CBSE 12th Standard Biology Molecular Basis of Inheritance Sample Question Papers Study Material - QB365

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Questions:

Assertion and reason

45 x 1 = 45

Statement I: BAC& YAC are the vectors used for studying the sequencing of DNA
Statement II : 100 percent of base sequence among humans is the same.
Codes:
a) Statement I is True, Statement II is True
b) Statement I is True, Statement II is False
c) Statement I is False, Statement II is False
d) Statement I is False, Statement II is True

Statement I: Chromosome one has 2968 genes
Statement II : Dystrophin gene is the largest gene in humans
Codes:
a) Statement I is True, Statement II is True
b) Statement I is True, Statement II is False
c) Statement I is False, Statement II is False
d) Statement I is False, Statement II is True

Statement I : DNA FP helps in identifying the true father, criminal, etc.
Statement II : It also can solve the problems of Evolution
Codes:
a) Statement I is True, Statement II is True
b) Statement I is True, Statement II is False
c) Statement I is False, Statement II is False
d) Statement I is False, Statement II is True

Statement I: Uracil is present in RNA at the place of thymine.
Statement II : The complex of DNA and protein in chromosome is called chromatin.
Codes:
a) Statement I is True, Statement II is True
b) Statement I is True, Statement II is False
c) Statement I is False, Statement II is False
d) Statement I is False, Statement II is True

Assertion (A): Scientists have identified about 1.8 billion locations where single base DNA differences occur in humans
Reason (R): Less than 2 percent of the genome codes for proteins
Codes:
a) Both (A) and (R) are true and (R) is the correct explanation of (A)
b) Both (A) and (R) are true and (R) is not correct explanation of (A)
c) (A) is true but (R) is false
d) (A) is false but (R) is true

Assertion (A) : Repetitive sequences make up very large portion of human genome.
Reason (R): Repetitive sequences do not have direct coding functions in the genome.
Codes:
a) Both (A) and (R) are true and (R) is the correct explanation of (A)
b) Both (A) and (R) are true and (R) is not correct explanation of (A)
c) (A) is true but (R) is false
d) (A) is false but (R) is true

Assertion (A) : DNA is considered to be better genetic material than RNA for most organisms.
Reason (R): 2°-OH group present in DNA makes it labile and less reactive.
Codes:
a) Both (A) and (R) are true and (R) is the correct explanation of (A)
b) Both (A) and (R) are true and (R) is not correct explanation of (A)
c) (A) is true but (R) is false
d) (A) is false but (R) is true

Assertion (A) : The sugar phosphate backbone of tow chains in DNA double helix show anti – parallel polarity.
Reason (R): The phosphodiester bonds in one strand go from a 3' carbon of one nucleotide to a 5° carbon of adjacent nucleotide whereas those in complementary strand to vice versa.
Codes:
a) Both (A) and (R) are true and (R) is the correct explanation of (A)
b) Both (A) and (R) are true and (R) is not correct explanation of (A)
c) (A) is true but (R) is false
d) (A) is false but (R) is true

Assertion (A) : In a DNA molecule, A-T rich part melt before-G-C rich parts.
Reason (R): In between A and T there are three H-bond, whereas in between G and C there are two H-bonds
Codes:
a) Both (A) and (R) are true and (R) is the correct explanation of (A)
b) Both (A) and (R) are true and (R) is not correct explanation of (A)
c) (A) is true but (R) is false
d) (A) is false but (R) is true

10.

Assertion: Template or antisense strand, having 3′ → 5′ polarity takes part in transcription.
Reason: Non-template or sense strand, having 5′ → 3′ polarity, does not take part in transcription.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

11.

Assertion: Viruses having RNA genome have shorter life span and mutate faster.
Reason: RNA is unstable and thus mutates faster.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

12.

Assertion: Scaffold proteins are nonhistone chromosomal proteins.
Reason: They are rich in lysine and arginine.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

13.

Assertion: The uptake of DNA during transformation is an active, energy requiring process.
Reason: Transformation occurs only in those bacteria, which possess the enzymatic machinery involved in the active uptake and recombination.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

14.

Assertion: In Griffith’s experiment, a mixture of heat-killed virulent bacteria R and live non-virulent bacteria S, lead to the death of mice.
Reason: ‘Transforming principle’ got transferred from heat killed R strain to S strain and made it virulent.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

15.

Assertion: DNA acts as a genetic material in all organisms.
Reason: It is a single-stranded biomolecule.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

16.

Assertion : DNA is associated with proteins.
Reason : DNA binds around histone proteins that form a pool and the entire structure is called a nucleosome.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

17.

Assertion : Histones are basic proteins of major importance in packaging of eukaryotic DNA. DNA and histones comprise chromatin forming the bulk of eukaryotic chromosome.
Reason : Histones are of five major types H1, H2A, H2B, H3 and H4.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

18.

Assertion: Adenine cannot pair with cytosine.
Reason: Adenine and cytosine do not have a perfect match between hydrogen donor and hydrogen acceptor sites. Hence, they cannot pair.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

19.

Assertion : In a DNA molecule, A–T rich parts melt before G–C rich parts.
Reason : In between A and T there are three H–bond, whereas in between G and C there are two H-bonds.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

20.

Assertion (A) : In E. coli, the lac operon gets switched on in presence of lactose.
Reason (R) : Lactose binds to the repressor.
(a) If both A and Rare true and R is the correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

21.

Assertion (A) : A fully processed hnRNA is called mRNA.
Reason (R) : hnRNA undergoes, splicing and other post-transcriptional like modifications, capping and tailing
(a) If both A and Rare true and R is the correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

22.

Assertion (A) : Most of the amino acids are represented by more than one codon.
Reason (R) : The genetic code is non-ambiguous.
(a) If both A and Rare true and R is the correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

23.

Assertion (A) : Replication on one strand of DNA is continuous and on another it is discontinuous
Reason (R) : The DNA polymerase works in 3' → 5' direction.
(a) If both A and Rare true and R is the correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

24.

Assertion (A) : Cytidine is a nucleoside.
Reason (R) : A nucleoside is formed by the combination of sugar and phosphate group.
(a) If both A and Rare true and R is the correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

25.

Assertion (A) ln molecular diagnosis, single stranded DNA or RNA tagged with radioactive molecule is called a probe.
Reason (R) A probe always searches and hybridises with its complementary DNA in a clone of cells.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A),
(c) Assertion (A) is true, but Reason (R) is false
(d) Assertion (A) is false, but Reason (R) is true

26.

Assertion (A) The sugar-phosphate backbone of two chains in DNA double helix show anti-parallel polarity.
Reason (R) The phosphodiester bonds in one strand go from a 3' carbon of one nucleotide to a 5' carbon of adjacent nucleotide, whereas those in complementary strand go vice versa.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A),
(c) Assertion (A) is true, but Reason (R) is false
(d) Assertion (A) is false, but Reason (R) is true

27.

Assertion: Regulator and operator genes are not associated with constitutive genes.
Reason: Constitutive genes need not be repressed.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

28.

Assertion: Lactose in lac operon is promoter gene.
Reason: Lactose inactivates the repressor gene.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

29.

Assertion: No lac mRNA is made in the presence of glucose.
Reason: In the presence of glucose and lactose activity of lac operon is not needed.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

30.

Assertion: Synthesis of tryptophan is self regulatory.
Reason: Tryptophan works both as co-repressor and through feedback inhibition.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

31.

Assertion: Constitutive genes are continuously being expressed.
Reason : Constitutive genes are frequently needed for various metabolic functions.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

32.

Assertion: Ribosomes attached to endoplasmic reticulum release proteins into lumen of ER.
Reason: Such proteins are used for formation of hydrolytic enzymes or are modified.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

33.

Assertion: UAA, UAG and UGA terminate protein synthesis.
Reason: They are not recognised by tRNA.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

34.

Assertion: Initiation step of protein synthesis in prokaryotes and eukaryotes has several differences.
Reason: They both form mRNA - tRNA complex with smaller subunit of ribosome.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

35.

Assertion: The subunits of ribosomes come together only at the time of protein formation.
Reason: Mg²⁺ causes their association or dissociation.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

36.

Assertion: Same tRNA can recognise more than one codons differing only at the third position.
Reason : The specificity of a codon is particularly determined by the first two bases
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

37.

Assertion: The genetic code is degenerate.
Reason: For a particular amino acid more than one codons can be used.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

38.

Assertion: tRNA acts as an adapter molecule.
Reason: tRNA recognizes codon sequence of mRNA during translation.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

39.

Assertion: Core enzyme catalyses chain elongation of RNA.
Reason: The presence of sigma factor is required for initiation of transcription.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

40.

Assertion: The concept of one gene-one enzyme was changed to one gene-one polypeptide.
Reason: Each enzyme may consist of two or more different polypeptides.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

41.

Assertion: Z-DNA follows a zig-zag course.
Reason: Z-DNA is left handed
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

42.

Assertion: Sequences of bases in one polynucleotide chain of DNA can determine the sequence of bases in the other chain.
Reason: In a DNA, amount of adenine equals that of thymine and amount of guanine equals that of cytosine, i.e., A = T and C = G.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

43.

Assertion: B-DNA has a constant diameter of 20 Â.
Reason: A pyrimidine always pairs with a purine.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

44.

Assertion: Adenine and guanine are double - ring bases.
Reason: Adenine and guanine are pyrimidines.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

45.

Assertion: R-type of Pneumococcus is non-virulent.
Reason: R-type of Pneumococcus can be virulent by having transformation with S - type of Pneumococcus.
Codes :
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

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Answers Key:

Assertion and reason

45 x 1 = 45

a) Statement I is True, Statement II is True

d) (A) is false but (R) is true

b)Both (A) and (R) are true and (R) is not correct explanation of (A)

c) (A) is true but (R) is false

a) Both (A) and (R) are true and (R) is the correct explanation of (A)

c) (A) is true but (R) is false

10.

(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

11.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Explanation:
Unlike DNA, RNA is usually singlestranded. Additionally, RNA contains ribose sugars rather than deoxyribose sugars, which makes RNA more unstable and more prone to degradation. RNA is synthesized from DNA by an enzyme known as RNA polymerase during a process called transcription. Viruses having RNA have shorter life span and mutate at faster rate.

12.

(c) If Assertion is true but Reason is false.
Explanation:
Structural nonhistone chromosomal proteins are called scaffold proteins as they constitute the core axis of the chromosome. They contain very little lysine and arginine but instead possess abundant tyrosine and tryptophan types of amino acids.

13.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Explanation:
Transformation does not involve passive entry of DNA molecules through permeable cell walls and membranes. It does not occur ‘naturally’ in all species of bacteria, only in those species possessing the enzymatic machinery involved in the active uptake and recombination processes. Even in these species, all cells in a given population are not capable of active uptake of DNA. Only competent cells, which possess a so – called competence factor are capable of serving as recipients in transformation.

14.

(d) If both Assertion and Reason are false.
Explanation:
When bacteria Streptococcus pneumoniae are grown on a culture plate, some produce smooth shiny colonies (S) while others produce rough colonies (R). This is because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not. Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia. In Griffith’s experiment, some ‘transforming principle’, transferred from the heat-killed S strain, had enabled the R strain to synthesize a smooth polysaccharide coat and become virulent which must be due to the transfer of the genetic material. This is known as transformation.

15.

(d) If both Assertion and Reason are false.
Explanation:
DNA is the hereditary material found in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells that determines the composition of the organism. There is another type of genetic material found in cells and viruses known as ribonucleic acid (RNA). DNA is double stranded as well as single stranded biomolecule.

16.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

17.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

18.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Explanation:
In DNA, the code letters are A, T, G, and C, which stand for the chemicals adenine, thymine, guanine, and cytosine, respectively. In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine.

19.

(c) If Assertion is true but Reason is false.
Explanation: In a DNA molecule, A-T rich parts melt before G-C rich parts because there are two H-bond between A and T whereas in between G and C, there are three H-bond.

20.

(a) If both A and Rare true and R is the correct explanation of A

21.

(a) If both A and Rare true and R is the correct explanation of A

22.

(b) If both A and R are true, but R is not the correct explanation of A

23.

(a) If both A and Rare true and R is the correct explanation of A

24.

(a) If both A and Rare true and R is the correct explanation of A

25.

(a) Both A and R are true and R is the correct explanation of A.
A single stranded DNA or RNA, tagged with a radioactive molecule called probe is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography.

26.

(a) Both A and R are true and R is the correct explanation of A.
The backbone of a DNA strand is built up of alternate deoxyribose sugar and phosphate group. 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' \(\rightarrow\) 5' phosphodiester bonds. The two DNA chains are antiparallel, i.e. they run in opposite direction. In one chain, the direction is 5' \(\rightarrow\) 3', while in the opposite one, it is 3' \(\rightarrow\) 5'.

27.

(a): Regulator gene controls the operator gene in cooperation with a chemical compound called inducer present in the cytoplasm. The regulation gene codes for and produce a protein substance called repressor. The repressor substance combines with the operator gene to repress its function. Therefore it is called regulator gene.
The constitutive genes keep on functioning all the time. They need not be repressed. Therefore, the regulator and operator genes are not associated with them.

28.

(d): Lactose is not a promotor gene but an inducer of lac operon as it combines with repressor protein formed by repressor or regulatory gene and not the gene itself. The inducer joins the repressor, forming a repressor-inducer complex. This complex prevents the repressor from binding with the operator gene of the operon. This frees the operator gene so that the RNA polymerase can move from the promoter to the structural genes.
The structural genes are then transcribed, forming a piece of polycistronic mRNA. The latter is transcribed by tRNA and ribosomes into enzymes.

29.

(a): The function of \(\beta\)-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 \(\beta\)-galactosidase is formed until virtually all of the glucose in the culture medium is consumed. The lack of synthesis of \(\beta\)-galactosidase is a result of lack of synthesis of lac mRNA. No lac mRNA is made in the presence of glucose, because in addition of an inducer to inactivate 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. However, the inhibitory effect of glucose on expression of lac operon is quite indirect.

30.

(a): Tryptophan regulates its own active synthesis by regulating the expression of its gene via feedback mechanism and also by acting as co- repressor which attaches with repressor proteins produced by regulator gene and blocking the promotor gene site thus blocking m-RNA synthesis and further steps.
It is thus obvious that the synthesis of tryptophan is self regulatory, since it, when present in plenty, work firstly by feedback inhibition, and secondly through co- repression to stop further synthesis of tryptophan.

31.

(a): Certain gene-products, such as tRNA molecules, rRNA molecules, ribosomal proteins, RNA polymerase components (polypeptides) and other enzymes catalysing metabolic processes that are frequently referred to as cellular "housekeeping" functions, are essential components of almost all living cells. Genes that specify products of this type are continually being expressed in most cells. Such genes are said to be expressed constitutively and are frequently referred to as constitutive genes.

32.

(b): Polyribosomes attached to membranes of endoplasmic reticulum produce proteins which either pass into their lumen or become integrated into the membranes. The proteins released into the lumen generally reach Golgi apparatus for modifications like formation of hydrolytic enzymes and glycosylation (addition of sugar residues). The modified proteins are packed in vesicles for export or formation of lysosomes, cell wall enzymes, plasma membrane, etc.

33.

(a): Synthesis of polypeptide terminates when a nonsense codon of mRNA reaches the A - site. There are three nonsense codons - UAA, UAG and UGA. These codons are not recognised by any of the tRNAs. Therefore, no more aminoacyl tRNA reaches the A - site. The P - site tRNA is hydrolysed and the completed polypeptide is released in the presence of release factor. Thus termination occurs.

34.

(b): The differences between initiation step of protein synthesis in eukaryotes and prokaryotes are:
(i) In prokaryotes initiation factors are three - IF1, IF2 and IF3. Eukaryotes have at least ten initiation factors - elF1, eIF2, e1F3, eIF4A, eIF4B, eIF4C, eIF4D, eIF4F, elF5 and e1F6.
(ii) In eukaryotes, formylation of methionine does not take place. In prokaryotes tRNA is charged with formylated methionine.
(iii) The larger subunit of ribosome .combines with 40 S - mRNA - tRNAMet (in case of prokaryotes, 30 S) complex to form intact ribosome. It requires initiation factor IF1 in prokaryotes and factors elF1, elF4 (A, B, C) in eukaryotes.

35.

(b): During protein synthesis, two subunits of ribosomes associate. Mg²⁺ is essential for it. Soon after the completion of protein synthesis, the subunits separate. The phenomenon is called dissociation.

36.

(a): It has been shown, for instance that the same tRNA can recognise more than one codons differing only at the third position. This pairing is not very stable and is allowed due to wobbling in base pairing at this third position. This kind of wobbling allows economy of the number of tRNA molecules, since several codons meant for same amino acid are recognised by same tRNA. For instance, anticodon CGC can recognise codons GCU, GCC and GCA.

37.

(a): For a particular amino acid, more than one codons can be used. This phenomenon is described by saying that the code is degenerate. A non - degenerate code would be one where there is one to one relationship between amino acids and the codons, so that 44 codons out of 64, will be useless or nonsense codons. However, there are no nonsense codons. The codons which were earlier called nonsense codons are also known to mean stop signals.

38.

(b): t-RNA is an adaptor molecule because it adapts amino acid to bring it to protein synthesis site in activated form and not because it recognises the codon on mRNA.

39.

(b): The "core' enzyme which catalyses covalent chain extension, consists of two a - polypeptides (each of molecular weight about 41,000), one S - polypeptide ( molecular weight about 155,000) one S'-polypeptide (molecular weight about 165,000) and one ro-polypeptide (molecular weight about 12,000). The "holoenzyme" contains in addition, a -polypeptide (molecular weight about 95,000). The presence of the sigma factor is required for initiation at the proper transcription initiation (or promoter) sites. After each RNA chain - initiation event, sigma is released and the core enzyme catalyses chain elongation.

40.

(a): In 1948, Beadle and Tatum proposed that a gene controls the synthesis of one enzyme. But, many enzymes, as well as the haemoglobins were shown to consist of two or more different polypeptide chains and each polypeptide was found to be the product of a separate gene. Tryptophan synthetase of E. coli, for example, contains an \(\alpha\) - polypeptide, the product of the trp A gene and a \(\beta\) - polypeptide, the product of the \(\beta\) gene. It was necessary, therefore, to change the concept of one gene-one enzyme to one gene-one polypeptide.

41.

(b): Z-DNA is left-handed double helix with zig-zag back - bone, alternate purine and pyrimidine bases, single turn of 45 Â length with 12 base pairs and a single groove. Due to a different arrangement of molecules within Z - DNA polymer, phosphate backbone follows a zig-zag course, while in B - DNA it is regular. In Z - DNA, sugar residues have alternating orientation so that the repeating unit is a dinucleotide.

42.

(b): Although A = T and C = G, there is no any restriction or sequence of bases in one polynucleotide chain. Since A is always linked to T and C to G as determined from the above evidences, sequence of bases in one of polynucleotide should determine the sequence of bases in the other polynucleotide of the double helix.

43.

(a): B-DNA is a helical structure with diameter of 20 Â. If pairing occurs between two purines, it would need too much space and if pairing occurs between two pyrimidines, it would occupy too little space. The constancy of DNA diameter is maintained only when a pyrimidine always pairs with a purine

44.

(c): The bases of nucleic acids are of two types (i) pyrimidines and (ii) purines. Adenine and guanine are double-ring bases called purines; cytosine, thymine and uracil are single - ring bases called pyrimidines.

45.

(b): Transformation is the change in the genetic constitution of an organism by picking up genes present in the environment. Pneumococcus has two strains - virulent (S) and non-virulent (R). The virulent strain causes pneumonia. R-type bacteria form irregular or rough colonies and did not produce any disease while the S-type bacteria cause pneumonia and then death in the mice. Griffith injected a combination of live R-type and heat killed S-type bacteria into mice. While some mice survived, others developed the disease of pneumonia and died. Autopsy of the dead mice showed that they possessed both the types of bacteria in living state though the mice had been injected with dead virulent and living non-virulent bacteria. The occurrence ofliving S-type virulent bacteria is possible only by their formation from R-type non-virulent bacteria which pick up the trait of virulence from dead bacteria. The phenomenon is called transformation.