CHAPTER 10 Cell Division Why Cell Division We

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 • G 1: & G 2 phases: growth • S Phase: “synthesis”when the DNA is replicated

2 Important Parts of Cell Division 1. Mitosisdivision 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 duplicated chromosome chromatin 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.