Cell Cycle

Overview of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It consists of two major periods: Interphase and Cell Division (Mitotic Phase).

• Interphase: The cell grows and carries out its usual activities.

• Cell Division (Mitotic Phase): The cell divides into two daughter cells.

Interphase

Interphase is the longest phase of the cell cycle and is subdivided into three subphases:

• G1 (Gap 1): Period of vigorous growth and metabolism.

  • Cells that permanently cease dividing are said to be in G0 phase.

• S (Synthetic): DNA replication occurs during this phase.

• G2 (Gap 2): Preparation for cell division.

DNA Replication

Process of DNA Replication

Prior to cell division, the cell must make an exact copy of its DNA to ensure that each daughter cell receives a complete set of genetic instructions. This process is known as DNA replication.

• Double-stranded DNA helices unwind and unzip to expose the bases.

• The replication fork is the point where the DNA strands separate.

• Each strand serves as a template for the formation of a new complementary strand.

Semiconservative Replication

The end result of DNA replication is two identical "daughter" DNA molecules, each composed of one old (parental) strand and one newly synthesized strand. This is called semiconservative replication.

• Semiconservative replication: Each new double-stranded DNA molecule contains one original strand and one new strand.

Key Terms and Concepts

• Chromosome: A structure composed of DNA and proteins that contains genetic information.

• Replication fork: The region where the DNA double helix is unwound to allow replication of each strand.

• DNA polymerase: The enzyme responsible for adding nucleotides to the growing DNA strand during replication.

• Nucleotides: The building blocks of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base (Adenine, Thymine, Cytosine, Guanine).

Example: DNA Replication Steps

1. DNA helicase unwinds the double helix.

2. Single-strand binding proteins stabilize the unwound DNA.

3. DNA polymerase synthesizes the new DNA strand by adding complementary nucleotides.

4. Each new DNA molecule consists of one parental and one new strand.

Table: Phases of the Cell Cycle

Additional info: The cell cycle is tightly regulated by checkpoints to ensure proper division and prevent errors that could lead to disease, such as cancer.