Question Set B

CBSE 12th Standard Biology Molecular Basis of Inheritance Important Questions And Answers Study Material - QB365

Download CBSE Class 12th Standard CBSE Biology question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Biology

Questions:

1 Marks

11 x 1 = 11

Give the name of the type of synthesis A and B in the replication fork of DNA as shown below.

Mention the polarity of the DNA strands A-B and C-D shown in the replicating fork given below.

Give below is a schematic representation of a lac operon in the absence of an inducer.Identify A and B in it.

Name the types of synthesis 'a' and 'b' occurring in the replication fork of DNA as shown below:

What is the function of histones in DNA packaging?

NAme the parts 'A' and 'B' of the transcription unit given below:

A structural gene has two DNA strands X and Y shown above. Identify the template strand.

What will be the ratio of ¹⁵N/¹⁵N :¹⁵N/¹⁴N : ¹⁴N/¹⁴N containing DNAs,if Meselson and Stahl experiment is cotinued for four generations in the bacteria?

In some viruses DNA is synthesised using RNA template. What term is given to such a DNA?

10.

What would happen if histones were to be mutated and made rich in amino acids and glutamic acid in place of basic amino acids such as lysine and arginine?

11.

In an experiment DNA is treated with a compound which tends to place itself amongst the stacks of nitrogenous base pairs. As a result of this the distance between two consecutive base pairs increases from 0.34nm to 0.44 nm. Calculate the length of DNA double helix, which has 2 x 10⁹bp in the presence of saturating amount of this compound.

Generic 2

7 x 2 = 14

12.

Explain when is a genetic code said to be
(i) Degenerate (ii) Universal

13.

(i) Accoring to Watson and Crick model,the DNA molecule consists of_____long,parellel strands.The two strands are_______around a common axis in a regular manner to form a____helix.
(ii)These strands are made of ___ units.Each such units consists of_____,_____and_____
(iii)In each chain,nitrogenous base molecules are joined to the sugar molecules by_____bonds and project into the space enclosed in the helix at about____to the long axis of the helix
(iv)The nitrogenous bare may be a 9-membered,double ringed____or a 6-membered single ringed___
(v)The double helix of DNA has a constant diameter of___and one complete spiral (turn) of the helix is ___long and has____base pairs.
(vi)The mode of DNA replication is
(vii)Enzyme___cannot initiate the synthesis of a new DNA strand,although it can catalyze the growth of a DNA chain.Therefore,a short chain of ___is formed on the DNA template at the 5' end.This is called___
(viii)During DNA replication,one new strand formed in continuous stretch in the 5'-3' direction.it is called____strand.Other strand is formed in small fragments called_____Which are later joined to form a continuous strand termed___strand

14.

(a) Name the molecule 'X' synthesised by 'i' gene.How does this molecule get inactivated?
(b)Which one of the structural genes code for \(\beta \)-galactosidase?
(c)When will the transcription of this gene stop?

15.

Study the figure below and answer the questions:

(a)What does the figure express?
(b)When does the transcription of lac mRNA stop?
(c)Name the enzyme transcribed by the gene 'Z'

16.

How can DNA segments, separated by gel electrophoresis, be visualised and located?

17.

What are two functions of DNA polymerase?

18.

What are the functions of
(i) methylated guanosine cap and
(ii) poly A-tail in a mature mRNA?

Generic 5

4 x 5 = 20

19.

According to Human Genome Project, about 99.9% nucleotide bases are exactly the same in all human. On the basis of this information answer the following questions.
(i) People may be discriminated on the basis of caste creed, colour and religion. What do you think and Why?
(ii) What percentage of human genome codes for protein?
(iii) Which chromosome has the maximum number of genes & which has their least number.

20.

Garima is a bright fair girl but orphan by birth. One she got much disturbed after learning that a couple had claimed her to be their daughter. Although it is good but she felt that she did not belong to them. One of her close friends Nisha who was very much caring for her contacted the orphanaqe executives to find out the validity of the claim of the couple through DNA profiling.
Answer the following questions on the basis of above information:
(i) How DNA profiling can be made use of for testing the validity of parenthood claim of the couple.
(ii) Which branch of biology was this programme associated with?
(iii) What values were shown by Nisha.

21.

(a) Identify strands 'A' and 'B' in the diagram of transcription unit given above and write the basis on which you identified them.
(b) State the functions of Sigma factor and Rho factor in the transcription process in a bacterium.
(c) Write the functions of RNA polymerase-I and RNA polymerase-Ill in eukaryotes
(OR)
Describe the packaging of DNA helix in a prokaryotic cell and an eukaryotic nucleus.

22.

Raj was a known sportsman in his school.While returning home he found unknown miscreants beating a young fellow.He tried to drive them off but by that time the fellow died of injury.The police arrested Raj and he was put on trial.The judge being convinced by Raj's plea, ordered for DNA fingerprinting reports.
(i) What is the basis of DNA fingerprinting?
(ii) Explain the steps in DNA fingerprinting.
(iii) Write the applications of DNA fingerprinting.
(iv) Raj's fingerprints on the dead body were sufficient to convict him but the judge asked for authentic proof.What values can observed by the judge?

Visit QB365-SLMS - https://www.qb365.in/slms/

Answers Key:

1 Marks

11 x 1 = 11

()
A-Continuous synthesis,
B-Discontinuous synthesis

()
A-B is 3'\(\rightarrow \)5' and C-D is 5'\(\rightarrow \)3'.

()
A - Repressor protein
B - Repressor bound to the operator it prevents transcription of structural genes.

Synthesis 'a' is continuous(3'--->5') and synthesis 'b' is discontinuous(5'--->3')

()
Eight molecules of histones (paired \({ H }_{ 2 }A{ ,\quad H }_{ 2 }B,\quad { H }_{ 3 },\quad { H }_{ 4 }\) ) join to form an octamer, on which the negatively charged DNA becomes wrapped around to form a nucleosome: Thus very long DNA molecules can be accommodated within the nucleus. \({ H }_{ 1 }\) protein acts as a linker between two adjacent nucleosomes.

()
DNA- ligase

()
Y

()
¹⁵N/¹⁵N O :¹⁵N/¹⁴N 2 : ¹⁴N/¹⁴N 14

()
Complementary DNA (cDNA)

10.

()
If acidic amino acids replace the basic amino acids, the histone will become negatively charged; so it may not have a role in packaging of DNA and hence no nucleosome or chromatin fibre will be formed.

11.

()
Length of DNA = 2 X 10⁹ X 0.44 X 10^-9 nm.

Generic 2

7 x 2 = 14

12.

The differences between unambiguous and universal genetic codes are as follows

Unambiguous	Universal
In genetic code, one codon codes for only one amino acid hence, it is unambiguous	The genetic code is universal.i.e. each codon codes for same amino acid in all organisms

(ii) The differences between degenerate and initiator codes are as follows

Degenerate	Initiator
Some amino acids are coded by more than one codon, hence the code is degenerate, e.g. serine, leucine, arginine are encoded by 6 codons.	These codons act as start signal for translation. e.g. AUG acts as initiator codon and it codes for methionine

13.

(i) two,spirally coiled, double
(ii),phosphate,dexyribose sugar,nitrogenous basedexyirbonucleotide
(iii) glycosidic,90⁰
(iv) purine,pyrimidine
(v)2 nm (20 \(\mathring { A } \)),3.4nm(34 \(\mathring { A } \))
(vi) semiconservative
(vii) DNA polymerase,RNA,RNA primer
(viii) Leading,Okazaki fragments,lagging.

14.

(a)Molecule 'X' synthesised by 'i ' gene is repressor of the Lac operon.The repressor is inactivated by interaction with the inducer(i.e.,lactose)
(b)The gene 'Z' codes for beta-galactosidase
(c)Transcription of this stops as soon as the inducer is usedup i.e in absence of inducer.Once whole of lactose is consumed and there is no inducer present to blind to the repressor,the repressor becomes active and switches off the operon.

15.

(a) In presence of an inducer(such as lactose or allolactose), the repressor is inactivated by intersection with the inducer.
(b) Transcription of lac mRNA stops when the repress of the operon is synthesised from the i gene.The repress protein binds to the operator region of the operon and stops transcription.
(c) The gene 'Z' codes for beta-galactosidase.

16.

DNA segments that have been separated on an agarose gel by electrophoresis are transferred and permanently affixed to a nylon membrane, a process called southern blotting.The DNA bands are invisible to the eye so that they are flagged with some kind of tag that one can visualize.Therefore,a solution containing radioactive probe is spread over the membrance so that they bind to complementry DNA sequence and then can be visualized by autoradiography.

17.

DNA polymerase catalyses synthesis of DNA and help also in proof-reading

18.

(i) The methylated guanosine cap helps in the binding of mRNA to the smaller subunit of ribosome during initiation of translation.
(ii) Poly-A tail has a direct relatioship with the logevity of mRNA.

Generic 5

4 x 5 = 20

19.

(i) No. such discrimination of people is not at all correct because all the people have the same genetic material.
(ii) Only less then 2% of human genome codes for proteins.
(iii) Chromosome-1 has the most number of genes. It has about 2968 genes and chromosome Y has the least number of genes. It has only 231genes.

20.

(a) The couple's claim of being parent of Garima by DNA finger printing technique the main steps of which are as follows :
(i) DNA is extracted from certain cell of the body of Garima and the parents claiming for parenthood and is amplified using PCR.
(ii) This DNA is cut in fragments with the help of specific restriction enzymes which are then subjected to get electrophoresis
(iii) Double stranded DNA is then split into single stranded DNA.
(iv) The separated DNA sequences are later transferred from gel nylon membrane (Southern blotting).
(v) The nylon sheet is immersed in a bath where radioactive synthetic DNA segments called as probes or markers are added and hybridized with VNTR.
(vi) The hybridized DNA fragments are detected by autoradiography. They are observed as dark bands on X-Ray film which represent the DNA finger prints or DNA profiles.
(vii) If the bands of Garima's DNA match will the DNA print of claiming couple, the claim of the couple of being her parents is true otherwise not.
(b) HGP is closely associated with the development of new era of biology called as Bioinformatics.
(c) The values like humility, sense of responsibility awareness and tendency to help the needy persons were shown by Nisha a close friend of Garima.

21.

(a) A-Template strand = 1
B-Coding strand =1
Template strand has polarity 3'-5'
Coding strand has polarity 5'-3'
On the basis of polarity with respect to promoter
(b) In initiation sigma factor associates with RNA polymerase to initiate transcription, Rho factor gets associated to RNA polymerase to terminate transcription.
(e) RNA polymerase I -Transcribes -RNAs
RNA polymerase III-Transcribes tRNA / 5srRNA/5nRNA
(OR)
Prokaryotes : Negatively charged DNA, is held with positively charged proteins, in nucleoid, DNA in nucleoid is organised in large loops held by protein.
Eukaryotes : In nucleus the negatively charged DNA, is wrapped around positively charged histone octomer, to formnucleosome, nucleosomes are repeated, to constitute chromatin, at higher level additional set of non-histone chromosomal protein gets associated with chromatin.

22.

(i) DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA.
(iii) Applications of DNA fingerprinting are:
(a) as a tool in forensic investigation.
(b) to settle paternity disputes.
(iv) The judge showed wisdom and intention to search the truth.