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# Molecular Basis of Inheritance

#### Multiple Choice Questions

11.

Which type of DNA is found in bacteria

• Helical DNA

• Membrane bound DNA

• Straight DNA

• Circular free DNA

D.

Circular free DNA

Bacteria are prokaryotic in nature, in which typical chromosomes are lacking. DNA is circular and naked as it is not surrounded by histones (basic proteins which are responsible for coiled structure of nucleosome).

12.

Lac is obtained from :

• Laccifer

• Bombyx

• Dactylopius

• Lytta

A.

Laccifer

Lac is obtained fom Laccifer or Kerria lacca or lac insect that belongs to Phylum- Arthropoda.

13.

What is true about tRNA?

• It binds with an amino acid at it 3' end

• It has five double stranded regions

• It has a codon at one end which recognizes the anticodon on messenger RNA

• It looks like clover leafin the three dimensional structure

A.

It binds with an amino acid at it 3' end

tRNA has four recognition sites among these one is the amino acid attachment site. It has the amino acid attachment site with the 3' terminal - CCA sequence.

# 14.Which one of the following pairs is correctly matched with regard to the codon and the amino acid coded by itUUA - valine AUG - cysteine AAA - lysine CCC - alanine

C.

AAA - lysine

15.

DNA polymerase enzyme is required for synthesis of

• DNA from RNA

• RNA from DNA

• DNA from DNA

• RNA from RNA

C.

DNA from DNA

The enzyme needed for replication of DNA i.e. formation of DNA from DNA is DNA polymerase III. DNA replication is initiated by RNA primer which is later removed by DNA polymerase I.

16.

Which one of the following correctly represents the manner of replication of DNA?

D.

DNA replication is the process by which DNA makes a copy of itself during cell division. It takes place discontinuously. This process consists of 4 main steps:

1. Replication Fork formation
2. Primer binding
3. Elongation
4. Termination

Okazaki fragments are short sequences of DNA nucleotides which are synthesized discontinuously. One strand may synthesize a continuous strand. Both new strands are synthesized in 5' $\to$3' direction. Thus one strand is synthesized forwards and the other backwards.

17.

Mutations which alter nucleotide sequence within a gene are :

• frame shift mutations

• base pair substitutions

• both 'a' and 'b'

• none of these

A.

frame shift mutations

Gene mutation or point mutation is the result of a change in the nucleotide sequence of the DNA molecule in a particular region of the chromosome. It occurs in the form of duplication, insertion, deletion, inversion or substitution of bases. Frame- shift mutation is the addition or deletion of a base that may change the reading frame of nucleotide sequence.

Base pair substitution is a type of mutation involving replacement or substitution of a single nucleotide base with another in DNA or RNA molecule.

18.

Which one of the following pairs of terms/ names mean one and the same thing?

• Gene pool - genome

• Codon - gene

• Cistron - triplet

• DNA fingerprinting - DNA profiling

D.

DNA fingerprinting - DNA profiling

Gene pool is the total gene present in a population. Genome is the total genetic constitution of an organism. Codon is the basic unit of genetic code, a sequence of three adjacent nucleotide in DNA or mRNA that code for an amino acid. Gene is the basic unit of heredity; a sequence of DNA nucleotide that encodes a protein.

Cistron is a segment of DNA nucleotides that codes for a polypeptide chain. Triplet is a three nucleotides sequence coding for an amino acid.

Therefore, codon $\approx$ triplet
cistron $\approx$ gene
DNA fingerprinting is technically called DNA profiling or DNA typing.

19.

In split genes the coding sequences are called

• introns

• exons

• cistrons

• operons

B.

exons

Split genes were discovered by Phillip Sharp and Robert Richard. The part of DNA which express itself by making mRNA is called exon. One exon is separated from others by inactive part of DNA called intron. This is called split DNA.

20.

Which one of the following codons codes for the same information as UGC?

• UGU

• UGA

• UAG

• UGG

A.

UGU

UGU codes for the same information as UGC as both code for cystine. UGA and UAG are nonsense codons and UGG codes for tryptophan.