All Free Biology MCQs with Answers
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19844 questions · page 722 of 1985
7211. In a labeled diagram of transcription, enzyme "X" synthesizing RNA is:
- A. DNA polymerase
- B. RNA polymerase
- C. Ligase
- D. Helicase
Explanation: RNA polymerase reads the DNA template strand and synthesizes a complementary RNA strand. DNA polymerase is used in replication, not transcription. Ligase joins DNA fragments, while helicase unwinds DNA strands.
Correct answer: RNA polymerase7212. In the DNA replication diagram, Okazaki fragments are formed on:
- A. Strand A
- B. Strand B
- C. Both strands
- D. None
Explanation: The lagging strand is synthesized discontinuously in short segments called Okazaki fragments. These fragments are later joined by DNA ligase. The leading strand, however, is synthesized continuously toward the replication fork.
Correct answer: Strand B7213. In the DNA replication diagram, the enzyme joining Okazaki fragments is:
- A. DNA polymerase I
- B. Ligase
- C. Primase
- D. Topoisomerase
Explanation: During lagging strand synthesis, short DNA segments (Okazaki fragments) are produced. DNA polymerase fills the gaps but leaves nicks between fragments. DNA ligase seals these nicks by forming phosphodiester bonds, joining fragments into one continuous strand.
Correct answer: Ligase7214. In the labeled tRNA diagram, the region that binds to the codon on mRNA is:
- A. Acceptor arm
- B. Anticodon loop
- C. Variable arm
- D. D-loop
Explanation: The anticodon loop carries a sequence of three bases complementary to the mRNA codon. This ensures correct amino acid placement during translation. Each tRNA's anticodon matches a specific codon on mRNA through base pairing.
Correct answer: Anticodon loop7215. In the tRNA diagram, the region where amino acid attaches is:
- A. Anticodon loop
- B. Acceptor stem (3′ end)
- C. D‑loop
- D. Variable arm
Explanation: The 3' end of tRNA always ends with the sequence CCA, where the amino acid binds. This bond is formed by the enzyme aminoacyl-tRNA synthetase. It's the "charging site" that loads the correct amino acid before translation begins.
Correct answer: Acceptor stem (3′ end)7216. The chromosome with centromere near the end of chromatids is:
- A. Acrocentric
- B. Telocentric
- C. Sub metacentric
- D. Metacentric
Explanation: Acrocentric is defined as the position where centromere is present near the end.
Correct answer: Acrocentric7217. The bead like structure present in the chromosome is:
- A. Histone
- B. Nucleosome
- C. Nucleolus
- D. None of the above
Explanation: Every 200 nucleotides, the DNA duplex is coiled around a core of eight histone proteins forming a complex known as a nucleosome which resembles string of beads.
Correct answer: Nucleosome7218. The structure formed by super coiling of DNA is:
- A. Nucleosome
- B. Chromatin
- C. Chromosome
- D. All of the above
Explanation: Coiling occurs when the string of nucleosomes wraps up into higher order coils called super coils, which results in formation of chromatin.
Correct answer: Chromatin7219. Experiments on mice were performed by:
- A. Walter Sutton
- B. Oswald Avery
- C. Frederick Griffith
- D. Karl Correns
Explanation: The first evidence of the hereditary nature of DNA was provided by a British microbiologist Frederick Griffith who made some unexpected observations while experimenting with pathogenic bacteria by injecting it in mice.
Correct answer: Frederick Griffith7220. Experiments on bacteriophage were performed by:
- A. Walter Sutton
- B. Hershy and Chase
- C. Fred Griffith
- D. Karl Correns
Explanation: Additional evidence supporting Avery's conclusion was provided in 1952 by Alfred Hershey and Martha Chase, who experimented with bacteriophages T2.
Correct answer: Hershy and Chase