Ch # 10 – Cell Growth & Division (Mitosis, Meiosis, and the Cell Cycle)

I. Cell Growth *Most living things grow by producing more cells. Eukaryotic cells are all about the same size. A. Limits to cell growth Cells divide for 2 major reasons : 1. To avoid DNA “overload” – larger cells place more demand on DNA (where info is control center). 2. To exchange materials more easily – food, oxygen, water, & wastes enter/exit cell via cell membrane.

Cell Size Matters -The rate of exchange depends on a cell’s surface area (total area of the cell membrane). -Rate of food/O2 use & waste production depends on a cell’s volume. BIG = slow rate of exchange for food, O2, & waste disposal. Need more food, make more waste. *To avoid getting too large, cells divide. Cell division – process by which a cell divides into two new daughter cells.

Cell Division

Two Types of Cell Division : Mitosis & Meiosis

II. Cell Division A. Chromosomes *In eukaryotic cells, genetic info is passed from generation to generation by the chromosomes, which are made up of DNA. -Every organism’s cells have a specific # of chromosomes – 46 in humans. -Before cell division, each chromosome is replicated (copied) & consists of 2 identical “sister” chromatids. As a cell divides, sister chromatids separate & 1 goes in each daughter cell.

Chromosome Structure -Pairs of chromatids are attached by a centromere that appears in the middle of the chromatids.

B. The Cell Cycle Cell cycle – the series of events that cells go through as they grow & divide. During the cell cycle the cell : 1. Grows to its mature size. 2. Prepares for cell division. 3. Divides to form 2 daughter cells. The cell cycle consists of 4 phases : 1. G1 phase – period of activity in which cells do most of their growing. -During G1 (gap 1), cells increase size & synthesize new proteins & organelles.

4 Phases of the cell cycle con’t. 2. S phase – phase in which chromosomes are replicated & the synthesis of DNA molecules takes place. *Once cells enter this phase, they will complete the cell cycle. 3. G2 phase – phase in which many of the organelles & molecules required for cell division are produced. Is the shortest phase of Interphase. 4. M phase – phase in which mitosis and cytokinesis occur.

Interphase, Mitosis & Cytokinesis *Phases G1, S, and G2 of the cell cycle make up Interphase of the cell cycle. Interphase - stage of intense growth & preparation before cell division occurs. Is the longest part of the cell cycle; cell division is very fast. Mitosis – stage in eukaryotic cell division during which the cell nucleus divides (karyokinesis) to form 2 daughter cells. It is somatic cell division – division that occurs in non-sex cells. Cytokinesis – stage during which division of the cytoplasm occurs.