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# Biology : Molecular Basis of Inheritance

#### Multiple Choice Questions

21.

Which of the following constitute about 10-20% of total circular RNA?

• m-RNA

• r -RNA

• t-RNA

• hn -RNA

C.

t-RNA

Transfer RNA (t-RNA) constitute about 10-20% of total cellular RNA. Since t-RNA are difficult to be separated by ultra- centrifugation, they are also called as soluble RNA (s-RNA).

22.

In DNA, which is absent ?

• Guanine

• Uracil

• Cytosine

C.

Uracil

Uracil is absent in DNA. It is present in RNA, instead of thymine.

In DNA, adenine and guanine are purines and thymine and cytosine are pyrimidines.

In RNA, uracil and cytosine makes pyrimidine.

23.

DNA replication generally proceeds in a

• $\to$3 direction

• $\to$5 direction

• $\to$3 direction

• $\to$5 direction

A.

$\to$3 direction

DNA is made up of double helix of two complementary strands. Both the strands get seperated during replication. Each strand of the original DNA molecule then serves as a template for the production of its counterpart, hence, a process is known as semi- conservative replication.

DNA synthesis or replication always proceeds in 5' $\to$3' direction because DNA polymerase acts on the 3'- OH of the existing strand for adding the free nucleotides.

24.

Assertion : Replication and transcription occur in the nucleus but translation occurs in the cytoplasm.

Reason : mRNA is transferred from the nucleus into the cytoplasm where ribosomes and amino acids are available for protein synthesis.

• If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

• If both Assertion and Reason are true but the Reason is not the correct explanation of the assertion

• If Assertion is true but Reason is false

• If both Assertion and Reason are false

A.

If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

DNA replication is the process of forming a copy of DNA. Transcription is the formation of RNA over DNA template. They both occur in nucleus as the required material DNA and RNA are present in the nucleus.

Translation is the process of protein synthesis. It is separated from transcription in both space and time. It prevents the intermixing of raw materials, protect DNA from respiratory enzymes and ribosomal machinery from nuclease.

25.

Mutation is more common when it is present in:

• dominant condition

• recessive condition

• constant in population

• none of the above

A.

dominant condition

Mutation is present in dominant condition because dominant mutant gene can express in both homozygous and heterozygous condition. While recessive gene can express only in homozygous condition.

26.

In DNA, which is absent :

• Thymine

• Guanine

• Uracil

D.

Uracil

Uracil is absent in DNA. It is present in RNA, instead of thymine.

In DNA, adenine and guanine are purines and thymine and cytosine are pyrimidines.

In RNA, uracil and cytosine makes pyrimidine.

27.

Which organism was used by Beadle and Tatum to proposed one gene-one enzyme hypothesis ?

• E. coli

• Nostoc

• Drosophila

• Neurospora

D.

Neurospora

G.W. Beadle and E.L. Tatum demonstrated by the biochemical mutation experiment in Neurospora that genes express themselves through synthesis of enzymes. They proposed a concept called "one gene-one enzyme hypothesis".

28.

Sequence of DNA (Non- coding) is known as:

• exon

• intron

• cistron

• none

B.

intron

Intrans are DNA sequence lying within a coding sequence, i.e. Exons but not usually encoding cell product and resulting so called split genes cistron is a segment of linear DNA encoding a specific and functional product, usually protein.

29.

Which is called soluble RNA ?

• rRNA

• tRNA

• mRNA

• hnRNA

B.

tRNA

There are following three types of cellular RNA

(1) Transfer RNA or soluble RNA

(2) Messnger RNA or template RNA

(3) Ribosomal RNA

Transfer RNA (t-RNA) and messenger RNA (m-RNA) are synthesized on DNA template of chromosomes while ribosomal RNA (r-RNA) is derived from nucleolale DNA.

30.

What's the difference between RNA and DNA?

• Base

• Sugar

• Sugar and base

• Phosphate

C.

Sugar and base

DNA has deoxy ribose pentose sugar and four nitrogenous bases i.e. Adenine (A), Guanine (G), both are purines; Cytosine (C) and Thymine (T), both are pyrimidines.

RNA has ribose pentose sugar and four nitrogenous bases as in DNA except Uracil (U) in place of Thymine (T).