Prokaryotic cells like bacteria do not have a
nucleus. Their DNA is found bunched up in the cytoplasm.
Because of this, their cell division is simpler than the division
of eukaryotic cells. Bacteria reproduce by splitting in two. Each
daughter cell contains one copy of the DNA from the original cell.
What are Chromosomes?
Eukaryotic cells are usually larger and more complex than
prokaryotic cells. The DNA of a eukaryotic cell is found in the
nucleus. That DNA is organized into structures called
chromosomes. A chromosome is a structure made of DNA and
protein in the nucleus of a eukaryotic cell. Chromosomes organize
DNA into distinct units. Different organisms have different
numbers of chromosomes (Figure 8.2). Humans for example, have
46 chromosomes. The proteins in a chromosome help support its
structure and function. But the genetic information of the cell is
stored in the DNA.
Individual chromosomes are not clearly visible under a microscope
until just before a cell begins to divide. Before cell division,
chromosomes exist as long strands of DNA loosely coiled in the
nucleus. Just before cell division begins, the amount of DNA
doubles and so do the chromosomes. The DNA and protein in the
doubled chromosomes coil up tightly. Each doubled chromosome
consists of two copies of the original chromosome joined at the
LIFE OF A CELL
It consists of three stages:
interphase, mitosis, and cytokinesis
Interphase is the stage that occurs in between cell divisions.
During interphase the cell grows and develops and performs
its functions. Toward the end of interphase (just before the cell
begins to divide), the amount of DNA doubles. Organelles of the
cytoplasm (like mitochondria) also double in number.
The second stage of the cell cycle is called mitosis. Mitosis is the
process in cell division where the nucleus divides into two nuclei,
each with an identical set of chromosomes. Mitosis is divided into
four phases: prophase, metaphase, anaphase, and telophase. The
illustration on the facing page shows what happens during each
During most of interphase, the chromosomes are not visible.
They appear as a grainy substance inside of the nucleus. Another
way to identify interphase is to look for the nucleolus inside of the
nucleus. The nucleolus disappears before mitosis begins.
The first clue that mitosis has begun is the appearance of
chromosomes. Because the amount of DNA has doubled, each
chromosome appears as two identical strands joined at the center.
Also, the nuclear membrane breaks down during this phase. You
may also be able to see threads of protein called spindle fibers.
In metaphase, you can see the chromosomes lined up across the
center of the cell. Each half is pointing in the opposite direction.
The spindle fibers are attached to the center of each chromosome.
In anaphase, the chromosomes split. Each half is pulled toward
the point where the spindle fibers come together. Anaphase is the
phase of mitosis where the doubled chromosomes separate from
You can identify telophase by finding cells where the chromosomes
are clustered at separate ends of the cell. The forming daughter
cells begin to separate. A nuclear membrane forms around each
cluster of chromosomes.
-I got this information from the 7th grade cpo life science book...THANKS CPO!!
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