of the sugar residue of the next nucleotide.
Reason (R) : Phosphate group provides acidity to the nucleic acids.
8. Assertion (A): In prokaryotes, translation begins even before mRNA is fully formed.
Reason (R) : Prokaryotic mRNA does not require elaborate processing to become active.
9. Assertion (A) : The genetic code normally represents DNA language.
Reason (R) : Cytoplasmic constituents can read the code from DNA present inside in the nucleus.
10. Assertion (A): Transposons are segments of DNA that jump from one place in the genome to another. Reason (R): Transposons possess repetitive DNA sequences, either similar or inverted at their ends.

1. (c)
Explanation of ‘A’ & ‘R’ RNA is highly reactive, labile and easily degradable because 2′ -OH group present in ribose sugar of every nucleotide of RNA is a reactive group. Being unstable, RNA mutates at a much faster rate than DNA. Such rapid changes are harmful to higher forms of life which hence possess DNA as genetic material.
Result: Hence, it is proved that ‘A’ is true and ‘R’ is false, so the answer is option (c).
2. (a)
Explanation of ‘A’ & ‘R’ The function of (3-galactosidase enzyme in lactose metabolism is to form glucose by cleaving lactose. Thus if both glucose and lactose are present in the growth medium, activity of lac operon is not needed, and indeed, no p-galactosidase is formed until virtually all of the glucose in the culture medium is consumed. The lack of synthesis of p-galactosidase is a result of lack of synthesis of lac mRNA. No lac mRNA is made in the presence of glucose, because in addition to an inducer for inactivating the lac i repressor, another element (cAMP-CAP) is needed for initiating lac mRNA synthesis. The activity of this element is regulated by the concentration of glucose.
Result: Hence, it is proved that both ‘A’ and ‘R’ are true and as ‘R’ is the correct explanation of ‘A’, so the answer is option (a).
3. (c)
Explanation of ‘A’ & ‘R’ Operator gene controls a specific series of structural genes, and lies adjacent to them. It remains turned on because it is not blocked by the aporepressor protein produced by the regulator gene. Therefore, the cistrons keep functioning, producing enzymes. It is the complex of aporepressor-corepressor that turns off the operator gene and stops the expression of the structural genes.
Result: Hence, it is proved that ‘A’ is true and ‘R’ is false, so the answer is option (c). 4
4. (b)
Explanation of ‘A’ & ‘R’ Repetitive DNA sequences are nucleotide sequences that are repeated many times and make up a large portion of human genome. They have no direct coding function but provide information as to chromosome structure.
Result: Hence, it is proved that both A’ and ‘R’ are true but as ‘R’ is not the correct explanation of A’, so the answer is option (b).
5. (d)
Explanation of ‘A’ & ‘R’ The DNA strand which functions as template for RNA synthesis is known as template strand, minus (-) strand or antisense strand. Its complementary strand is named non-template strand, plus (+) strand, sense strand or coding strand. Only the template strand of DNA is transcribed. Both the DNA strands cannot be transcribed simultaneously because that will produce two types of proteins, one with correct sequence of amino acids and the other with reverse sequence of amino acids. Further, if two complementary RNAs are produced simultaneously, they would have a tendency to form double stranded RNA.
Result: Hence, it is proved that both A and ‘R’ are false, so the answer is option (d).
6. (b)
Explanation of ‘A’ & ‘R’ DNA of each organism has specific sequences that can be cleaved by restriction enzymes to produce fragments of different lengths. These fragments are called restriction fragments. Occurrence of different lengths of DNA sequences cleaved at restriction sites is referred to as restriction fragment length polymorphism (RFLP). RFLPs are used in fingerprinting of DNA for identification of persons. Short nucleotide repeats in the DNA are very specific in each individual and vary in number from person to person but are inherited. These are called as the ‘Variable Number Tandem Repeats’ (VNTRs).
Result : Hence, it is proved that both ‘A’ and ‘R’ are true but as ‘R’ is not the correct explanation of ‘A’, so the answer is option (b).
7. (b)
Explanation of ‘A’ & ‘R’ The back bone of a DNA chain is built up of alternate deoxyribose sugar and phosphoric acid groups. The phosphate group is connected to carbon 5′ of the sugar residue of its own nucleotide and carbon 3′ of the sugar residue of the next nucleotide by (3′ – 5′) phosphodiester bonds. Phosphate group provides acidity to the nucleic acids because at least one of its side group is free to dissociate.
Result : Hence, it is proved that both ‘A’ and ‘R’ are true but as ‘R’ is not the correct explanation of ‘A’, so the answer is option (b).
8. (a)
Explanation of ‘A’ & ‘R’ In prokaryotes, mRNA does not require any elaborate processing to become active. Further, transcription and translation occur in the same region i.e., cytoplasm. It results in beginning of translation even before mRNA is fully formed.
Result: Hence, it is proved that both ‘A’ and ‘R’ are true and as ‘R’ is the correct explanation of ‘A’, so the answer is option (a).
9. (d)
Explanation of ‘A’ & ‘R’ The code languages of DNA and mRNA are complementary. Normally genetic code represents mRNA language. This is because the cytoplasmic constituents can read the code from mRNA and not the DNA present inside the nucleus.
Result: Hence, it is proved that both A and ‘R’ are false, so the answer is option (d).
10. (b)
Explanation of ‘A’ & ‘R’ :-Transposons are segments of DNA that can jump or move from one place in the genome to another. Transposons possess repetitive DNA, either similar or inverted, at their ends, some 5, 7 or 9-nudeotide long. Enzyme transposase separates the segment from its original by cleaving the repetitive sequences at its ends.
Result : Hence, it is proved that both A’ and ‘R’ are true but as ‘R’ is not the correct explanation of A’, so the answer is option (b).

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