Unit 6 NOTES: Cell Cycle 6.A- Cell Size Cell Size is limited by… DNA Overload – there is not enough DNA to communicate with the rest of the cell, or organelles, if it gets too big. Material Exchange– there is not enough room for materials (Oxygen, Water, etc) to get into and out of the cell as quickly as needed, if the cell gets too big. 1 Surface Area and Volume- SA- the area available to the outside, V- the amount of space it takes up. Volume increases faster than surface area, so the cell divides to compensate.

What are new cells used for? 2 Growth Development/Specialization Reproduction Repair/Replace

Forms of a chromosome 6.B NOTES: Cell Cycle 3 DNA is a double helix in shape, but why don’t we see it? It’s so small, so it condenses into chromosomes. What form the DNA is in, depends on what stage the cell is in during their life cycle.

Chromatin Definition: Long stringy form of DNA “all the double helix is relaxed- uncoiled” Normal form of DNA 4

Chromatid Definition: ½ of a chromosome 5

Sister Chromatids Definition: Two Identical chromatids joined in the center by a centromere. Also called a chromosome. 6

Centrioles – 7 Only in Animal Cells. (Unit 3) Aid in cell division by growing ‘spindle fibers’ to help move chromosomes.

Cell Plate – 8 Only in Plant Cells. The new cell wall forms to divide the two cells. Once it reaches the sides, division is complete.

Cleavage Furrow – 9 Only in Animal cells. Cell Membrane and Cytoplasm pinch in, to divide the cells into two.

Phases of the Cell Cycle 10 1.Interphase 2.Mitosis 3.Cytokinesis

Cell Cycle Phases: INTERPHASE 11 Normal Cell Nucleus not undergoing mitosis yet. DNA is copied (in Chromatin form)

Cell Cycle Phases: PROPHASE 12 The nuclear membrane disintegrates. The chromosomes are floating in the cytoplasm and are composed of two chromatids joined at the centromere. Centrioles have completed their migration to opposite poles.

Cell Cycle Phases: METAPHASE 13 The chromosomes are lined up across the center. Spindle fibers develop and attach to the chromosomes at the centromere.

Cell Cycle Phases: ANAPHASE 14 Chromatids are pulled apart and travel up the spindle fibers. The chromatids are now single stranded chromosomes. The cell membrane starts to pinch the cytoplasm.

Cell Cycle Phases: TELOPHASE 15 Chromosomes uncoil and the nucleus begins to reform. Division of cytoplasm has begun

Cell Cycle Phases: CYTOKINESIS 16 Mitosis and cell division are complete producing two new daughter cells. Normal nuclei are to be seen.

Real Pictures of the Cell Cycle ANIMAL CELLS 17 AT THE END OF MITOSIS: You have 2 new cells (daughter cells) that have the same amount of DNA as the original.

Real Pictures of the Cell Cycle ANIMAL CELLS 18

Real Pictures of the Cell Cycle PLANT CELLS 19 So, if a cell has 4 chromosomes, during interphase (when DNA doubles) you would see 8 chromosomes. But by the end of Mitosis, you would have 2 cells, each with 4 chromosomes.

Real Pictures of the Cell Cycle PLANT CELLS 20