Question

What is the relationship between control of DNA synthesis in eukaryotes and the stages of the cell cycle?

Short answer

DNA synthesis in eukaryotes is controlled by cell cycle checkpoints during G1 (before S phase) and G2 (after DNA replication).

Step-by-step solution

Identify the Stages of the Cell Cycle

The cell cycle in eukaryotes consists of four main stages: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each stage has a specific role in cell division and DNA replication.

Understand DNA Synthesis

DNA synthesis occurs during the S phase of the cell cycle. During this phase, the cell duplicates its DNA to ensure that both daughter cells have a complete set of chromosomes after cell division.

Control Mechanisms in the Cell Cycle

The cell cycle is regulated by a series of checkpoints, namely the G1 checkpoint, G2 checkpoint, and the M checkpoint. These checkpoints ensure that the cell only progresses to the next stage when conditions are favorable and the previous processes have been completed accurately.

The G1 Checkpoint and DNA Synthesis Control

The G1 checkpoint controls the progression to the S phase. It checks for DNA damage and ensures the cell has adequate resources and cellular components before DNA synthesis begins.

The G2 Checkpoint and DNA Repair

The G2 checkpoint monitors the DNA that was synthesized during the S phase. It ensures all DNA has been replicated successfully and repairs any DNA damage before the cell enters mitosis.

Summarize the Relationship

Control of DNA synthesis in eukaryotes is intricately linked to the cell cycle stages. Specific checkpoints like G1 and G2 ensure that DNA synthesis only occurs when the cell is ready and that the replicated DNA is free from errors before proceeding to the next stages of the cell cycle.

Key concepts

cell cycle stages

The cell cycle is a series of stages that a cell goes through to grow and divide. It consists of four main stages: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis).
Each stage has a unique function, ensuring that the cell divides correctly and with perfect DNA:

• G1 (Gap 1): This is the growth phase. The cell increases in size, produces RNA, and synthesizes proteins. This phase ensures all cell components are prepared for DNA synthesis.
• S (Synthesis): During this phase, DNA replication occurs. The cell duplicates its genetic material so that two complete sets of chromosomes are available, one for each daughter cell.
• G2 (Gap 2): After DNA synthesis, the cell enters another growth phase. It produces proteins and continues to grow, ensuring all cellular components are ready for mitosis.
• M (Mitosis): Finally, the cell undergoes mitosis, where it divides into two daughter cells. This phase includes prophase, metaphase, anaphase, and telophase.

Understanding these stages is crucial for learning how cells control DNA synthesis and ensure healthy cell division.

S phase

The S phase, or Synthesis phase, is a critical period in the cell cycle where DNA replication occurs. During this phase, each chromosome is duplicated to produce two identical sister chromatids.
Ensuring precise DNA replication prevents mutations and ensures genomic integrity in daughter cells. Let's break down the key events in the S phase:

• Initiation: DNA replication begins at specific sites known as origins of replication. Replication machinery assembles at these sites to start unwinding the DNA.
• Elongation: New DNA strands are synthesized by DNA polymerase enzymes. Nucleotides are added to the growing DNA strand, using the original strand as a template. This ensures the new strands are accurate copies of the original DNA.
• Completion: Once the entire genome is replicated, the cell has two complete sets of chromosomes. Replication forks meet and merge, followed by the disassembly of replication machinery.

The accurate completion of the S phase is essential. Errors during replication can lead to mutations, which may cause diseases such as cancer.

checkpoints

Checkpoints are crucial control mechanisms in the cell cycle. They ensure that each phase is completed accurately before the cell proceeds to the next phase. Checkpoints act as the cell's surveillance system, preventing errors and ensuring the integrity of cell division. The main checkpoints are:

• G1 Checkpoint: This checkpoint occurs at the end of the G1 phase. It checks for DNA damage, ensuring the cell has sufficient resources for DNA synthesis. If conditions are favorable, the cell proceeds to the S phase.
• G2 Checkpoint: Located at the end of the G2 phase, this checkpoint verifies that DNA replication during the S phase has been completed successfully. It also checks for DNA damage and repairs it before the cell enters mitosis.
• M Checkpoint: Also known as the spindle checkpoint, this ensures that all chromosomes are properly aligned and attached to the spindle fibers during mitosis. This checkpoint prevents the cells from dividing until all chromosomes are accurately distributed to the daughter cells.

Understanding these checkpoints helps highlight how cells control DNA synthesis and ensure accurate division. This control system prevents the accumulation of genetic errors and maintains healthy cell populations.