All Free Biology MCQs with Answers
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19844 questions · page 721 of 1985
7201. In three-dimensional view, the molecule of tRNA is:
- A. L-shaped
- B. S-shaped
- C. Y-shaped
- D. E-shaped
Explanation: tRNA folds into an L-shape in 3D, fitting correctly into ribosomes during translation.
Correct answer: L-shaped7202. During translation initiation in prokaryotes, a GTP molecule is needed in the:
- A. Formation of formyl-met-tRNA
- B. Binding of 30S subunit of ribosome with mRNA
- C. Association of 30S-mRNA with formyl-met-tRNA
- D. Association of 50S subunit of ribosome with initiation complex
Explanation: In prokaryotic translation initiation, a GTP molecule is required for the step where the 50S ribosomal subunit joins the 30S initiation complex to form the complete 70S initiation complex. This GTP is hydrolyzed by initiation factor IF2 to facilitate the joining of the 50S subunit.
Correct answer: Association of 50S subunit of ribosome with initiation complex7203. Using imprints from a bacterial plate, streptomycin resistant mutants can be selected. These imprints need to be used:
- A. On plates with and without streptomycin
- B. On plates with minimal medium
- C. Only on plates with streptomycin
- D. Only on plates without streptomycin
Explanation: Imprints on both plates (with and without streptomycin) help identify streptomycin-resistant mutants by comparing growth patterns.
Correct answer: Only on plates with streptomycin7204. The 3′-5′ phosphodiester linkages in a polynucleotide chain join:
- A. One DNA strand with another
- B. One nucleoside with another
- C. One nucleotide with another nucleotide
- D. One nitrogenous base with a pentose sugar
Explanation: Phosphodiester bonds connect 3′-OH of one sugar with 5′ phosphate of next nucleotide, forming the DNA backbone.
Correct answer: One nucleotide with another nucleotide7205. Satellite DNA is important because it:
- A. Codes for enzymes needed for DNA replication
- B. Codes for protein needed in cell cycle
- C. Does not code for proteins and is same in all members of population
- D. Shows high polymorphism in the population and is inherited
Explanation: Satellite DNA varies greatly among individuals. Its polymorphism is used in DNA fingerprinting, paternity tests, and forensic studies.
Correct answer: Shows high polymorphism in the population and is inherited7206. In the given diagram of a chromosome, label 'A' represents:
- A. Centromere
- B. Chromatid
- C. Telomere
- D. Kinetochore
Explanation: The centromere is the constricted region joining the two sister chromatids and is essential for spindle attachment during cell division.
Correct answer: Centromere7207. In the given diagram of DNA, X represents:
- A. Sugar-phosphate backbone
- B. Nitrogenous base
- C. Nucleotides
- D. Hydrogen bonds
Explanation: The sugar-phosphate backbone of DNA is formed by alternating deoxyribose sugar and phosphate groups linked by phosphodiester bonds. This backbone gives structural stability, while base pairs form the rungs of the DNA double helix.
Correct answer: Sugar-phosphate backbone7208. In the diagram of a chromosome, the part labelled as X is :
- A. Sister Chromatid
- B. Centromere
- C. Chromatin
- D. Telomere
Explanation: The label X points to the tip (end) of the chromatid arm. Telomeres are the protective caps at the ends of chromosomes that prevent degradation and fusion with neighboring chromosomes. The brown regions at both ends of the chromosome represent the telomeric regions in this illustration.
Correct answer: Telomere7209. In a labeled DNA replication fork diagram, enzyme 'A' is:
- A. Ligase
- B. Helicase
- C. Primase
- D. Polymerase
Explanation: Helicase is the enzyme responsible for unwinding and separating the two strands of the DNA double helix at the replication fork, creating single-stranded templates for replication. Ligase joins fragments, primase synthesizes RNA primers, and polymerase adds new nucleotides.
Correct answer: Helicase7210. In a diagram showing transcription bubble, the DNA region actively being copied is:
- A. Template strand
- B. Coding strand
- C. Okazaki fragment
- D. Introns
Explanation: The transcription bubble is the unwound portion of DNA where RNA is being synthesized. RNA polymerase uses only one strand of DNA as a template to make complementary RNA. The opposite strand (coding strand) has the same base sequence as the mRNA, except U replaces T.
Correct answer: Template strand