Quiz: Gene Expression and RNA Processing — 10 perguntas

1. What is the primary role of RNA polymerase during transcription in both prokaryotic and eukaryotic cells?

A. It recognizes promoter sequences and synthesizes RNA complementary to the DNA template strand.

B. It unwinds DNA and synthesizes DNA strands.

C. It processes pre-mRNA by splicing introns.

D. It transports mRNA from the nucleus to the cytoplasm.

Answer: (A)

Explicação

RNA polymerase is responsible for recognizing specific promoter sequences and synthesizing RNA that is complementary to the DNA template strand. It unwinds the DNA and catalyzes the formation of phosphodiester bonds to produce the RNA transcript in the 5′-to-3′ direction.

2. What is the primary enzyme responsible for transcribing DNA into RNA?

A. DNA polymerase

B. RNA polymerase

C. Reverse transcriptase

D. Ligase

Answer: (B)

Explicação

RNA polymerase synthesizes RNA from a DNA template during transcription, making it the key enzyme in this process. DNA polymerase, on the other hand, synthesizes DNA during replication, not transcription.

3. Which of the following accurately describes the process of RNA splicing?

A. The addition of a 5′ cap and a poly-A tail.

B. The removal of introns and joining of exons, involving snRNPs and lariat formation.

C. The translation of mRNA into protein.

D. The removal of exons and joining of introns.

Answer: (B)

Explicação

RNA splicing involves the removal of introns and the joining of exons to produce a continuous coding sequence. This process is mediated by small nuclear ribonucleoproteins (snRNPs) and involves the formation of a lariat structure at the branch point.

4. Which of the following is a common feature of eukaryotic promoters?

A. TATA box

B. -35 and -10 regions

C. Pribnow box

D. operator sequence

Answer: (A)

Explicação

The TATA box is a conserved promoter element in eukaryotes; bacteria typically have -10 and -35 regions instead.

5. What is the significance of the genetic code being degenerate, especially at the third codon position?

A. It ensures that each amino acid is encoded by only one unique codon.

B. It prevents mutations from affecting protein synthesis.

C. It allows for multiple amino acids to be encoded by a single codon.

D. It provides redundancy, reducing the impact of mutations at the third position of codons.

Answer: (D)

Explicação

The degeneracy of the genetic code, particularly at the third codon position, means that multiple codons can encode the same amino acid. This redundancy provides a buffer against mutations, as changes at the third position often do not alter the amino acid sequence of the resulting protein.

6. What is the role of snRNPs in gene expression?

A. Initiating transcription

B. Processing splicing of pre-mRNA

C. Facilitating translation

D. Degrading mRNA

Answer: (B)

Explicação

snRNPs are involved in splicing, removing introns from pre-mRNA to produce mature mRNA.

7. What modification occurs at the 5' end of eukaryotic mRNA that enhances its stability?

A. Poly-A tail

B. 5' cap

C. Splicing

D. Ubiquitination

Answer: (B)

Explicação

The 5' cap is added to eukaryotic mRNA and protects it from degradation, aiding in stability and translation.

8. Which statement correctly describes the function of the ribosome during translation?

A. Synthesizes DNA from RNA

B. Decodes mRNA codons and assembles amino acids into proteins

C. Transcribes DNA into mRNA

D. Removes introns from pre-mRNA

Answer: (B)

Explicação

The ribosome decodes mRNA codons and assembles amino acids accordingly, synthesizing proteins.

9. Which of the following is NOT a function associated with RNA modifications?

A. Enhancing mRNA stability

B. Facilitating splicing

C. Promoting ribozyme activity

D. Encoding amino acids

Answer: (D)

Explicação

RNA modifications do not encode amino acids; rather, they modify RNA molecules to influence stability and function.

10. In prokaryotic transcription, what are the roles of the -10 and -35 regions?

A. Binding sites for RNA polymerase and sigma factor

B. Start and stop codons

C. Termination signals

D. Enhances mRNA stability

Answer: (A)

Explicação

The -10 and -35 regions are promoter sequences recognized by RNA polymerase and sigma factor, initiating transcription in bacteria.