Wednesday 11/4/15 Learning Goal: Identify the events take place during the three stages of the cell cycle. Warm-up: When an organism grows, what is happening to their cells? Homework: Finish pages if you didn’t finish in class

CHAPTER 3 SECTION 5 Cell Division

Cell Cycle The regular sequence of growth and division that cells undergo  Cell grows  Prepares for division  Divides into two new cells, “daughter cells” Three main stages:  Interphase  Mitosis  cytokinesis

Stage 1: Interphase Period before cell division  The cell grows to full size  Replicates  Makes an EXACT copy of its DNA in its nucleus  Each daughter cell must have a complete set of DNA to survive  End of replication, cell contains two identical sets of DNA  Prepares to divide

Stage 2: Mitosis Mitosis  The second stage of the cell cycle  Cell’s nucleus divides into two new nuclei  One copy of the DNA is distributed into each of the two daughter cells 4 Parts of Mitosis  Prophase  Metaphase  Anaphase  Telophase

4 Parts of Mitosis Prophase  Threadlike chromatin in the nucleus condenses to form double-rod structure called chromosomes  Each chromosome has two rods, due to replication  Each identical rod in a chromosome is called a chromatid  Two chromatids are held together by a centromere

4 Parts of Mitosis Metaphase  The chromosomes line up at the center of the cell  Each chromosome attaches to a spindle fiber at its centromere

4 Parts of Mitosis Anaphase  The centromeres split  The chromatids separate by spindle fibers (go to opposite ends of the cell)

4 Parts of Mitosis Telophase  Chromosomes begin to stretch out, lose rodlike appearance  Nuclear envelope forms around each region of chromosomes

Stage 3: Cytokinesis Cytokinesis  Final stage of the cell cycle  The cytoplasm divides  Organelles are distributed into each of the two new cells The cell will then enter interphase… and the cycle begins again. Cytokinesis in Animal Cells: cell membrane squeezes together Cytokinesis in Plant Cells: cell wall cannot squeeze together, a cell plate forms that gradually will develop into the cell membrane

The Structure of DNA Looks like a twisted ladder, or spiral staircase The sides of the ladder are made up of  Deoxyribose (sugar)  Phosphate Each rung of the ladder is made up of a pair of molecules called nitrogen bases  Adenine (A)  Thymine (T)  Guanine (G)  Cytosine (C)

The Replication Process The two sides of the DNA molecule unzip and separate Nitrogen bases floating in nucleus pair up with the bases on each half of the DNA molecule New bases attach, two new DNA molecules form