Problem 6 - Campbell Biology

Question

Which of the following occurs during \(\mathrm{S}\) phase? (A) condensation of the chromosomes (B) replication of the DNA (C) separation of sister chromatids (D) spindle formation

Step-by-Step Solution

Answer

Replication of the DNA

Step 1: Identify the S phase function

Understand what the S phase of the cell cycle is responsible for. The S phase (synthesis phase) is primarily involved in replicating the DNA in the cell, ensuring that each daughter cell will have an identical set of chromosomes.

Step 2: Evaluate each option

Assess which of the given options aligns with the activities during the S phase. Compare and discard the activities that relate to other phases of the cell cycle. For example, chromosome condensation occurs during prophase of mitosis, separation of sister chromatids happens in anaphase, and spindle formation occurs during prophase and metaphase.

Step 3: Confirm the correct answer

Determine which activity specifically occurs during the S phase. Based on the functions reviewed, the replication of DNA is the process that takes place during the S phase of the cell cycle.

Key Concepts

DNA replication

During the S phase of the cell cycle, DNA replication is the key event that takes place. This phase is crucial because it ensures the genetic material is accurately copied.

The process begins at specific locations on the DNA molecule known as origins of replication. Specialized proteins then unwind the DNA helix and create a replication fork. This is the site where the DNA is divided into two single strands, and each strand serves as a template for the creation of a new, complementary strand.

Enzymes called DNA polymerases add nucleotides, the building blocks of DNA, to the growing strand by matching them with the complementary bases on the template strand. As a result, two identical DNA molecules are formed.

This replication process is important for maintaining genetic consistency across cell generations. Any errors during replication can lead to mutations, which might cause diseases or malfunctions in the cell.

Cell cycle phases

The cell cycle consists of several distinct phases that a cell undergoes during its life cycle. The major phases include:

* G1 phase: This is the first gap phase where the cell grows and prepares for DNA replication.
* S phase: The synthesis phase where DNA replication occurs. This ensures each daughter cell will inherit an identical set of chromosomes.
* G2 phase: The second gap phase where the cell continues to grow and prepares for mitosis. It ensures all the replicated DNA is intact and undamaged.
* M phase: The mitosis phase where the cell divides its copied chromosomes into two identical sets before finally splitting into two daughter cells.

Interphase, which includes G1, S, and G2 phases, is when the cell prepares for division. The actual division process happens in the M phase, which includes prophase, metaphase, anaphase, and telophase followed by cytokinesis.

Chromosome duplication

Chromosome duplication is a critical step during the S phase of the cell cycle where each chromosome is copied to produce two identical sister chromatids. These chromatids are held together at a region called the centromere.

The duplication process ensures that when the cell divides, each daughter cell receives an exact copy of the genetic material. If chromosome duplication did not occur, the daughter cells would end up with an incomplete set of genetic instructions, leading to dysfunction or cell death.

Before a cell enters mitosis, the integrity of the duplicated chromosomes is checked during the G2 phase. Any errors found are repaired to ensure the genetic material is faithfully passed on.

Chromosome duplication is pivotal not only for routine cellular function but also for growth and development in multicellular organisms. Without precise replication and distribution of chromosomes, organisms could not maintain their genetic identity across generations.