- The enzyme responsible for synthesizing RNA primers during DNA replication is:
a) DNA polymerase
b) Helicase
c) Primase
d) Ligase
Answer: c) Primase
Explanation: Primase synthesizes short RNA primers that provide a starting point for DNA polymerase to begin synthesizing the new DNA strand. These primers are necessary because DNA polymerase cannot start a new strand on its own.
- Which of the following statements is true about the degeneracy of the genetic code?
a) One codon codes for multiple amino acids
b) Multiple codons can code for the same amino acid
c) The code is overlapping
d) There are no stop codons
Answer: b) Multiple codons can code for the same amino acid
Explanation: The genetic code is degenerate, meaning that several codons can code for the same amino acid. For example, the amino acid leucine is specified by six different codons.
- Which of the following is NOT a post-transcriptional modification that occurs in eukaryotes?
a) 5′ capping
b) 3′ polyadenylation
c) Intron splicing
d) DNA methylation
Answer: d) DNA methylation
Explanation: DNA methylation is a form of epigenetic regulation that affects gene expression but is not a post-transcriptional modification. Post-transcriptional modifications include 5′ capping, 3′ polyadenylation, and the removal of introns through splicing.
- Which of the following is true about histone proteins?
a) They are involved in DNA methylation
b) They are enzymes that unwind DNA
c) They help package DNA into nucleosomes
d) They are responsible for DNA replication
Answer: c) They help package DNA into nucleosomes
Explanation: Histone proteins are involved in the packaging of DNA in eukaryotic cells. They form the core around which DNA is wrapped, creating nucleosomes, which allow for efficient compaction of DNA within the nucleus.
- Which of the following statements correctly describes a missense mutation?
a) A single nucleotide change results in a stop codon
b) A nucleotide change does not affect the amino acid sequence
c) A nucleotide change results in the substitution of one amino acid for another
d) It results in the insertion of multiple nucleotides
Answer: c) A nucleotide change results in the substitution of one amino acid for another
Explanation: A missense mutation is a type of point mutation in which a single nucleotide change leads to the substitution of one amino acid for another in the protein. This can affect protein function.
- The enzyme reverse transcriptase is commonly associated with which of the following?
a) DNA replication
b) RNA splicing
c) Transcription
d) Retroviruses
Answer: d) Retroviruses
Explanation: Reverse transcriptase is an enzyme found in retroviruses (like HIV). It catalyzes the synthesis of DNA from an RNA template, allowing the viral RNA to integrate into the host’s DNA.
- Which of the following mechanisms is primarily responsible for the regulation of gene expression in prokaryotes?
a) DNA methylation
b) RNA interference
c) Operon model
d) Chromatin remodeling
Answer: c) Operon model
Explanation: Gene expression in prokaryotes is primarily regulated by the operon model, in which groups of related genes are transcribed together under the control of a single promoter and operator region (e.g., lac operon).
- Which scientist discovered the transforming principle in Streptococcus pneumoniae that led to the identification of DNA as the genetic material?
a) Watson and Crick
b) Frederick Griffith
c) Avery, MacLeod, and McCarty
d) Hershey and Chase
Answer: b) Frederick Griffith
Explanation: Frederick Griffith discovered the “transforming principle” in his experiments with Streptococcus pneumoniae. His work showed that a substance from dead bacteria could genetically transform live bacteria. Later, Avery, MacLeod, and McCarty identified this substance as DNA.
- Which of the following enzymes is responsible for removing RNA primers and replacing them with DNA during replication?
a) DNA polymerase I
b) DNA polymerase III
c) DNA helicase
d) DNA ligase
Answer: a) DNA polymerase I
Explanation: DNA polymerase I in prokaryotes removes RNA primers and replaces them with DNA. In eukaryotes, a similar function is carried out by other DNA polymerases and associated enzymes.
- Which of the following describes a major difference between prokaryotic and eukaryotic gene expression?
a) Prokaryotes process their mRNA, while eukaryotes do not
b) Eukaryotic transcription and translation are coupled, while in prokaryotes they are separate
c) Eukaryotes have introns, which must be spliced out of the mRNA before translation
d) In prokaryotes, mRNA must undergo splicing and 5′ capping
Answer: c) Eukaryotes have introns, which must be spliced out of the mRNA before translation
Explanation: Eukaryotic genes often contain introns, which are non-coding regions that must be spliced out before mRNA can be translated. Prokaryotic genes typically do not contain introns, and transcription and translation occur almost simultaneously in the cytoplasm.
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