CHAPTER 5 NOTES – PART I
Cell Growth
Why do cells divide, instead of just getting larger?
Exchange of Materials
Diffusion limits size: as a cell’s size increases, it begins to take too long for diffusion to occur.
In large cells, the surface area to volume ratio is too small to move material in and out of the cell
Not enough DNA to carry out all the cell’s processes
“DNA overload”
Cell Division
One cell divides to form two daughter cells
Both new cells have the same genetic information
The surface area to volume ratio has increased
Cell Division
Two parts
Mitosis: Division of the nucleus
Cytokinesis: Division of the cytoplasm
Some organisms reproduce by mitosis
Bacteria (prokaryotes)
Reproduce asexually by binary fission (mitosis), which creates identical offspring
DNA is circular; it copies and then splits apart
Chromosomes
Contain genetic material (DNA) coiled up, along with protein
Visible during cell division
Sister Chromatids
Before cell division, each chromosome is replicated
Because of this, each chromosome has two identical “sister” pieces
Two halves of duplicated chromosomes with the same genetic information
When the cell divides, the chromatids separate and each new cell gets ONE chromatid
Centromere
Holds sister chromatids together near the center
Centrosome
Area that organizes spindles
In animal cells, contains centrioles (cell walls of plants does a similar job)
Telomere
Area of the chromosome that does not include any genes and protects DNA
Centrioles
Cylindrically shaped
Made of microtubules
Found in animal cells
Spindle (Fibers)
Thin fibers of microtubules that separate the chromosomes
Form between centrioles in animal cells and similarly in plant cells

The Cell Cycle
The series of events that cells go through as they grow and divide.
Interphase is the period of growth that occurs between cell divisions.
During the cell cycle: a cell grows prepares for division divides to form two daughter cells each of which begins the cycle again
4 Phases:
G1 (1st Gap Phase)
Cell growth
S Phase
Chromosome replication (AKA: Synthesis)
G2 (2nd Gap Phase)
Cell organelles are copied
M Phase
Mitosis and Cytokinesis
Interphase
Lasts much longer than mitosis
G1
Cell grows in size
New proteins and organelles are made
S
DNA duplicates (chromosomes are replicated)
G2
Cell parts needed for division are copied
Preparation for Mitosis
Mitosis (PMAT)
Prophase
The first and longest phase of mitosis.
Centrioles separate and move toward opposite sides of the nucleus.
The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes.
Chromatin (DNA wrapped around histones) condenses into chromosomes.
The nuclear envelope breaks down.

Metaphase
The chromosomes line up across the center of the cell.
Microtubules connect the centromere of each chromosome to the poles of the spindle.
At the end of metaphase, the centromere are cut
Anaphase
The sister chromatids separate into individual chromosomes.
The chromosomes continue to move until they have separated into two groups.
Telophase
Chromosomes gather at opposite ends of the cell and lose their distinct shape.
Spindle fibers break down
The cell membrane begins to separate the new cells
A new nuclear envelope forms around each cluster of chromosomes.
Cytokinesis
Cytoplasm pinches in half.
Each daughter cell has an identical set of duplicate chromosomes
In plants, a structure known as the cell plate forms midway between the divided nuclei.

10.3: Uncontrolled Cell Growth
Controls on Cell Division
____________________________________________
Experiments show that normal cells will reproduce until they come into _______________ with other cells.
When