A mutant i gene of E. coli makes a repressor that still binds the operator but can no longer bind the inducer. What happens when this cell is grown with lactose as its only sugar?

The structural genes stay repressed although lactose is present

The structural genes are transcribed even after lactose is used up

The operator is deleted and the repressor is no longer made

Only gene z is transcribed while y and a stay off

Molecular Basis of Inheritance

27 NEET-UG practice questions on Molecular Basis of Inheritance, part of Botany. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Arrange these levels of DNA packaging from the simplest to the most condensed. A. Chromatin fibre B. Metaphase chromosome C. Nucleosome D. Beads-on-string structure
1. AC, A, D, B
2. BD, C, A, B
3. CC, D, A, B
4. DA, C, D, B
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Answer: C · C, D, A, B
DNA wrapped on a histone octamer forms the nucleosome. Repeating nucleosomes look like beads on a string, this packs into chromatin fibres, and the fibres coil and condense into chromosomes at metaphase.
- A: The fibre forms by packing the beads-on-string structure.
- B: The string of beads is made of nucleosomes, so these cannot be reversed.
- D: The nucleosome is the first level, not the fibre.
Remember this
Nucleosome, beads-on-string, chromatin fibre, metaphase chromosome; the higher levels need non-histone chromosomal proteins.
Question 2 · Hard
A mutant i gene of E. coli makes a repressor that still binds the operator but can no longer bind the inducer. What happens when this cell is grown with lactose as its only sugar?
1. AThe structural genes are transcribed even after lactose is used up
2. BThe operator is deleted and the repressor is no longer made
3. COnly gene z is transcribed while y and a stay off
4. DThe structural genes stay repressed although lactose is present
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Answer: D · The structural genes stay repressed although lactose is present
The inducer normally binds the repressor and frees the operator. A repressor that cannot bind the inducer stays on the operator, so RNA polymerase cannot transcribe z, y and a.
- A: This describes a repressor that cannot bind the operator.
- B: A change in the repressor protein does not delete the operator.
- C: Genes z, y and a are transcribed together as one polycistronic unit.
Remember this
Inducer inactivates repressor; repressor deaf to inducer means permanently off, repressor unable to bind operator means permanently on.
Question 3 · Easy
In a nucleoside, the nitrogenous base is joined to the pentose sugar by which linkage?
1. APhosphoester linkage
2. BHydrogen bond
3. CPhosphodiester linkage
4. DN-glycosidic linkage
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Answer: D · N-glycosidic linkage
A nitrogenous base joins the 1' carbon of the pentose through an N-glycosidic linkage, forming a nucleoside. A phosphate added at the 5'-OH by a phosphoester linkage then gives a nucleotide.
- A: This bond joins phosphate to the 5'-OH of the sugar.
- B: These bonds join bases of opposite strands.
- C: This bond joins two nucleotides in a strand.
Remember this
Base to sugar is N-glycosidic, sugar to phosphate is phosphoester, nucleotide to nucleotide is 3'-5' phosphodiester.
Question 4 · Medium
Arrange these steps of DNA fingerprinting in the correct order. A. Digestion of DNA by restriction endonucleases B. Hybridisation with a labelled VNTR probe C. Transfer of DNA fragments to a nitrocellulose or nylon membrane D. Separation of DNA fragments by electrophoresis
1. AA, D, C, B
2. BA, D, B, C
3. CD, A, C, B
4. DA, C, D, B
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Answer: A · A, D, C, B
After isolation, DNA is cut, the fragments are separated by size, then blotted to a membrane, and then hybridised with the VNTR probe. Autoradiography then shows the bands.
- B: The probe is applied on the membrane, after blotting.
- C: Fragments must exist before they can be separated.
- D: Blotting cannot come before the fragments are separated.
Remember this
Isolate, digest, electrophorese, blot, hybridise with VNTR probe, autoradiograph.
Question 5 · Hard
Which of these are salient findings of the Human Genome Project? A. Less than 2 per cent of the genome codes for proteins. B. The human genome contains 3164.7 million nucleotide bases. C. Functions are known for nearly all the genes discovered. D. Dystrophin, at 2.4 million bases, is the largest known human gene.
1. AA and D only
2. BA, B and D only
3. CA, B and C only
4. DB, C and D only
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Answer: B · A, B and D only
A, B and D are stated findings. C is wrong because the functions are unknown for over 50 per cent of the discovered genes.
- A: This omits B, which is correct.
- C: This includes C, though over half the gene functions are unknown.
- D: This includes C and drops A, which is correct.
Remember this
Under 2% codes for protein, about 30,000 genes, functions unknown for over 50%, dystrophin largest, 99.9% of bases identical between people.
Question 6 · Medium
Match List-I with List-II. List-I (enzyme or factor) A. RNA polymerase I B. RNA polymerase II C. RNA polymerase III D. Sigma factor List-II (role) I. Transcribes hnRNA II. Transcribes tRNA and 5S rRNA III. Transcribes 28S, 18S and 5.8S rRNA IV. Initiates transcription in bacteria
1. AA-I, B-III, C-II, D-IV
2. BA-III, B-II, C-I, D-IV
3. CA-III, B-I, C-II, D-IV
4. DA-II, B-I, C-III, D-IV
Answer and explanation in LearnFree account
Question 7 · Easy
Which factor associates transiently with bacterial RNA polymerase to end transcription?
1. ADNA ligase
2. BRelease factor
3. CRho factor
4. DSigma factor
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Question 8 · Medium
Match List-I with List-II. List-I (term) A. Anticodon loop B. Amino acid acceptor end C. Untranslated region D. Aminoacylation List-II (description) I. Part of tRNA that holds the amino acid II. Part of tRNA whose bases pair with the mRNA codon III. Linking an amino acid to its tRNA using ATP IV. Part of mRNA needed for efficient translation
1. AA-II, B-I, C-IV, D-III
2. BA-I, B-II, C-IV, D-III
3. CA-II, B-IV, C-I, D-III
4. DA-II, B-I, C-III, D-IV
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Question 9 · Easy
Histones can bind tightly to DNA because they are rich in which amino acids?
1. AGlycine and alanine
2. BAspartate and glutamate
3. CLysine and arginine
4. DTryptophan and phenylalanine
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Question 10 · Medium
Given below are two statements: Statement I: Treating the purified S-strain extract with DNase stopped the change of R strain into S strain. Statement II: Treating the purified S-strain extract with proteases or RNases also stopped this change. Choose the correct answer.
1. ABoth Statement I and Statement II are incorrect
2. BStatement I is correct but Statement II is incorrect
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are correct
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Question 11 · Medium
Given below are two statements: Statement I: In eukaryotes, RNA polymerase II transcribes the precursor of mRNA, called hnRNA. Statement II: Tailing adds 200-300 adenylate residues at the 3' end of hnRNA without a DNA template. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is incorrect but Statement II is correct
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are incorrect
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Question 12 · Hard
A DNA molecule is 6.8 mm long and is fully packed into nucleosomes of 200 bp each. Take the distance between adjacent base pairs as 0.34 nm. About how many nucleosomes does it form?
1. A1 × 10⁵
2. B2 × 10⁵
3. C2 × 10⁷
4. D1 × 10⁴
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Question 13 · Easy
For which of these mRNA codons does a cell carry no matching tRNA?
1. AUUU
2. BGUG
3. CAUG
4. DUGA
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Question 14 · Medium
Which of these statements about the genetic code are correct? A. Codons are read in a contiguous manner without punctuation. B. A single codon may specify more than one amino acid. C. Some amino acids are coded by more than one codon. D. AUG codes for methionine and also acts as the initiator codon.
1. AB, C and D only
2. BA, B and D only
3. CA and C only
4. DA, C and D only
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Question 15 · Medium
Assertion A: Viruses with an RNA genome and a short life span mutate and evolve faster. Reason R: RNA is chemically more stable than DNA. Choose the correct answer.
1. ABoth A and R are correct but R is not the correct explanation of A
2. BA is not correct but R is correct
3. CBoth A and R are correct and R is the correct explanation of A
4. DA is correct but R is not correct
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Question 16 · Medium
Match List-I with List-II. List-I (workers) A. Griffith B. Hershey and Chase C. Meselson and Stahl D. Taylor and colleagues List-II (experimental material) I. Bacteriophage labelled with ³²P and ³⁵S II. Vicia faba with radioactive thymidine III. Streptococcus pneumoniae injected into mice IV. E. coli with ¹⁵N and a CsCl density gradient
1. AA-III, B-I, C-II, D-IV
2. BA-I, B-III, C-IV, D-II
3. CA-III, B-I, C-IV, D-II
4. DA-III, B-IV, C-I, D-II
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Question 17 · Easy
The y gene of the lac operon codes for which protein?
1. ARepressor
2. BPermease
3. CBeta-galactosidase
4. DTransacetylase
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Question 18 · Easy
According to the Human Genome Project, which human chromosome carries the fewest genes?
1. AX
2. B1
3. C21
4. DY
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Question 19 · Medium
The template strand of a short gene reads 3'-TACCGATTC-5'. Which mRNA is transcribed from it?
1. A5'-AUGGCUAAG-3'
2. B5'-UACCGAUUC-3'
3. C3'-AUGGCUAAG-5'
4. D5'-ATGGCTAAG-3'
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Question 20 · Medium
Assertion A: On a replication fork, one new strand is made continuously and the other discontinuously. Reason R: DNA-dependent DNA polymerase catalyses polymerisation only in the 5'→3' direction. Choose the correct answer.
1. ABoth A and R are correct but R is not the correct explanation of A
2. BA is correct but R is not correct
3. CA is not correct but R is correct
4. DBoth A and R are correct and R is the correct explanation of A
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Question 21 · Medium
A deletion removes exactly one complete codon, in frame, from the middle of a gene. What is the expected effect on the protein?
1. AIt loses one amino acid and the frame after the deletion stays the same
2. BAll amino acids after the deletion change because the frame shifts
3. COne amino acid is replaced by another and the length stays the same
4. DTranslation fails because the start codon is lost
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Question 22 · Medium
E. coli grown for many generations in ¹⁵NH₄Cl is transferred to medium with ¹⁴NH₄Cl. Its generation time is 20 minutes. In the DNA extracted after 60 minutes, what is the ratio of hybrid to light molecules?
1. A1 : 1
2. B1 : 7
3. C1 : 3
4. D3 : 1
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Question 23 · Medium
Given below are two statements: Statement I: A bacterial mRNA must have its introns spliced out before it can be translated. Statement II: In bacteria, transcription and translation can be coupled because both occur in the same compartment. Choose the correct answer.
1. AStatement I is correct but Statement II is incorrect
2. BBoth Statement I and Statement II are correct
3. CBoth Statement I and Statement II are incorrect
4. DStatement I is incorrect but Statement II is correct
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Question 24 · Hard
A bacterial mRNA is 1000 nucleotides long: a 60-nucleotide 5' UTR, 900 nucleotides from AUG to UAA inclusive, and a 40-nucleotide 3' UTR. How many amino acids does the newly formed polypeptide have?
1. A300
2. B299
3. C298
4. D333
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Question 25 · Medium
Match List-I with List-II. List-I (segment in the figure) A. Segment K B. Segment L C. Segment M D. Segment N List-II (role) I. Binding site of the repressor II. Binding site of RNA polymerase III. Gene coding for the repressor IV. Gene coding for β-galactosidase
Figure: MedExams
1. AA-IV, B-II, C-I, D-III
2. BA-II, B-III, C-I, D-IV
3. CA-III, B-I, C-II, D-IV
4. DA-III, B-II, C-I, D-IV
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2 more Molecular Basis of Inheritance questions

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Study Botany

Molecular Basis of Inheritance

Arrange these levels of DNA packaging from the simplest to the most condensed. A. Chromatin fibre B. Metaphase chromosome C. Nucleosome D. Beads-on-string structure

A mutant i gene of E. coli makes a repressor that still binds the operator but can no longer bind the inducer. What happens when this cell is grown with lactose as its only sugar?

In a nucleoside, the nitrogenous base is joined to the pentose sugar by which linkage?

Arrange these steps of DNA fingerprinting in the correct order. A. Digestion of DNA by restriction endonucleases B. Hybridisation with a labelled VNTR probe C. Transfer of DNA fragments to a nitrocellulose or nylon membrane D. Separation of DNA fragments by electrophoresis

Match List-I with List-II. List-I (enzyme or factor) A. RNA polymerase I B. RNA polymerase II C. RNA polymerase III D. Sigma factor List-II (role) I. Transcribes hnRNA II. Transcribes tRNA and 5S rRNA III. Transcribes 28S, 18S and 5.8S rRNA IV. Initiates transcription in bacteria

Which factor associates transiently with bacterial RNA polymerase to end transcription?

Histones can bind tightly to DNA because they are rich in which amino acids?

Given below are two statements: Statement I: Treating the purified S-strain extract with DNase stopped the change of R strain into S strain. Statement II: Treating the purified S-strain extract with proteases or RNases also stopped this change. Choose the correct answer.

Given below are two statements: Statement I: In eukaryotes, RNA polymerase II transcribes the precursor of mRNA, called hnRNA. Statement II: Tailing adds 200-300 adenylate residues at the 3' end of hnRNA without a DNA template. Choose the correct answer.

A DNA molecule is 6.8 mm long and is fully packed into nucleosomes of 200 bp each. Take the distance between adjacent base pairs as 0.34 nm. About how many nucleosomes does it form?

For which of these mRNA codons does a cell carry no matching tRNA?

Assertion A: Viruses with an RNA genome and a short life span mutate and evolve faster. Reason R: RNA is chemically more stable than DNA. Choose the correct answer.

The y gene of the lac operon codes for which protein?

According to the Human Genome Project, which human chromosome carries the fewest genes?

The template strand of a short gene reads 3'-TACCGATTC-5'. Which mRNA is transcribed from it?

Assertion A: On a replication fork, one new strand is made continuously and the other discontinuously. Reason R: DNA-dependent DNA polymerase catalyses polymerisation only in the 5'→3' direction. Choose the correct answer.

A deletion removes exactly one complete codon, in frame, from the middle of a gene. What is the expected effect on the protein?

E. coli grown for many generations in ¹⁵NH₄Cl is transferred to medium with ¹⁴NH₄Cl. Its generation time is 20 minutes. In the DNA extracted after 60 minutes, what is the ratio of hybrid to light molecules?

Given below are two statements: Statement I: A bacterial mRNA must have its introns spliced out before it can be translated. Statement II: In bacteria, transcription and translation can be coupled because both occur in the same compartment. Choose the correct answer.

A bacterial mRNA is 1000 nucleotides long: a 60-nucleotide 5' UTR, 900 nucleotides from AUG to UAA inclusive, and a 40-nucleotide 3' UTR. How many amino acids does the newly formed polypeptide have?

Match List-I with List-II. List-I (segment in the figure) A. Segment K B. Segment L C. Segment M D. Segment N List-II (role) I. Binding site of the repressor II. Binding site of RNA polymerase III. Gene coding for the repressor IV. Gene coding for β-galactosidase