Biology Unit 5

 DNA “overload” Cells require a certain amount of DNA (the instructions for protein synthesis and other processes)  Exchange of materials (Surface Area to Volume ratio) When cells grow too large, they cannot absorb and excrete materials through the membrane fast enough to function

 Is necessary when cells grow too large or when the cell is old, or when new cells are needed to repair damaged tissue.  This is the dividing of a non sex cell, such as a skin cell or mucosal cell in the intestine.

 This division produces two genetically identical diploid (2N) cells.  The resulting “daughter cells” have sets of chromosomes and alleles that are identical to each other and to the original “parent” cell.

 Has 4 main stages a. G 1 b. S phase c. G 2 d. M phase INTERPHASE

After the interphase stage, cells go through 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 5. Cytokinesis

Genetic material organized into a thread-like structure that is found in the Nucleus. Chromatid is one, of two, identical parts of a duplicated chromosome. The 2 parts are called “sister chromatids”.

- G-1 Phase: Cells grow in size; make new protein and organelles. - S Phase: Key proteins associated with the chromosomes are synthesized. - After DNA replication, G-2 Phase occurs, in which many of the organelles and molecules required for cell division are produced.

Cell Cycle Interphase The nucleus and nucleolus are clearly visible. It’s the longest stage of cell cycle - where cell increases in size and chromosomes are duplicated.

-Longest phase of mitosis. -Chromosomes are visible during this phase. -Chromatin condenses into discrete chromosomes, -the nuclear envelope breaks down, -the centrioles separate, -and a spindle forms at poles 1. PROPHASE

Chromosomes align in middle of cell and spindle fibers attach to center of chromosomes (at centromere). Nuclear membrane completely disappears. 2. Metaphase

3. Anaphase Sister chromatids separate into individual chromosomes and are moved apart.

4. Telophase Photos from biology.about.com Chromosomes gather at opposite ends of new cell and unwind. Two new nuclear envelopes begin forming.

5. Cytokinesis Cytoplasm of mother cell divides, can see the two new nuclear envelopes. cytokinesis

IPMATCIPMATC Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

 Be sure you labeled: Nucleus Nuclear envelope Centrioles Chromosomes Chromatin Spindle Fibers Cytoplasm

1. What happens to the volume of a cell as the surface area gets bigger? 2. During which phase do the chromosomes replicate?