All Free Biology MCQs with Answers
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19844 questions · page 753 of 1985
7521. If one strand of DNA has the nitrogenous base sequence as ATCTG, what would be the complementary RNA strand sequence?
- A. TTAGU
- B. UAGAC
- C. AACTG
- D. ATCGU
Explanation: In RNA, thymine is substituted with uracil; thus, the RNA strand complementary to the DNA strand ATCTG will be UAGAC.
Correct answer: UAGAC7522. Ribosomal RNA is actively synthesized in:
- A. Lysosomes
- B. Nucleolus
- C. Nucleoplasm
- D. Ribosomes
Explanation: The nucleolus is the centre for the synthesis of ribosomal RNA (rRNA) that forms ribosomal subunits. Ribosomal proteins migrate to the nucleolus from their assembly sites in the cytoplasm and are packaged into ribonucleoproteins. These return to the cytoplasm where they become mature ribosome particles.
Correct answer: Nucleolus7523. Removal of RNA polymerase III from the nucleoplasm will affect the synthesis of:
- A. tRNA
- B. hnRNA
- C. mRNA
- D. rRNA
Explanation: In eukaryotes, RNA polymerase enzymes (Type I, II, III) catalyse the synthesis of RNA using as a template either an existing DNA strand or an RNA strand. Type I is responsible for the synthesis of rRNA, type II for mRNA, and type III for tRNA synthesis.
Correct answer: tRNA7524. The unequivocal proof of DNA as the genetic material came from the studies on a:
- A. Bacterium
- B. Fungus
- C. Viroid
- D. Bacterial virus
Explanation: Avery, MacLeod, and McCarty first established that DNA was the genetic material by working on the same bacteria as Griffith. However, they could not convince all the biologists. The unequivocal proof that DNA is the genetic material came from the experiments performed by Alfred Hershey and Martha Chase. They worked with bacteriophages (virus that infects bacteria). The unequivocal proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages.
Correct answer: Bacterial virus7525. Which one of the following does not follow the central dogma of molecular biology?
- A. Pea
- B. Mucor
- C. Chlamydomonas
- D. HIV
Explanation: The oneway flow of information from DNA to mRNA and then to protein is known as the central dogma of molecular biology by F.H.C. Crick (1958). But later on, two American workers, H. Temin and D. Baltimore, reported that DNA is also formed from RNA in retroviruses such as HIV. This is called reverse transcription. This reverse transcription occurs under the influence of the reverse transcriptase enzyme. So, HIV does not follow the central dogma.
Correct answer: HIV7526. Select the two correct statements out of the four (i-iv) statements given below about the lac operon.(i) Glucose or galactose may bind with the repressor and inactivate it.(ii) In the absence of lactose, the repressor binds with the operator region.(iii) The z-gene codes for permease.(iv) This was elucidated by Francois Jacob and Jacques Monod.The correct statements are:
- A. (ii) and (iii)
- B. (i) and (iii)
- C. (ii) and (iv)
- D. (i) and (ii)
Explanation: The two French scientists, Jacob and Monod, proposed the lac operon of E.coli. The lac operon (an inducible operon) contains a promoter, an operator, a regulator gene, and three structural genes z, y, and a, coding for the enzyme b-galactosidase, b-galactoside permease, and b-galactoside, respectively.
Correct answer: (ii) and (iv)7527. In eukaryotic cell transcription, RNA splicing and RNA capping take place inside the:
- A. Ribosomes
- B. Nucleus
- C. Dictyosomes
- D. Endoplasmic Reticulum
Explanation: Unlike in prokaryotes, where transcription and translation take place in the same compartment, in eukaryotes, the primary transcript is first processed in the nucleus and then transported outside of the nucleus. Since the primary transcripts of the eukaryotes contain both the expressed genes (exons) and non-expressing genes (introns), they undergo splicing of introns and later capping and tailing at the 5' and 3' ends respectively.
Correct answer: Nucleus7528. Whose experiments cracked the DNA and discovered unequivocally that the genetic code is a "triplet"?
- A. Hershey and Chase
- B. Morgan and Sturtevant
- C. Beadle and Tatum
- D. Nirenberg and Mathaei
Explanation: Marshall Nirenberg and J. Heinrich Matthaei were pioneering scientists who, in 1961, performed a landmark experiment that cracked the first piece of the genetic code, showing that the RNA sequence UUU codes for the amino acid phenylalanine, launching the race to decipher the full triplet code and revealing how DNA's instructions translate into proteins.
Correct answer: Nirenberg and Mathaei7529. Semi-conservative replication of DNA was first demonstrated in:
- A. Escherichia coli
- B. Streptococcus pneumoniae
- C. Salmonella typhimurium
- D. Drosophila melanogaster
Explanation: The semi-conservative replication of DNA was first experimentally demonstrated by Matthew Meselson and Franklin Stahl in 1958. They used the bacterium Escherichia coli (E. coli) for their classic experiment, in which they used heavy nitrogen isotope (15N) and light nitrogen isotope (14N) to label and track the DNA strands across generations. The results of their density gradient centrifugation analysis confirmed the prediction of the Watson-Crick model that DNA replication is semi-conservative.
Correct answer: Escherichia coli7530. Removal of introns and joining the exons in a defined order in a transcription unit is called:
- A. Tailing
- B. Transformation
- C. Capping
- D. Splicing
Explanation: mRNA is not made directly in a eukaryotic cell. It is transcribed as heterogeneous nuclear RNA (hnRNA) in the nucleus. hnRNA contains introns and exons. The introns are removed by RNA splicing, leaving behind the exons, which contain the information. The exonic regions of RNA are joined together to produce a single-chain RNA required for functioning as a translational template.
Correct answer: Splicing