Q.1 What is the basic unit of DNA?
Amino acid
Nucleotide
Polypeptide
Fatty acid
Explanation - DNA is composed of nucleotides, each consisting of a sugar, a phosphate group, and a nitrogenous base.
Correct answer is: Nucleotide
Q.2 Which enzyme is responsible for unzipping the DNA strands during replication?
Ligase
Polymerase
Helicase
Topoisomerase
Explanation - Helicase breaks the hydrogen bonds between DNA strands to initiate replication.
Correct answer is: Helicase
Q.3 What is the complementary base of adenine in DNA?
Thymine
Cytosine
Guanine
Uracil
Explanation - In DNA, adenine pairs with thymine via two hydrogen bonds.
Correct answer is: Thymine
Q.4 In RNA, which base replaces thymine?
Cytosine
Uracil
Adenine
Guanine
Explanation - RNA uses uracil instead of thymine to pair with adenine.
Correct answer is: Uracil
Q.5 What is the function of DNA polymerase?
Breaking DNA strands
Synthesizing new DNA
Carrying amino acids
Forming ribosomes
Explanation - DNA polymerase adds nucleotides to form the new DNA strand during replication.
Correct answer is: Synthesizing new DNA
Q.6 What type of bond connects base pairs in DNA?
Ionic bonds
Hydrogen bonds
Covalent bonds
Peptide bonds
Explanation - Hydrogen bonds connect complementary bases, allowing the double helix to unzip during replication.
Correct answer is: Hydrogen bonds
Q.7 Which of the following is a purine base?
Adenine
Cytosine
Thymine
Uracil
Explanation - Purines are adenine and guanine, larger double-ring bases.
Correct answer is: Adenine
Q.8 The Central Dogma of Molecular Biology states information flows from:
DNA → Protein → RNA
Protein → DNA → RNA
DNA → RNA → Protein
RNA → DNA → Protein
Explanation - Genetic information is transcribed from DNA to RNA and then translated into proteins.
Correct answer is: DNA → RNA → Protein
Q.9 Which enzyme seals gaps in the DNA backbone during replication?
Helicase
Ligase
Primase
Polymerase
Explanation - DNA ligase joins Okazaki fragments on the lagging strand.
Correct answer is: Ligase
Q.10 What is a codon?
A set of two bases
A triplet of bases in mRNA
A protein structure
A sugar molecule
Explanation - Each codon specifies one amino acid during translation.
Correct answer is: A triplet of bases in mRNA
Q.11 What is the start codon in mRNA translation?
AUG
UAA
UAG
UGA
Explanation - AUG codes for methionine and signals the start of translation.
Correct answer is: AUG
Q.12 What are Okazaki fragments?
DNA fragments on leading strand
RNA primers
Fragments on lagging strand
Pieces of RNA in nucleus
Explanation - The lagging strand is synthesized in short fragments called Okazaki fragments.
Correct answer is: Fragments on lagging strand
Q.13 Which organelle is primarily responsible for protein synthesis?
Nucleus
Ribosome
Mitochondria
Golgi apparatus
Explanation - Ribosomes translate mRNA into amino acid chains.
Correct answer is: Ribosome
Q.14 What type of RNA carries amino acids to the ribosome?
mRNA
tRNA
rRNA
snRNA
Explanation - tRNA carries amino acids and matches them to codons on mRNA.
Correct answer is: tRNA
Q.15 Which strand is synthesized continuously during DNA replication?
Lagging strand
Leading strand
Template strand
RNA strand
Explanation - The leading strand is synthesized continuously toward the replication fork.
Correct answer is: Leading strand
Q.16 What is the function of RNA polymerase?
Replicating DNA
Synthesizing RNA from DNA template
Transporting amino acids
Cutting DNA
Explanation - RNA polymerase transcribes DNA into RNA.
Correct answer is: Synthesizing RNA from DNA template
Q.17 Which nitrogenous base is unique to DNA?
Uracil
Cytosine
Thymine
Adenine
Explanation - Thymine is present only in DNA, while uracil replaces it in RNA.
Correct answer is: Thymine
Q.18 Which process converts mRNA into a protein?
Replication
Transcription
Translation
Splicing
Explanation - Translation occurs at ribosomes where amino acids are assembled into proteins based on mRNA.
Correct answer is: Translation
Q.19 The sugar in RNA is:
Deoxyribose
Glucose
Ribose
Sucrose
Explanation - RNA contains ribose sugar, while DNA contains deoxyribose.
Correct answer is: Ribose
Q.20 Which process produces an identical copy of DNA?
Replication
Transcription
Translation
Mutation
Explanation - Replication copies DNA so each daughter cell receives a complete genome.
Correct answer is: Replication
Q.21 Which RNA type is part of the ribosome structure?
mRNA
tRNA
rRNA
snRNA
Explanation - Ribosomal RNA forms the structural and catalytic components of ribosomes.
Correct answer is: rRNA
Q.22 Which bond connects nucleotides in the DNA backbone?
Hydrogen bonds
Covalent phosphodiester bonds
Ionic bonds
Disulfide bonds
Explanation - The sugar-phosphate backbone is held together by strong covalent phosphodiester bonds.
Correct answer is: Covalent phosphodiester bonds
Q.23 What is the role of primers in DNA replication?
They unzip DNA
They provide starting point for DNA polymerase
They join Okazaki fragments
They cut DNA
Explanation - Primase synthesizes RNA primers to allow DNA polymerase to begin elongation.
Correct answer is: They provide starting point for DNA polymerase
Q.24 What is an intron?
Coding sequence in mRNA
Non-coding sequence removed during splicing
A ribosomal protein
A tRNA binding site
Explanation - Introns are removed during RNA splicing, leaving exons that code for proteins.
Correct answer is: Non-coding sequence removed during splicing
Q.25 What is the main difference between prokaryotic and eukaryotic transcription?
Prokaryotes use introns
Eukaryotes lack RNA polymerase
Prokaryotic transcription occurs in cytoplasm, eukaryotic in nucleus
Prokaryotes use multiple RNA polymerases
Explanation - In prokaryotes, transcription and translation are coupled in the cytoplasm; in eukaryotes, transcription occurs in the nucleus.
Correct answer is: Prokaryotic transcription occurs in cytoplasm, eukaryotic in nucleus