Here below some basic MCQ with Answer molecular basis of inheritance. Which is explained in details. Let’s check one by one.
- DNA is a polymer of nucleotides, which are made of three components. Which of the following is NOT a component of a nucleotide?
a) Phosphate group
b) Ribose sugar
c) Deoxyribose sugar
d) Nitrogenous base
Answer: b) Ribose sugar
Explanation: Nucleotides in DNA consist of a phosphate group, a deoxyribose sugar (not ribose, which is found in RNA), and a nitrogenous base (adenine, thymine, cytosine, or guanine). Ribose is present in RNA, not DNA.
- Which of the following is responsible for the semiconservative nature of DNA replication?
a) DNA polymerase I
b) DNA helicase
c) Meselson and Stahl experiment
d) Okazaki fragments
Answer: c) Meselson and Stahl experiment
Explanation: The Meselson and Stahl experiment demonstrated the semiconservative nature of DNA replication, where each daughter DNA molecule consists of one parental and one newly synthesized strand.
- The enzyme that facilitates the unwinding of the DNA double helix during replication is:
a) Ligase
b) DNA polymerase
c) Primase
d) Helicase
Answer: d) Helicase
Explanation: Helicase unwinds the DNA double helix by breaking the hydrogen bonds between the two strands, allowing replication to proceed.
- Which type of RNA is involved in carrying amino acids to the ribosome during protein synthesis?
a) mRNA
b) tRNA
c) rRNA
d) snRNA
Answer: b) tRNA
Explanation: Transfer RNA (tRNA) is responsible for transporting specific amino acids to the ribosome, where they are added to the growing polypeptide chain during translation.
- In eukaryotic cells, which of the following processes occurs in the nucleus?
a) Transcription
b) Translation
c) Glycolysis
d) Electron transport chain
Answer: a) Transcription
Explanation: Transcription (the process of copying DNA into mRNA) occurs in the nucleus of eukaryotic cells. Translation occurs in the cytoplasm, while glycolysis happens in the cytosol and the electron transport chain takes place in the mitochondria.
- In a DNA molecule, the amount of adenine is always equal to the amount of thymine because of:
a) Meselson-Stahl rule
b) Chargaff’s rule
c) Watson-Crick rule
d) Central dogma
Answer: b) Chargaff’s rule
Explanation: Chargaff’s rule states that in a DNA molecule, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C), due to the base pairing between them.
- Which enzyme is responsible for adding new nucleotides to a growing DNA strand during replication?
a) DNA ligase
b) DNA helicase
c) DNA polymerase
d) RNA polymerase
Answer: c) DNA polymerase
Explanation: DNA polymerase catalyzes the addition of new nucleotides to the growing DNA strand during replication, ensuring accurate DNA synthesis.
- The discontinuous segments of newly synthesized DNA on the lagging strand are called:
a) Okazaki fragments
b) Leading strands
c) Replication bubbles
d) Primers
Answer: a) Okazaki fragments
Explanation: The lagging strand is synthesized in short segments called Okazaki fragments, which are later joined by DNA ligase to form a continuous strand.
- Which of the following sequences represents the flow of genetic information according to the central dogma of molecular biology?
a) DNA → Protein → RNA
b) RNA → DNA → Protein
c) DNA → RNA → Protein
d) Protein → RNA → DNA
Answer: c) DNA → RNA → Protein
Explanation: The central dogma of molecular biology describes the flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation).
- Which of the following scientists is credited with the discovery of the structure of DNA?
a) Rosalind Franklin
b) Erwin Chargaff
c) James Watson and Francis Crick
d) Frederick Griffith
Answer: c) James Watson and Francis Crick
Explanation: James Watson and Francis Crick are credited with discovering the double helix structure of DNA in 1953, though they used critical data from Rosalind Franklin’s X-ray diffraction work.
- Which of the following is true about introns and exons?
a) Introns are coding regions and exons are non-coding regions
b) Exons are coding regions and introns are non-coding regions
c) Both introns and exons are non-coding regions
d) Introns and exons are not found in eukaryotic DNA
Answer: b) Exons are coding regions and introns are non-coding regions
Explanation: In eukaryotic genes, exons are coding regions that are spliced together to form mature mRNA, while introns are non-coding regions that are removed during RNA processing.
- What role does RNA polymerase play in transcription?
a) It unwinds the DNA double helix
b) It adds amino acids to the growing protein chain
c) It synthesizes RNA from a DNA template
d) It connects Okazaki fragments
Answer: c) It synthesizes RNA from a DNA template
Explanation: RNA polymerase synthesizes RNA by using one strand of DNA as a template during transcription.
- Which of the following is a feature of the genetic code?
a) It is ambiguous
b) It is overlapping
c) It is universal
d) It is not degenerate
Answer: c) It is universal
Explanation: The genetic code is almost universal, meaning the same codon codes for the same amino acid in nearly all organisms, from bacteria to humans. It is also degenerate (multiple codons code for the same amino acid) and non-overlapping.
- In a DNA molecule, if the sequence of one strand is 5’-ATTGCA-3’, what is the complementary sequence of the other strand?
a) 5’-TAACGT-3’
b) 3’-TAACGT-5’
c) 5’-UAACGU-3’
d) 3’-AUUGCA-5’
Answer: b) 3’-TAACGT-5’
Explanation: DNA strands are complementary and antiparallel. Adenine pairs with thymine, and guanine pairs with cytosine. The complementary sequence to 5’-ATTGCA-3’ is 3’-TAACGT-5’.
- Which of the following enzymes seals the gaps between Okazaki fragments during DNA replication?
a) DNA polymerase
b) DNA ligase
c) Primase
d) Helicase
Answer: b) DNA ligase
Explanation: DNA ligase joins the Okazaki fragments on the lagging strand during DNA replication by forming phosphodiester bonds between adjacent nucleotides.
- The process by which RNA is synthesized from a DNA template is called:
a) Translation
b) Replication
c) Transcription
d) Splicing
Answer: c) Transcription
Explanation: Transcription is the process where a single strand of DNA serves as a template for the synthesis of RNA, mediated by RNA polymerase.
- What is the role of a promoter in transcription?
a) It terminates transcription
b) It synthesizes RNA
c) It initiates transcription by binding RNA polymerase
d) It acts as a primer
Answer: c) It initiates transcription by binding RNA polymerase
Explanation: The promoter is a specific sequence of DNA that signals RNA polymerase to bind and begin transcription of the gene.
- Which of the following nitrogenous bases is unique to RNA?
a) Thymine
b) Adenine
c) Guanine
d) Uracil
Answer: d) Uracil
Explanation: In RNA, uracil replaces thymine and pairs with adenine. RNA contains the bases adenine, guanine, cytosine, and uracil.
- Which of the following is NOT a function of ribosomal RNA (rRNA)?
a) It provides the structural framework for ribosomes
b) It catalyzes the formation of peptide bonds
c) It carries amino acids to the ribosome
d) It helps position the mRNA for translation
Answer: c) It carries amino acids to the ribosome
Explanation: Transfer RNA (tRNA), not rRNA, is responsible for carrying amino acids to the ribosome during translation. rRNA plays a role in the structure of the ribosome and catalyzing peptide bond formation.
- The process by which mRNA is converted into a sequence of amino acids is called:
a) Replication
b) Translation
c) Transcription
d) Splicing
Answer: b) Translation
Explanation: Translation is the process by which the sequence of codons in mRNA is read by the ribosome to assemble amino acids into a polypeptide chain (protein).
- What is the role of telomerase in DNA replication?
a) It adds nucleotides to the ends of chromosomes to prevent shortening
b) It synthesizes RNA primers
c) It unwinds the DNA double helix
d) It repairs mismatched nucleotides
Answer: a) It adds nucleotides to the ends of chromosomes to prevent shortening
Explanation: Telomerase adds repetitive nucleotide sequences (telomeres) to the ends of eukaryotic chromosomes, protecting them from degradation during replication.
- Which of the following is true about the lac operon in E. coli?
a) It is an example of a repressible operon
b) It is activated when lactose is absent
c) It is regulated by the repressor protein binding to the operator
d) It controls the synthesis of tryptophan
Answer: c) It is regulated by the repressor protein binding to the operator
Explanation: The lac operon in E. coli is an inducible operon. When lactose is absent, the repressor binds to the operator, blocking transcription. When lactose is present, it binds to the repressor, preventing it from binding to the operator and allowing transcription.
- Which of the following is an example of a point mutation?
a) Deletion of three nucleotides
b) Duplication of a gene segment
c) Substitution of one base pair
d) Insertion of a large sequence
Answer: c) Substitution of one base pair
Explanation: A point mutation is a change in a single base pair, such as substitution, where one nucleotide is replaced by another. This may result in a silent, missense, or nonsense mutation.
- In prokaryotes, which of the following helps in the termination of transcription?
a) Helicase
b) rho protein
c) DNA polymerase
d) Telomerase
Answer: b) rho protein
Explanation: In prokaryotes, the rho protein is involved in the rho-dependent termination of transcription. It unwinds the RNA-DNA hybrid, causing the termination of RNA synthesis.
- Which of the following is involved in the splicing of introns from pre-mRNA?
a) rRNA
b) snRNA
c) tRNA
d) siRNA
Answer: b) snRNA
Explanation: Small nuclear RNA (snRNA) plays a crucial role in the splicing of pre-mRNA by recognizing splice sites and helping to remove introns from the transcript during the formation of mature mRNA.
- Which of the following statements about DNA replication is correct?
a) DNA replication occurs in the 3′ to 5′ direction
b) The leading strand is synthesized discontinuously
c) DNA polymerase adds nucleotides to the 3′ end of the new strand
d) The process does not require a primer
Answer: c) DNA polymerase adds nucleotides to the 3′ end of the new strand
Explanation: DNA polymerase can only add nucleotides to the free 3′ hydroxyl end of the growing DNA strand, which means replication always occurs in the 5′ to 3′ direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments (Okazaki fragments).
- What is the role of a codon in protein synthesis?
a) It signals the end of transcription
b) It directs the assembly of amino acids into a protein
c) It binds to the anticodon on tRNA
d) It unwinds the DNA double helix
Answer: b) It directs the assembly of amino acids into a protein
Explanation: A codon is a sequence of three nucleotides on mRNA that specifies a particular amino acid or signals the start or stop of protein synthesis during translation. The anticodon on tRNA pairs with the codon on mRNA to ensure the correct amino acid is added to the growing polypeptide chain.
- Which of the following is a stop codon in the genetic code?
a) AUG
b) UUU
c) UAA
d) UGG
Answer: c) UAA
Explanation: The three stop codons are UAA, UAG, and UGA, which signal the termination of protein synthesis. AUG is the start codon, and UUU codes for phenylalanine.
- The term “antiparallel” in the context of DNA structure refers to:
a) The arrangement of the sugar-phosphate backbone
b) The direction of the two DNA strands relative to each other
c) The orientation of the nitrogenous bases
d) The helical twist of the DNA strands
Answer: b) The direction of the two DNA strands relative to each other
Explanation: DNA strands run in opposite directions; one strand runs in the 5′ to 3′ direction, while the complementary strand runs in the 3′ to 5′ direction. This antiparallel arrangement is critical for the function and replication of DNA.
- In eukaryotes, the RNA that is synthesized directly from the DNA template is called:
a) mRNA
b) tRNA
c) rRNA
d) hnRNA
Answer: d) hnRNA
Explanation: Heterogeneous nuclear RNA (hnRNA) is the precursor to mRNA in eukaryotes. It contains both introns and exons and undergoes processing (splicing, capping, and polyadenylation) to form mature mRNA, which is then translated into protein.
- During protein synthesis, what is the function of the ribosome?
a) It transcribes mRNA from DNA
b) It links amino acids together to form a polypeptide chain
c) It transports amino acids to the growing polypeptide chain
d) It synthesizes tRNA molecules
Answer: b) It links amino acids together to form a polypeptide chain
Explanation: The ribosome is the cellular machinery responsible for translating mRNA into a protein. It facilitates the formation of peptide bonds between amino acids, creating a polypeptide chain.
- Which of the following types of RNA carries the genetic code from the nucleus to the ribosome for protein synthesis?
a) tRNA
b) mRNA
c) rRNA
d) siRNA
Answer: b) mRNA
Explanation: Messenger RNA (mRNA) carries the genetic information transcribed from DNA in the nucleus to the ribosome, where it is translated into a protein.
- In the lac operon, when lactose is present:
a) The repressor protein binds to the operator
b) The repressor protein is inactivated by lactose
c) RNA polymerase is blocked from transcribing the genes
d) Glucose inhibits the operon
Answer: b) The repressor protein is inactivated by lactose
Explanation: When lactose is present, it binds to the repressor protein, causing a conformational change that inactivates the repressor. This allows RNA polymerase to bind to the promoter and transcribe the genes needed to metabolize lactose.
- In DNA, the pyrimidine bases are:
a) Adenine and guanine
b) Cytosine and thymine
c) Adenine and thymine
d) Cytosine and guanine
Answer: b) Cytosine and thymine
Explanation: Pyrimidine bases in DNA are cytosine and thymine. Adenine and guanine are purine bases. Pyrimidines have a single-ring structure, while purines have a double-ring structure.
- Which of the following RNA molecules is part of the spliceosome complex?
a) mRNA
b) tRNA
c) rRNA
d) snRNA
Answer: d) snRNA
Explanation: Small nuclear RNA (snRNA) is a component of the spliceosome, the complex responsible for splicing introns from pre-mRNA in eukaryotic cells.
- Which of the following processes is responsible for increasing the variability in eukaryotic gene expression by producing different proteins from the same gene?
a) Transcription
b) Translation
c) Alternative splicing
d) RNA editing
Answer: c) Alternative splicing
Explanation: Alternative splicing is a process by which different combinations of exons are joined together to produce multiple proteins from the same pre-mRNA, thus increasing the diversity of proteins a single gene can encode.
- Which of the following sequences can be recognized as the start codon in both prokaryotes and eukaryotes?
a) UAG
b) AUG
c) UGA
d) UAA
Answer: b) AUG
Explanation: AUG is the start codon in both prokaryotes and eukaryotes, coding for the amino acid methionine, which initiates protein synthesis.
- Which type of mutation is caused by the insertion or deletion of nucleotides that is not in multiples of three?
a) Missense mutation
b) Nonsense mutation
c) Silent mutation
d) Frameshift mutation
Answer: d) Frameshift mutation
Explanation: Frameshift mutations occur when nucleotides are inserted or deleted in numbers that are not multiples of three, shifting the reading frame of the codons and potentially altering every downstream amino acid.
- Which of the following enzymes is responsible for transcribing tRNA?
a) RNA polymerase I
b) RNA polymerase II
c) RNA polymerase III
d) DNA polymerase
Answer: c) RNA polymerase III
Explanation: RNA polymerase III transcribes transfer RNA (tRNA) and other small RNAs like 5S rRNA. RNA polymerase II transcribes mRNA, and RNA polymerase I transcribes rRNA.
- Which of the following genetic elements is NOT involved in regulating gene expression in the lac operon?
a) Operator
b) Promoter
c) Repressor
d) Enhancer
Answer: d) Enhancer
Explanation: Enhancers are distant regulatory sequences that increase the transcription of eukaryotic genes. In the lac operon, gene expression is regulated by the promoter, operator, and repressor, but enhancers are not involved.
- 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.
- Which of the following is involved in post-transcriptional regulation of gene expression?
a) DNA polymerase
b) RNA polymerase
c) MicroRNA (miRNA)
d) Topoisomerase
Answer: c) MicroRNA (miRNA)
Explanation: MicroRNAs (miRNAs) are involved in post-transcriptional regulation by binding to complementary sequences on mRNA molecules, often leading to mRNA degradation or inhibition of translation.
- The Hershey and Chase experiment, which demonstrated that DNA is the genetic material, used which of the following to label DNA?
a) Radioactive sulfur (35S)
b) Radioactive phosphorus (32P)
c) Radioactive carbon (14C)
d) Radioactive nitrogen (15N)
Answer: b) Radioactive phosphorus (32P)
Explanation: Hershey and Chase used radioactive phosphorus (32P) to label DNA because phosphorus is found in the DNA backbone but not in proteins. They used radioactive sulfur (35S) to label the protein coat of the bacteriophages.
- Which of the following best describes the function of topoisomerase during DNA replication?
a) Unwinding the DNA double helix
b) Preventing the DNA strands from tangling by relieving supercoiling
c) Synthesizing RNA primers
d) Adding nucleotides to the growing DNA strand
Answer: b) Preventing the DNA strands from tangling by relieving supercoiling
Explanation: Topoisomerase enzymes relieve the supercoiling tension generated ahead of the replication fork by temporarily cutting the DNA strands and then rejoining them.
- Which of the following types of RNA carries amino acids to the ribosome during protein synthesis?
a) mRNA
b) rRNA
c) tRNA
d) snRNA
Answer: c) tRNA
Explanation: Transfer RNA (tRNA) carries specific amino acids to the ribosome during translation, where they are added to the growing polypeptide chain.
- The phenomenon of “semi-conservative replication” in DNA means that:
a) Each new DNA molecule consists of two newly synthesized strands
b) Each new DNA molecule consists of one parental and one newly synthesized strand
c) One DNA molecule is completely new and the other is old
d) Half of the original DNA is degraded during replication
Answer: b) Each new DNA molecule consists of one parental and one newly synthesized strand
Explanation: In semi-conservative replication, each of the two new DNA molecules retains one original (parental) strand, and one newly synthesized strand, ensuring accurate duplication.
- Which enzyme initiates DNA replication by synthesizing a short RNA primer?
a) DNA polymerase
b) Primase
c) Ligase
d) Helicase
Answer: b) Primase
Explanation: Primase synthesizes a short RNA primer to provide a starting point for DNA polymerase to begin adding nucleotides during DNA replication.
- Which of the following enzymes is responsible for sealing the nicks between Okazaki fragments during DNA replication?
a) DNA polymerase
b) DNA ligase
c) Helicase
d) Primase
Answer: b) DNA ligase
Explanation: DNA ligase is responsible for joining the Okazaki fragments on the lagging strand by forming phosphodiester bonds between the sugar-phosphate backbones of adjacent DNA fragments.
- Which of the following is the correct sequence of events in translation?
a) Initiation → Elongation → Termination
b) Elongation → Initiation → Termination
c) Termination → Initiation → Elongation
d) Elongation → Termination → Initiation
Answer: a) Initiation → Elongation → Termination
Explanation: In translation, the process begins with initiation (assembly of the ribosome at the start codon), followed by elongation (addition of amino acids to the growing polypeptide chain), and ends with termination (release of the newly synthesized protein upon reaching a stop codon).
- Which of the following correctly pairs a type of RNA with its function?
a) mRNA – brings amino acids to the ribosome
b) tRNA – carries genetic information from the nucleus
c) rRNA – forms the core structure of the ribosome
d) snRNA – catalyzes peptide bond formation
Answer: c) rRNA – forms the core structure of the ribosome
Explanation: Ribosomal RNA (rRNA) forms the structural and functional core of the ribosome. tRNA brings amino acids to the ribosome, and mRNA carries the genetic information for protein synthesis. Small nuclear RNA (snRNA) is involved in splicing.
- Which of the following statements about the central dogma of molecular biology is correct?
a) DNA → Protein → RNA
b) RNA → DNA → Protein
c) DNA → RNA → Protein
d) Protein → RNA → DNA
Answer: c) DNA → RNA → Protein
Explanation: The central dogma of molecular biology states that genetic information flows from DNA to RNA through transcription and from RNA to protein through translation.
- Which of the following statements about telomeres is true?
a) Telomeres are found in prokaryotic chromosomes
b) Telomeres shorten with each round of DNA replication
c) Telomerase degrades telomeres to prevent cancer
d) Telomeres are synthesized during RNA splicing
Answer: b) Telomeres shorten with each round of DNA replication
Explanation: Telomeres are repetitive nucleotide sequences at the ends of eukaryotic chromosomes. They shorten with each round of DNA replication because DNA polymerase cannot fully replicate the ends of chromosomes. Telomerase helps restore telomere length in some cells.
- Which type of bond forms between nitrogenous bases in a DNA double helix?
a) Covalent bonds
b) Ionic bonds
c) Hydrogen bonds
d) Disulfide bonds
Answer: c) Hydrogen bonds
Explanation: Hydrogen bonds form between complementary nitrogenous bases in the DNA double helix. Adenine pairs with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds.
- Which of the following statements about the lac operon is false?
a) The lac operon is induced in the presence of lactose
b) The lac repressor binds to the operator when lactose is absent
c) The lac operon is an example of positive regulation
d) The genes of the lac operon are required for lactose metabolism
Answer: c) The lac operon is an example of positive regulation
Explanation: The lac operon is primarily regulated through negative regulation, where the lac repressor binds to the operator and prevents transcription in the absence of lactose. In the presence of lactose, the repressor is inactivated, allowing transcription.
- Which of the following is a feature of RNA but not DNA?
a) Double-stranded structure
b) Contains thymine instead of uracil
c) Ribose sugar in its backbone
d) Stable under alkaline conditions
Answer: c) Ribose sugar in its backbone
Explanation: RNA contains ribose sugar, while DNA contains deoxyribose sugar. Additionally, RNA contains uracil instead of thymine and is typically single-stranded. RNA is less stable than DNA under alkaline conditions.
- Which of the following processes does NOT occur in prokaryotes?
a) Transcription
b) Translation
c) RNA splicing
d) DNA replication
Answer: c) RNA splicing
Explanation: Prokaryotic genes do not contain introns, so RNA splicing does not occur in prokaryotes. RNA splicing is a feature of eukaryotic cells where introns are removed from pre-mRNA before translation.
- Which of the following mechanisms allows a single gene to encode multiple proteins?
a) DNA replication
b) Alternative splicing
c) RNA editing
d) RNA interference
Answer: b) Alternative splicing
Explanation: Alternative splicing allows a single gene to produce different mRNA transcripts by including or excluding certain exons, leading to the production of multiple proteins from the same gene.
- The process by which a bacterial cell takes up DNA from its surroundings and incorporates it into its own genome is called:
a) Conjugation
b) Transformation
c) Transduction
d) Transcription
Answer: b) Transformation
Explanation: Transformation is the process by which a bacterial cell takes up extracellular DNA and incorporates it into its genome. This can result in genetic changes. Conjugation and transduction are other mechanisms of genetic exchange in bacteria.
- Which of the following statements best describes the function of snRNPs (small nuclear ribonucleoproteins)?
a) They help in the degradation of mRNA
b) They assist in the assembly of ribosomes
c) They are involved in RNA splicing
d) They synthesize rRNA
Answer: c) They are involved in RNA splicing
Explanation: Small nuclear ribonucleoproteins (snRNPs) are part of the spliceosome, a complex responsible for removing introns from pre-mRNA during RNA splicing in eukaryotes.
- Which enzyme in prokaryotes is responsible for the synthesis of most of the new DNA during replication?
a) DNA polymerase I
b) DNA polymerase III
c) Primase
d) Ligase
Answer: b) DNA polymerase III
Explanation: DNA polymerase III is the main enzyme responsible for synthesizing new DNA strands during replication in prokaryotes. DNA polymerase I mainly functions in removing RNA primers and filling in the gaps with DNA.
- What is the consequence of a nonsense mutation?
a) It changes one amino acid in a protein
b) It introduces a stop codon, prematurely ending translation
c) It shifts the reading frame of the gene
d) It has no effect on the protein sequence
Answer: b) It introduces a stop codon, prematurely ending translation
Explanation: A nonsense mutation changes a codon to a stop codon, which leads to the premature termination of protein synthesis, often resulting in a truncated, nonfunctional protein.
- Which of the following techniques is used to amplify a specific DNA sequence?
a) Gel electrophoresis
b) Polymerase chain reaction (PCR)
c) Southern blotting
d) DNA sequencing
Answer: b) Polymerase chain reaction (PCR)
Explanation: PCR is a technique used to amplify a specific DNA sequence by repeatedly heating and cooling the sample to denature the DNA, anneal primers, and extend the new DNA strand using a DNA polymerase.
- What is the role of DNA helicase during DNA replication?
a) Synthesizing new DNA strands
b) Adding RNA primers to the template strand
c) Unwinding the double-stranded DNA helix
d) Connecting Okazaki fragments on the lagging strand
Answer: c) Unwinding the double-stranded DNA helix
Explanation: DNA helicase unwinds the double-stranded DNA at the replication fork by breaking the hydrogen bonds between the complementary bases, allowing the DNA polymerase to access the template strands for replication.
- Which of the following RNA types is involved in carrying genetic information from DNA to the ribosome for protein synthesis?
a) mRNA
b) tRNA
c) rRNA
d) siRNA
Answer: a) mRNA
Explanation: Messenger RNA (mRNA) carries the genetic code transcribed from DNA to the ribosome, where it is translated into a specific sequence of amino acids to form a protein.
- Which of the following is a characteristic feature of a codon?
a) It is made up of four nucleotides
b) Each codon is recognized by an anticodon on tRNA
c) There are 64 stop codons
d) All amino acids are coded by a single codon
Answer: b) Each codon is recognized by an anticodon on tRNA
Explanation: Codons are sequences of three nucleotides on mRNA that correspond to specific amino acids. Each codon is recognized by a complementary anticodon on tRNA, which brings the correct amino acid during translation.
- Which type of DNA sequence in eukaryotes is typically involved in regulating gene expression by silencing transcription?
a) Exons
b) Promoters
c) Enhancers
d) Silencers
Answer: d) Silencers
Explanation: Silencers are regulatory DNA sequences that bind to repressor proteins, inhibiting transcription and decreasing gene expression. Enhancers, in contrast, increase the transcription of associated genes.
- Which of the following enzymes catalyzes the synthesis of DNA from an RNA template in retroviruses?
a) RNA polymerase
b) DNA polymerase
c) Reverse transcriptase
d) DNA ligase
Answer: c) Reverse transcriptase
Explanation: Reverse transcriptase is an enzyme found in retroviruses that catalyzes the synthesis of DNA from an RNA template, allowing the viral RNA genome to integrate into the host DNA.
- The process of removing introns and joining exons in a pre-mRNA transcript is called:
a) RNA capping
b) RNA splicing
c) RNA interference
d) Polyadenylation
Answer: b) RNA splicing
Explanation: RNA splicing is the process by which non-coding introns are removed from a pre-mRNA transcript, and coding exons are joined together to form the mature mRNA that will be translated into a protein.
- Which of the following best describes the function of telomerase in eukaryotic cells?
a) It repairs mismatched bases during DNA replication
b) It shortens telomeres during each round of cell division
c) It adds repetitive nucleotide sequences to the ends of chromosomes
d) It prevents the unwinding of DNA during replication
Answer: c) It adds repetitive nucleotide sequences to the ends of chromosomes
Explanation: Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of chromosomes (telomeres) to prevent their shortening during DNA replication, maintaining chromosome stability.
- In eukaryotic cells, transcription takes place in the:
a) Cytoplasm
b) Mitochondria
c) Nucleus
d) Ribosomes
Answer: c) Nucleus
Explanation: In eukaryotic cells, transcription (the process of synthesizing RNA from DNA) occurs inside the nucleus, while translation (protein synthesis) takes place in the cytoplasm at the ribosomes.
- Which of the following correctly defines a frameshift mutation?
a) A mutation that results in a premature stop codon
b) A point mutation that changes one amino acid
c) A deletion or insertion of nucleotides that changes the reading frame
d) A mutation that does not alter the amino acid sequence
Answer: c) A deletion or insertion of nucleotides that changes the reading frame
Explanation: A frameshift mutation occurs when nucleotides are inserted or deleted from the DNA sequence, altering the reading frame of the genetic code, which can result in an entirely different protein being synthesized.
- The process by which DNA is transferred from one bacterium to another via a bacteriophage is called:
a) Transformation
b) Conjugation
c) Transduction
d) Transcription
Answer: c) Transduction
Explanation: Transduction is the process by which a bacteriophage (a virus that infects bacteria) transfers DNA from one bacterium to another, facilitating genetic exchange between bacteria.
- Which of the following is a key function of RNA polymerase during transcription?
a) Proofreading the newly synthesized DNA
b) Synthesizing RNA from a DNA template
c) Binding amino acids to tRNA
d) Adding a 5′ cap and poly-A tail to mRNA
Answer: b) Synthesizing RNA from a DNA template
Explanation: RNA polymerase synthesizes RNA by reading the DNA template strand and assembling complementary RNA nucleotides during transcription.
- In the Hershey-Chase experiment, which part of the bacteriophage was labeled with radioactive phosphorus?
a) Protein coat
b) DNA
c) RNA
d) Lipid envelope
Answer: b) DNA
Explanation: In the Hershey-Chase experiment, DNA was labeled with radioactive phosphorus (32P), and the protein coat was labeled with radioactive sulfur (35S). The experiment demonstrated that DNA is the genetic material.
- What is the significance of the 5′ cap and poly-A tail added to eukaryotic mRNA?
a) They help in mRNA splicing
b) They signal termination of transcription
c) They protect mRNA from degradation and help in translation initiation
d) They mark the mRNA for degradation by nucleases
Answer: c) They protect mRNA from degradation and help in translation initiation
Explanation: The 5′ cap and poly-A tail are important for protecting the mRNA from degradation by nucleases and play a role in the initiation of translation by ribosomes.
- Which of the following is true about gene expression in prokaryotes?
a) Transcription occurs in the nucleus, and translation occurs in the cytoplasm
b) mRNA processing involves the addition of a 5′ cap and poly-A tail
c) Transcription and translation occur simultaneously
d) Introns are removed from mRNA before translation
Answer: c) Transcription and translation occur simultaneously
Explanation: In prokaryotes, transcription and translation are coupled, meaning that translation begins before transcription is complete since both processes occur in the cytoplasm and there is no nuclear membrane separating them.
- In eukaryotes, which of the following elements enhances the transcription of a gene located far from its site?
a) Promoter
b) Operator
c) Silencer
d) Enhancer
Answer: d) Enhancer
Explanation: Enhancers are DNA sequences that can increase the transcription of a gene even if they are located far from the gene they regulate. They function by interacting with specific transcription factors to enhance gene expression.
- Which of the following best describes a silent mutation?
a) A mutation that changes an amino acid codon into a stop codon
b) A mutation that does not change the amino acid sequence of the protein
c) A mutation that shifts the reading frame
d) A mutation that deletes large segments of DNA
Answer: b) A mutation that does not change the amino acid sequence of the protein
Explanation: A silent mutation is a point mutation in the DNA sequence that does not result in a change in the amino acid sequence of the protein, often due to the redundancy of the genetic code.
- Which of the following enzymes is responsible for the synthesis of the lagging strand during DNA replication?
a) DNA polymerase I
b) DNA polymerase III
c) Ligase
d) Primase
Answer: b) DNA polymerase III
Explanation: DNA polymerase III synthesizes the lagging strand in short fragments called Okazaki fragments. DNA polymerase I removes RNA primers and fills in the gaps with DNA, while DNA ligase joins the fragments.
- Which of the following enzymes is responsible for relieving the supercoiling tension ahead of the replication fork?
a) Helicase
b) DNA polymerase
c) Topoisomerase
d) Ligase
Answer: c) Topoisomerase
Explanation: Topoisomerase helps to relieve the supercoiling tension ahead of the replication fork that is caused by the unwinding of the DNA double helix. It cuts and rejoins the DNA to prevent tangling.
- Which of the following is the role of tRNA during translation?
a) Synthesizes mRNA from a DNA template
b) Carries amino acids to the ribosome
c) Catalyzes the formation of peptide bonds
d) Regulates transcription
Answer: b) Carries amino acids to the ribosome
Explanation: Transfer RNA (tRNA) carries specific amino acids to the ribosome, where the anticodon on tRNA pairs with the corresponding codon on mRNA during protein synthesis, allowing the ribosome to link amino acids into a growing polypeptide chain.
- Which of the following correctly explains the difference between euchromatin and heterochromatin?
a) Euchromatin is transcriptionally active, while heterochromatin is transcriptionally inactive
b) Euchromatin consists of repetitive DNA, while heterochromatin consists of coding DNA
c) Heterochromatin is found in the nucleus, while euchromatin is in the cytoplasm
d) Euchromatin contains tightly packed DNA, while heterochromatin is loosely packed
Answer: a) Euchromatin is transcriptionally active, while heterochromatin is transcriptionally inactive
Explanation: Euchromatin is a less condensed form of chromatin that is accessible for transcription, making it transcriptionally active. Heterochromatin, on the other hand, is more tightly packed and transcriptionally inactive.
- Which of the following statements about the genetic code is false?
a) The genetic code is degenerate, meaning multiple codons can code for the same amino acid
b) The genetic code is nearly universal among all organisms
c) A single codon can code for multiple amino acids
d) The genetic code includes start and stop codons to signal the beginning and end of translation
Answer: c) A single codon can code for multiple amino acids
Explanation: A single codon cannot code for multiple amino acids. Each codon specifies only one amino acid, but multiple codons can code for the same amino acid, which is known as the degeneracy of the genetic code.
- Which of the following processes does not contribute to genetic variation?
a) Crossing over during meiosis
b) Independent assortment of chromosomes
c) Mitosis
d) Mutation
Answer: c) Mitosis
Explanation: Mitosis is a process of cell division that produces genetically identical daughter cells, so it does not contribute to genetic variation. Genetic variation is generated by processes like mutation, crossing over, and independent assortment during meiosis.
- Which of the following statements best describes an inducible operon?
a) It is always active unless repressed by a repressor protein
b) It is turned on by the presence of a specific substance
c) It is turned off by the presence of a specific substrate
d) It regulates genes responsible for amino acid synthesis
Answer: b) It is turned on by the presence of a specific substance
Explanation: An inducible operon, such as the lac operon, is normally inactive but becomes activated in the presence of a specific inducer, such as lactose, which binds to the repressor and allows transcription of the operon.
- Which of the following statements is true regarding RNA interference (RNAi)?
a) RNAi leads to the degradation of mRNA, preventing translation
b) RNAi enhances the translation of specific mRNAs
c) RNAi increases the stability of mRNA
d) RNAi promotes DNA replication in eukaryotes
Answer: a) RNAi leads to the degradation of mRNA, preventing translation
Explanation: RNA interference (RNAi) is a biological process in which small RNA molecules, such as siRNA or miRNA, bind to complementary mRNA and trigger its degradation, thus preventing translation and gene expression.
- In prokaryotes, which of the following proteins binds to the promoter region to initiate transcription?
a) RNA polymerase
b) Sigma factor
c) DNA polymerase
d) Helicase
Answer: b) Sigma factor
Explanation: In prokaryotes, the sigma factor is a subunit of RNA polymerase that recognizes and binds to the promoter region of a gene to initiate transcription. Once transcription begins, the sigma factor is released.
- Which of the following is true about histones?
a) Histones are proteins that help in the packaging of DNA into chromatin
b) Histones bind to RNA to stabilize its structure
c) Histones are enzymes that synthesize DNA during replication
d) Histones are non-protein coding regions of DNA
Answer: a) Histones are proteins that help in the packaging of DNA into chromatin
Explanation: Histones are positively charged proteins that package negatively charged DNA into nucleosomes, forming chromatin. This packaging allows DNA to be efficiently organized and condensed within the nucleus.
- The A site, P site, and E site are part of which of the following structures?
a) RNA polymerase
b) Ribosome
c) Spliceosome
d) DNA polymerase
Answer: b) Ribosome
Explanation: The A site (aminoacyl site), P site (peptidyl site), and E site (exit site) are the three key functional sites on a ribosome involved in the translation of mRNA into protein. These sites facilitate the binding of tRNA and the addition of amino acids to the growing polypeptide chain.
- What is the function of the TATA box in eukaryotic transcription?
a) It is a start codon in mRNA
b) It is a promoter sequence that helps RNA polymerase bind to the DNA
c) It is a region where translation terminates
d) It is a sequence that signals the addition of a poly-A tail
Answer: b) It is a promoter sequence that helps RNA polymerase bind to the DNA
Explanation: The TATA box is a conserved DNA sequence found in the promoter region of many eukaryotic genes. It helps RNA polymerase bind to the promoter, initiating the process of transcription.
- Which of the following is an outcome of DNA methylation?
a) Increased gene expression
b) Decreased gene expression
c) Increased rate of DNA replication
d) Promotion of mRNA stability
Answer: b) Decreased gene expression
Explanation: DNA methylation typically results in the repression of gene expression. When methyl groups are added to cytosine residues in DNA, it can prevent transcription factors from binding, leading to decreased transcriptional activity.
- The initiation codon for protein synthesis in both prokaryotes and eukaryotes is:
a) UAA
b) UAG
c) AUG
d) UGA
Answer: c) AUG
Explanation: AUG is the initiation codon that signals the start of translation and codes for the amino acid methionine in eukaryotes and formylmethionine in prokaryotes. It sets the reading frame for protein synthesis.
- Which of the following molecules is involved in post-transcriptional gene silencing?
a) miRNA
b) rRNA
c) tRNA
d) mRNA
Answer: a) miRNA
Explanation: MicroRNA (miRNA) is involved in post-transcriptional gene silencing by binding to complementary mRNA sequences, either degrading the mRNA or preventing its translation into protein.
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