Problem 2 - Biology of Humans: Concepts, Applications, and Issues

Question

DNA is synthesized (replicated) during a. interphase. b. prophase. c. metaphase. d. anaphase.

Step-by-Step Solution

Answer

DNA is synthesized during interphase (option a).

Step 1: Understanding Cell Cycle Phases

The cell cycle is divided into four main phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Understanding when DNA replication occurs is essential to determine the correct answer.

Step 2: Identifying the S Phase

During the S phase of interphase, DNA is synthesized and replicated. This ensures that each daughter cell will have an identical set of DNA after cell division.

Step 3: Reviewing Mitosis Phases

The phases of mitosis (prophase, metaphase, anaphase, telophase) focus on the separation of chromosomes and the division of the cell, not the replication of DNA.

Step 4: Eliminating Incorrect Options

Since DNA replication happens during the S phase of interphase, any options from the mitosis phase (prophase, metaphase, anaphase) can be eliminated.

Step 5: Final Answer

By understanding that DNA synthesis occurs during interphase, the correct answer is option 'a' – interphase.

Key Concepts

Cell Cycle

The cell cycle is a series of stages that cells go through to grow and divide. It consists of four main phases:

• G1 (Gap 1)
• S (Synthesis)
• G2 (Gap 2)
• M (Mitosis)

The primary purpose of the cell cycle is to ensure that cells can replicate and divide, producing two identical daughter cells.
In the G1 phase, cells grow and perform regular functions. The G2 phase is another period of growth and preparation for cell division. Mitosis is the final phase where the actual division of the cell occurs.
Understanding these phases helps in identifying when critical processes like DNA replication take place within the cycle.

Interphase

Interphase is the phase of the cell cycle between cell divisions. It consists of three stages: G1, S, and G2.
During interphase, the cell prepares itself for division by growing, increasing the number of organelles, and replicating its DNA.

• G1 Phase: The cell grows and synthesizes proteins essential for cell functions.
• S Phase: DNA is synthesized and replicated. This ensures that each daughter cell will have an identical set of DNA post-division.
• G2 Phase: The cell continues to grow and makes final preparations for mitosis.

Interphase is crucial because it sets the stage for a successful division, ensuring that all cellular components are adequate and the DNA is accurately duplicated.

Mitosis

Mitosis is the phase of the cell cycle where the cell divides its replicated DNA and cytoplasm to form two daughter cells. It consists of several stages:

• Prophase: Chromosomes condense, and the nuclear envelope begins to dissolve.
• Metaphase: Chromosomes line up at the metaphase plate, ensuring equal distribution to each daughter cell.
• Anaphase: Chromatids separate and move toward opposite poles of the cell.
• Telophase: Nuclear envelopes re-form around each set of chromosomes, completing the division process.

Though mitosis is essential for cellular division, it does not involve DNA replication. The replication occurs earlier in the S phase during interphase. Understanding mitosis helps in comprehending how cells evenly divide their genetic material and ensure each daughter cell receives an identical set of chromosomes.