Cell Cycle

Cell Division Cell division is the process where a parent cell divides into two daughter cells. There are two types of cell division: Mitosis occurs in somatic cells. Meiosis occurs in the sex organs and produces sex cells (gametes). Sperm Ovum (egg)

Introduction to Mitosis During mitosis, an existing parent cell divides into two new daughter cells (right). The cells are genetically identical. There is no change in chromosomal number. Cells are diploid, containing two sets of chromosomes. In humans the diploid number is 46 Mitosis is associated with the growth and repair of somatic cells in the body.

The cell cycle Mitosis is just one phase of the cell cycle. There are three main phases in the cell cycle: Interphase (three stages) Mitosis (nuclear division) Cytokinesis (division of the cytoplasm) Mitosis and the Cell Cycle Interphase Mitosis C Cytokinesis

Interphase Interphase accounts for 90% of the cell cycle. It is the longest phase of the cell cycle. Interphase consists of three stages: Growth 1: G 1 The cell grows and develops Synthesis (S) The cell duplicates its genetic material (chromosomes). Growth 2: G 2 Further growth G0G0 Nondividing state M G1G1 G2G2 S C The cell cycle Nuclear membrane Centrosome is replicated Chromosome Nucleolus

Mitosis The mitotic cycle is broken down into six phases. Anaphase Late AnaphaseTelophase Early ProphaseLate ProphaseMetaphase

Mitosis: Early Prophase Prophase is the first stage of mitosis. In early prophase: the nuclear membrane disintegrates the nucleolus disappears the chromatin condenses into visible chromosomes. Replicated centrosomes Nucleolus disappears Nuclear membrane disintegrates

Mitosis: Prophase In late prophase: the chromosomes continue to coil and appear as double chromatids. the chromatids are each joined by a centromere. the centrosomes (including centrioles in animal cells) move to opposite ends of the cell. As they do so, they form the mitotic spindle between the poles. Centromere Centrosome Chromatids

Mitosis: Metaphase During metaphase the chromosomes become aligned at the equator of the cell. Mitotic spindle Chromosomes

Mitosis: Early Anaphase In anaphase, the sister chromatids split and the chromosomes are pulled to opposite poles of the cell. ChromosomesSpindle Anaphase is the shortest mitotic phase

Mitosis: Late Anaphase By late anaphase, the chromosomes have moved to opposite poles. By the end of anaphase, the two poles of the cell have equivalent, and complete, collections of chromosomes. Mitotic spindle Chromosomes Centrosome

Mitosis: Telophase Telophase is characterized by the formation of two new nuclei. The nucleoli reappear and the chromatin becomes less tightly coiled (less condensed). In plant cells, the cell plate forms where the new cell wall will form.

Cytokinesis The division of the cytoplasm is termed cytokinesis. Cytokinesis begins towards the end of telophase. In plant cells, the cell plate forms where the new cell wall will form. In animal cells, a cleavage furrow pinches the cell in two. Nucleus Cell wall Two cells are formed

Mitosis: Review Interphase Cytokinesis Early ProphaseLate Prophase Metaphase Chromosomes line up on the metaphase plate. Chromosomes separate to opposite poles. Cell elongates Chromosomes appear as chromatids. Mitotic spindle forms. Centrosomes move to opposite poles. Two independent cells. Nuclei reform. Cell plate forms (plants) TelophaseLate Anaphase Cell enters mitosis Anaphase DNA continues condensing. Nuclear membrane disintegrates. Nucleolus disintegrates. DNA replicated. Centrosome replicated. Nucleus still well defined.

Mitosis animation Mitosis Animation

Mitosis in the Root Tip Mitosis in plant cells occurs only in regions of meristematic tissue. The meristematic tissue is located at the tip of every stem and every root. In contrast, mitosis can occur throughout the body of a growing animal. Zone of specialization Zone of elongation Zone of cell division Meristematic tissue (area of cell division) Root cap Root tip growing in this direction