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CHAPTER 10 CELL GROWTH AND DIVISION.
Section 1: Cell Reproduction
As the body of the multicellular organism grows larger, it cells do not also grow larger. Instead,
cells reproduce. Larger cells require more nutrients and produce more waste, which will be
harder to move into and out of the cell fast enough. Larger cells require more proteins which
will make it impossible for the cell to copy DNA fast enough. Cells of multicellular organism
reproduce to:
1. To grow
2. To replace old cells
3. To heal a tear or wound
When cells divides to make more cells it is essential that it’s DNA is accurately copied and then
distributed to its offspring cell.
Gene is a segment of DNA that codes for RNA or protein. DNA is organized into units called
genes. A human cell contains about 25,000 genes. Inside the nucleus DNA is packaged into
chromosomes.
Prokaryotic cells have one circular chromosome. (a loop)
Eukaryotic cells contain many linear chromosomes.
Eukaryotic chromosomes are composed of a substance called chromatin, which consists of
specific proteins, DNA, and small amounts of RNA.
Genes→ DNA → chromosomes → nucleus
As cells get ready to divide, the DNA is duplicated and the chromosomes change form. Each of
the duplicated DNA strands coils up tightly into a structure called chromatid.
The two sister chromatids are held together at a region called the centromere.
Section 2:
Cell Cycle
Cell grows, gets larger, and eventually divides. This repeating sequence of growth and division
is called Cell cycle.
The eukaryotic cell cycle is made up of 5 phases:
First 3 phases during which the cell is growing are called
INTERPHASE:
1. G1 ( gap1) – cell is growing and produces new organelles. Most cells spend most of their lives in G1.
Cell leaves G1 phase when it’s preparing for cell division.
2. S (synthesis)- cell’s DNA is copied. At the end of this phase, the nucleus contains twice as much DNA.
3. G2 ( second gap)- cell continues to grow and prepares to divide.
Next two phases are called
CELL DIVISION:
4. Mitosis- the nucleus of the cell divides and forms two nuclei. Each contains a complete set of chromosomes.
5. Cytokinesis- the organelles and cytoplasm of the cell divide. Two daughter cells form.
MITOSIS- division of the nucleus
There are 4 stages.
Prophase – the chromosomes begin to condense, the nuclear membrane breaks down. A spindle forms, a special
structure made up of spindle fibers, which are microtubules.
Metaphase- chromosomes line up along the equator of the cell.
Anaphase – the spindle fibers shorten, the chromatids are pulled to opposite sides of the cell.
Telophase - the final stage. A new nuclear envelope forms at each pole, the spindle fibers break down and disappear.
CYTOKINESIS – division of the cytoplasm
The cell membrane grows in the center of the cell, dividing the cell into two daughter cells.
In animal cells protein threads put the cellular membrane in.
In plant cells vesicles containing cell wall material line up across the middle of the cell and fuse
to form a cell plate, which divides the cell into two.
Section 3: CELL REGULATION
List four events or circumstances that take place in a multicellular organism, such as a deer, which require cell division.
Signals from within the cell, from other cells, or from the environment cause cells to grow, divide, or stop growing.
Cells cannot move between the phases at just any time. To ensure that cells move only when they are ready and the
environment is favorable, there are several checkpoints in the cell cycle.
There are three main checkpoints in the eukaryotic cell cycle:
1. The G₁ checkpoint- determines whether a cell’s DNA is replicated. If conditions are right, and the cell is healthy
and large enough to divide, the S phase begins.
2. The G₂ checkpoint- determines whether mitosis can begin. Checks for errors in DNA copied, enzymes correct
mistakes, proteins double-check if the cell is large enough to divide.
3. The metaphase checkpoint – ensures that genetic material is evenly split between daughter cells. Cells checks to
make sure that the chromosomes are properly attached to the spindle fibers.
Cancer is a disease that is caused by uncontrolled cell growth and division.
Cells that continue dividing in an uncontrolled way may form a mass called tumor.
Benign tumor does not spread to other parts of the body and usually can be removed by surgery.
Malignant tumor invades nearby healthy tissues, can travel to other parts of the body (metastasis) and is more
difficult to treat.
Treatment of cancer:
1. Chemotherapy – using drugs to kill cancer cells
2.
Radiation
3. Surgery