Chapter 10
Cell Growth & Division
CELL GROWTH, DIVISION &
REPRODUCTION
Why does a cell divide?
If the cell is too large… its DNA cannot meet all of the cell’s
needs Ex: library for a growing town
nutrients and wastes cannot be moved across the cell membrane well surface area : volume ratio
Surface area : Volume
rate of exchange over the cell membrane depends on its’ surface area
rate at which food and oxygen are used and waste is produces depends on its’ volume
as a cell grows larger, its’ surface area : volume ratio gets SMALLER waste will be
produced faster (bigger
volume), but it can’t be
removed as quickly (smaller
surface area)
Sooo… The cell must divide!
Cell division
process by which a cell divides, forming two daughter cells
before dividing, each cell duplicates its DNA so that each daughter cell gets one copy
THE PROCESS OF CELL DIVISION
Chromosomes
Made of DNA & proteins.
Carry the cells genetic info.
Every organism has a specific number of chromosomes Bacteria = 1 circular chromosome in the
cytoplasm Humans = 46 chromosomes
Chromosomes (continued)
In eukaryotes, they are normally spread throughout the nucleus & aren’t visible (called chromatin).
Before cell division, each chromosome is replicated, forming 2 chromatids,
attached by a centromere.
The Prokaryotic Cell Cycle = Binary Fission
The Eukaryotic Cell Cycle
During the cell cycle, the cell grows, prepares for division, and divides into 2 daughter cells, each of which begins the cycle again.
Phases: G1: cell growth S: DNA replication Interphase G2: preparation for mitosis M: mitosis (division of the cell nucleus) & cytokinesis
Mitosis
Interphase Prophase Metaphase Anaphase Telophase/Cytokinesis
Interphase
Chromosomes are copied.
Chromosomes and copies appear as chromatin.
Prophase
Chromosomes become visible. Centrioles appear and move to opposite
ends of cell. Spindle fibers form. Nuclear membrane
disappears.
Metaphase
Chromosomes line up across center of cell.
Spindle fibers attach to centromeres.
Anaphase
Sister chromatids are pulled apart.
Telophase/Cytokinesis
Chromosomes lose shape, appearing as chromatin.
Nuclear membranes reform. Cytoplasm pinches in half (cytokinesis).
Clip1 Clip2
REGULATING THE CELL CYCLE
How long does cell division take?
Some cells (ex: muscle & nerve cells) do not divide at all once developed, while others (ex: skin & digestive tract cells) divide every few hours.
How is the cell cycle regulated?
Regulatory Proteins regulate the timing of the cell cycle
Both internal & external to the cell.
Most cells will stop growing when they come in contact with other cells.
Apoptosis
programmed cell death
Cells chromatin shrinks, its cell membrane breaks apart & neighboring cells clean up the remains.
AIDs & Parkinson’s disease can result when apoptosis doesn’t occur as it should.
Cancer
uncontrolled cell growth
Tumor: mass of cells formed from cancer
May be benign (nonspreading) or malignant (spreads to other tissue).
Lecture 1: 9.20- 22 min
Stem Cells
Cells that have not differentiated yet. Can sometimes be manipulated and become
different cells.
Differentiation: the process where cells become specialized