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Name: Date:Biology 11E: Cell Cycle and Mitosis

Chapter: 12 Big Ideas:

Big Idea Chapters Illustrative Examples3. Living systems store, retrieve, transmit and respond to information essential to life processes.3.A.2 In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis, or meiosis plus fertilization.

12.1-12.3 • Mitosis-promoting factor (MPF) • Action of platelet-derived growth factor (PDGF)• Cancer results from disruptions in cell cycle control

-By the end of this unit you should also 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

The Process and Importance of Cell Division

-Watch Activity: Roles of Cell Division from masteringbiology, Chapter 12.

-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?

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-What is the difference between chromatin and chromosomes?

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-What are the differences between the cells to the right?

-What are these cells called and what are two examples of each?

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Chromosomes During Cell Division

-Review the basic process of chromosome duplication and distribution during cell division.

-Does the image above depicting cytokinesis, mitosis or meiosis?

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-What occurs in meiosis? How is the chromosome number of daughter cells different?


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-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?


The Cell Cycle Ensures Genetic Continuity

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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) S: 10-12 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 sub-phases 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.


-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 Important features of phase.

G2 of Interphase

-Prophase

Protomet-aphase

Metaphase

Anaphase

TelophaseAnd Cytokinesis

*Other Useful Animations of Mitosis are:

a) Bioflix Mitosis, masteringbiology, chapter 12

b) http://www.johnkyrk.com/mitosis.html

c) To see what mitosis looks like under a microscope visithttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artaug99/mitosis.html

*Complete the Online Mitosis Lab

*Complete Lab 3: Mitosis and Meiosis

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?

Microtubules and associated proteins (another portion of the cytoskeleton is dismantled to provide these)

-In animal cells, the assembly of spindle microtubules starts at the centrosome. What is the function of this subcellular region?

-Microtubule organizing centre.

-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.


http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artaug99/mitosis.html

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artaug99/mitosis.html

http://www.johnkyrk.com/mitosis.html

What is a kinetochore?

-Proteins and sections of chromosomal DNA at centromeres. Link sister chromatids to the mitotic spinndle.

-Face opposite directions in a chromosome = chromatids pulled to opposite poles.

Explain the difference between kinetochore and nonkinetechore microtubules. What is the function ofeach?

-KM: Attached to K during Prometaphase, separate sister chromatids

Non KM: Overlap at MP, elongate cell during anaphase

What are the components of the mitotic spindle?

-Centrosome, microtubules, asters


At which end do kinetochore microtubules shorten during anaphase? Explain the data that supports where this shortening occurs.

-“Pac Man Mechanism”

Microtubules labelled with yellow dye and then dye is removed from one region between the kinetochore and spindle.

During Anaphase the microtubules on the kinetochore side of the unmarked region shorted while those on the spindle side stay the same length.

Motor proteins walk chromosomes along the microtubules, which depolymerize once the motor protein passes.


Mitosis and Cytokinesis

-Analyse the diagram below and try to determine the difference between cytokinesis in animal and plant cells.

-Cleavage furrow: -Only forms in animal cells and occurs near the metaphase plate.

-Contractile ring of actin microfilaments associated with the motor protein myosin. Myosin causes the ring to contract, pinching the cell in two.

What is the source of the material for the cell plate?

Cell plate is formed from vesicles from the Golgi which contain cellulose.Cell plate grows until its membrane fuses with the plasma membrane.


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:


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?

-Asexual as identical bacterial chromosomes (circular DNA and associated proteins) produced.

1. Origin of replication: 2 origins move to

opposite ends of the cell

2. At the same time the cell elongates (2x

its original size)

3. Plasma membrane pinches in to form 2

cells.

-Proteins play a role in this process, but it is

not fully understood. For example, an

actin-like protein helps chromosome

movement.

-Bacterial method is thought to be the

precursor of Mitosis, which is supported by

the similarity in proteins and possible

intermediate stages as seen in

dinoflagellates, diatoms/yeasts.


Concept 12.3 The eukaryotic cell cycle is regulated by a molecular control system

R4: Explain how the cell cycle is regulated.

-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:a) Some human cells divide frequently throughout life (skin cells).b) Others human cells have the ability to divide but keep it in reserve (liver cells).c) Mature nerve and muscle cells do not appear to divide at all after maturity.

-Here are some experiments to help understand this:

Suggests that molecules present in cytoplasm during S or M phase control the progression of that phase.


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 go-ahead signals regulate the cycle

What happens if a cell does not pass the G1

checkpoint?

-For many cells the G1 checkpoint, the “restriction point” is the most important checkpoint:

a) If the cell receives a go-ahead signal at the G1 checkpoint, it usually completes the cell cycle and divides.b) If the cell does not receive a go-ahead signal, the cell exits the cycle and switches to a non-dividing state, the G0 phase.

-Most cells in the human body are in the G0

phase.a) Liver cells can be “called back” to the cell cycle by external cues, such as growth factors released during injury.b) 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. a) A kinase needs to be attached to a cyclin to be activated (cyclin-dependent kinases, Cdks)b) Activity of Cdks rises and falls with concentration of cyclin.


Passing the G2 checkpoint means that the cell will enter the mitotic phase. What controls the G2 checkpoint?

-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

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. a) Fibroblasts, a type of connective tissue cell, have PDGF receptors on their plasma membranes.b) PDGF molecules bind to these receptor tyrosine kinases, triggering a signal transduction pathway that allows cells to pass the G1 checkpoint and divide.

-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.a) Cultured cells normally divide until they form a single layer on the inner surface of the culture container.b) If a gap is created, the cells will grow to fill the gap.

R5: Explain how aberrations in the cell cycle can lead to tumour formation


Cancer cells exhibit different behaviors than normal cells. Here are two normal behaviors they no longer show. Explain each behavior.


1) Density-dependent inhibition -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.a) In contrast, nearly all mammalian cells divide 20–50 times under culture conditions before they

stop, age, and die.

-Cancer cells may be “immortal.”a) HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in

culture.

2) Anchorage dependence

-To divide normal cells must be anchored to a substrate, but this is lost in cancerous cells.

Activity: Causes of Cancer (Chapter 12)

-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!

HeLa Cells: http://www.youtube.com/watch?v=0gF8bCE4wqA

-The image right shows a normal mammogram and one showing a breast tumour:

Identify each phase of the cell cycle.


http://www.youtube.com/watch?v=0gF8bCE4wqA

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