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71.

In the context of the lac operon in E. coli, what induces the expression of genes required for lactose metabolism?

Glucose

Galactose

Lactose

Sucrose

Explanation Comments

Answer: Lactose

Explanation:

Lactose acts as an inducer by binding to the lac repressor, causing it to release from the operator region and allowing transcription of the lac operon genes.

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72.

Which specific protein complex is responsible for the removal of introns from pre-mRNA?

RNA polymerase II

Ribosome

Spliceosome

Proteasome

Explanation Comments

Answer: Spliceosome

Explanation:

The spliceosome is a large RNA-protein complex that removes introns from pre-mRNA by splicing together the exons to form mature mRNA.

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73.

What is the function of ubiquitin in the cell?

Facilitates protein synthesis

Tags proteins for degradation

Assists in DNA replication

Regulates gene expression

Explanation Comments

Answer: Tags proteins for degradation

Explanation:

Ubiquitin is a small protein that attaches to other proteins to mark them for degradation by the proteasome, a process essential for protein quality control and regulation.

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74.

Which phase of meiosis is characterized by the formation of chiasmata and the exchange of genetic material between homologous chromosomes?

Telophase I

Metaphase I

Prophase I

Anaphase I

Explanation Comments

Answer: Prophase I

Explanation:

During prophase I of meiosis, homologous chromosomes pair up and exchange genetic material through a process called crossing over, forming structures known as chiasmata.

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75.

Which enzyme is directly involved in transcribing the leading strand during DNA replication?

Primase

DNA polymerase III

DNA ligase

Topoisomerase

Explanation Comments

Answer: DNA polymerase III

Explanation:

DNA polymerase III is the primary enzyme responsible for synthesizing the leading strand continuously during DNA replication in prokaryotes.

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76.

In the regulation of the trp operon in E. coli, what molecule acts as a corepressor to inhibit the operon's expression?

Lactose

Galactose

Tryptophan

Glucose

Explanation Comments

Answer: Tryptophan

Explanation:

Tryptophan acts as a corepressor by binding to the trp repressor protein, enabling it to bind to the operator and inhibit transcription of the trp operon.

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77.

What is the main function of telomerase in eukaryotic cells?

Unwinding DNA during replication

Repairing DNA damage

Synthesizing RNA primers

Extending the telomeres of chromosomes

Explanation Comments

Answer: Extending the telomeres of chromosomes

Explanation:

Telomerase adds repetitive nucleotide sequences to the ends of chromosomes, thereby maintaining their length and stability during replication.

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78.

Which molecule is a secondary messenger produced in response to the activation of G-protein-coupled receptors (GPCRs) by ligands?

NADH

ATP

FADH2

cAMP

Explanation Comments

Answer: cAMP

Explanation:

Cyclic AMP (cAMP) is a secondary messenger produced from ATP by the enzyme adenylate cyclase in response to the activation of GPCRs.

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79.

In the Calvin cycle, which enzyme catalyzes the fixation of carbon dioxide to ribulose-1,5-bisphosphate (RuBP)?

ATP synthase

Rubisco

Hexokinase

Phosphofructokinase

Explanation Comments

Answer: Rubisco

Explanation:

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the fixation of carbon dioxide to RuBP, forming 3-phosphoglycerate in the Calvin cycle.

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80.

Which protein is a key regulator of the cell cycle and is frequently mutated in various cancers?

Myosin

p53

Ras

Actin

Explanation Comments

Answer: p53

Explanation:

p53 is a tumor suppressor protein that regulates the cell cycle and apoptosis. Mutations in the p53 gene are common in many types of cancer, leading to uncontrolled cell growth.

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