Chapter 3 Lesson 1 From Cell to Organism Cell Cycle and Cell Division

CELL CYCLE  What is the cell cycle? Cells in an organism go through a cycle of growth, development, and division  Most dividing human cells complete the cell cycle in 24 hours.  There are 2 main phases in the cell cycle  Interphase – is the period during the cell cycle of a cell’s growth and development  Mitotic phase – follows interphase. This phase of the cell cycle is responsible for reproduction and division of the cytoplasm  What is the cell cycle? Cells in an organism go through a cycle of growth, development, and division  Most dividing human cells complete the cell cycle in 24 hours.  There are 2 main phases in the cell cycle  Interphase – is the period during the cell cycle of a cell’s growth and development  Mitotic phase – follows interphase. This phase of the cell cycle is responsible for reproduction and division of the cytoplasm

Interphase – makes up most of the cell cycle.  There are 3 stages of Interphase:  1.) G1 stage - the cell performs everyday functions. The cell grows larger, it is a period of rapid growth  2.) S stage - in this 2 nd stage of the cell cycle, the cell duplicates its DNA.  Each strand of DNA forms a chromosome. Identical chromosomes join together forming sister chromatids.  3.) G2 stage - The DNA is checked by enzymes and repaired. The cell stores energy that will be used during the mitotic phase of the cell cycle and prepares for division.  There are 3 stages of Interphase:  1.) G1 stage - the cell performs everyday functions. The cell grows larger, it is a period of rapid growth  2.) S stage - in this 2 nd stage of the cell cycle, the cell duplicates its DNA.  Each strand of DNA forms a chromosome. Identical chromosomes join together forming sister chromatids.  3.) G2 stage - The DNA is checked by enzymes and repaired. The cell stores energy that will be used during the mitotic phase of the cell cycle and prepares for division.

The Mitotic Phase – follows the interphase of a cell cycle  Two stages in the Mitotic Phase – Mitosis and Cytokinesis  Mitosis – cell division begins and new cells are born. The nucleus and its contents divide. 1.) The nuclear membrane dissolves and DNA thickens (PROPHASE) 2.) Special fibers called Spindle fibers form on each end of the cell. a) They grow toward DNA chromosomes b) The fibers attach to centromeres on the chromosomes and pull them into a line in the middle of the cell (METAPHASE) c) The spindle fibers pull apart the chromosomes, to opposite sides of the cell (ANAPHASE) d) Two nuclei form (TELEPHASE) Cytokinesis – the cytoplasm divides and forms the two new daughter cells  Two stages in the Mitotic Phase – Mitosis and Cytokinesis  Mitosis – cell division begins and new cells are born. The nucleus and its contents divide. 1.) The nuclear membrane dissolves and DNA thickens (PROPHASE) 2.) Special fibers called Spindle fibers form on each end of the cell. a) They grow toward DNA chromosomes b) The fibers attach to centromeres on the chromosomes and pull them into a line in the middle of the cell (METAPHASE) c) The spindle fibers pull apart the chromosomes, to opposite sides of the cell (ANAPHASE) d) Two nuclei form (TELEPHASE) Cytokinesis – the cytoplasm divides and forms the two new daughter cells