Part 1 Mitosis Slides 1-35 Packet #2.pdf1 S Mitosis is the division of the nucleus. Cytokinesis is...
Transcript of Part 1 Mitosis Slides 1-35 Packet #2.pdf1 S Mitosis is the division of the nucleus. Cytokinesis is...
Part 1 Mitosis Slides 1-35
The larger a cell becomes, the …….
…. more demands the cell places on its DNA.
If the cell grows too large, it will have trouble moving enough nutrients and wastes across the cell membrane.
There are two main reasons why cells divide rather than continuing to grow larger and larger:
• All of the information that a cell needs to
function is stored in the DNA of the cell.
• DNA is packaged into chromosomes. A
chromosome consists of one very long linear
DNA molecule consisting of 1000's of genes.
• Each gene is the instructions for making a
particular protein that the cell needs.
• The cell is constantly making copies of these
genes and sending the copies (in the form of
RNA) out to the ribosomes.
• When the cell is small, the information stored
in the cell’s DNA is adequate to meet the
needs of the cell.
• As the cell grows too large, there is an
“information crisis”. The DNA cannot keep
up with the demands of running a larger cell.
A cell must take in a constant inflow of food, oxygen and water across the membrane.
Waste products must constantly be crossing the membrane in order to leave the cell.
A larger cell will require much more food, oxygen and water. A larger cell will generate much more waste.
As the cell grows, the volume of the cell increases much more rapidly than the surface area of the cell membrane.
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.
Cell division is the process by which cellular material is divided between two new daughter cells.
1 Mother Cell 2 Daughter cells.
The two daughter cells will be….
…identical to each other and to the mother cell.
Each daughter is half the size of the parent cell, but immediately begins growing.
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.
Each species has a characteristic number of chromosomes in each cell nucleus; humans have 23 pairs or 46.
Each cell must first __________________before cell division occurs.
copy its chromosomes
Each daughter cell gets a complete copy of that information.
Cell division occurs in two main stages:Mitosis – The division of the nucleus
Cytokinesis – The division of the cytoplasm
The chromosomes are not visible except during cell division. At the beginning of cell division, the chromosomes condense into compact, visible structures that are easily seen with a microscope.
Replicated chromosome
consisting of 2 sister chromatids.
centromere
Well before cell division takes
place, each chromosome is
replicated or copied.
At the beginning of cell division, each chromosome consists of two identical “_______________”. These chromatids are connected at an area called a __________.
sister chromatids
centromere
The Cell Cycle
The cell cycle 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: 1. A cell grows.
2. The cell prepares for division.
3. The cell divides to form two daughter cells.
The cell cycle consists of five major phases:
G1 (first gap)
S (synthesis)
G2 (second gap)
Mitosis
Cytokinesis
G2
SG1
Mitosis is the division of the nucleus.
Cytokinesis is the division of the cytoplasm.
Two new cells are produced.
Before a cell can begin mitosis and actually divide, it
must do two things:
a) It must form duplicates of its chromosomes.
b) It must produce a supply of organelles for the two daughter cells.
These preparations occur during the G1, S, and G2
phases of the cell cycle.
These three (G1, S, and G2) are collectively known as interphase.
interphase
G1 phase
S phase
G2 Phase
a) The cell doubles in size.b) The enzymes, cytoplasmic
organelles and other molecules double in number.
Replication of DNA occurs.
The cell assembles the special structures needed for cell division
When interphase (G1, S, G2) is complete, the cell
is ready to begin the process of cell division.
“Let’s break
mitosis down
into its
individual
stages and see
what is going
on in each
stage.”
centrioles
nuclear membrane
nucleolus
chromosomes
Nucleus is ___________ and bounded by the ________________.well defined nuclear membrane
Outside of the nucleus are two __________. Their function is to:centrioles
organize the microtubules into a spindle.
They will begin to move apart as spindle microtubules grow out of them.
centrioles
nuclear membrane
nucleolus
chromosomes
G1 phase is a period of intense biochemical activity:
The cell doubles in size and the enzymes, cytoplasmic organelles and other molecules double in number.
The chromosomes have duplicated during the S phase and they appear as a jumbled mass of fibers. They have not yet condensed.
G2 Phase: The cell assembles the special structures needed for cell division
Remember!Interphase includes the
G1 phase, the S phase,
and the G2 phase. It is
the period of time
preceding mitosis.
Mitosis has 4 stages:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Prophase Early prophase
The chromosomes coil and thicken and become distinctfrom one another. The chromosomes are now visible.
The nucleolus __________.disappears
The chromosomes are doubled throughout their length.
Each half of the double chromosome is a __________.chromatid
The chromatids are connected by a ___________.centromere
The __________ separate and start moving to opposite ends of the cell. A ________ made of ____________ begins to form.
centriolesspindle microtubules
Chromatids connected by a centromere.
centrioles
Spindle made of microtubules
Prophase Late prophase
The _________________ fragments and the microtubules invade the nuclear area. The spindle is completely formed.
nuclear membrane
The spindle is a structure that will help to _______________________. During prophase the pairs of __________ become attached to the fibers of the spindle.
separate the chromosomes
chromatidsThe centrioles have moved to the opposite poles, forming the spindle as they go.
centrioles
Microtubulesform a complete spindle.
chromatids
centrioles
MetaphaseThe centrioles are now at opposite sides of the cell.
The spindle fibers will push and pull the chromosomes.
The chromosomes line up at the center of the cell.
Each chromosome is connected to a spindle fiber at its centromere.
centrioles
chromatids
Spindle composed of microtubules
centrioles
Anaphase
The centromeres divide and the chromatids move to opposite sides of the cell.
The microtubules begin to shorten and this pulls the chromatids apart to opposite sides of the cell.
By the end of anaphase, the two ends of the cell have equivalent and complete sets of chromosomes.
Chromatids are being pulled to opposite sides of the cell.
Shortening of the microtubules
Telophase
cleavage furrow
Nuclear membrane is returning.
Nuclear membrane begins to form.
Nucleolus returns.
The cell begins to pinch in. This is called a cleavage furrow.
The end result is two cells that are exact
copies of each other.
Can you name these phases?
1 - Prophase 2 - Metaphase 3 - Anaphase
4 - Telophase 5 - Interphase
metaphase
anaphase
anaphase
Telophase
Prophase
Metaphase
At the end of mitosis, __________ have been formed. Each nucleus has an identical set of _____________.
two nuclei
Cytokinesis is: the division of the cytoplasm.
Cytokinesis usually occurs at the same time as telophase.
chromosomes
In animal cells, a ______________ pinches the cell membrane inward until the cell is pinched into two separate cells. Each new cell contains its own nucleus, cytoplasm, and organelles.
cleavage furrow
In plants, it is __________ for the cell to pinch inward because of the rigid _______.
not possible
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.
cell plate
cell wall
Takes between 30 minutes and 2
hours.
One Mother Cell = Two Daughter
cells.
The two daughter cells are identical
to the mother cell.
M
I
T
O
S
I
S
• In unicellular plants and animals, it results in new offspring by asexual reproduction.
• In multicellular organisms, it results in the growth and repair of the organism.
Results of Mitosis
• The two new cells are exact duplicates.
• Insures that the new cells will be able to carry on the same functions as the mother cell.
Importance of Mitosis
The frequency of cell division varies with the type of cell.
_________ divide frequently throughout our lives.
Skin cells
_________ maintain the ability to divide but only do so on rare occasion - say to repair a wound.
Liver cells
The most specialized cells, such as muscle cells and nerve cells, do not divide at all.
When cells come into contact with other cells, they respond by not growing.
When an injury, like a cut in the skin occurs, the cells at the edge of the injury begin to divide rapidly.
When the healing process nears completion, the rate of cell
division slows down.
There are many proteins found on the inside and the outside
of the cell that regulate cell division.
Some of these proteins are
responsible for starting and stopping
cell division.
Other proteins seem to speed up or slow
down the cell division process.
These proteins send out signals that prevent
excessive cell growth. This keeps the tissues of the body from disrupting
one another.
Cell Cycle Regulators
Uncontrolled Cell Growth
If the cells in a tissue grow uncontrollably,
the consequences may be severe.
Cancer cells do not respond to the signals that regulate the growth of cells.
Cancer cells divide uncontrollably and form masses of cells called tumors.
These tumors can damage the surrounding healthy tissues.
All cancers have one thing in common:
The protein regulators that control the cell cycle have failed to do their job.
Part 2 Meiosis
Slides 35-57
Asexual Reproduction
Each parent passes ALL of
its genes to the offspring.
Offspring are produced by only
one parent.
Sexual reproduction requires two parents. Each parent passes on HALF its genes to its offspring.
Must have male and female: male to produce sperm and female to produce eggs.
Sexual Reproduction involves:Gametes: Sex cells (egg and
sperm)Fertilization: The union of sperm
and egg.Zygote: A fertilized egg.
If an organism is the result of sexual reproduction, it will have ____ sets of chromosomes. two
One set comes from the mother and one set comes from the father.
These two sets are called homologous chromosomes.
Homologous chromosomes are the two copies of each chromosome, one coming from the mother and one coming from the father.
Homologous chromosomes carry the same genes, but they may have different expressions of that gene.
You are a “diploid”organism.
Diploid means that …
…there are two of each kind of chromosome in each cell.
The symbol for diploid is 2N.
“N” is the number of different chromosomes an
organism has. Humans are 2N because we have
2 of each kind of chromosome.
Diploid cells contain two complete sets of chromosomes.
So in mitosis:1 (2N) cell -------> 2 (2N) cells
Human egg cell
Human sperm cells
_____________ cells must have _____ the number of chromosomes so that when added together, the ______ will have the proper number.
Egg and sperm half
zygote
Example: Gametes of the Human Body
Egg (23) + sperm (23) zygote (46)
1N + 1N 2N
Gametes are said to be haploid or
1N because they contain only one
of each kind of chromosome.
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 is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes.
Phases of Meiosis
Occurs in the sex
cells only: the egg
and sperm.
Purpose is to reduce the
chromosome number of
the egg and sperm by
half.
Meiosis, like mitosis, is
preceded by the replication of
chromosomes. Unlike mitosis, this replication is then followed by two
divisions: meiosis I and meiosis II.
The stages of meiosis I and II
Interphase Prophase I Metaphase I Anaphase I
Telophase I
Prophase II Metaphase II Anaphase II Telophase II
(and cytokinesis)
(and cytokinesis)
The Stages of Meiosis I
Interphase
The chromosomesreplicate. It is similar to chromosome replication of mitosis. Two identical sister chromatids are held together by a centromere.
Prophase I
Chromosomes shorten and thicken. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad.
Metaphase I
Tetrads line up at the center of the cell.
Anaphase I
The tetrads break apart and the pairs move to opposite sides of the cell. Sister chromatids remain attached at their centromeres.
The Stages of Meiosis II
Telophase I
Prophase II Metaphase II Anaphase II
(and cytokinesis)
The cell separates into two cells.
Telophase II
(and cytokinesis)
Meiosis I results
in 2 haploid (1N)
daughter cells
Each daughter cell has half the number of chromosomes as the original cell.
The pairs of sister chromatids start toward the center.
Pairs of sister chromatids line up at the center.
The pairs of sister chromatids separate and move to opposite sides of the cell.
Results in 4
new cells
that are 1N.
The chromosome number of the egg and sperm is cut in half to insure that the zygote will have the proper number of chromosomes.
1 (2N) cell -------> 4 (1N) cells
The Importance of Meiosis
“Crossing Over” During Meiosis
During ________, each pair of chromatids lines up next to its _________.
prophase I
homologue homologous chromosomes
This pairing of homologous chromosomes produces _______.tetrads
tetrad
A tetrad consists of ___________.4 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.
This process is called “___________”crossing over
“Crossing over” is the exchange of genetic information (genes) between segments of homologous chromosomes during meiosis.
Crossing over leads to ______________.
The result is that the offspring will receive a new combination of genetic information. This leads to ________ in the offspring.variation
Variation leads to ____________________. These variations will cause some of the offspring to be ___________ for their particular environment. If they are better suited for their environment, it is _________ that they will _______ to reproductive age and pass these favorable variations on to their offspring.
adaptation and changebetter suited
more likely survive
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. Evolution!
Meiosis produces four haploid cells that are different.
In males, meiosis results in 4 sperm cells.
In females, 4 cells are produced, but only one will become an eggcell. All of the cytoplasm and all of the organelles are put into one egg cell. The other three cells will never be functional.
Mitosis occurs in all cells of the _____ except _____________.
Meiosis only occurs in the formation of _____________.
body egg and sperm
egg and sperm
In meiosis, each _______ cell divides ______ to produce a total of ___ cells.
In mitosis each _______ cell divides _____ to form ___ cells.
diploid
diploid
twice
once
4
2
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.
half
same
In mitosis, the homologous pairs do not come together to form _______.
In meiosis, the homologous pairs do come together to form _______. While the chromosomes are in tetrads, _____________ may occur. There will be no crossing over in _______.
tetrads
tetradscrossing over
mitosis
In meiosis, the four haploid cells contain ________ combinations of chromosomes from each other.
In mitosis, the new cells contain ________ copies.
different
identical