6

Q1. Initiation codon for methionine is

• AAA
• UUU
• UAA
• AUG

Solution

ATG and AUG denote sequences of DNA and RNA, respectively, which are the start codon or initiation codon encoding the amino acid methionine (Met) in eukaryotes and a modified Met (fMet) in prokaryotes.

Q2. According to Chargaff's rule, which one is correct?

• [A] + [T] = [G] + [C]
• [A] + [C] = [G] + [T]
• [A] + [G] = [T] + [C]
• All  of these

Solution

The purines and pyrimidines are always in equal amounts, i.e. A + G = T + C

Q3. The coding segment of DNA is

• Exon
• Replicon
• Intron
• Muton

Solution

The coding sequences or expressed sequences are defined as exons which appear in mature or processed RNA. The exons are interrupted by introns.

Q4. DNA has genetic properties was revealed for the first time by

• Griffith
• Avery
• Wilkins
• Chargaff

Solution

In 1944, Avery, Macleod and McCarty separated the extract of smooth, virulent bacteria into protein and DNA, which gave evidence that DNA is the only genetic material in organisms.

Q5. Copying genetic information from one strand of DNA into RNA is

• Translation
• Transcription
• Transformation
• Transduction

Solution

DNA transcription is a process which involves transcribing genetic information from DNA to RNA.

Q6. The enzyme needed in biological systems for joining two molecules is called

• Ligase
• Diastases
• Polymerase
• Hydrolase

Solution

Ligase is an enzyme which can catalyse the joining of two large molecules. Diastase enzyme is known for breaking down any form of starch. Polymerase synthesises polymers of nucleic acids. Hydrolase catalyses the hydrolysis of proteins and nucleic acids. 

Q7. Semi-conservative replication of DNA was first demonstrated in

• Drosophila melanogaster
• Escherichia coli
• Streptococcus pneumoniae
• Salmonella typhimurium

Solution

Meselson and Stahl first showed semiconservative replication in Escherichia coli and subsequently in higher organisms.

Q8. The main aim of the human genome project is

• To introduce new genes into humans
• To identify and sequence all the genes present in human DNA
• To develop better techniques for comparing two different human DNA samples
• To remove disease-causing genes from human DNA

Solution

The main goal of the human genome project is to fully map and sequence all of the genetic material of humans. The human genome project is used to attain information of the human genes and their sequences. 

Q9. Which of the following is a structural subunit of DNA?

• Protein
• Carbohydrate
• RNA
• Nucleotides

Solution

Nucleotides make up the structural subunit of DNA, which in turn makes three subunits - a phosphate group, a 5-carbon sugar (deoxyribose) and a nitrogen base.

Q10. The human chromosome which has the least number of functional genes is

• Chromosome X
• Chromosome Y
• Chromosome 1
• Chromosome 12

Solution

In the human chromosomes, chromosome 1 has the highest number of genes, while chromosome Y has the lowest number of genes.

Q11. The beginning of understanding genetic transformation in bacteria was made by

• Frederick Griffith
• Hershey and Chase
• Watson and Crick
• T. H. Morgan

Solution

Frederick Griffith witnessed genetic transformation in Streptococcus pneumoniae.

Q12. Nitrogenous bases present in DNA:

• Adenine, guanine, cytosine, thymine
• Adenine, guanine, cytosine, uracil
• Adenine, thymine, uracil
• Guanine, uracil

Solution

The nitrogenous bases consist of purines (adenine, guanine) and pyrimidines (cytosine, thymine and uracil).

Q13. To initiate translation, the mRNA first binds to

• The smaller ribosomal sub-unit
• The larger ribosomal sub-unit
• The whole ribosome
• No such specificity exists

Solution

The first step of the initiation stage of translation is the binding of mRNA to the small ribosomal subunit through base pairing with appropriate sequences on rRNA.

Q14. The vectors used in the Human Genome Project for cloning segments of the human DNA were

• BACs
• YACs
• Both BACs and YACs
• T4 phages

Solution

For the cloning of human DNA, both bacterial and yeast host cells were used. The cloning vectors used were BACs (bacterial artificial chromosomes) and YACs (yeast artificial chromosomes).

Q15. The study of migration patterns of human beings over a long period of time is known as

• Demography
• Genography
• Population genetics
• Migration prediction

Solution

The study of migration patterns of human beings over a long period of time is known as genography.

Q16. In a DNA molecule, the distance between two bases is

• 2 nm/20 A
• 0.2 nm/2 A
• 3.4 nm/34 A
• 0.34 nm/3.4 A

Solution

One complete turn of the helix is 3.4 nm and has 10 base pairs. The bases face the interior of the double helix and are attacked at the 0.34 nm (3.4 A°) position.

Q17. Removal of the introns and joining of the exons in a defined order in a transcription unit is called

• Splicing
• Tailing
• Transformation
• Capping

Solution

Splicing is the modification of the ongoing process of synthesis of a polypeptide chain by removal of introns and joining of exons.

Q18. In genetic fingerprinting, the 'probe' refers to

• A radioactively labelled single-stranded DNA molecule
• A radioactively labelled single-stranded RNA molecule
• A radioactively labelled double-stranded RNA molecule
• A radioactively labelled double-stranded DNA molecule

Solution

The DNA probe is when one strand or a piece of DNA molecule is used in laboratory experiments. This is to search for the availability of a complementary sequence in a combination of different other single-stranded DNA molecules. In DNA fingerprinting, these probes are made radioactive. 

Q19. Which of the following statements is the most appropriate for sickle cell anaemia?

• It cannot be treated with iron supplements.
• It is a molecular disease.
• It confers resistance to acquiring malaria.
• All of the above.

Solution

Sickle cell disease is caused by a genetic abnormality in the gene for haemoglobin, which results in the production of sickle haemoglobin.

Q20. The prokaryotic enzyme which carries out the function of eukaryotic enzymes helicase and topoisomerase is

• Helix-stabilising protein
• Single-stranded DNA-binding protein
• Gyrase
• Replicase

Solution

The prokaryotic enzyme gyrase does the work of helicase and topoisomerase.

Q21. Hargobind Khorana got the Nobel Prize for

• Gene synthesis
• Determining genetic code
• Producing disease-resistant maize
• Discovery of transposons

Solution

Hargobind Khorana’s synthetic nucleic acids caused protein synthesis just as in the cell; comparing these proteins with the nucleic acid showed which portions of the nucleic acid were the codes for each part of the protein.   Marshall Nirenberg helped the code to be deciphered.   Barbara McClintock discovered transposons. 

Q22. A nucleoside differs from a nucleotide. It lacks the

• Base
• Sugar
• Phosphate group
• Hydroxyl group

Solution

A nucleoside differs from a nucleotide in that it lacks the phosphate group.

Q23. In Hershey and Chase experiments, radioactive ³²P was used to culture bacteriophages which resulted in radioactive

• Viral DNA
• Bacterial capsule
• Viral proteins
• Protein capsule of bacteriophage

Solution

Hershey and Chase conducted the experiment by using radioactive P32 which proved that only the bacteriophage DNA enters the bacterial cell resulting in viral DNA.

Q24. In the Lac operon system, β-galactosidase is coded by

• a-gene
• z-gene
• I-gene
• y-gene

Solution

The lac operon consists of one regulatory gene (i-gene) and three structural genes (z, y, a). z-gene codes for β-galactosidase (β-gal) which is responsible for the hydrolysis of the disaccharide lactose into its monomeric units galactose and glucose.

Q25. DNA replication requires the presence of which of the following ions?

• Magnesium
• Calcium
• Nitrogen
• Carbon

Solution

The replication of DNA requires DNA polymerase as well as the metal ions Mn⁺⁺ and Mg⁺⁺.

Q26. DNA polymerase which helps in DNA replication is of

• Two types
• Three types
• Four types
• Only one type

Solution

DNA polymerase is an enzyme which catalyses the polymerisation of deoxyribonucleotides into a DNA strand. DNA polymerases are best-known for their role in DNA replication. DNA polymerase I is an enzyme which participates in the process of DNA replication.

Q27. DNA contains nucleobases, sugar and phosphate. Removal of which among these from a DNA sample will not significantly affect the length of DNA?

• Nucleobases
• Sugar
• Phosphate
• None of the above

Solution

According to the DNA structure, the vertical bars of the ladder are formed of alternating phosphate and deoxyribose sugar components. So, the nucleobases depend on the width of the DNA.

Q28. Which enzyme helps in proofreading of DNA?

• Lipase
• Replicase
• Nuclease
• Helicase

Solution

Nuclease is an enzyme which cleaves off mutated regions of the DNA molecule during proofreading.

Q29. Locations on sites in the human DNA where single base DNA differences occurs are called

• Repetitive DNA
• VNTR
• SNP
• SSCP

Solution

Variations in DNA occur when a single nucleotide in the genome differs between members of a biological species or paired chromosomes called single nucleotide polymorphism.

Q30. Phages which show a lysogenic cycle are known as

• Lytic phages
• Temperate phages
• Virulent phages
• Avirulent phages

Solution

Temperate phages

Q31. RNA polymerase III catalyses the synthesis of which type of RNA molecule in eukaryotes?

• mRNA
• rRNA
• tRNA
• All RNA molecules

Solution

In eukaryotes, three different types of RNA polymerases are found. Each of these polymerases catalyses the formation of a different type of RNA molecule. RNA polymerase I catalyses the synthesis of rRNA, RNA polymerase II catalyses the synthesis of mRNA and RNA polymerase III catalyses the synthesis of tRNA.

Q32. Which of the following are the functions of RNA?

• It is a carrier of genetic information from DNA to ribosomes synthesising polypeptides.
• It carries amino acids to ribosomes.
• It is a constituent component of ribosomes.
• All of the above.

Solution

RNA is a type of nucleic acid which carries amino acids to ribosomes, and it also acts as genetic material.

Q33. The inducer for switching 'on' the lac operon in bacteria is

• Presence of lactose
• Number of bacteria
• Presence of structural genes in the bacteria
• Presence of sucrose

Solution

There are two types of operons - inducible operons and repressible operons. The inducible operon is switched on when an inducer is present. When lactose is added to an E. coli culture, the structural genes produce mRNA which synthesises specific polypeptides on the ribosomes.

Q34. Which of the following is not a requirement for the process of transcription?

• RNA polymerase
• Mg²⁺
• RNA primer
• DNA template

Solution

The process of transcription does not require the presence of a primer as RNA polymerase unlike DNA polymerase can synthesise an RNA molecule without the presence of a RNA primer.

Q35. During splicing, the exons are joined and the enzyme which catalyses this reaction is

• RNA ligase
• RNA catalase
• RNA permease
• RNA polymerase

Solution

Ribonucleases cleave the RNA and ligases join the exons, and the enzyme responsible in splicing is RNA ligase.

Q36. Retroviruses have genetic material

• DNA only
• RNA only
• DNA or RNA only
• Either DNA or RNA only

Solution

A retrovirus is an RNA virus which is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The genetic material of retroviruses consists of RNA instead of DNA.

Q37. A typical nucleosome contains

• 100 bp of DNA helix
• 200 bp of DNA helix
• 300 bp of DNA helix
• 400 bp of DNA helix

Solution

The nucleosome core particle consists of approximately 147 base pairs of DNA wrapped in superhelical turns around a histone octamer consisting of 2 copies each of the core histones H2A, H2B, H3 and H4 leading to 200 bp of DNA helix.

Q38. Out of 64 codons, the number of codons with GGG is

• 1
• 2
• 4
• 6

Solution

GGG codon codes for glycine, and only a single triplet is formed when the code is deciphered.

Q39. Which one of the following pairs of nitrogenous bases of nucleic acids is wrongly matched with the category mentioned against it?

• Guanine, adenine - purines
• Adenine, thymine - purines
• Thymine, uracil- pyrimidines
• Uracil, cytosine - pyrimidines

Solution

The purines consist of adenine and guanine, while the pyrimidines consist of thymine and cytosine. Thymine is replaced by uracil in RNA.

Q40. DNA replication in humans is

• Conservative
• Semi-conservative
• Semi-discontinuous
• Both semi-conservative and semi-discontinuous