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Transcript of Mitosis
Make Sure You Can:
The Cell Cycle
The "continuity of life"
- In order to survive, the individual must replace damaged cells.
- In order to grow, cell production must be greater than cell death.
A dividing amoeba
A dividing bone marrow cell
A dividing sea urchin embryo
The phases of a cell's life
S- DNA replication
G2- preparation for division
M - Mitosis
G0- Non-dividing state (most cells in you)
Very tightly controlled (why?)
Tightly coiled pieces of DNA that condense prior to division
(humans have 23 pairs)
Prokaryotes only have one, circular chromosome.
Eukaryotes have many, linear chromosomes
Most somatic (non-reproductive) eukaryotic cells have 2 copies of every chromosome.
They form in attached, identical pairs.
1 member of the pair
region where they are joined
Make sure you understand the chromosome, chromatid relationship
It can be confusing...
Nuclear envelope breaks down
Mitotic spindle begins to form
Chromosomes begin to migrate to cell equator.
2 complete spindles at cell poles.
Spindle attaches to "kinetochore" of chromosomes at centromere
Chromatids split apart at centromere.
Nuclear envelope reforms
Replication of DNA
Preparation for division
Roughly 90% of a cell's life cycle
Differences between animal-like and plant-like cells:
Cytokinesis occurs by a process known as
, forming a cleavage furrow, where a contractile ring of microfilaments pinches the cell in two
Cytokinesis occurs by vesicles from both cells depositing a new cell wall partition (
) in the middle of the cell.
Organelle apportionment is essentially random.
Mitosis at a Glance
The Evolution of Mitosis
There are a fair amount of similarities between eukaryotic and prokaryotic cell division
Proteins involved in binary fission & eukaryotic cell division have a large degree
Some unicellular eukaryotes (like protists) demonstrate "intermediate" modes of division.
Let's play "spot the phases"
"Non-Reductive" Eukaryotic Cell Division
Describe the roles that mitosis plays in eukaryotic organisms.
Explain how mitosis produces two genetically identical cells
Explain how interphase prepares a cell for mitosis.
Explain why many cells never divide.
Explain the function of each stage of mitosis
Compare the events of mitosis in plant-like and animal-like cells
Why do cells need to divide?
How does cell division provide for continuity of life processes in an individual and in a species?
The splitting of the cell into two.
Watch it Happen!
- In unicellular organisms, division of one cell reproduces the entire organism
- Multicellular organisms depend on cell division for:
~ Development from a fertilized cell
- Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division
Eukaryotic cell division consists of:
- Mitosis, the division of the nucleus
- Cytokinesis, the division of the cytoplasm
The cell cycle consists of:
- Mitotic (M) phase (mitosis and cytokinesis)
- Interphase (cell growth and copying of chromosomes in preparation for cell division)
Can be divided into subphases:
- G1 phase (“first gap”)
- S phase (“synthesis”)
- G2 phase (“second gap”)
The cell grows during all three phases, but chromosomes are duplicated only during the S phase
G1 (Gap 1)
G1 phase is when the cell grows and synthesizes mRNA and proteins required by the young cells for their growth and maturity in preparation for subsequent steps leading to mitosis
S phase is when DNA gets duplicated, ending with the cell containing nearly double the amount of chromosomes
G2 (Gap 2)
G2 phase is when there is an increase in the synthesis of RNA and protein, which is followed by another round of proof reading and repair among the newly synthesized DNA sequences before the cell cycle transits to the mitotic cycle.
is an apparatus of microtubules that controls chromosome movement during mitosis.
During prophase, assembly of spindle microtubules begins in the
, the microtubule organizing center.
The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them
(a radial array of short microtubules) extends from each centrosome. The
includes the centrosomes, the spindle microtubules, and the asters
During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
At metaphase, the chromosomes are all lined up at the metaphase plate, the midway point between the spindle’s two poles
In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell. The microtubules shorten by depolymerizing at their kinetochore ends. Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell
In telophase, genetically identical daughter nuclei form at opposite ends of the cell
- Prokaryotes (bacteria and archaea) reproduce by a type of cell division called
- In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart
If the cell does not receive the go-ahead signal after proof reading, it will exit the cycle, switching into a nondividing state called the
Checkpoints and Signaling
- Two types of regulatory proteins are involved in cell cycle control:
cyclin-dependent kinases (Cdks)
- Cdks are present in constant amounts
- Cyclin is the Cdk "on switch" and is made in increasing amount as the cell moves through interphase
(maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase and turns on other proteins needed for mitosis
An example of an
is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase
are growth factors, proteins released by certain cells that stimulate other cells to divide
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
- Another example of external signals is
, in which crowded cells stop dividing
- Most animal cells also exhibit
, in which they must be attached to a substratum in order to divide
- Cancer cells exhibit neither of these inhibitions
- Cancer cells do not respond normally to the body’s control mechanisms
- Cancer cells may not need growth factors to grow and divide:
~ They may make their own growth factor
~ They may convey a growth factor’s signal without the presence of the growth factor
~ They may have an abnormal cell cycle control system
- A normal cell is converted to a cancerous cell by a process called
- Cancer cells form tumors, masses of abnormal cells within otherwise normal tissue. If abnormal cells remain at the original site, the lump is called a
invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors
Evidence suggests that there are molecules present during the cell cycle that cause cells to progress
No cyclin, no Mitosis