Important Questions for Class 12 Chapter 6: Molecular Basis of Inheritance
Molecular basis of inheritance question bank
Question 1
If a double stranded DNA has 20 percent of cytosine, calculate the percentage of adenine n the DNA. Solution
Percent of adenine = percentage of thymine.
Percent of guanine = percentage of cytosine.
From the question, percentage of cytosine = 20%
Therefore, Percentage of guanine = 20%
Total percentage of cytosine and guanine in DNA = 20 + 20 = 40%
Therefore, Percentage of adenine and thymine in DNA = 100 – 40 = 60% in a double stranded DNA,
As adenine and thymine are present in equal amount, the percentage of adenine will be
$= \frac{60}{2} = 30%$.
Question 2
Mention the importance of LH surge during menstrual cycle? Solution
(a) Polymorphism, i.e. variation at genetic level, arises due to mutations.
It forms the basis of genetic mapping og human genome and DNA-fingerprinting.
DNA polymorphism refers to an inheritable mutation that is observed in a population at a high frequency.
The DNA polymorphism ranges from a single nucleotide change to very large scale changes.
Such polymorphisms play very important role in speciation and evolution. (b) Bioinformatics is a new area in biology which involves the use of high speed computational devices and statistical techniques. During human gemone project (HGP), an enormous amount of data has been generated, which has to be managed and stored for easy access and future use by scientists; this led to the development of field of bioinformatics.
Bioinformatics involves the creation of biological databases which store the vast information of biology.
It also develops certain tool by which information can be accessed and utilized easily and efficiently.
Bioinformatics has also developed statistical methods by which one can easily find out the relationship between the data and predict the structure of find out the relationship between the data and predict the structure of proteins and their function.
With the help of bioinformatics, protein sequences can be clustered into their related families.
Question 4
State Chargaff’s base complementarily rule Solution
For a double stranded DNA, the ratios between adenine and thymine and guanine and cytosine are constant and equal to one.
Question 5
How does HIV differ from a bacteriophage? Solution
HIV has RNA as its genome, while bacteriophage has double-stranded DNA as its gemone.
Transformation is a phenomenon by which the DNA isolated from one type of cell, when introduced into another type, is able to bestow some of the properties of the former to the latter.
Question 7
Name the enzyme that is referred to as Ochoa enzyme. Solution
Polynucleotide phosphorylase
Question 8
Mention any two ways in which ingle nucleotide polymorphism (SNPs) identified in human genome, can bring out revolutionary changes in biological and medical sciences? Solution
(i) By finding chromosomal locations for disease- associated sequences.
(ii) By tracing human history.
Question 9
How is repetitive/ satellite DNA separated from bulk genomic DNA for genetic experiments? Solution
It is separated by density gradient centrifugation.
Question 10
10. Mention how DNA polymorphism does arise in a population? Solution
VNTR is a mini- satellite DNA, in which a small sequence of DNA is arranged tandemly in many copy numbers.
Question 12
12. Protein synthesis machinery revolves around RNA but in the course of evolution it was replaced by DNA. Justify. Solution
DNA has evolved as genetic material because:
RNA being a catalyst and more reactive, is unstable and prone to mutate faster; hence DNA evolved from RNA with chemical modifications to make it more stable.
DNA is double- stranded and the two strands are complimentary; so it resists changes by evolving a mechanism of repair.
Question 13 Give two reasons why both the strand of DNA are not copied during transcription. Solution
Both the strands of DNA are not copied dung transcription for the following reasons:
If both the strands of DNA are copied, two different RNAs (complementary to each other) and hence two different polypeptides would be formed; if a segment of DNA produces two polypeptides, the genetic information machinery becomes complicated.
The two complementary RNA molecules (produced simultaneously) would form a double- strands RNA rather than getting translated into polypeptides.
RNA polymerase carries out polymerization in the 5’ -----3’ direction and hence, the DNA strand with 3’ -------5’ polarity acts as the template strand.
Question 14
14. Differentiate between a cistron and n exon. Solution
Question 15
15. State the difference between the structural genes in a transcription unit of prokaryotes ad Eukaryotes. Solution
Question 16
16. Distinguish between codons and anticodons. Solution
Question 17
17. Mention the role of ribosomes in peptide bond formation. how does ATP facilitate it?
Role of Ribosomes:
Solution
Ribosomes are the main cellular factory (site) of protein synthesis; the large subunt has two sites (P and A) for binding of amino acids, so that they are close to each other for formation of peptide bond.
They also act as catalyst (23S rRNA) in prokaryotes for formation of peptide bonds.
ATP provides energy for the activation of amino acids
Question 18
18. Why does DNA replication occur in small replication forks and not in its entire length?
(ii) Why is DNA replication continuous and discontinuous in a replication fork?
(iii) Explain the importance of ‘origin of replication’ in a replication fork. Solution
(i) Replication of DNA occurs in small replication fork, because DNA is a such a long molecule that the separation of the two strands along its entire length requires a very high amount of energy.
(ii) DNA polymerase can catalyse the polymerization of nucleotides only in 5’---3’ direction.
- So on the template strands with 3’—5’ polarity, DNA replication is continuous.
- On the template strand with 5’—3’ polarity, DNA synthesis occurs in short stretches as the opening of replication fork continues; later these short stretches are joined by the action of DNA ligases.
(iii) Replication of DNA dos not initiate randomly, and DNA polymerases on their own cannot initiate replication.
- So there is a specific sequence on DNA, called origin of replication; DNA polymerase binds to it and continues the process.
Question 19
Monocistronic structural genes in eukaryotes have interrupted coding sequences. Explain. How are they different in prokaryotes? Solution
In eukaryotes, the hnRNA (primary transcript of mRNA) has coding sequences, called exons as well as on-coding sequence, called introns, i.e. the information is split.
- It undergoes a process, called splicing, in which the introns are removed and the exons are joined together in a particular manner, to form the functional mRNA.
- In eukaryotes, the mRNA is polycistronic, i.e. codes for more than one polypeptide.
- The information is continuous and no splicing is required.
Question 20
Why is tRNA called an ‘adapter’? Solution
Since tRNA on one hand bind to a specific amino acid and on the other handreads the codon of the amino acid bound to it through its anticodon, it is called an ‘adapter’.
Question 21 (a) A tRNA I charged with the amino acid methionine.
Name the process involved in the attachment.
Pont out the mRNA codon and anticodon on tRNA for this amino acid.
(b) The part of the chromatin that is densely packed and stains dark, s called heterochromatin.
Question 22
What is satellite DNA n a genome? Explain their role in DNA fingerprinting. Solution
Satellite DNA refers to the bulk of the genomic DNA, whose sequences do not code for proteins, but form major peaks during density gradient centrifugation.
The sequences of satellite DNA show high degree of polymorphism.
Since DNA from every tissue of an individual shows the same degree of polymorphism, it forms the basis of DNA fingerprinting.
Since the polymorphism is also inherited by children from the parents, it helps in paternity testing in case of disputes.
Question 23
Mention the contributions of the following scientists:
(i) Maurice Wilkins and Rosalind Franklin.
(ii) Erwin Chargaff
Solution
(i) Maurice Wilkins and Rosalind Franklin provided the X-ray diffraction data of DNA.
(ii) Erwin Chargaff observed that for a double- stranded DNA, the ratio between adenine and thymine and between guanine and cytosine are constant.
Question 24 Name two basic amino acids that provide positive charge to histone proteins? Solution
Lysine and arginine.
Question 25
25. Write the two specific codons that a translational units of mRNA is flanled by, one on its either sides? Solution
The start/inintiation codon (AUG) at the 5’ end and the stop codon (UAA/UAG/UGA) at the 3’ end.
Question 26
Which chromosome has the maximum number of genes and the one which has least number of genes? Solution
Chromosome 1 has the maximium number of genes and chromosome Y has the least number of genes.
Question 27
It is established that RNA is the first genetic material. Explain giving three reasons. Solution
RNA is the first genetic material because:
RNA can directly code for the synthesis of proteins and hence can easily express the character; it is the genetic material in many viruses.
Rna can also act as a catalyst; there are some important biochemical reactions in living systems that are catalysed by RNAs and not protein.
Many essential life processes like splicing, translation, ete. Have evolved around RNA.
Question 28
What would happen if histnes were mutated and made rich in amino acids, aspartic acid and glutamic acid in place of basic amino acids such as lysine and arginine?
Solution
If acidic amino acids replace the basic amino acids, the histine will become negetively charged; so that it may not have a role in packaging of DNA and hence, no nucleosome or chromatin fibres will be formed.
