Download Chapter 14 Cellular Reproduction

Chapter 14 ­ Cellular Reproduction
Title: Chapter 14 (1 of 54)
Section 14.1 ­ How Body Cells Reproduce
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The Cell Cycle
One vital ability for all living things is the capacity for reproduction.
Reproduction may not be essential for the survival of an individual organism, but without the capacity to produce the next generation, a species will vanish very quickly. During this chapter, we will look in detail at reproduction at the level of individual cells...so, we will be exploring the process of cell division.
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The Cell Cycle
There are two major forms of cellular reproduction.
1)
Reproduction of body cells
This form of reproduction generates an exact copy of
the parent cell. This form of cell reproduction occurs
constantly in most of the cells that make up the
human body. It is also used by simple organisms
during asexual reproduction, where the entire
individual is replicated. (For example, amoebas)
This form of cell division is called MITOSIS.
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The Cell Cycle
What 2 molecules are responsible for storing instructions on how to carry out all cell activities, and function to control the cell?
So, during cell division, these instructions must be copied and passed on to the new cells. This is accomplished through the process of replication.
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The Cell Cycle
Each cell in the body (with a few exceptions) carry a complete set of the organism's DNA. Muscle cells, skin cells, stomach cells...all of these carry the instructions for the entire organism.
DNA is not just random strands floating around in the nucleus...they are arranged in separate, distinct molecules. Each organism has a specific number of DNA strands.
Most of the time, they are in the form of chromatin..., long thin, strands, ready to participate in creating RNA for protein synthesis
as necessary.
During cell division, however, these strands will coil, tightly winding to form thicker, recognizable structures called chromosomes .
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The Cell Cycle
A chromosome is an individual strand of DNA which has shortened and thickened by winding around small groups of proteins called histones.
DNA is not just random strands floating around in the nucleus...they are arranged in separate, distince molecules. Each organism has a specific number of DNA strands.
Most of the time, they are unwound, long and thin, ready to participate in creating RNA for protein synthesis as necessary.
During cell division, however, these strands will coil, tightly winding to form thicker, recognizable structures called chromosomes .
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The Cell Cycle
As mentioned, the cells of each species will contain a specific number of chromosomes.
For example, a mosquito has 6 chromosomes, a pea plant has 14,
a sunflower 34, a human being 46, and a dog 78.
Chromosomes are arranged in pairs, with each pair composed of
chromosomes that contain the same genes...one chromosome from each pair is inherited from each parent.
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The Cell Cycle
A gene is a section of a chromosome that controls the expression
of a specific characteristic.
What exactly does the code contain? Instructions to build a...
PROTEIN!
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The Cell Cycle
The second form of cell division is called MEIOSIS.
1)
Reproduction of sex cells
This form of cell division is only used in organisms that
undergo sexual reproduction. In meiosis, the goal is not
to create an exact copy of the parent cell's DNA, but a half copy...during sexual reproduction, two parent organisms each provide one cell that has undergone
meiosis...the combination of two half copies (one from each
parent) results in a new cell with a complete set of DNA
instructions.
Note that meiosis is a form of reproduction at the individual
cell level, but the function is related to reproduction of more
complex organisms.
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The Cell Cycle
Why is it necessary for meiosis to create cells with only a half set of DNA?
Consider a cell which has 4 chromosomes. What would happen if meiosis
created sex cells containing a complete chromosome set?
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The Cell Cycle
G2 phase: centrioles
replicate; cell prepares
for division
Cell Division: mitosis (division of nucleus)
and cytokinesis (division of cytoplasm)
G1 phase: rapid growth
and metabolism
S phase: DNA synthesis
and replication
Interphase...the period between divisions
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Homework
Read pages 458­462, stopping at "The Phases of Mitosis"
Take notes on these pages, and complete the "Thinking Lab" on
page 463.
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Mitosis
Animation: Stages of Mitosis
Take notes on these pages, and complete the "Thinking Lab" on
page 463.
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Mutations Affecting Cell Division
What is a mutation?
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Mutations Affecting Cell Division
Most mutations have little impact on the body. Even if they prevent the cell from functioning properly, it will simply be destroyed by the immune
system, and replaced by other fully functioning cells.
There are two main types of mutations: replacement mutations, and insertion or deletion mutations. We can use the sentence above to illustrate these types.
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Mutations Affecting Cell Division
A replacement mutation involves switching one piece of the genetic code with another, similar to replacing a letter in a sentence with a different letter.
Most of the time, this makes little difference, and the meaning of the sentence can still be interpreted.
Most mutations have little impact in the body. Even if they prevent the cell from functioning properly, it will simply be destroyed by the immune
system, and replaced by other fully functioning cells.
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Mutations Affecting Cell Division
A delection or insertion mutation is more serious. These involve either removing a piece from the genetic code, or inserting a new piece. While that may not sound like a big difference, it can radically change the functioning of a gene.
Look at how removing one letter changes this sentence:
Most mutations have little impact nt heb ody.E veni ft heyp reventt hec
ellf romf unctioningp roperly,i tw ills implyb ed estroyedb yt hei mmunes ystem,a ndr eplacedb yo therf ullyf unctioningc ells.
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Mutations Affecting Cell Division
If a mutation occurs in the genes that control cell division, cancer may result.
Cancer occurs when the growth of cells in the body is out of control and cells divide too rapidly. These cells are unable to perform their normal function, and if unchecked may form a mass called a tumor.
There are many different kinds of cancers. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.
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Mutations Affecting Cell Division
At any given time, the body will contain many of these potential cancer cells; most are identified and destroyed very quickly.
There are multiple causes of cancers, including:
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Radiation Sunlight Chemicals (such as found in tobacco)
Viruses Some plant toxins
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Mutations Affecting Cell Division
The problems from cancer come because these rapidly growing cells interfere with normal cells' ability to function. They also rob the body of resources (rapid growth and cell division uses a great deal of energy).
The specific symptoms depends on the type and location of the cancer, however, the following symptoms are common with most cancers:
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Fever
Chills
Night sweats Weight loss
Loss of appetite
Fatigue
Malaise
Cancer Treatment
The three most commonly used treatments for cancer are:
• Surgery
• Radiation therapy
• Chemotherapy
If a tumor is localized, it may be able to be surgically removed. If this is the option taken, it is important to remove all cancerous cells...if any remain behind, they may quickly regenerate, forming a new tumor.
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Cancer Treatment
Radiation therapy involves the use of radiation, either applied by an external beam or deliverd through internal wires or pellets. The goal is to target and kill cancer cells directly. This could involve multiple beams which converge on the area of the tumor, or release of radiation through a wire at a specific point.
However, some non­cancerous cells will still be affected. A common side effect of radiation therapy is irritation or inflammation of skin and areas surrounding the treatment.
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Cancer Treatment
Chemotherapy or drug therapy is used to kill cancer cells, while attempting to limit the damage to normal cells. Chemotherapy is useful in fighting cancer that has spread to other parts of the body and cannot be easily detected or treated with surgery or radiation therapy.
The drugs used in chemotherapy often attempt to disrupt the cell division process, which naturally will have the greatest impact on cancer cells. However, other cells in the body will be affected as well.
Some of the most common side effects of chemotherapy are:
nausea and vomiting; hair loss; fatigue; increased chance of bleeding or infection; anemia
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Section 14.2 ­ How Reproductive Cells are Produced
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Meiosis: Division of Reproductive Cells
Meiosis is a specialized form of cell division that occurs in reproductive cells only. During mitosis, an exact copy of the entire genetic code, all of the cell's chromosomes, is made, and each of the new cells receives a complete copy of this code.
During meiosis, though, the chromosomes are divided, and each cell receives only half of the entire genetic code.
Why is this?
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Chromosome Complement
Most cells carry two copies of each chromosome. These paired chromosomes will carry the same genes.
What is a gene?
Different organisms will have different numbers of chromosomes.
(See Table 14.1 on page 471). Notice, though, that all have an even number...the chromosomes are paired.
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Chromosome Complement
Understand, though, that while paired chromosomes carry the same genes, they are not identical. Each chromosome in a pair may carry different versions of the gene, called alleles.
For example, the chromosomes in a pair may carry a gene that produces a pigment in eye color. However, one chromosome may code for a blue pigment, while the other codes for a brown pigment.
These genes combine to determine eye color. Note also that many human characteristics are controlled by not one but several genes.
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Chromosome Complement
Because there are two copies of each chromosome, the total complement of chromosomes is called diploid.
When body cells divide, the two daughter cells are also diploid.
During meiosis, though, the reproductive cells go through two divisions, and the result is four daughter cells, each with half of the full chromosome complement. These cells are haploid.
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Stages of Meiosis
As mentioned, meiosis involves two cell divisions. During the first division, the number of chromosomes is divided in half, creating two haploid cells.
These cells will then go through a second division, similar to mitosis, resulting in two more cells, (for a total of four) that are all haploid.
The individual stages of meiosis are given the same names as those in mitosis, and the general process are very similar.
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Stages of Meiosis
Interphase is the same in reproductive cells as in body cells. The cell grows and prepares for division. Before meiosis begins, the chromosomes replicate, creating identical sister chromatids joined by a centromere.
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Prophase I
Homologous chromosomes (ie: the pairs carrying the same genes) pair up and begin to coil. During this process, crossing over of genes may occur, where sections of the chromosomes are exchanged.
Cell is diploid , or 2N;
contains 8 chromosomes
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Metaphase I
Homologous chromosomes align at the equator of the cell. The centrioles migrate to the poles, and the spindle forms.
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Anaphase I
The chromosomes are drawn to opposite poles. However, the sister chromatids do not separate...instead, one chromosome from each homologous pair is drawn to each pole.
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Telophase I
The cell divides (cytokinesis). In some cells, the chromosomes begin to unwind, and the nuclear membrane begins to reform. In other cells, this process is skipped, and the cell goes directly to the second division.
Cells are haploid , or N;
contain 4 chromosomes
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Prophase II
The haploid cells from Meiosis I prepare to divide. Centrioles replicate. The chromosomes are not arranged ar the equator yet.
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Metaphase II
Centrioles to the poles, spindle forms, chromosomes align at equator.
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Anaphase II
Sister chromatids separate at the centromere, and are drawn along the spindle to the poles.
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Telophase II
The cell divides (cytokinesis). Each new cell contains half of the total chromosome complement found in the body cells.
Cells are haploid , or N;
contain 4 chromosomes
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Homework
Review Section 14.2, and complete Questions #5, 7, 8 on page 480
Practice sketching out the stages of meiosis in an animal cell that has a diploid number of 2n = 8
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Identify the Stage of Cell Division
• Chromosome number 2n = 6
• Name the process and the phase;
ex: meiosis, telophase I
• Be prepared to explain how you can
recognize the phase
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A, B, C, & D:
A)
B)
C)
D)
E, F, G, & H:
H)
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G)
F)
E)
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