Essential Question

1. Cell Growth and DivisionSB1a. Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction.

2. Essential Question • Finish the sentence. • When I cut myself shaving, I began to bleed. Soon my wound healed. It healed because my skin cells …….

3. Cell Division • Cell division is the process in which a cell divides into 2 new daughter cells. 1. Before cell division can occur, the DNA must be replicated. 2. Cell division reduces cell volume thus making the cell work more efficiently.

4. Why Cells Divide? A. Larger cells need more DNA. B. Larger cells need more space. Surface to Volume ratio: 1. Volume increases faster than the cell membrane (surface area). The result is the inability to exchange oxygen, food, and wastes. ** Larger cells are more difficult to maintain.

5. In eukaryotic cells, the genetic information is carried on structures called chromosomes. Chromosome numbers are specific to each species. Chromosome

6. Where are chromosomes found in the cell? • Mitochondria • Nucleus • Cell Membrane • Golgi apparatus

7. Chromosome Number Examples Fruit fly – 8 Humans – 46 Chimpazee – 48 Crayfish- 200 Carrots – 18

8. Chromosome Structure • Chromosomes are made of DNA wrapped around proteins which are called histones. • Before cell division, genetic information is spread out in thin thread-like form called chromatin.

9. Chromosome Structure • Just prior to cell division, the DNA in chromosomes condense and become visible (with a light microscope). a. The visible chromosomes consist of 2 sister chromatids. b. The sister chromatids are attached at a central point called the centromere.

10. Chromosome Diagram

11. The Cell Cycle Cell Cycle – a series of events that a cell goes through as they grow and divide. • It’s divided into the following stages…… • G1, S, and G2, collectively, are called interphase. • In cell division, the cell divides and splits with mitosis and cytokinesis.

12. The Cell Cycle • G1 phase (Gap 1) – a period of growth – cell increases in size as they build new proteins. • S phase – (synthesis) – DNA is replicated. • G2 phase (Gap 2) – cell builds organelles needed for division. • M phase – (Mitosis) – is the orderly division of the cell’s nucleus. • Cytokinesis – the cytoplasm divides.

13. Get your Cell Cycle Chains and decorate them. You also need to write down the cell cycle rap. It will be useful to you in the next few days. Cell Cycle Rap (to the tune of Do Your Ears Hang Low) Do your cells hang low Do they reproduce and grow Interphase lets begin G1, S, G2 my friends Then the cell will divide Now you have 2 nuclei Do your cells hang low

14. What is the end product of the cell cycle? • A bigger cell • More DNA in one cell • A new daughter cell • Who knows????

15. Mitosis Prophase Metaphase Anaphase Telophase 2 new daughter cells

16. Prophase • Prophase- 1. Chromosomes become visible because of continuous coiling. 2. Two centrioles form out- side the nucleus and move to the opposite sides of the cell called poles. 3. Spindle fibers form and attach to the centromere of the chromosomes. 4. The nucleolus & the nuclear envelope disappear as they begin to break down.

17. Metaphase • Metaphase chromosomes line up in the middle of the cell at the area called the equator. • Remember those prefixes: they aren’t going away!!! (meta = middle) middle phase.

18. Anaphase Anaphase-chromatids pull apart and migrate to opposite poles.

19. Telophase • Telophase – final phase of mitosis. • 1. Chromosomes disperse back into chromatin. • 2. New nuclear envelopes form around each pole, forming 2 new daughter nuclei. • Spindle fibers and centrioles disappear. • Each new nucleus develops a new nucleolus.