Problem 107 - Objective Biology for NEET

Question

\(\mathrm{G}_{1}\) phase is (a) End of mitosis and the start of S-phasc (b) End of S-phase and the start of mitosis (c) Start of S-phase and the start of mitosis (d) End of S-phase and the end of mitosis

Step-by-Step Solution

Answer

The correct answer is (a) End of mitosis and the start of S-phase.

Step 1: Understanding the Cell Cycle

The Cell Cycle is divided into two main parts: Interphase and the Mitotic (M) phase. Interphase is further divided into three sub-phases: the first gap (G1) phase, the synthesis (S) phase, during which the DNA is replicated, and the second gap (G2) phase. The Mitotic (M) phase is the part of the cell cycle where mitosis or meiosis occurs and it comes in five stages: prophase, prometaphase, metaphase, anaphase and telophase.

Step 2: Determining the Role of \(\mathrm{G}_{1}\) Phase

\(\mathrm{G}_{1}\) phase is a period in the cell cycle during interphase, right after cytokinesis (completion of cell division) and before the S phase. In this phase, the cell grows in size and synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis.

Step 3: Matching the Options with the Role of \(\mathrm{G}_{1}\) Phase

Upon examining the options given, we can see that option (a) states 'End of mitosis and the start of S-phase'. This is consistent with the timing of the \(\mathrm{G}_{1}\) phase in the cell cycle, which occurs after mitosis and before the S phase, where DNA replication occurs.

Key Concepts

G1 Phase

The G1 Phase is an essential part of the cell cycle. It is the first of the three stages of interphase. After a cell divides, it enters the G1 phase. Here, the cell focuses on growth and preparation for DNA replication.
During the G1 phase, several important things happen:

• The cell increases in size.
• Proteins and mRNA necessary for DNA synthesis are produced.
• The cell's organelles are duplicated.
• The cell's metabolic activities are vigorous.

This phase is crucial because it ensures the cell is fully prepared for the next phase, the S phase, where DNA replication occurs. If a cell does not grow properly during G1, it might not be able to replicate its DNA accurately or divide properly, leading to defects.

Interphase

Interphase is the longest phase in the cell cycle and consists of three sub-stages: G1 phase, S phase, and G2 phase. This phase is all about preparation. Let’s break down these stages:

• G1 Phase: This is where the cell grows and prepares for DNA replication.
• S Phase: The DNA replication phase, doubling the cell's genetic material for the next division.
• G2 Phase: The cell continues to grow and prepare for mitosis, checking for any DNA errors and repairing them.

The overall goal of interphase is to prepare the cell for division. Notably, cells spend most of their lifetime in this phase, ensuring all cellular components are ready for an upcoming cell division.

Mitosis

Mitosis is the process where a cell divides its chromosomes into two identical sets, leading to two daughter cells. It follows interphase in the cell cycle. Mitosis is divided into several stages:

• Prophase: Chromosomes condense and become visible; spindle fibers start forming.
• Prometaphase: Nuclear membrane breaks down, and chromosomes attach to spindle fibers.
• Metaphase: Chromosomes align in the center of the cell.
• Anaphase: Chromosomes are pulled apart to opposite ends of the cell.
• Telophase: Nuclear membranes form around each set of chromosomes, which decondense back into chromatin.

After mitosis, the cell undergoes cytokinesis, where the cytoplasm divides, resulting in two genetically identical daughter cells. Mitosis is essential for growth, repair, and maintenance in multicellular organisms.