Molecular Basis of Inheritance

Previous Years' CBSE Board Questions

5.1 The DNA

MCQ

L What would be the effect on histone proteins in the nucleus, on neutralisation of their positive charge?

1. They would bind the DNA tighter.
2. They would separate from DNA.
3. They would no longer attract each other.
4. They would cause supercoiling of DNA.

(Term I, 2021-22) U

2 A DNA molecule is 160 base pairs long. It has 30% guanine. How many adenine bases are present in this DNA molecule?

1. 48 (b) 64 (c) 96 (d) 192 (Term I, 2021-22) (Ey

How are the following formed and involved in

1. In prokaryotes like E.coli the DNA in the nucleoid DNA packaging in a nucleus of a cell?

region is organised as (i) Histone octamer

1. negatively charged DNA wrapped around (ii) Nucleosome

histone (iii) Chromatin

1. densely packed chromatin with NHC proteins
2. large loops held by the proteins
3. many repeating units of nucleosomes.

(Term I, 2021-22) R

VSA (1 mark)

(1 mark) VSA

1. Name the transcriptionally active region of chromatin in a nucleus. (Delhi 2015)
2. Name the negatively charged and positively charged components of a nucleosome. (Delhi 2015C)

SAI (2 marks)

1. Although a prokaryotic cell has no defined nucleus, yet DNA is not scattered throughout the cell. Explain. (2018)
2. Describe the structure of a nucleosome. (Delhi 2017)
3. What is central dogma? Who proposed it? (2/5, AI 2015C) R

(2020)

SA II (3 marks)

1. The length of DNA in any cell is far greater than the dimension of its nucleus. Explain how this enormous DNA is packaged in a eukaryotic cell. (2023)
2. A DNA segment has a total of 1000 nucleotides. out of which 240 are adenine containing nucleotides. How many pyrimidine bases this DNA segment possesses?
3. Draw a diagrammatic sketch of a portion of DNA segment to support your answer. (Delhi 2015)
4. (a) A DNA segment has a total of 1,500 nucleotides, out of which 410 are guanine containing

nucleotides. How many pyrimidine bases this

segment possesses?

1. Draw a diagrammatic sketch of a portion of DNA segment to support your answer. (Delhi 2015)
2. (a) A DNA segment has a total of 2,000 nucleotides, out of which 520 are adenine containing nucleotides. How many purine bases this DNA segment possesses?
3. Draw a diagrammatic sketch of a portion of DNA segment to support your answer.

(Delhi 2015) Ev

Draw a labelled diagram of a nucleosome. Where is it

found in a cell? (Foreign 2014)

LA (5 marks)

1. Differentiate between euchromatin and heterochromatin. (Delhi 2016)

5.2 The Search for Genetic Material

15. Why is RNA more reactive in comparison to DNA?

(Delhi 2015C)

SA II (3 marks)

Explain the discovery made by Hershey and Chase

using radioactive sulphur and phosphorus in their

experiment. (2020) R

Why is DNA a better genetic material when compared

to RNA? (Delhi 2015C) U

LA (5 marks)

1. Describe the experiment carried out by Hershey and Chase. Write the conclusion they arrived at.
2. (a) Explain Griffith's 'transforming principle' experiment.
3. In the above experiment, "heat which killed one type of bacteria, did not destroy the properties of genetic material." Justify. (2019 C)
4. (a) State the 'central dogma' as proposed by Francis Crick. Are there any exceptions to it? Support your answer with a reason and an example.
5. Explain how the biochemical characterisation (nature) of 'Transforming Principle' was determined, which was not defined from Griffith's experiments. (2018)

1. List the criteria a molecule that can act as genetic material must fulfill. Which one of the criteria are best fulfilled by DNA or by RNA thus making one of them a better genetic material than the other? Explain. (Delhi 2016) U

1. Answer the following questions based on Hershey and Chase experiments:
2. Name the kind of virus they worked with and why?
3. Why did they use two types of culture media to grow viruses in? Explain.

(2023) R

1. What was the need for using a blender and later a centrifuge during their experiments?
2. State the conclusion drawn by them after the experiments. (Delhi 2016)
3. (a) Describe the series of experiments of F. Griffith. Comment on the significance of the results obtained.

Heat killed

S bacteria

Bacterial Filtrate

1. State the contribution of MacLeod, McCarty and Avery. (Al 2016)

RNase Protease DNase Lipase

How did Hershey and Chase established that DNA is transferred from virus to bacteria? (Delhi 2015)

1. (a) Describe the experiment which demonstrated the existence of "transforming principle".

1. How was the biochemical nature of this "transforming principle" determined by Avery, MacLeod and McCarty? (Foreign 2015) OR

R bacteria R bacteria R bacteria R bacteria

(live) (live) (live) (live)

No No

transformation Transformation transformation Transformation (a)

1. Describe the various steps of Griffith's experiments that led to the conclusion of the transforming principle. 40.0
2. How did the chemical nature of the transforming principle get established? (NCERT Exemplar, Al 2014)

How did Alfred Hershey and Martha Chase conclusively establish that DNA is the genetic material? Explain. (Foreign 2015) (d) DNA from tRNA. (2020) R OR Describe the Hershey and Chase experiment. Write the conclusion drawn by the scientist after their experiment. (AI 2014)

1. How did Griffith prove transforming principle in genetics? Explain the procedure. (Delhi 2015C)

5.4 Replication

MCQ

1. Given below is a list of steps Meselson and Stahl carried out in their experiment to prove that DNA replication is semi-conservative. Select the option that gives the correct sequence of steps followed by them.
2. Bacteria transferred to a N14 medium and sampled every 20 minutes.
3. All bacteria contain hybrid DNA (N14 DNA and N¹⁵ DNA).
4. Bacteria grown in N15 medium for many generations.
5. All bacteria contain N¹⁵ DNA.
6. Bacteria contain either all N14 DNA or all hybrid DNA.
7. (ii) → (iv) → (iii) → (i) → (v)
8. (i) → (ii) → (v) → (iv) → (iii)
9. <math>(iii) \rightarrow (iv) \rightarrow (i) \rightarrow (ii) \rightarrow (v)</math>
10. <math>(iv) \rightarrow (iii) \rightarrow (ii) \rightarrow (v) \rightarrow (i)</math>
11. Given below are the illustration of the different steps of experiments conducted by MacLeod, Mc Carty and Avery to find the chemical nature of the 'transforming principle' as DNA. Select the option that incorrectly depicts the step of the experiment.
12. Meselson and Stahl carried out centrifugation in CsCl₂ density gradient to separate:
13. DNA from RNA
14. DNA from protein
15. the normal DNA from 15N-DNA

VSA (1 mark)

31. Write the dual purpose served by deoxyribo-

nucleoside triphosphates in polymerisation. (2018)

Name the source of energy for the replication of DNA.

(1/3, Delhi 2015C)

Why is it not possible for an alien DNA to become

part of chromosome anywhere along its length and

replicate normally? (Al 2014)

What will happen if DNA replication is not followed

by cell division in a eukaryotic cell? (AI 2014C)

SAI (2 marks)

Discuss the role, the enzyme DNA ligase plays during

DNA replication. (Delhi 2016)

Show DNA replication with the help of a diagram

only. (Delhi 2014C)