CHAPTER 10: Cell Division

Why Cell Division? (We will use the following analogy to understand cell division.) ANALOGY A cell is like a town. The DNA in the nucleus is like the books in a library. The nucleus doesn’t grow and the DNA doesn’t increase in a cell.

Town Library Analogy SITUTION: You have a research project. Your town has grown from 1000 to 10, 000 people, but the library is unchanged. QUESTION: What is going to happen when you go to check out books for your project?

Town Library Analogy ANSWER: Books won’t be available. The staff may be having a hard time restocking books, even if they have been returned.

Town Library Analogy SOLUTION : Build another library in another section of town, stock it with additional copies of books.

CELL The cell has the same 2 problems. DNA Overload: The DNA gets to a point where it can’t do more things at the same time. Exchange of Materials: After a certain size, the cell can’t efficiently transport nutrients (in) and wastes (out)

CELL SOLUTION: The cell will make an exact copy of itself and divide. 2 small cells with identical information and able to transport materials easily.

DNA Replication DNA stores genetic information It gets replicated (copied) before the cell divides Therefore, each generation of cells is identical

CELL CYCLE: The process a cell repeats every time it divides

INTERPHASE: When the Cell is NOT Dividing G1: & G2 phases: growth S Phase: “synthesis”- when the DNA is replicated

2 Important Parts of Cell Division 1. Mitosis- division of the nucleus 2. Cytokinesis- Division of the cytoplasm (cell splits)

MITOSIS ↓ CYTOKINESIS ↓

STAGE 1 OF MITOSIS: PROPHASE DNA is Packaged into Chromosomes Centrioles move to opposite sides of cell as spindle begins to form Nuclear envelope breaks down chromatin duplicated chromosome prophase

STAGE 2 OF MITOSIS: METAPHASE Chromosomes line up in center of cell Each chromatid is attached to a spindle fiber at its centromere metaphase

STAGE 3 OF MITOSIS: ANAPHASE Sister chromatids separate & move to opposite ends of cell.

STAGE 4 OF MITOSIS: TELOPHASE Chromosomes are at opposite ends of cell & become chromatin again New nuclear envelopes form

Mitosis in Action Blue shows DNA, green shows spindle fibers.

AFTER MITOSIS: CYTOKINESIS cell divides into 2 cells ANIMAL CELL: Pinches into 2 cells PLANT CELL: cell walls forms between 2 new cells

REGULATION OF CELL CYCLE Cyclins are chemicals that control cell division 1. Internal Regulators-cyclins inside the cell that control its division 2. External regulators- cyclins outside the cell that control its division

Example of Regulators Internal: When you get a cut, your cells send out cyclins so that new cells will be made (cell division) External: When the cells touch (cut is healed), cyclins tell cells to stop dividing.

Cancer Is One Outcome of A Runaway Cell Cycle Licentious division - prostate cancer cells during division.

CANCER: Regulators out of Control Cancer: cells dividing out of control Often an error in the p 53 gene that regulates cell division

Why Cancer is a Problem –Cancer cells aren’t poisonous –They rob your body of nutrients. –They can develop their own network of blood vessels. Rob your body faster Pathway for cancer to spread through your body. (“metastasis”)

Cancer Treatment Chemotherapy & Radiation are used to kill cancer cells. 1.Benefits: cancer cells are killed 2.Drawbacks: many healthy cells can be killed too.

Chemotherapy Use of medications

Radiation Use of exposure to radioactive elements, which destroy cells.