Transcript Section 8.2 Summary – pages 201

1. According to the cell theory, where do all cells come
from?
• Cells divide to make a new identical cell.
• At this moment, cells in your body are growing,
dividing, and dying.
• Old cells on your scalp, palms of your hands, and
soles of your feet are shedding and being replaced.
• Cuts and bruises are healing
• Your intestines are producing millions of new cells
each second.
• Early biologists noticed that just before cells divide,
several short structures suddenly appeared in the
nucleus.
• Then they noticed that after cellular division that these
structures would vanish.
WAIT TO ANSWER: Where is DNA found in a eukaryotic cell?
Nucleus
• For most of a cell’s life, DNA exists in long
strands called chromatin.
CELL REPRODUCTION
• Before a cell divides, chromatin coils up into
tightly packed structures called chromosomes.
Chromosome
CELL REPRODUCTION
• Chromosomes are the carriers of genetic material
that is copied and passed from generation to
generation of cells.
CELL REPRODUCTION
Before a cell can divide- a copy of all the chromosomes
needs to be made so that the new “daughter” cell has
the exact DNA as the “parent” cell.
“Parent Cell”
Chromosomes
“Daughter Cell”
Chromosomes
TALK TO YOUR NEIGHBOR:
(I will randomly call on someone in a few seconds)
DNA can be very stringy and called _______
When a cell is about to divide, it coils up tightly
and is now a “fatter” structure called _________
TALK TO YOUR NEIGHBOR:
(I will randomly call on someone in a few seconds)
Why does a cell make a copy of it’s
chromosomes before it divides and makes
another cell?
The Cell Cycle
• The cell cycle is the sequence of growth
and division of a cell. (life cycle)
• The cell cycle
consists of
Interphase,
Mitosis, and
Cytokinesis
The Cell Cycle
• The majority of a
cell’s life is spent in
the growth period
known as
interphase.
The Cell Cycle
Interphase
• During Interphase, under a microscope, there doesn’t appear to
be much going on.
• BUT, Interphase is the busiest phase of the cell cycle
• During this time the cell is
growing,
making more organelles,
and chromatin (DNA) is replicating.
Chromatin
Replicated
Chromatin
The Cell Cycle
Mitosis
• Following interphase, a cell enters its period of
nuclear division called mitosis.
• There are four phases in mitosis…
PROPHASE:
1. The membrane around the nucleus and nucleolus
disintegrate (disappear)
2. (In animal cells) centrioles begin to move to opposite
ends of the cell and spindle fibers begin to form
Nucleus
Centrioles
Spindle Fiber
3. Chromatin coils up to form visible chromosomes
Replicated
Chromatin
Replicated
Chromosome
• The two halves of the doubled structure are
called sister chromatids.
• Sister chromatids are identical to each other.
Sister
chromatids
• Sister chromatids are held together by a structure
called a centromere, which plays a role in
chromosome movement during mitosis.
Centromere
PROPHASE
METAPHASE:
1. The chromosomes move to the middle (equator) of
the cell
2. Spindle fibers on attach to the centromeres on
either side of the chromosome
Centromere
Spindle
fibers
METAPHASE
ANAPHASE:
1. The spindle fibers pull on the centromeres, break
them, and pull the sister chromatids apart to either
side of the cell- toward the centrioles.
ANAPHASE
TELOPHASE:
1. Two complete cells are forming.
2. Chromosomes unravel back into chromatin
3. Nuclear membrane begins to re-appear around the
chromatin
TELOPHASE
The Cell Cycle
Cytokinesis
• Following telophase, the cell’s cytoplasm completely
divides in a process called cytokinesis.
• This is the final step in the cell cycle.
The Cell Cycle
Cytokinesis
• Cytokinesis differs between plants and animals.
• Toward the end of telophase in ANIMAL cells,
the plasma membrane pinches in along the
equator.
The Cell Cycle
Cytokinesis
Cytokinesis
• Plant cells have a rigid cell wall, so the plasma
membrane does not pinch in.
• A structure known as the cell plate is laid down
across the cell’s equator.
Result of Mitosis
• When mitosis is complete, unicellular organisms
remain as single cells.
Result of Mitosis
• Following mitosis, in multi-cellular organisms, cell
growth and reproduction result in groups of cells that
work together as tissue to perform a specific function.
Control of Cell Cycle
• Occasionally , cells lose control of the cell cycle.
• Cancer is a growth resulting from uncontrolled
cell division.
• This loss of control may be caused by environmental
factors or certain inheritances.
Control of Cell Cycle
• There are enzymes (proteins) that control the rate of
the cell’s life cycle.
• Scientists believe that if something goes wrong with
these enzymes, they cause cells to skip a long
interphase and divide a lot faster than they should.
CANCER
• A bunch of cancer cells together form masses of
tissue called tumors that deprive normal cells of
nutrients.
CANCER
• The causes of cancer are difficult to pinpoint because
both genetic and environmental factors are involved.
• Cancer may also be caused by viral infections that
damage the genes.