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Biology MCQ, Class-11th, Chapter-18, Neural Control and Coordination
NCERT Based MCQ with Explanation:
1. What are the components of a nucleotide?
(A) Nitrogenous base, pentose sugar, and a phosphate group
(B) Amino acid, phosphate group, and ribose sugar
(C) Nitrogenous base, glucose, and phosphate
(D) Ribose, uracil, and amino acid
Explanation: A nucleotide is made up of a nitrogenous base, a five-carbon sugar (pentose), and a phosphate group, forming the building blocks of nucleic acids.
2. Which nitrogenous base is found in RNA but not in DNA?
(A) Thymine
(B) Adenine
(C) Uracil
(D) Cytosine
Explanation: RNA contains uracil instead of thymine, which pairs with adenine during transcription.
3. What type of bond holds the two strands of a DNA molecule together?
(A) Phosphodiester bonds
(B) Hydrogen bonds
(C) Ionic bonds
(D) Covalent bonds
Explanation: Hydrogen bonds between complementary nitrogenous bases (A-T and G-C) stabilize the double-helix structure of DNA.
4. What is the structural difference between DNA and RNA?
(A) DNA has uracil, while RNA has thymine
(B) RNA has deoxyribose, while DNA has ribose
(C) DNA has thymine, while RNA has uracil
(D) RNA is double-stranded, while DNA is single-stranded
Explanation: DNA contains thymine as a nitrogenous base, whereas RNA contains uracil in place of thymine. Additionally, RNA has ribose sugar instead of deoxyribose.
5. What is the function of the phosphate group in a nucleotide?
(A) Forms hydrogen bonds with bases
(B) Provides energy for DNA synthesis
(C) Connects nucleotides through phosphodiester bonds
(D) Stabilizes the helical structure
Explanation: The phosphate group links the 3' carbon of one nucleotide to the 5' carbon of another, forming the sugar-phosphate backbone of nucleic acids.
6. Which scientist first identified DNA as an acidic substance present in the nucleus?
(A) Watson and Crick
(B) Erwin Chargaff
(C) Friedrich Miescher
(D) Rosalind Franklin
Explanation: Friedrich Miescher discovered DNA in 1869 and called it "nuclein" because it was found in the nucleus.
7. What is the length of DNA in a typical human cell?
(A) 1.36 mm
(B) 2.2 m
(C) 3.4 μm
(D) 4.6 × 10⁶ bp
Explanation: The total length of DNA in a human cell is approximately 2.2 meters when fully extended, despite being tightly packed within the nucleus.
8. Which of the following describes the polarity of DNA strands?
(A) Both strands are 5' to 3'
(B) One strand is 5' to 3', and the other is 3' to 5'
(C) Both strands are 3' to 5'
(D) Polarity is not defined
Explanation: DNA strands are antiparallel, meaning one strand runs in the 5' to 3' direction, while the complementary strand runs in the 3' to 5' direction.
9. What does the term "complementary base pairing" mean in DNA?
(A) Pairing of identical bases
(B) Pairing of purines with purines and pyrimidines with pyrimidines
(C) Specific pairing of adenine with thymine and guanine with cytosine
(D) Random pairing of nitrogenous bases
Explanation: Complementary base pairing ensures that adenine pairs with thymine (via 2 hydrogen bonds) and guanine pairs with cytosine (via 3 hydrogen bonds) in the DNA structure.
10. Who proposed the double-helix model of DNA?
(A) Hershey and Chase
(B) Watson and Crick
(C) Meselson and Stahl
(D) Avery, MacLeod, and McCarty
Explanation: James Watson and Francis Crick proposed the double-helix model of DNA in 1953, based on X-ray diffraction data from Rosalind Franklin and Maurice Wilkins.
Science MCQ, Class 10th, Chapter-14, Sources Of Energy11. What is the distance between two consecutive base pairs in the DNA double helix?
(A) 0.34 nm
(B) 3.4 nm
(C) 34 nm
(D) 0.03 nm
Explanation: The distance between two consecutive base pairs in the DNA double helix is 0.34 nanometers, contributing to the overall helical structure.
12. Which enzyme is responsible for unwinding the DNA helix during replication?
(A) DNA ligase
(B) Helicase
(C) DNA polymerase
(D) Topoisomerase
Explanation: Helicase unwinds the DNA double helix by breaking the hydrogen bonds between complementary base pairs.
13. What is the role of DNA polymerase in replication?
(A) Synthesizing RNA primers
(B) Joining Okazaki fragments
(C) Adding nucleotides to the growing DNA strand
(D) Unwinding the DNA helix
Explanation: DNA polymerase adds nucleotides to the 3' end of the growing strand, using the template strand for guidance.
14. Which type of replication does DNA undergo?
(A) Conservative
(B) Semi-conservative
(C) Dispersive
(D) Non-replicative
Explanation: In semi-conservative replication, each new DNA molecule consists of one parental strand and one newly synthesized strand.
15. What are Okazaki fragments?
(A) RNA primers synthesized during replication
(B) Short fragments of DNA synthesized on the lagging strand
(C) Proteins involved in DNA repair
(D) Sequences of RNA removed during splicing
Explanation: Okazaki fragments are short DNA segments synthesized discontinuously on the lagging strand during replication.
16. Which enzyme seals the gaps between Okazaki fragments?
(A) DNA ligase
(B) Primase
(C) Helicase
(D) DNA polymerase
Explanation: DNA ligase joins Okazaki fragments by forming phosphodiester bonds between them, ensuring a continuous strand.
17. What is the origin of replication?
(A) The region where transcription starts
(B) The point where DNA replication begins
(C) The sequence where RNA polymerase binds
(D) The site of ribosome assembly
Explanation: The origin of replication is a specific sequence in the genome where DNA replication is initiated.
18. Which scientist(s) provided experimental proof of the semi-conservative model of DNA replication?
(A) Watson and Crick
(B) Meselson and Stahl
(C) Hershey and Chase
(D) Avery, MacLeod, and McCarty
Explanation: Meselson and Stahl demonstrated the semi-conservative nature of DNA replication using isotopic labeling and density gradient centrifugation.
19. Which nitrogenous base pairs with guanine in DNA?
(A) Adenine
(B) Thymine
(C) Cytosine
(D) Uracil
Explanation: Guanine forms three hydrogen bonds with cytosine, maintaining the complementary base pairing in DNA.
20. How many base pairs are present in a complete turn of the DNA double helix?
(A) 5
(B) 10
(C) 20
(D) 15
Explanation: Each complete turn of the DNA double helix consists of approximately 10 base pairs, contributing to the helical structure.
21. What is the primary function of mRNA in the cell?
(A) To transfer amino acids to ribosomes
(B) To serve as a template for protein synthesis
(C) To catalyze peptide bond formation
(D) To stabilize the DNA double helix
22. Which enzyme is responsible for synthesizing RNA during transcription?
(A) RNA polymerase
(B) DNA polymerase
(C) Helicase
(D) Ligase
23. What is the coding strand in transcription?
(A) The strand of DNA complementary to the RNA
(B) The strand of DNA identical to the RNA (except for uracil)
(C) The strand used as a template for RNA synthesis
(D) The strand degraded during transcription
24. What is the role of the promoter region in transcription?
(A) It codes for proteins
(B) It signals where transcription should start
(C) It terminates transcription
(D) It removes introns from RNA
25. Which RNA base pairs with adenine in DNA during transcription?
(A) Thymine
(B) Guanine
(C) Cytosine
(D) Uracil
26. What process occurs after transcription in eukaryotic cells?
(A) Replication
(B) RNA splicing
(C) Protein folding
(D) DNA methylation
27. Which of the following is NOT a type of RNA?
(A) mRNA
(B) tRNA
(C) rRNA
(D) cDNA
28. What is the main role of tRNA?
(A) To carry genetic information
(B) To transport amino acids to ribosomes
(C) To catalyze RNA splicing
(D) To stabilize ribosomes
29. What are introns?
(A) Coding regions of a gene
(B) Non-coding regions removed during RNA processing
(C) Sequences that initiate transcription
(D) Regulatory sequences of DNA
30. What is the 5' cap added to eukaryotic mRNA composed of?
(A) A methylated guanine nucleotide
(B) A polyadenine tail
(C) A ribose sugar
(D) An amino acid sequence
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