All Free Biology MCQs with Answers
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19844 questions · page 723 of 1985
7221. In the next generation of phage virus, the virus found radioactive were with:
- A. S34
- B. S35
- C. P31
- D. P32
Explanation: The 32P label was transferred to the interior of the bacteria and was found in viruses subsequently released from the infected bacteria. Hence, the hereditary information injected into the bacteria that specified the new generation of viruses was DNA and not protein.
Correct answer: P327222. DNA was discovered in 1869 by:
- A. Walter Sutton
- B. Rosalind Franklin
- C. F. Miescher
- D. Karl Correns
Explanation: A German Chemist, Friedrich Miescher, discovered DNA in 1869, only four years after Mendel's work was published. Miescher extracted a white substance from the nuclei of human cells and fish sperm. He called this substance "nuclein" because it seemed to be specifically associated with the nucleus.
Correct answer: F. Miescher7223. Basic structure of nucleic acid was determined by:
- A. P.A. Levene
- B. Walther Fleming
- C. F. Miescher
- D. Watson and Crick
Explanation: In the 1920s, the basic structure of nucleic acids was determined by the biochemist P.A.Levene.
Correct answer: P.A. Levene7224. Double helical structure of DNA was proposed by:
- A. P.A. Levene
- B. Walther Fleming
- C. F. Miescher
- D. Watson and Crick
Explanation: James Watson and Francis Crick, two young researchers at the University of Cambridge, quickly worked out a likely structure of the DNA molecule, which we now know was substantially correct.
Correct answer: Watson and Crick7225. The model in which both strands break is:
- A. Dispersive
- B. Conservative
- C. Semi-conservative
- D. None of the above
Explanation: The dispersive model predicted that parental DNA would completely break and that each strand of all the daughter molecules would be a mixture of old and new DNA.
Correct answer: Dispersive7226. The semi conservative model of DNA was proved by:
- A. P.A. Levene
- B. Meselson - Stahl
- C. F. Miescher
- D. Watson and Crick
Explanation: Meselson and Stahl interpreted their results as follows: after the first round of replication, each daughter DNA duplex was a hybrid possessing one heavy strand and one light strand. When this hybrid duplex replicated, it contributed one heavy strand to form another hybrid duplex and one light strand to form a light duplex. This experiment clearly confirmed the prediction of the Watson-Crick model that DNA replicates in a semi-conservative manner.
Correct answer: Meselson - Stahl7227. Meselson and Stahl used radioactive isotope of:
- A. Carbon
- B. Phosporus
- C. Sulphur
- D. Nitrogen
Explanation: Meselson and Stahl grew bacteria in radioactive isotope of nitrogen, N15.
Correct answer: Nitrogen7228. The enzyme which attaches the fragments of DNA is:
- A. DNA polymerase I
- B. Primase
- C. Ligase
- D. DNA polymerase II
Explanation: When the polymerase reaches the 5' end of the lagging strand, it binds with another enzyme called DNA ligase, which then connects the fragment to the lagging strand.
Correct answer: Ligase7229. The true replicating enzyme is:
- A. DNA polymerase III
- B. Ligase
- C. Primase
- D. DNA polymerase II
Explanation: The true E.coli replicating enzymes is DNA polymerase III which is 10 times larger and far more complex in structure.
Correct answer: DNA polymerase III7230. The enzyme which plays a supporting role in DNA replication is:
- A. DNA polymerase I
- B. Pirmase
- C. Ligase
- D. DNA polymerase II
Explanation: DNA polymerase I is a relatively small enzyme that plays a supporting role in DNA replication.
Correct answer: DNA polymerase I