CHAPTER 10: Cell Division
Dec 25, 2015
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
Division1. Mitosis-division of the nucleus2. 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
duplicatedchromosome
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: CYTOKINESIScell divides into 2 cells
ANIMAL CELL:
Pinches into 2 cells
PLANT CELL: cell walls forms between 2 new cells
REGULATION OF CELL CYCLECyclins are chemicals that control
cell division1. 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 TreatmentChemotherapy & 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.