6 Molecular Basisof Inheritance

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ASSERTION

&REASON

CORNERDirections: In the following questions,

a statement ofassertion is tollowed by a

statement of reaco

Mark the corect choice as

d Doth assertion andreason are true and reason is

the correct explanation ofaSsertion.

0 Doth assertionand reason are true but

reason is not the correct explanationof assertion.

(Cf assertion is true butreason S Talse.

(a) both assertion and reason are talse.

Reason : Eukaryotic transcripts possesSextra non

functional segments called introns.1. Assertion The sugar phosphate backbone of two

chains in DNA double helix show anti-parallel polarity.

Reason: Ihe phosphodiester bonds in one Strand go 9from a 3' carbon of one nucleotide to a 5' carbon of

Assertion : A change in nitrogen base at the third

position of a codon causes change in the expressionof

adjacent nucleotide, whereas those in complementarystrand go ice versa.

the codon.

Reason: A codon is mostly read by all the three

nitrogen bases2. Assertion: In Griffith's experiment, a mixture of heat-killed virulent bacteria R and live non-virulent bacteriaS, lead to the death of mice.

10. Assertion RNA recognises its corresponding codonn mRNA.

Reason Transtorming principle" got transferred from Reason: For each codon, there is an individual RNAheat-killed R strain to S strain and made it virulent.

3. Assertion: DNA is considered to be better geneticmaterial than RNA for most organisms.

11. Assertion: Untranslated regions are sequences of RNAbefore initiation codon and after termination codon.

Reason:2-OH group present in DNA makes it labileand less reactive.

Reason Untranslated regions provide stability tomRNA and also increase translational efticiency.

12. Assertion: The predominant site for control of geneexpression in prokaryotes is transcription initiation.Reason: The activity of RNA polymerase is regulatedby accessory proteins, which affect recognition of start

4. Assertion: The mechanism of DNA replication is semi-Conservative in nature

Reason Each of the complementary strands of theparental double helix is conserved during the process.

SItes.Assertion:Synthesis of daughter or new strand occurs 13. Assertion : Lac operon is a repressible operon.Continuouslyalong the parent 3>5 strand.Reason: DNA polymerase can polymerise nucleotidesin 3> 5 direction on 5 3 strand.

Reason: The product of gene activity stops the activilyof the said gene.

14. Assertion : Repetitive sequences make up very largportion ot human genome.Reason Repetitive sequences do not have direccoding functions in the genome.

6. Assertion : Template or antisense strand, having3 5 polarity takes part in transcription.

Reason: Non-template or sense strand, having53 polarity, does not take part in transcription.

7. Assertion: Polycistronic mRNA,found in prokaryotes,specity a number of polypeptides.Reason: Monocistronic mRNA,found in eukaryotes,specity only a single polype

8. Assertion: Eukaryotic mRNA requires post-transcriptionprocessing tor tormation of functional mRNA.

15. Assertion : When the DNA sequences of two peopirare cut using the same restriction enzyme, the lenguand number of fragments obtained are different 1oboth.de.

Reason DNA sequence is arranged tandemlymany copy numbers which varies from chromosomehromosome in an individual, showing high degree opolymorphism.

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ASSERTION & REASON CORNER

1. (a) 2. (d) 3. (c) 4. (a) (6. (b) 8. (a) 9. (d)(b)14. (b) 15. (a)5. 7.

10. (c) 11. (b) 12. (a) 13. (d)

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ASSERTION &REASON CORNER

1. (a) The backbone of a DNA chain or strand is built

up of alternate deoxyribose sugar and phosphate groups.

Ihe 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. The two DNA chains are antiparallel, that is, they

run parallel but in opposite directions. In one chain the

direction is 5' 3, while in the opposite one, it is

35'.2. (d):When bacteria Streptococcus pneumoniae aregrown on a culture plate, some produce smooth shiny colonies

5) while others produce rough colonies (R). This is because theS 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 experiement,

some 'transforming principle', transferred frorm the heat-killedS strain, had enabled the R strain to synthesise a smooth

polysaccharide coat and become virulent which must be

due to the transfer of the genetic material. This is known as

transtormation.

(c):2-OH group present at every nucleotide in RNA is a

reactive group and makes RNA labile and easily degradable.3

4. (a) : DNA replication is semi-conservative, a type ofreplication in which one strand of the daughter duplex is

derived from the parent while the other strand is formed

new. This is carried out by the separation of two strands. The

separated strands function as templates. The new strands built

up over the templates of old strands will have complementarybase pairs (A opposite T and G opposite C). The two daughterDNA molecules thus formed will be carbon copies of the parentmolecule but shall have one new strand and one old strand.

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C):DNA-polymerase can polymerise nucleotides only in however, the numberor KNA MOlecule types discovered i

direction on 3> 5' strand because it adds them at much less than61. Inis implies tnat the anticodons of sone

the 3' end. RNAS readmore than one codon on mRNA.

6. (b) 7. (b) 11. (b)

àre split. he coding sequences or expressed sequences are

defined as exons. They are said to be those sequence that appear

in mature or processed RNA. The exons are interrupted by

introns or intervening sequences which do not appear in mature

or processed RNA. Thus, post-transcription processing, which

involves splicing of introns and fusion of exons, is required to

8. (a):In eukaryotes, the monocistronic structural genes 12. (a): in proKaryotes, Controlof therate oftranscriptional

have interupted coding sequences ie, the genes in eukaryotes initiation is the predominant siteforcontrolof gene expression.Ina transcription unit, the activity of RNA polymeraseata givenpromoter is in turn regulated by interaction with accessory

proteins, which affect its ability to recognise start sites. These

regulatory proteins can act both positively (activators) andnegatively (repressors).

13. (d): An operon is a part of genetic material (or DNA)which acts as a single regulated unit having one or more

structural genes, an operator gene, a promoter gene, a

form functional mRNA.

9. (d): According to the Wobble hypothesis, onty the firsttwO position of a triplet codon on mRNA have a precise pairingwith the bases of the RNA anticodon. The pairing of the third

regulator gene, a repressor and inducer or corepressor (trom

outside). LaC operon is an inducible operon. An inducible

operon system is a regulated unit of genetic material which is

SWitched on in response to the presence of a chemcial.

position bases of the codon may be ambiguOus and variesaccording to the nucleotide present in this position. Thus, asingle RNA type is able to recognise two or more codonsditfering only in the third base. The same is called wobble 14. (6): Repeated or repetitive sequences make up a large

portion of human genome. These sequences are nucleotidesequences that are repeated many times, sometimes hundredto thousand times. They have no direct coding function but

position.

10. (c): RNA has an anticodon loop which has 7 bases,out of which three bases form anticodon for recognising andattaching to the codon of mRNA. Since there are 61 codons Povide intormations as to chromosome structure, dynamicsspecifying amino acids, the cell should contain 61 differenttRNA molecules, each with a different anticodon. Actually, | 15. (a)

and evolution.

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