CBSE Class 12 Biology HOTs Molecular Basis of Inheritance

Question. DNA is a
(a) long polymer of deoxyribonucleotides
(b) short polymer of deoxyribonucleotides
(c) monomer polymer of deoxyribonucleotides
(d) long polymer of ribonucleotides
Answer : A

Question. The length of DNA usually depends on
(a) position of nucleotides
(b) number of nucleotides
(c) Both (a) and (b)
(d) None of the above
Answer : B

Question.  Find the incorrect match.
(a) A bacteriophage (f × 174) –5386 nucleotides
(b) Bacteriophage lamda – 48502 base pairs
(c) E. coli – 4 6 106 . × bp
(d) Haploid content of human DNA – 3.3 10× 6 bp
Answer : D

Question. Purines found both in DNA and RNA are 
(a) adenine and guanine
(b) guanine and cytosine
(c) cytosine and thymine
(d) adenine and thymine
Answer : A

Question. Nitrogenous bases are linked to sugar by
(a) hydrogen bond
(b) phosphodiester bond
(c) N-glycosidic bond
(d) O-glycosidic bond
Answer : C

Question. Choose the correct option.
(a) Pyrimidines include adenine and guanine
(b) Pyrimidines include cytosine, uracil and thymine
(c) Purines include adenine and thymine
(d) Purines include guanine and cytosine
Answer : B

Question. Which of the following are all nucleotides?
(a) Adenosine, cytidilic acid, cytosine AIIMS 2019
(b) Adenylic acid, cytidilic acid, guanylic acid
(c) Cytidine, adenine, adenylic acid
(d) Uracil, thymidine, thymidylic acid
Answer : B

Question. A polymer or a polynucleotide chain has at one end a free ........A....... at 5¢ end of sugar, similarly at the other end of the polymer the sugar has a free .....B.....of 3¢ group.
(a) A – Phosphate moiety, B – OH
(b) A – OH, B – Phosphate moiety
(c) A – COOH, B – Phosphate moiety
(d) A – Phosphate moiety, B–COOH
Answer : A

Question. Backbone of DNA is formed by
(a) sugar
(b) phosphates
(c) Both (a) and (b)
(d) nitrogenous bases (purine and pyrimidine)
Answer : C

Question. Thymine is also called
(a) 2 methyl uracil
(b) 3 methyl uracil
(c) 4 methyl uracil
(d) 5 methyl uracil
Answer : D

Question. Choose the incorrect option.
(a) Friedrich Miescher in 1869 identified DNA as an acidic substance and named it nuclein
(b) Erwin Chargaff said, the ratio between A and T and G and C of dsDNA are constant and equals one
(c) The two strands of dsDNA are complementary to each other
(d) None of the above
Answer : D

Question. X-ray data diffraction of DNA was produced by
(a) Watson and Crick
(b) Wilkins and Franklin
(c) Bateson and Punnett
(d) Both (a) and (b)
Answer : B

Question. In DNA 20% bases are adenine. What percentage of bases are pyrimidines? JIPMER 2019
(a) 30%
(b) 60%
(c) 50%
(d) 20%
Answer : C

Question. In sea urchin DNA, which is double-stranded 17% of the bases were shown to be cytosine. The percentages of the other three bases expected to be present in this DNA are 
(a) G/34%, A/24.5%, T/24.5%
(b) G/17%, A/16.5%, T/32.5%
(c) G/17%, A/33%, T/33%
(d) G/8.5%, A/50%, T/24.5%
Answer : C

Question. In the given diagram of chemical structure of DNA,identify the type of bonding shown by A, B and C. (Image 18)
(a) A–N-glycosidic bonding, B–Phosphodiester bonding, C–Hydrogen bonding
(b) A–N-glycosidic bonding, B–Phosphodiester bonding, C–Covalent bonding
(c) A–N-glycosidic bonding, B–Phosphodiester bonding, C–Coordinate bonding
(d) A–N-glycosidic bonding, B–Hydrogen bonding, C–Phosphodiester bonding
Answer : D

Question. Given the diagram showing Watson and Crick model of DNA structure. Identify the parameters of A, B and C.  (Image 19)
(a) A–0.34 Å, B–20 Å, C–3.4 Å, D–Phosphate backbone,E–Major groove, F–Minor groove
(b) A–3.4 Å, B–20 Å, C–34 Å, D–Sugar backbone,E–Major groove, F–Minor groove
(c) A–34 Å, B–20 Å, C–3.4 Å, D–Sugar phosphate backbone, E–Major groove, F–Minor groove
(d) A–34 Å, B–20 Å, C–0.34 Å, D–Major groove, E–Minor groove, F–Sugar phosphate bone
Answer : C

Question. Which of the following is not the correct salient feature of double-helix structure of DNA?
(a) Two polynucleotide chains have backbone of sugar and phosphate and bases project inside
(b) Two chains have antiparallel polarity, i.e. one is 5¢® 3¢ and other is 3¢® 5¢
(c) Adenine forms three hydrogen bonds with thymine and guanine forms two hydrogen bonds with cytosine
(d) The plane of one base pair stacks over the other in double helix in addition to H-bond to confer extra statbility to helical structure
Answer : C

Question. The diagram shows an important concept in thege netic implication of DNA. Fill in the blanks A to C. (Image 21)
(a) A–transcription, B–replication, C–James Watson
(b) A–translation, B–transcription, C–Erwin Chargaff
(c) A–transcription, B–translation, C–Francis Crick
(d) A–translation, B–extension, C–Rosalind Franklin
Answer : C

Question. In prokaryotes (such as E. coli) ...A... nucleus is not present, the DNA is not scattered throughout the cell. DNA is ...B... charged and holded by the ...C...charged proteins. This structure in prokaryotes is called ...D... .
Choose the correct option for A, B, C and D.
(a) A–undefined, B–negatively, C–positively, D–nucleoid
(b) A–undefined, B–negatively, C–positively, D–nucleus
(c) A–defined, B–negatively, C–positively, D–nucleoid
(d) A–defined, B–positively, C–negatively, D–nucleoid
Answer : C

Question. Positively charged basic proteins that are found in eukaryotes are called
(a) histones
(b) protamine
(c) arginine
(d) lysine
Answer : A

Ques. In DNA, when AGCT occurs, their association is as per which of the following pair?
(a) AT-GC
(b) AG-CT
(c) AC-GT
(d) All of these 
Answer: A

Ques. The eukaryotic genome differs from the prokaryotic genome because
(a) the DNA is complexed with histone in prokaryotes
(b) the DNA is circular and single stranded in prokaryotes
(c) repetitive sequences are present in eukaryotes
(d) genes in the former case are organised into operons. 
Answer: B

Ques. Genes are packaged into a bacterial chromosome by
(a) acidic protein
(b) actin
(c) histones
(d) basic protein. 
Answer: D

Ques. Radiotracer technique shows that DNA is in
(a) multi-helix stage
(b) single-helix stage
(c) double-helix stage
(d) none of these. 
Answer: C

Ques. Nucleosome core is made of
(a) H0, H2A, H2B and H3
(b) H1, H2A, H2B, H4
(c) H1, H2A, H2B, H3 and H4
(d) H2A, H2B, H3 and H4. 
Answer: D

Ques. A DNA with unequal nitrogen bases would most probably be
(a) single stranded
(b) double stranded
(c) triple stranded
 (d) four stranded. 
Answer: A

Ques. Nucleotide arrangement in DNA can be seen by
(a) X-ray crystallography
(b) electron microscope
(c) ultracentrifuge
(d) light microscope.
Answer: A

Ques. An octamer of 4 histones complexed with DNA forms
(a) endosome
(b) nucleosome
(c) mesosome
(d) centromere. 
Answer: B

Ques. The experimental proof for semi-conservative replication of DNA was first shown in a
(a) fungus
 (b) bacterium
(c) plant
(d) virus. 
Answer: B

Ques. Select the correct match.
(a) Ribozyme - Nucleic acid
(b) F2 × Recessive parent - Dihybrid cross
(c) T.H. Morgan - Transduction
(d) G. Mendel - Transformation
Answer: A

Ques. The final proof for DNA as the genetic material came from the experiments of
(a) Hershey and Chase
(b) Avery, MacLeod and McCarty
(c) Hargobind Khorana
(d) Griffith. 
Answer: A

Ques. Taylor conducted the experiments to prove semiconservative mode of chromosome replication on
(a) Vinca rosea
(b) Vicia faba
(c) Drosophila melanogaster
(d) E. coli. 
Answer: B

Ques. A molecule that can act as a genetic material must fulfill the traits given below, except
(a) it should be able to express itself in the form of ‘Mendelian characters’
(b) it should be able to generate its replica
(c) it should be unstable structurally and chemically
(d) it should provide the scope for slow changes that are required for evolution.
Answer: C

Ques. Transformation was discovered by
(a) Meselson and Stahl
(b) Hershey and Chase
(c) Griffith
 (d) Watson and Crick.
Answer: C

Ques. The unequivocal proof of DNA as the genetic material came from the studies on a
(a) bacterium
(b) fungus
(c) viroid
(d) bacterial virus.
Answer: D

Ques. Semi-conservative replication of DNA was first demonstrated in
(a) Escherichia coli
(b) Streptococcus pneumoniae
(c) Salmonella typhimurium
(d) Drosophila melanogaster.
Answer: A

Ques. Transformation experiment was first performed on which bacteria?
(a) E. coli
(b) Diplococcus pneumoniae
(c) Salmonella
(d) Pasteurella pestis 
Answer: B

Ques. The Pneumococcus experiment proves that
(a) bacteria do not reproduce sexually
(b) RNA sometime controls the production of DNA and proteins
(c) DNA is the genetic material
(d) bacteria undergo binary fission. 
Answer: C

Ques. DNA synthesis can be specifically measured by estimating the incorporation of radio-labelled
(a) thymidine
(b) deoxyribose sugar
(c) uracil
(d) adenine.
Answer: A

Ques. The transforming principle of Pneumococcus as found out by Avery, MacLeod and McCarty was
(a) mRNA
(b) DNA
(c) protein
(d) polysaccharide.
Answer: B

Ques. Who proved that DNA is basic genetic material?
(a) Griffith
(b) Watson
(c) Boveri and Sutton
(d) Hershey and Chase 
Answer: D

Ques. Escherichia coli fully labelled with 15N is allowed to grow in 14N medium. The two strands of DNA molecule of the first generation bacteria have
(a) different density and do not resemble parent DNA
(b) different density but resemble parent DNA
(c) same density and resemble parent DNA
(d) same density but do not resemble parent DNA.
Answer: A

Ques. Which one of the following is not applicable to RNA?
(a) Heterocyclic nitrogenous bases
(b) Chargaff’s rule
(c) Complementary base pairing
(d) 5’ phosphoryl and 3’ hydroxyl ends 
Answer: B

Ques. Similarity in DNA and RNA is that
(a) both are polymer of nucleotides
(b) both have similar pyrimidine
(c) both have similar sugar
(d) both are genetic material. 
Answer: A

Ques. During DNA replication, Okazaki fragments are used to elongate
(a) the lagging strand towards replication fork
(b) the leading strand away from replication fork
(c) the lagging strand away from the replication fork
(d) the leading strand towards replication fork.
Answer: C

Ques. During replication of a bacterial chromosome DNA synthesis starts from a replication origin site and
(a) RNA primers are involved
(b) is facilitated by telomerase
(c) moves in one direction of the site
(d) moves in bidirectional way. 
Answer: D

Ques. Method of DNA replication in which two strands of DNA separate and synthesise new strands is called
(a) dispersive
(b) conservative
(c) semi-conservative
(d) non conservative.
Answer: C

Ques. There are special proteins that help to open up DNA double helix in front of the replication fork. These proteins are
(a) DNA ligase
(b) DNA topoisomerase I
(c) DNA gyrase
(d) DNA polymerase I.
Answer: B

Ques. During DNA replication, the strands separate by
(a) DNA polymerase
(b) topoisomerase
(c) unwindase/helicase
(d) gyrase. 
Answer: C

Ques. Experimental material in the study of DNA replication has been
(a) Escherichia coli
(b) Neurospora crassa
(c) Pneumococcus
(d) Drosophila melanogaster. 
Answer: A

Ques. DNA replication is
(a) conservative and discontinuous
(b) semi-conservative and semi-discontinuous
(c) semi-conservative and discontinuous
(d) conservative. 
Answer: B

Ques. Name the enzyme that facilitates opening of DNA helix during transcription.
(a) DNA ligase
(b) DNA helicase
(c) DNA polymerase
(d) RNA polymerase
Answer: D

Ques. What will be the sequence of mRNA produced by the following stretch of DNA ?
3′ATGCATGCATGCATG5′TEMPLATE STRAND
5′ TACGTACGTACGTAC3′ CODING STRAND
(a) 3′AUGCAUGCAUGCAUG5′
(b) 5′UACGUACGUACGUAC 3′
(c) 3′ UACGUACGUACGUAC 5′
(d) 5′ AUGCAUGCAUGCAUG 3′
Answer: B

Ques. Match the following RNA polymerase with their transcribed products :
1. RNA polymerase I (i) tRNA
2. RNA polymerase II (ii) rRNA
3. RNA polymerase III (iii) hnRNA
Select the correct option from the following :
(a) 1-i, 2-iii, 3-ii
(b) 1-i, 2-ii, 3-iii
(c) 1-ii, 2-iii, 3-i
(d) 1-iii, 2-ii, 3-i
Answer: C

Ques. Select the correct statement.
(a) Franklin Stahl coined the term ‘‘linkage’’.
(b) Punnett square was developed by a British scientist.
(c) Spliceosomes take part in translation.
(d) Transduction was discovered by S. Altman.
Answer: B

Ques. AGGTATCGCAT is a sequence from the coding strand of a gene. What will be the corresponding sequence of the transcribed mRNA?
(a) AGGUAUCGCAU
(b) UGGTUTCGCAT
(c) ACCUAUGCGAU
(d) UCCAUAGCGUA
Answer: A

Ques. Which of the following RNAs should be most abundant in animal cell?
(a) tRNA
(b) mRNA
(c) miRNA
(d) rRNA 
Answer: D

Ques. Spliceosomes are not found in cells of
(a) fungi
(b) animals
(c) bacteria
(d) plants. 
Answer: C

Ques. The equivalent of a structural gene is
(a) muton
(b) cistron
(c) operon
(d) recon. 
Answer: B

Ques. Which of the following rRNAs acts as structural RNA as well as ribozyme in bacteria?
(a) 5S rRNA
(b) 18S rRNA
(c) 23S rRNA
(d) 5.8S rRNA
Answer: C

Important Questions for NCERT Class 12 Biology Molecular Basis of Inheritance

Question. If total number of base pair is multiplied with distance between two consecutive bases, length of DNA comes out to be appropriate 2.2 m .How is the packaging of DNA helix done in a tiny nucleus of dimensions of approximately 10^-6 m?
Answer. Negatively charged DNA is wrapped around positively changed histone protein octamer to form nucleosome each containing 200 bp. Nucleosomes are the reapting units of chromatin which are packed to form chromatin fibers which are further coiled & condensed to form chromosome .

Question. In Griffith experiment why Streptococcus pneumoniae with smooth shiny colonies(Sstrain) is virulent in nature. Explain stepwise the Griffith’s experiment?
Answer. S-strain have mucous coat which protect it in host body & help it to cause disease. Refer NCERT book for details of Griffith’s experiment.

Question. How is the transforming principle explained by this experiment?
Answer. The conversion of non-pathogenic living R-strain into living pathogenic S-strain indicates that some thing( transforming factors) have been passed from S- to R- strain.

Question. How Oswald Avery, Colin Macleod and Maclyn MC Corty while determining the biochemical nature of transforming principle in Griffith’s experiment proved that DNA is the heredity material?
Answer. They used DNAses, Proteases & RNAses & found that proteases & RNAses did not affect transformation but DNAses when applied to heat killed S-strain did inhibit transformation of living R-strain to S-strain.

Question. Harshey & Chase selected radioactive 35S ,35P and decided to include the radiation studies in their experiments. What was the logic behind this decision?
Answer. ‘S*’ is an important constituent of protein & is not found in DNA where as ‘P*’ is an important constituent of DNA not found in protein.

Question. How could Harshey and Chase by their experimentation proved that it was not protein but DNA from the virus entered the Bacteria. What did they conclude from their experiment?
Answer. Explanation of the experiment. & Conclusion from the experimental result.

Question. State the qualities of a genetic material? Out of DNA & RNA, which one fulfills all the prerequisites of being a genetic material and why?
Answer. Able to replicate, chemically & structurally stable, scope for mutation, able to express itself in the form of Mendelian characters. DNA the genetic material.As –OH functional group at 2` position of deoxy-ribose in RNA is a reactive group making RNA labile & easily degradable, presence of Uralic instead of thiamine in RNA more ability of RNA to mutation.

Question. RNA was the first genetic material. Justify the statement?
Answer. Codes for protein synthesis, DNA is dependent on RNA for its synthesis etc.

Question. Why Meselson and Stahl grow E.coli in a medium containing 15 NH4Cl for many generation. In which medium were they transferred later on? What were their observations? Analyse their results to prove that DNA is Semi Conservative in Nature?
Answer.. To get an E coli with all its nitrogen as heavy isotope. 14 NH₄Cl . Observation & conclusion of the experiment.

Question. What will happen if a cell fails to divide after DNA replication? Name the main enzyme for the process of replication. This enzyme catalyses polymerization only in one direction that is 5’- 3’. What happens due to this during replication? What is the role of DNA ligase and origin of replication in DNA replication?
Answer. Polyploidy
DNA dependant DNA polymerase.
Replication of one strand is continuous while on the other it is discontinuous.
Discontinuous fragments are joined by DNA ligase.

Question. Give the scientific term for the process of copying genetic message from one strand of DNA into RNA. Only one strand of DNA is used during transcription. Why?
Answer. Transcription.
If both are copied they would code for m-RNA molecules with different sequences hence different proteins will be formed from same DNA sequence. If two strands of m-RNA are produced simultaneously they would coil being complementary to each other.

Question. i)The DNA strand with Polarity 3’-5’ acts as a template during transcription. Why?
ii) The other strand with polarity 5’- 3’ is called coding strand. Why?
Answer. i) DNA dependant RNA polymerase catalyses the polymerization in 5`- 3` direction.
ii) It has sequence same as m-RNA which contains the codes.

Question. In Arushi Murder Case the criminals could be identified with the help of special Biotechnological procedure. Name the technique used and where is it carried out?
Answer. DNA finger printing –main steps.
Forensic laboratory.

Question. In a Forensic Laboratory, a scientist during his research stared cutting the nucleotide polymer with the help scissor. Name the special type of scissor used by him and also the material that was cut.
Answer.. Restriction endo-nuclease, DNA.

QUESTIONS:

1) Name the Amino acid residues of histones. 

2) What function does B-galoctosidase carry out? 

3) Which factor determines the coding strand and the template strand? 

4) Why only one mRNA is produced in transcription? 

5) Why the strand 5'-3' is called coding strand though it does not take part in transcription? 

6) What are ESTs? 

7) DNA is a polynucleotide characterised by two types of peaks. Which peak is known as satellite DNA? 

8) A criminal case of 10 years old was registered for investigation. What samples they might have tested? 

9) A particular human gene has the largest number of bases. Identify it. 

10) Isolation, digestion and separation of DNA in a specific gene. Name the technique. 

11) Three enzymes required for metabolism of lactose, what would happen to the machinery of the operon if mutation occur in z-gene. 

12) A point mutation leads to adverse change in the function of hemoglobin (Bglobin chain). Identify the disease that may occur due to this mutation. Mention the change of amino acids in the polypeptide due to this mutation. 

13) i) Label the amino acid at A, and write the name of RNA s below. 

ii) Name the process in progress.

14) One student has drawn mRNA but he made some mistake in codons

18) 

19.Illustrate below in a DNA segment which constitute a gene.

i) Will the whole gene be transcribed in RNA primarily?

ii) Name the shaded & unshaded part to the gene.

iii)Explain how is gene expressed.

iv) How is this gene different from prokaryotic gene in its expression?

20) Given below schematic representation of two interacting bacterial cells.

i) Name the bacterium and describe the process illustrate.

ii) What is the use of such process in genetics?

iii) Which of two cells act as male?

iv) Draw a labeled diagram of stage immediately next to the one shown here.

 

ANSWERS:

1) Lysine and Arginine.

2) It hydrolyses lactose into galactose and glucose.

3) The polarity 3'-5' determines the template strand and 5'-3' and determines coding strand.

4) Template strand only is involved in transcription.

5) All the reference point is made with coding strand.

6) Expressed sequence Tags is one of the methodologies involved in Human Genome project.

7) Small peaks are referred as satellite DNA.

8) A sample of hair follicle or bone.

9) Dystrophin-2.4 million bases.

10) PCR/DNA finger printing

11) Z-gene can not produce beta-galactosidose. 

12) Sickle cell anemia, glutamate to valine

13) i) A- Methionine, B-.t-RNA ii) Transcription

14) i) the initiating and terminating codon changed.
ii) AUG as initiating codon, UGA- terminating codon.

15) A-Hydrogen bond between base pairs. B-Phosphate and sugar bonds. CBond between sugar and basis

16) The biological father can be identified by DNA finger printing technique.

No. of base pair in Mammalian cell = No. of Nucleosome
Base pairs in one nucleosome
66x10⁹
200 = 3.3x10
Nucleosome

18) i) A-leading strand
B-lagging strand.
ii) DNA- replication
iii) S-phase of the cell cycle.

19)
ii) The shaded parts are introns and un shaded parts are exons.
iii) The primary RNA script undergoes splicing, in this process, the introns are removed exons are joined together to form m-RNA.
iv) In prokaryotes, the information is continuous and there is no need for splicing, the entire DNA is transcribed into RNA.

20) i) E. coli, The figure illustrate conjugation between Hfr cell and F cell, in which a portion of donor DNA has come into the recipient (F~cell). The conjugation bridge last only for a short period before the entire DNA move into the recipient, it breaks. It will be incorporated into recipient DNA by replacing an equivalent segment.
ii)it is one of the method by which genetic recombination is effected is bacterial cell.
iii) Hfr cell is the male (donor).