Molecular Basis of Inheritance

NEET Biology · 262 questions · Page 21 of 27 · Click an option or "Show Solution" to reveal answer

Q201

One gene -one enzyme hypothesis was postulated by

A Hershey and Chase

B A. Garrod

C Beadle and Tatum

D R. Franklin

Correct Answer

Option C

Solution

(c) Beadle & Tatum postulated the theory of One gene-one enzyme in which they stated that in any living cell there are number of genes present on chromosomes in a linear fashion.

One single gene controls the synthesis of one particular enzyme (or protein) in the cell which is responsible for its phenotypic character.

Q202

One gene-one enzyme relationship was established for the first time in

A Salmonella typhimurium

B Escherichia coli

C Diplocococcus pneumoniae

D Neurospora crassa.

Correct Answer

Option D

Solution

(d) It was given by geneticists George W.

Beadle and E.

Tatum, which states that each gene in an organism controls the production of a specific enzyme.

It is the enzyme that catalyses the reactions that lead to the phenotype of the organism.

Q203

The okazaki fragments in DNA chain growth

A polymerize in the

3^{\prime}

- to - 5 direction and forms replication fork

B prove semi-conservative nature of DNA replication

C polymerize in the

5^{\prime}

- to - 3 direction and explain 3 - to - 5 DNA replication

D result in transcription.

Correct Answer

Option C

Solution

Replication always occurs in 5-3 direction.

Okazaki fragments synthesised on 3-5 DNA template, join to form lagging strand.

Q204

Which one of the following also acts as a catalyst in a bacterial cell ?

A 5S rRNA

B sn RNA

C hn RNA

D 23s rRNA

Correct Answer

Option D

Solution

(d) 23S rRNA acts as a ribozyme (peptidyl transferase activity) in prokaryotic ribosomes.

Q205

In the DNA molecule, the nitrogenous bases pair specifically with each other through hydrogen bonds.

A the total amount of purine nucleotides and pyrimidine nucleotides is not always equal

B there are two strands which run antiparallel in the

5^{\prime} \to 3^{\prime}

direction

C the proportion of Adenine in relation to thymine varies with the organism

D there are two strands which run anti parallel one in

5^{\prime} \to 3^{\prime}

direction and other in

3^{\prime} \to 5^{\prime}

Correct Answer

Option D

Solution

(d) In the DNA molecule, there are two strands which run anti parallel, one is $5^{\prime}-3^{\prime}$ direction and the other in 3-5 direction.

The two strands are held together by hydrogen bonds between their bases.

Adenine (A), a purine of one chain is exactly opposite to thymine (T), a pyrimidine of the other chain.

Similarly, cytosine (C), a pyrimidine lies opposite to guanine (G), a purine.

This allows a sort of lock & key arrangement between large sized purine & small sized pyrimidine.

It is strengthened by the appearance of hydrogen bonds between the two.

Q206

Semi-conservative replication of DNA was first demonstrated in:

A Escherichia coli

B Streptococcus pneumoniae

C Salmonella typhimurium

D Drosophila melanogaster

Correct Answer

Option A

Solution

(a) Semiconservative replication of DNA was first demonstrated in Escherichia coli.

E. coli is a common type of bacteria that can get into food, like beef and vegetables.

The strange thing about these bacteria is that they are not always harmful to you.

E. coli normally lives inside your intestines, where it helps your body breakdown and digest the food you eat.

Q207

Which one of the following also acts as a catalyst in a bacterial cell ?

5S

rRNA

B sn RNA

C hn RNA

D 23s rRNA

Correct Answer

Option D

Solution

(d) $23 S$ rRNA acts as a catalyst in a eukaryotic cell.

Q208

In an inducible operon, the genes are

A Always expressed

B Usually not expressed unless a signal turns them on

C Usually expressed unless a signal turns them off

D Never expressed

Correct Answer

Option B

Solution

(b) Inducible operons are usually switched off.

This is a type of operon which is switched on when a chemical called inducer is present. the inducer is almost always a substrate.

Q209

Which enzymes will be produced in a cell in which there is a nonsense mutation in the lac Y gene?

A Lactose permease

B Transacetylase

C Lactose permease and transcetylase

\beta

- galactosidase

Correct Answer

Option D

Solution

(d) A nonsense mutation is the one which stops polypeptide synthesis due to formation of a terminating or nonsense codon e.g.

ATT (UAA), ATG (UAG), ACT (UGA).

The lactose or lac operon of Escherichia coli contains structural genes $(z, y, a)$ .

If y codes for termination of polypeptide chain then only the product of z gene transcribe to form $\beta$ galactosidase.

Q210

The diagram shows an important concept in the genetic implication of DNA. Fill in the blanks A to C.

A A-translation B - transciption C-Erwin Chargaff

B A-transcription B - translation C-Francis Crick

C A-translation B - extension C-Rosalind Franklin

D A-transcription B - replication C-James Watson

Correct Answer

Option B

Solution

(b) In this question A is transcription, B - translation and $C$ is Francis Crick (central dogma) It is unidirectional flow of information from DNA to mRNA (transcription) and then decoding the information present in mRNA in the formation of polypeptide chain or protein (translation).

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