Cell Division and the Cell Cycle

Cell Division

• Cell division is the process by which a parent cell produces daughter cells.
• Unicellular organisms reproduce through cell division.
• Multicellular organisms use cell division to increase their number of cells or to generate sex cells (gametes).
• The frequency of cell division varies depending on the type and physiological state of each cell.
• In the human body, some cells, such as those in the epidermis and bone marrow, are constantly multiplying to replace those that die.
• More specialized cells, such as neurons, red blood cells, and muscle cells, rarely or never divide.
• The set of stages a cell goes through to divide into daughter cells is called the cell cycle.

The Cell Cycle

• The cell cycle begins with the origin of a cell from a previous cell division and ends when the cell divides into daughter cells.
• The cell cycle is divided into two phases: interphase and cell division.

Interphase

• Interphase is the phase in which the cell is not dividing, representing the longest period of the cell cycle.
• During interphase, events occur that allow for cell division, such as DNA replication, centriole division, and protein production.
• Interphase is subdivided into three phases: G1, S, and G2.
• During the G1 phase, cells grow in size, produce RNA, and produce proteins.
• During the S phase, DNA synthesis occurs and the amount of DNA in the cell nucleus is replicated.
• Before any cell division, DNA duplication takes place during interphase.
• The G2 phase is the interval between DNA synthesis and mitosis. During this phase, the cell continues to grow and produce proteins.

Types of Cell Division

• In eukaryotes, there are two types of cell division: mitosis and meiosis.

Mitosis

• Mitosis is the type of cell division in which a parent cell, haploid or diploid, gives rise to two daughter cells with the same number of chromosomes as the parent cell.
• Mitosis is a type of cell division that occurs during asexual reproduction.
• Mitosis has the following functions:
  • Growth and regeneration of tissues.
  • Healing.
  • Gamete formation in plants.
  • Divisions of the zygote during embryonic development.

Meiosis

• Meiosis is the type of cell division where a parent cell, always diploid, with doubled chromosomes, produces four daughter cells with half the number of chromosomes of the parent cell through two successive divisions.
• Meiosis is called reductional division.
• Meiosis has the following functions:
  • Gamete formation in animals.
  • Spore formation in plants and some fungi.

Summary

• Mitosis is the cell division process that gives rise to two cells identical to the original, with the same number of chromosomes.
• Meiosis involves two cell divisions resulting in four cells with half the genetic material of the parent cell.
• The word "MEIO" (half) in "MEIOsis" reminds us that it involves half the genetic material.