Q.1 Which nitrogenous base is found in RNA but not in DNA?
Thymine
Adenine
Uracil
Guanine
Explanation - RNA contains uracil (U) instead of thymine (T), which is present in DNA.
Correct answer is: Uracil
Q.2 Which type of bond connects the sugar and phosphate groups in the DNA backbone?
Hydrogen bond
Phosphodiester bond
Peptide bond
Glycosidic bond
Explanation - Phosphodiester bonds connect the 5' phosphate of one nucleotide to the 3' hydroxyl group of the next nucleotide, forming the DNA backbone.
Correct answer is: Phosphodiester bond
Q.3 Who are credited with the discovery of the double helical structure of DNA?
Watson and Crick
Hershey and Chase
Meselson and Stahl
Franklin and Wilkins
Explanation - James Watson and Francis Crick proposed the double helix model of DNA in 1953, based on X-ray diffraction data from Rosalind Franklin.
Correct answer is: Watson and Crick
Q.4 Which enzyme is responsible for synthesizing RNA from a DNA template?
DNA polymerase
RNA polymerase
Ligase
Helicase
Explanation - RNA polymerase synthesizes RNA by reading the DNA template during transcription.
Correct answer is: RNA polymerase
Q.5 What is the directionality of DNA strands?
5' to 3'
3' to 5'
Both strands are random
No directionality
Explanation - DNA strands have directionality due to the orientation of the sugar-phosphate backbone; nucleotides are added in the 5' to 3' direction.
Correct answer is: 5' to 3'
Q.6 Which process converts RNA into a polypeptide chain?
Replication
Transcription
Translation
Splicing
Explanation - Translation is the process where ribosomes read mRNA and synthesize proteins (polypeptide chains) based on the codons.
Correct answer is: Translation
Q.7 Which molecule carries amino acids to the ribosome during translation?
mRNA
tRNA
rRNA
snRNA
Explanation - Transfer RNA (tRNA) carries specific amino acids to the ribosome and matches its anticodon to the mRNA codon.
Correct answer is: tRNA
Q.8 In eukaryotes, where does transcription occur?
Cytoplasm
Mitochondria
Nucleus
Ribosome
Explanation - In eukaryotic cells, transcription occurs in the nucleus where DNA is located. The resulting RNA is then processed and exported to the cytoplasm.
Correct answer is: Nucleus
Q.9 Which form of DNA is the most common under physiological conditions?
A-DNA
B-DNA
Z-DNA
C-DNA
Explanation - B-DNA is the classic right-handed double helix and the most common form of DNA in living cells.
Correct answer is: B-DNA
Q.10 Which technique is used to amplify DNA fragments?
Southern blotting
PCR
Gel electrophoresis
Western blotting
Explanation - Polymerase Chain Reaction (PCR) is used to amplify specific DNA sequences exponentially.
Correct answer is: PCR
Q.11 Which type of RNA forms the structural and functional components of ribosomes?
mRNA
tRNA
rRNA
miRNA
Explanation - Ribosomal RNA (rRNA) combines with proteins to form the ribosome, which is the site of protein synthesis.
Correct answer is: rRNA
Q.12 Which statement about the genetic code is true?
It is universal
It is overlapping
It is ambiguous
It only codes for proteins in humans
Explanation - The genetic code is nearly universal across all organisms and is non-overlapping and unambiguous.
Correct answer is: It is universal
Q.13 Which enzyme relieves supercoiling during DNA replication?
Helicase
Topoisomerase
DNA polymerase
Ligase
Explanation - Topoisomerase prevents DNA from becoming overly coiled ahead of the replication fork by creating temporary breaks in the DNA strands.
Correct answer is: Topoisomerase
Q.14 What is the function of DNA ligase?
Separates DNA strands
Joins Okazaki fragments
Synthesizes RNA
Proofreads DNA
Explanation - DNA ligase seals nicks between Okazaki fragments during lagging-strand DNA synthesis, forming a continuous DNA strand.
Correct answer is: Joins Okazaki fragments
Q.15 Which of the following is a purine base?
Cytosine
Thymine
Adenine
Uracil
Explanation - Purines are double-ringed nitrogenous bases: adenine (A) and guanine (G). Cytosine, thymine, and uracil are pyrimidines.
Correct answer is: Adenine
Q.16 Which technique separates nucleic acids based on size?
PCR
Gel electrophoresis
Northern blot
DNA sequencing
Explanation - Gel electrophoresis separates nucleic acids by size and charge using an electric field.
Correct answer is: Gel electrophoresis
Q.17 Which of the following statements is true about prokaryotic mRNA?
It is monocistronic
It is polycistronic
It has a 5' cap
It undergoes splicing
Explanation - Prokaryotic mRNA often codes for multiple proteins from a single transcript (polycistronic), unlike eukaryotic mRNA which is usually monocistronic.
Correct answer is: It is polycistronic
Q.18 Which molecule provides energy for translation?
ATP
GTP
CTP
UTP
Explanation - GTP is hydrolyzed to provide energy for various steps in translation, including initiation, elongation, and termination.
Correct answer is: GTP
Q.19 Which type of RNA is involved in RNA interference?
tRNA
rRNA
miRNA
mRNA
Explanation - MicroRNAs (miRNAs) regulate gene expression by binding to target mRNA, leading to its degradation or translational inhibition.
Correct answer is: miRNA
Q.20 What is the main difference between DNA replication in prokaryotes and eukaryotes?
Prokaryotes have multiple origins
Eukaryotes have multiple origins
Only prokaryotes have Okazaki fragments
Only eukaryotes have leading and lagging strands
Explanation - Eukaryotic chromosomes are large, so replication starts at multiple origins to speed up DNA synthesis. Prokaryotic DNA has a single origin.
Correct answer is: Eukaryotes have multiple origins
Q.21 Which experiment demonstrated that DNA is the genetic material?
Griffith's experiment
Hershey-Chase experiment
Meselson-Stahl experiment
Avery-MacLeod-McCarty experiment
Explanation - The Hershey-Chase experiment using bacteriophages showed that DNA, not protein, carries genetic information.
Correct answer is: Hershey-Chase experiment
Q.22 What is the role of snRNA in eukaryotic cells?
Ribosome assembly
Splicing of pre-mRNA
Translation of mRNA
Replication of DNA
Explanation - Small nuclear RNAs (snRNAs) are part of the spliceosome, which removes introns from pre-mRNA during RNA processing.
Correct answer is: Splicing of pre-mRNA
Q.23 Which type of mutation does not change the amino acid sequence of a protein?
Missense mutation
Nonsense mutation
Silent mutation
Frameshift mutation
Explanation - Silent mutations involve a nucleotide change that does not alter the encoded amino acid due to the redundancy of the genetic code.
Correct answer is: Silent mutation
Q.24 Which of the following is true about telomeres?
They code for essential proteins
They prevent chromosomal shortening
They initiate DNA replication
They are only found in prokaryotes
Explanation - Telomeres are repetitive sequences at chromosome ends that protect chromosomes from loss of important DNA during replication.
Correct answer is: They prevent chromosomal shortening