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Section 3: Cell Division What events take place during the three states of the cell cycle? How does the structure of DNA help account for the way in which DNA copies itself?

The Cell Cycle Cell Cycle: The regular sequence of growth and division that cells undergo. Made up of 3 stages: Stage 1: Interphase Stage 2: Mitosis Stage 3: Cytokinesis

Interphase Cells spend most of their time in this phase. During Interphase, the following 5 events will occur: The cell will perform its “normal” functions and duties. The cell will grow to about twice it's original size. The cell's organelles will make copies of themselves and double in quantity. The cell's DNA will make a copy of itself right before Mitosis begins. Once the DNA is copied, the cell will make structures that it will use to help divide itself.

Mitosis During mitosis, the cell’s nucleus divides into two new nuclei. One copy of the DNA is distributed into each of the two daughter cells.

Mitosis Four stages in Mitosis: Prophase Metaphase Anaphase Telophase

Mitosis: Prophase “Chromatin” winds up into a condensed shape called “chromatid”. Chromatin: unwound DNA Chromatid: wound DNA

Mitosis: Prophase The cell gets ready for the “Tug of War” activity that occurs in Mitosis.

Mitosis: Prophase The cell gets ready for the “Tug of War” activity that occurs in Mitosis. The pair of centrioles move to opposite sides of the nucleus. Spindle fibers (the “ropes”) form between the centrioles. The nuclear envelope that surrounds the nucleus breaks down.

Mitosis: Metaphase The chromatids line up on the equator of the cell.

Mitosis: Anaphase The chromatids separate and move to opposite sides of the cell. The cell starts to stretch apart as it gets ready for Cytokinesis.

Mitosis: Telophase Chromatids unwind and return to their string- like chromatin shape. 2 new nuclear envelopes form to make 2 new nuclei.

Cytokinesis Must finish after Mitosis or else the cell will split into 2 cells before the DNA is evenly divided. The 2 new cells are called “daughter cells”. Each daughter cell is identical to the original parent cell.

The Cell Cycle