Replication, Transcription and Translation MCQ Quiz in मराठी - Objective Question with Answer for Replication, Transcription and Translation - मोफत PDF डाउनलोड करा

Key Points

• The correct answer is option 3: (A), (C) and (D) only.
• This means the regions of the transcription unit include the Promoter, Terminator, and the Structural Gene.
• The Promoter is a region of DNA that initiates transcription of a particular gene. It is where the RNA polymerase binds to start transcription.
• The Terminator is a sequence of nucleotides in DNA that marks the end of a gene or operon in genomic DNA during transcription.
• The Structural Gene consists of the DNA sequence that is actually transcribed into RNA, which may then be translated into a protein.

Additional Information

• Sigma factor is not part of the DNA sequence of the transcription unit but rather a protein needed for the initiation of transcription in bacteria. It helps the RNA polymerase to bind to the promoter.
• Options 1, 2, and 4 are incorrect because they include the Sigma factor, which is not a region of the transcription unit but rather a transcription initiation factor.

The correct answer is 3ʹ ATG 5ʹ

Explanation:

• Central Dogma of Molecular Biology: The central dogma explains the flow of genetic information from DNA to RNA to protein. The process involves transcription (DNA to RNA) and translation (RNA to protein).
• Codon and Anticodon: Codons are sequences of three nucleotides on mRNA that specify a particular amino acid. Anticodons are complementary sequences of three nucleotides on tRNA that pair with the codons during protein synthesis.
• Transcription: During transcription, the DNA sequence is copied into mRNA. For example, if the DNA sequence is 3ʹ ATG 5ʹ, the corresponding mRNA sequence will be 5ʹ UAC 3ʹ.
• Translation: During translation, tRNA molecules with anticodons pair with the mRNA codons to add the correct amino acids to the growing polypeptide chain. For instance, if the mRNA codon is 5ʹ UAC 3ʹ, the tRNA anticodon will be 3ʹ AUG 5ʹ.

During transcription, the template strand of DNA (also called the antisense strand) is used by RNA polymerase to synthesize mRNA. The mRNA is complementary to the template strand. Since the coding strand is complementary to the template strand, the mRNA sequence is nearly identical to the coding strand, except that:

• DNA's T is replaced by U in mRNA.

Correct answer:3

Solution:

Concept:

• Gene expression refers to the process by which the information in the genes is expressed in the form of a protein product.
• Regulation of gene expression may take place at various levels and may be controlled by metabolic, physiological, or environmental conditions.
• One of the regulation mechanisms is a transcriptional regulation system.
• In prokaryotes, we find polycistronic genes, which are mostly regulated at the transcription initiation site.
• In a transcription unit, the function of RNA polymerase is regulated by interactions with some regulatory proteins.
• This is known as an operon system, which can be either positively (by activators) or negatively controlled (by repressors). 

Key Points 

• An operon is a part of genetic material which acts as a single regulated unit having one or more structural genes.
• The lac operon consists of the following parts:
• Structural Gene - It consists of 3 genes:
  • z - codes for β-galactosidase
  • y - codes for permease
  • a - codes for transacetylase
• Operator -
  • It is present adjacent to the structural gene.
  • It is the site for the binding of repressor proteins.
• Regulator -
  • It comprises the i-gene, which codes for the repressor protein.
  • The repressor protein is synthesized all the time constitutively.
• Promoter -
  • It is the transcription initiation site where RNA polymerase binds.
• Inducer -
  • It is the molecule that determines whether the repressor will bind to the operator or not.
  • Hence, it regulates the operon.
  • Example - Lactose in lac operon.
• Lac operon is regulated by a repressor and hence it is a negative regulation.

Explanation:

• In the absence of lactose, the repressor protein binds at the operator site and prevents RNA polymerase to transcribe the structural genes.
• But in the presence of lactose, transcription of the genes takes place.
• The inducer binds to the repressor and inactivates it by forming the repressor-inducer complex.
• This complex prevents the repressor from binding with the operator.
• Thus, the RNA polymerase slides along the DNA without any hindrance, and thus, the genes get expressed.

So, the correct option is Option  3)  They can act both as activators and as repressors.

The correct answer is a modified guanine nucleotide 

Explanation:

• The cap structure, found at the 5' end of mRNA, is crucial for mRNA stability and the initiation of translation.
• It is formed by the addition of a methylated guanosine triphosphate (mGTP). This modification is known as the 5' cap.
• The primary transcripts contain both the exons and the introns and are non-functional. Hence, it is subjected to a process called splicing where the introns are removed and exons are joined in a defined order.
• hnRNA undergoes additional processing called as capping and tailing.
• In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5'-end of hnRNA.
• In tailing, adenylate residues (200-300) are added at 3'-end in a template independent manner. It is the fully processed hnRNA, now called mRNA, that is transported out of the nucleus for translation.

Fig: Process of Transcription in Eukaryotes

The correct option is: 2

Explanation:

• It binds to the TATA box and positions RNA polymerase II correctly: The TATA box is a DNA sequence that is recognized by the TATA-binding protein (TBP), not TFIIB. TBP, part of the TFIID complex, binds to the TATA box and helps position the RNA polymerase II correctly at the promoter region. Therefore, this statement is incorrect.

• It helps in the formation of the transcription initiation complex by interacting with RNA polymerase II and TBP: TFIIB plays a crucial role in the formation of the transcription initiation complex. It binds to both the TATA-binding protein (TBP) and RNA polymerase II, helping to position RNA polymerase II at the start site for transcription. TFIIB also helps recruit other transcription factors, making this the correct description of its function.

• It is responsible for the elongation phase of transcription: TFIIB is involved in the initiation phase of transcription, not the elongation phase. Once RNA polymerase II begins transcription, TFIIS and other factors are more directly involved in elongation. Therefore, this statement is incorrect.

• It acts as a coactivator by facilitating the binding of enhancers to the promoter region: TFIIB is a transcription factor involved in the initiation phase, not a coactivator that links enhancers to the promoter region. Coactivators often interact with the transcriptional machinery and enhancer regions, but this is not the role of TFIIB. Therefore, this statement is incorrect.

The correct answer is One

Explanation:

• RNA polymerase is an enzyme responsible for synthesizing RNA from a DNA template during the process of transcription.
• In prokaryotes, the transcription machinery is relatively simpler compared to eukaryotes.
• Prokaryotic cells typically have a single type of RNA polymerase that synthesizes all types of RNA, including mRNA, tRNA, and rRNA.
• In eukaryotes, there are three main types of RNA polymerases, each responsible for synthesizing different classes of RNA:
  • RNA polymerase I synthesizes ribosomal RNA rRNA, specifically the 28S, 18S, and 5.8S rRNAs.
  • RNA polymerase II synthesizes messenger RNA mRNA, most small nuclear RNAs snRNAs, and some microRNAs miRNAs.
  • RNA polymerase III synthesizes transfer RNA tRNA, 5S rRNA, and other small RNAs.

Concept:

• In eukaryotes, the mRNA is formed is the form of heterogenous RNA (hnRNA).
• This hnRNA needs to go through some post-transcriptional modification processes to form the mature mRNA that can be translated into polypeptide.
• Transcription in eukaryotes takes place inside the nucleus whereas the translation takes place in the cytoplasm.
• Thus, the mRNA also needs to be transported to the cytoplasm for translation to proceed.

Explanation:

• Statement I - CORRECT
  • Tailing is a process for post-transcriptional modification of mRNA in eukaryotes.
  • It is the process of adding about 200-300 adenylate residues to the 3'-end of the newly formed RNA.
  • These residues form a poly-A tail at the 3'-end of the mRNA and thus, the name "tailing".
  • The process is also known as polyadenylation.
• Statement II - INCORRECT
  • Tailing is a RNA-processing step that takes place in eukaryotic cells and NOT bacterial (prokaryotic) cells.
  • This is due to the complexity of the eukaryotic cell structure and also the transcription process.
  • The RNA molecules have the risk of being degraded by cytoplasmic enzymes when the RNA is transported from nucleus to cytoplasm.
  • Tailing helps in protecting the 3'-end of the coding sequence of the RNA from digestive enzymes.

Therefore, Statement I is correct but Statement II is incorrect.

Hence, the correct answer is option (3).

Concept:

• Transcription is the process of copying the genetic information from one strand of DNA onto the RNA.
• It takes place with the help of the enzyme DNA-dependent RNA polymerase.
• This RNA polymerase enzyme carries out all the steps of mRNA formation in a bacterial cell.
• However, in an eukaryotic cell, the process of transcription is more complex.
• There are multiple RNA polymerases that are distributed in the nucleus as well as in other organelles.
• This ensures a division of labour in the cell.

Explanation:

• There are 3 types of RNA polymerase in an eukaryotic nucleus:
  • RNA polymerase I - It forms ribosomal RNAs (rRNAs) - 28S, 18S, 5.8S. 
  • RNA polymerase II - It forms the hnRNA, which is the presursor for mature mRNA.
  • RNA polymerase III - It forms various types of RNAs - tRNA, snRNA, 5S rRNA.
• Therefore, among the given options, only 5S rRNA is transcribed by RNA polymerase III.

Hence, the correct answer is option (2).

Additional Information

• Transcription in eukaryotic cells are also complex due to the requirement for post-transcriptional modification of mRNA.
• The RNA formed is in hnRNA form, that contains both exons (coding regions) and introns (non-coding regions).
• The hnRNA undergoes 3 basic modification steps to become a mature mRNA:
  1. Splicing - Removal of introns from the mRNA
  2. Capping - Addition of methyl guanosine triphosphate at 5’-end of mRNA
  3. Tailing/Polyadenylation - Addition of adenylate residues at 3'-end of the mRNA
• Capping and tailing helps in protecting the ends of the mRNA when it is transported from the nucleus to the cytoplasm for translation.

Key Points

• The correct answer is option 3: (A), (C) and (D) only.
• This means the regions of the transcription unit include the Promoter, Terminator, and the Structural Gene.
• The Promoter is a region of DNA that initiates transcription of a particular gene. It is where the RNA polymerase binds to start transcription.
• The Terminator is a sequence of nucleotides in DNA that marks the end of a gene or operon in genomic DNA during transcription.
• The Structural Gene consists of the DNA sequence that is actually transcribed into RNA, which may then be translated into a protein.

Additional Information

• Sigma factor is not part of the DNA sequence of the transcription unit but rather a protein needed for the initiation of transcription in bacteria. It helps the RNA polymerase to bind to the promoter.
• Options 1, 2, and 4 are incorrect because they include the Sigma factor, which is not a region of the transcription unit but rather a transcription initiation factor.

The correct answer is Chromosome 1

Concept:

• The Human Genome Project (HGP) was an international effort aimed at sequencing the entire human genome, which consists of approximately 3 billion base pairs spread across 24 distinct chromosomes (22 autosomes and the sex chromosomes X and Y).
• Sequencing a chromosome involves determining the exact order of the nucleotide bases (adenine, thymine, cytosine, and guanine) that make up the DNA of that chromosome.
• Chromosome 1 is the largest human chromosome, containing about 249 million base pairs and approximately 2,000-2,100 genes. Its size and complexity posed significant challenges for sequencing efforts.
• Completion of the sequencing of Chromosome 1 marked a significant milestone in the Human Genome Project due to its size and complexity, which presented more difficulties compared to other smaller chromosomes.
• The sequencing of the human genome has provided critical insights into the genetic basis of many diseases, the functional elements of the genome, and evolutionary processes.

Explanation:

1. Chromosome 1: Chromosome 1 was the last human chromosome to be completely sequenced because it is the largest and most gene-rich chromosome, making its sequencing particularly challenging.
2. Chromosome 11: Although it contains important genes, it was sequenced before Chromosome 1. It is not recognized as the last chromosome to be sequenced.
3. Chromosome 21: This chromosome was sequenced relatively early due to its smaller size and its significance in Down syndrome research. It was not the last chromosome to be sequenced.
4. Chromosome X: The X chromosome is one of the sex chromosomes and was not the last to be sequenced. It was sequenced earlier in the project.

Therefore, the correct answer is Chromosome 1, as it was the last human chromosome to be completely sequenced.