Download Mitosis and Meiosis Notes

Cell Growth and Division
I. Limits to Cell Growth
A. Why do cells divide? Instead of dividing, why don’t cells just grow larger and larger?
There are two main reasons why cells divide rather than continuing to grow larger and larger:
1. The larger a cell becomes, the more demands the cell places on its ___________.
2. If the cell grows too large, it will have trouble moving enough _______________ and
___________________ across the cell membrane.
B. Problem #1: Our DNA has its limits!
1. All of the information that a cell needs to function is stored in the ___________ of the cell.
2. DNA is packaged into chromosomes. A chromosome consists of one very long linear DNA
molecule consisting of 1000's of genes.
3. Each gene is the instructions for making a particular __________________ that the cell needs.
4. The cell is constantly making copies of these genes and sending the copies (in the form of RNA)
out to the ribosomes.
5. When the cell is ________________l, the information stored in the cell’s DNA is adequate to meet
the needs of the cell.
6. As the cell grows too large, there is an “_________________________”. The DNA cannot keep
up with the demands of running a larger cell.
C. Problem #2: A Growing Cell Needs More Food!
1. A cell must take in a constant inflow of ____________________________across the membrane.
2. ______________________ products must constantly be crossing the membrane in order to leave
the cell.
3. A larger cell will require much more food, oxygen and water. A larger cell will generate much
more waste.
4. As the cell grows, the ____________________ of the cell increases much more rapidly than the
_____________________________ of the cell membrane.
5. When the cell gets too large, the membrane surface area is not adequate enough to transport the
large quantities of food and water in and waste products out.
II. Cell division
1. ____________________________ is the process by which cellular material is divided between two new
daughter cells.
2. ____Mother Cell --->____ Daughter cells. The two daughter cells will be _______________ to each
other and to the mother cell.
3. Each daughter is half the size of the parent cell, but immediately begins growing.
4. A typical human cell has about 2 meters of DNA. Before the cell can divide, all of this DNA must be
copied and then the two copies separated so that each daughter cell ends up with a complete set of
DNA.
5. Each species has a characteristic number of chromosomes in each cell nucleus; humans have
_______ pairs or 46 chromosomes.
III. Chromosomes During Eukaryotic Cell Division
A. Each cell must first copy its _____________________
before cell division occurs.
B. Each daughter cell gets a complete copy
of that information.
C. Cell division occurs in two main stages:
1. _________________ – The division of the nucleus
2. _________________ – The division of the cytoplasm
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D. The chromosomes are not visible except during
__________________. At the beginning of cell division,
the chromosomes _________________ into compact, visible
structures that are easily seen with a microscope.
E. Well before cell division takes place, each chromosome is ______________________ or copied.
F. At the beginning of cell division, each chromosome consists of two identical “sister chromatids”.
These chromatids are connected at an area called a _______________________.
IV. The Cell Cycle
1.
2.
3.
4.
5.
6.
7.
The ____________________ is the series of events that cells go through as they grow and divide.
The cell cycle is the life of the cell from the time it is first formed from a dividing parent cell until its
own division into two cells.
During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells.
The cycle consists of five major phases:
a) _________ (first gap)
b) _________(synthesis)
c) __________ (second gap)
d) ________________ - the division of the nucleus
e) __________________ - the division of the cytoplasm
Before a cell can begin mitosis and actually divide, it must form duplicates of its
__________________ and produce a supply of _____________________ for the two daughter cells.
These preparations occur during the ___________________________ phases of the cell cycle.
These three are collectively known as ___________________________.
8.
G1 phase
a) The cell ______________________ in size.
b) The enzymes, cytoplasmic organelles and other molecules double in number.
9.
S Phase
a) _________________________ of DNA occurs.
10. G2 Phase
a) The cell assembles the special structures needed for _____________________________.
11. When interphase (G1, S, G2) is complete, the cell is ready to begin the process of cell division.
12. Interphase
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(a) Of the cell cycle, interphase accounts for __________ of the time.
(b) The nucleus is well defined and bounded by the nuclear membrane.
(c) Outside of the nucleus are two ________________. Their function is to organize the
microtubules into a spindle. They will begin to move apart as spindle microtubules grow out of
them.
(d) ________ phase is a period of intense biochemical activity. The cell doubles in size and the
enzymes, cytoplasmic organelles and other molecules double in number.
(e) The chromosomes have duplicated during the _______ phase and they appear as a jumbled
mass of fibers. They have not yet condensed.
(f) ___________ Phase: The cell assembles the special structures needed for cell division
V. Mitosis
A. Has _________ Stages
1. ___________________
2. ___________________
3. ___________________
4. ___________________
B. Stages of Mitosis
1. Prophase
Early prophase
Late prophase
Early Prophase:
(a) The __________________________ coil and thicken and become distinct from one another.
The chromosomes are now visible.
(b) The _______________________ disappears.
(c) The chromosomes are _______________________ throughout their length.
(d) Each half of the double chromosome is a _________________________.
(e) The chromatids are connected by a ________________________.
(f) The centrioles _____________________ and start moving to ____________________ ends of
the cell. A spindle made of microtubules begins to form.
Late Prophase:
(g) The nuclear membrane fragments and the microtubules invade the nuclear area. The spindle is
completely formed.
(h) The _____________________ is a structure that will help to separate the chromosomes.
During prophase the pairs of chromatids become _______________ to the fibers of the spindle.
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(i)
The _____________________ have moved to the opposite poles, forming the spindle as they
go.
2. Metaphase
(a)
(b)
(c)
(d)
The centrioles are now at ____________________ sides of the cell.
The spindle fibers will _______________________ the chromosomes.
The chromosomes line up at the _____________________ of the cell.
Each chromosome is connected to a spindle fiber at its centromere.
3. Anaphase
(a) The centromeres divide and the _____________________ move to opposite sides of the cell.
(b) The microtubules begin to ___________________ and this pulls the chromatids apart to
_______________________ sides of the cell.
(c) By the end of anaphase, the two ends of the cell have _______________________ and
_____________________ of chromosomes.
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4. Telophase
(a) _____________________________ begins to form.
(b) ______________________ returns.
(c) The cell begins to pinch in. This is called the _________________________.
VI. Cytokinesis
A. At the end of mitosis, _____________ nuclei have been formed. Each nucleus has an
_____________________ set of chromosomes.
B. _______________________ is the division of the cytoplasm.
C. Cytokinesis usually occurs at the same time as ________________________.
D. In _________________________ cells, a cleavage furrow pinches the cell membrane inward until
the cell is pinched into two separate cells. Each new cell contains its own nucleus, cytoplasm, and
organelles.
E. In _____________________, it is not possible for the cell to pinch inward because of the rigid cell
wall. In plants, a ________________________ forms midway between the two nuclei. The cell
plate continues to form across the cell until two separate cells have been formed.
VII. The Importance of the Cell Division Process
A. Mitosis
1. Takes between ________ minutes and _______ hours.
2. __________ Mother Cell = ___________ Daughter cells.
3. The two daughter cells are _____________ to the mother cell.
B. Results of Mitosis
1. In _________________ plants and animals, it results in new offspring by asexual reproduction.
2. In ___________________ organisms, it results in the growth and repair of the organism.
C. Importance of Mitosis
1. The two new cells are exact duplicates.
2. Insures that the new cells will be able to carry on the same functions as the mother cell.
VIII. Regulation of the Cell Cycle
A.
The _____________________ of cell division varies with the type of cell. Skin cells divide
frequently throughout our lives. Liver cells maintain the ability to divide but only do so on rare
occasion - say to repair a wound. The most specialized cells, such as muscle cells and nerve
cells, do not divide at all.
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B. Controls on Cell Division
1. When cells come into contact with other cells, they respond by ____________ growing.
2. When an injury, like a cut in the skin occurs, the cells at the edge of the injury begin to
_________________ rapidly.
3. When the healing process nears completion, the rate of cell division ______________ down.
C. Cell Cycle Regulators
1. There are many _________________ found on the inside and the outside of the cell that
regulate cell division.
2. Some of these proteins are responsible for ______________________________ cell division.
3. Other proteins seem to ____________________________________ the cell division process.
4. These proteins send out signals that prevent ____________________ cell growth. This keeps
the tissues of the body from disrupting one another.
D. Uncontrolled Cell Growth
1. If the cells in a tissue grow uncontrollably, the consequences may be severe.
2. _______________________ cells do not respond to the signals that regulate the growth of
cells. Cancer cells divide uncontrollably and form masses of cells called _______________.
These tumors can damage the surrounding healthy tissues.
3. All cancers have one thing in common: The protein regulators that control the cell cycle have
__________________ to do their job.
Meiosis and Sexual Reproduction
I. Asexual and Sexual Reproduction
A. Asexual Reproduction
1. Offspring are produced by only __________ parent. Each parent passes ___________ of its
genes to the offspring.
2. Advantages of Asexual Reproduction
(a) It is __________________.
(b) _________________ numbers of offspring are produced.
(c) The parent does not have to ____________ a mate.
3. Disadvantage of Asexual Reproduction
(a) All of the offspring are exactly alike. There is no _____________________ in the offspring.
(b) The ability to adapt to a changing environment is greatly ___________________.
B. Sexual Reproduction
1. Requires ________ parents. Each parent passes on _______________ its genes to its offspring.
2. Must have male and female: male to produce ____________and female to produce _________.
3. Disadvantages:
(a) The parent must find a mate.
(b) Very ___________ offspring are produced.
(c) It takes _________________.
4. Advantage:
(a) All of the offspring are ______________________.
5. Sexual reproduction always involves:
(a) _____________________: sex cells
(b) ____________________________: union of sperm and egg
(c) ______________________: a fertilized egg
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II. Cell Division and Chromosome Number
A. If an organism is the result of sexual reproduction, it will have___________________ of
chromosomes. One set comes from the _______________ and one set comes from the
___________________.
B. These two sets are called _______________________ chromosomes.
C.
Homologous chromosomes are the two copies
of each chromosome, one coming from the mother
and one coming from the father.
D.
Homologous chromosomes carry the same ______________,
but they may have different ______________________
of that gene.
E. Diploid
1. _______________________ means that there are two of each kind of chromosome in each cell.
2. The symbol for diploid is __________. “N” is the number of different chromosomes that an
organism has. Humans are 2N because we have 2 of each kind of chromosome.
3. Diploid cells contain two complete sets of chromosomes.
4. So in mitosis:
_______ (2N) cell -------> _______ (2N) cells
F. Chromosome number in gametes
1. Egg and sperm cells must have ____________ the number of chromosomes so that when added
together, the ___________________ will have the proper number.
2. Example: human body
Egg (____) + sperm (____ ) --------> zygote (____)
1N
+
1N ---------------->
2N
3. Gametes are said to be _________________ or 1N because they contain only one of each kind of
chromosome.
4. The cells which produce eggs and the cells which produce sperm are diploid or 2N. So how do
the egg and sperm cells get to be 1N? MEIOSIS!!
5. _____________________ is a process of reduction division in which the number of chromosomes
per cell is cut in half through the separation of homologous chromosomes.
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III. Phases of Meiosis
A.
B.
C.
Occurs in the ____________ cells only---egg and sperm.
Purpose is to _______________ the chromosome number of the egg and sperm by ____________.
Meiosis, like mitosis, is preceded by the replication of chromosomes. Unlike mitosis, this replication
is then followed by two divisions, ________________ and _____________________.
D. Drawings of the stages of meiosis
E. Stages of Meiosis
1.
___________________: The chromosomes replicate. It is similar to chromosome replication of
mitosis. Two identical sister chromatids are held together by a centromere.
2.
____________________: Chromosomes shorten and thicken. Each chromosome pairs with its
corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad.
3.
____________________: Tetrads line up at the center of the cell.
4.
____________________: The tetrads break apart and the pairs move to opposite sides of the
cell. Sister chromatids remain attached at their centromeres.
5.
_____________________ and Cytokinesis: The cell separates into two cells. Meiosis I results
in 2 haploid (1N) daughter cells. Each daughter cell has half the number of chromosomes as the
original cell.
6.
__________________: The pairs of sister chromatids start toward the center.
7.
___________________: Pairs of sister chromatids line up at the center.
8.
___________________: The sister chromatids move to opposite sides of the cell.
9.
_______________________: Results in 4 new cells that are 1N.
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F. Importance of Meiosis
1. ______ (2N) cell -------> _______ (1N) cells
2. The chromosome number of the egg and sperm is cut in ___________ to insure that the zygote will
have the proper number of chromosomes.
G. “Crossing Over” During Meiosis
1.
2.
3.
4.
During prophase I, each pair of chromatids lines up next to its homologue.
This pairing of homologous chromosomes produces ________________.
A tetrad consists of _______ chromatids.
It is possible for the chromatids within a homologous pair to twist around one another. Portions of
the chromatids may break off and attach to adjacent chromatids.
5. This process is called “crossing over”.
6. ___________________________ is the exchange of genetic information (genes) between
segments of homologous chromosomes during meiosis.
7. The result is that the offspring will receive a ___________ combination of genetic information.
This leads to variation in the offspring.
8. Variation leads to adaptation and change. These variations will cause some of the offspring to be
better suited for their particular environment. If they are better suited for their environment, it is
more likely that they will survive to reproductive age and pass these favorable variations on to
their offspring.
9. If the result of crossing over causes the offspring to be less suited for its environment, it may not
survive. Or, if the offspring does survive, it may not be reproductively competitive. This means
that it may not be able to secure a mate. These “unfavorable” genes are not likely to be passed
on to the offspring.
10. Crossing over leads to evolution.
IV. Gamete Formation
A. Meiosis produces ___________________ cells that are different.
B. In males, meiosis results in 4 __________________ cells.
C. In females, 4 cells are produced, but only __________ will become an egg cell. All of the
__________________ and all of the _______________________ are put into one egg cell. The
other three cells will never be functional.
V. Comparison of Mitosis and Meiosis
A. _________________ occurs in all cells of the body except egg and sperm. _________________
only occurs in the formation of egg and sperm.
B. In meiosis, each diploid cell divides twice to produce a total of _____ cells. In mitosis each diploid
cell divides once to form 2 cells.
C. In meiosis, each of the four cells contains _________ the number of chromosomes as the parent
cell. In mitosis, each new cell contains the __________ number of chromosomes as the original cell.
D. In mitosis, the homologous pairs do not come together to form tetrads. In meiosis, the homologous
pairs do come together to form tetrads. While the chromosomes are in tetrads, crossing over may
occur. There will be no crossing over in mitosis.
E. In meiosis, the four haploid cells contain ___________________ combinations of chromosomes
from each other. In mitosis, the new cells contain ____________________ copies.
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© Amy Brown – Science Stuff
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