Download Cell Cycle and Mitosis

Biology 11 Enriched
Cell Cycle and Mitosis
References: Campbell Biology 12. 1 to 12.3
Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to
life processes.
3.A.2 In eukaryotes, heritable
12.1, 12.2, 12.3
• Mitosis-promoting factor
information is passed to the next 13.1, 13.2, 13.3
(MPF)
generation via processes that
• Action of platelet-derived
include the cell cycle and mitosis,
growth factor (PDGF)
or meiosis plus fertilization.
• Cancer results from disruptions
in cell cycle control
By the end of this unit you should be able to:








Explain how the cell cycle assures genetic continuity
Explain how mitosis allows for the even distribution of genetic information to new cells
Describe the mechanisms of cytokinesis
Explain how the cell cycle is regulated
Explain how aberrations in the cell cycle can lead to tumour formation
Describe the events of mitosis in animal and plant cells
Recognize the stages of mitosis in a plant or animal cell
Calculate the relative duration of the cell cycle stages
Biology 11E: Mitosis and Cell Cycle
Page 1
Start with 12A animation - Roles of Cell Division
What are the roles of cell division?
Cellular Organization and Mitosis Review
*Before we get too in-depth into the processes of Mitosis, it is important to review some key
terms and ideas.
Cellular Organization
-What is a cell’s genome? How is your genome
different from a prokaryote’s?
-A cell’s genetic information.
-We have a larger genome containing many more
genes
______________________________________________________________________________
______________________________________________________________________________
What is the difference between chromatin and chromosomes?
-Chromosomes are condensed DNA.
Biology 11E: Mitosis and Cell Cycle
Page 2
What is apoptosis? What is karyokinesis? What is cytokinesis?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
How many chromosomes are in a human somatic cell?
Name two types of somatic cells in your body.
What is a gamete?
Name the two types of gametes.
How many chromosomes in a human gamete? 23
Define chromatin.
Biology 11E: Mitosis and Cell Cycle
Page 3
-Chromatin includes both DNA and the proteins (histones) that allow DNA supercoiling.
Think carefully, now. How many DNA molecules are in each of your somatic cells?
Review concepts and terms associated with replicated chromosomes:
Biology 11E: Mitosis and Cell Cycle
Page 4
Fig. 12-UN3
What is mitosis? How is it different from cytokinesis?
Mitosis results in 2 identical daughter cells (diploid)
What occurs in meiosis? How is the chromosome number of daughter cells different?
Meiosis results in 4 haploid daughter cells. This is caused by halving the number of original
chromosomes = reduction division
Select either mitosis or meiosis to answer the following questions.
___________________ By what process are the damaged cells in a wound replaced?
___________________ By what process are eggs formed?
___________________ By what process does a zygote develop into a multicellular organism?
___________________ In which process are identical daughter cells produced?
___________________ Which process reduces chromosome number of daughter cells?
http://media.hhmi.org/biointeractive/click/cellcycle/ cell cycle in the colon - good video of
replacement cells
Biology 11E: Mitosis and Cell Cycle
Page 5
Explain how the cell cycle ensures genetic continuity.
Describe the important contributions of each phase to the cell cycle.
a) G1 5-6 Hours. First Gap or Growth Phase. Cell grows (needs to accommodate replicated
chromosomes in S phase).
b) S10-12 Hours. Chromosomes are duplicated and the cell continues to grow.
c) G2 4-6 Hours. Second Gap or Growth Phase. Cell makes final preparations for cell division
and continues to grow.
d) M 1 Hour. Mitosis and Cytokinesis.
-During all three subphases of interphase the cell grows by producing proteins and cytoplasmic
organelles.
-Since chromosome duplication is completed well before mitosis begins genetic continuity is
ensured.
-Review the ideas above by viewing Activity: The Cell Cycle, Chapter 12.
Biology 11E: Mitosis and Cell Cycle
Page 6
Describe the events of mitosis in plant and animal cells
In Mastering Biology Video: Animal Mitosis (time-lapse)
Video: Sea Urchin Embryonic Development
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopyuk.org.uk/mag/artaug99/mitosis.html is excellent in helping you to identify stages
Animation http://www.johnkyrk.com/mitosis.html
Biology 11E: Mitosis and cell cycle
Page 7
You will need to spend some serious time with Figure 12.7. Use it and Activity: Mitosis and
Cytokinesis to help you label the figure below. Label each phase by name, the cell features and make
two to three summary statements that indicate important features of each phase.
Phase
G2 of
Interphase
Important features of phase.
-2 centrosomes formed by duplication of 1
-Chromosomes already duplicated in S
phase.
-Prophase
-Chromatin condenses into chromosomes
-Nucleolus gone
-Sister Chromatids joined at centromeres
-Mitotic spindle forms and centrosomes
pushed away from each other by
lengthening microtubules between them.
-Chromosomes continue to condense
-Nuclear envelope
fragments=microtubules can enter and
interact with chromatid kinetochores or
each other
Protometaphase
Metaphase
Anaphase
Telophase
And
Cytokinesis
Biology 11E: Mitosis and cell cycle
-Centrosomes at opposite poles
-Chromosome centromeres on metaphase
plate
-Kinetochores for sister chromatids
attached to microtubule from opposite
poles.
-Cohesion proteins cleaved=sister
chromatids separate into individual
chromosomes
-Kinetochore microtubules
shorten=chromosomes pulled to poles
-Nonkinetochore microtubules
lengthen=cell elongates
-Daughter nuclei and nucleolus form
-Chromosomes de-condense
-Spindle microtubules broken up
-Division of cytoplasm (cleavage furrow in
animal cells)
Page 8
Mitosis and the Mitotic Spindle
-Key events during M Phase (Mitosis) rely on the Mitotic Spindle.
-What are the components of the mitotic spindle? What is the source of these components?
______________________________________________________________________________
______________________________________________________________ Mitotic spindle
consists of fibres of microtubules and associated proteins. Spindle includes ;
centrosome, microtubules and asters.
When mitotic spindle forms the other cell microtubules partly dissaccociate.
________________
-In animal cells, the assembly of spindle microtubules starts at the centrosome. What is the function
of this subcellular region?
Centrosome is also called the microtubule organising centre. Only present in
Biology 11E: Mitosis and cell cycle
Page 9
animal cells.
Centrioles at centre of centrosome are not essential to cell division.
__________________________________
-Duplicated during interphase, spindle microtubules grow out of them and push them apart
during prophase and pro-metaphase. Asters are short microtubules extending from the
centrosome.
-Mitotic Spindle= Centrosomes, asters, microtubules.
What is a kinetochore? A kinetochore is a structure of proteins on the chromosome that is attached
to the centromere that links each sister chromatid to the mitotic spindle.
-Structure of proteins and sections of chromosomal DNA at centromeres.
-Face opposite directions in a chromosome = chromatids pulled to opposite poles.
Explain the difference between
kinetochore and nonkinetechore
microtubules. What is the function of
each? -KM: Attached to K during
Prometaphase, separate sister
chromatids
Non KM: Overlap at MP, elongate
cell during anaphase
At which end do kinetochore
microtubules shorten during
anaphase? Explain the data that
supports where this shortening
occurs.
Biology 11E: Mitosis and cell cycle
Page 10
Motor proteins ‘walk’ the chromosomes along the microtubules toward the poles. “Pacman
mechanism”
Describe the mechanisms of cytokinesis
In plant cells the cell membrane forms when vesicles of cell membrane are laid down in the centre
of the cell. The membrane is manufactured by smooth endoplasmic reticulum which packages it
in vesicles to transport it to the centre of the cells.
Cellulose is laid down around this cell membrane to form the cell wall.
What is the source of the material for the cell plate?
Cellulose layer between the 2 new cells.
Biology 11E: Mitosis and cell cycle
Page 11
These photos summarize the stages of mitosis and the beginning of cytokinesis in a plant cell:
Here are the corresponding stages in an animal cell:
Biology 11E: Mitosis and cell cycle
Page 12
Prokayotes divide using binary fission. There is no mitosis because there is only one
chromosome. How do the daughter cells compare genetically to the parent cell?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
Binary Fission in a Prokaryote
Biology 11E: Mitosis and cell cycle
Page 13

The timing and rates of cell division in different parts of an animal or plant are crucial for normal growth,
development, and maintenance.

The frequency of cell division varies with cell type.
○ Some human cells divide frequently throughout life (skin cells).
○ Others human cells have the ability to divide but keep it in reserve (liver cells).
○ Mature nerve and muscle cells do not appear to divide at all after maturity.
R4: Explain how the cell cycle is regulated. Here are some experiments to help understand this:
____________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Biology 11E: Mitosis and cell cycle
Page 14
Here is a model to show some aspects
of how the cell cycle is controlled:

A checkpoint in the cell cycle is a
critical control point where stop and goahead signals regulate the cycle
What happens if a cell does not pass the
G1 checkpoint?

For many cells, the G1 checkpoint, the
“restriction point” in mammalian cells, is
the most important.
o If the cell receives a go-ahead signal
at the G1 checkpoint, it usually
completes the cell cycle and divides.
o If the cell does not receive a goahead signal, the cell exits the cycle
and switches to a nondividing state, the G0 phase.

Most cells in the human body are in the G0 phase.
○ Liver cells can be “called back” to the cell cycle by external cues, such as growth factors released
during injury.
○ Highly specialized nerve and muscle cells never divide.

Rhythmic fluctuations in the abundance and activity of cell cycle control molecules pace the events of the
cell cycle. These regulatory molecules are mainly proteins of two types: protein kinases and cyclins.
Biology 11E: Mitosis and cell cycle
Page 15
Not in student text
Biology 11E: Mitosis and cell cycle
Page 16
Passing the G2 checkpoint means that the cell will enter the mitotic phase. What controls the G2
checkpoint?
Fig 12.17

MPF (“maturation-promoting factor” or “M-phase-promoting factor”) triggers the cell’s passage
past the G2 checkpoint to the M phase.
○ MPF promotes mitosis, acts both directly as a kinase and indirectly by activating other
kinases, stimulates fragmentation of the nuclear envelope, contributes to the molecular events
required for chromosome condensation and spindle formation during prophase. (Protein
kinases are enzymes that activate or inactivate other proteins)
CDK = cyclin dependent kinases
Biology 11E: Mitosis and cell cycle
Page 17
How does platelet-derived growth factor (PDGF) influence the cell cycle in fibroblasts (cells of
the connective tissue)?

Platelet-derived growth factors (PDGFs), produced by platelet blood cells, are required for the
division of fibroblasts in culture.
○ Fibroblasts, a type of connective tissue cell, have PDGF receptors on their plasma
membranes.
○ PDGF molecules bind to these receptor tyrosine kinases, triggering a signal transduction
pathway that allows cells to pass the G1 checkpoint and divide.
Biology 11E: Mitosis and cell cycle
Page 18

The role of PDGF is easily seen in cell culture: Fibroblasts in culture divide only in the presence
of a medium that also contains PDGF.

In a living organism, platelets release PDGF in the vicinity of an injury. The resulting proliferation of
fibroblasts helps heal the wound.

The effect of an external physical factor on cell division can be seen in density-dependent inhibition of
cell division.
○ Cultured cells normally divide until they form a single layer on the inner surface of the culture
container.
○ If a gap is created, the cells will grow to fill the gap.
Explain how aberrations in the cell cycle can lead to tumour formation
Cancer
Biology 11E: Mitosis and cell cycle
Page 19
cells have lost density dependent cell inhibition.

Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence.
Cancer cells have escaped from cell cycle controls.

Cancer cells divide excessively and invade other tissues because they are free of the body’s control
mechanisms.
○ Cancer cells do not exhibit density-dependent inhibition when growing in culture; they do not stop
dividing when growth factors are depleted.
○ This is because a cancer cell manufactures its own growth factors, has an abnormality in the signaling
pathway, or has an abnormal cell cycle control system.

If and when cancer cells stop dividing, they do so at random points, not at the normal checkpoints in the
cell cycle.

Cancer cells may divide indefinitely if they have a continuous supply of nutrients.
○ In contrast, nearly all mammalian cells divide 20–50 times under culture conditions before they stop,
age, and die.

Cancer cells may be “immortal.”
○ HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in
culture.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Activity: Causes of Cancer (Chapter 12)
Biology 11E: Mitosis and cell cycle
Page 20
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Cancer cells also show loss of cell cycle controls and may divide without being checked. The story of
HeLa cells is worth noting. What is their source? How old are they? Note that, unlike normal cells,
HeLa cells are immortal!
Here is a normal mammogram and one showing a breast tumour:
Identify each phase of the cell cycle.
Biology 11E: Mitosis and cell cycle
Page 21
Biology 11E: Mitosis and cell cycle
Page 22