Chapter 12: The Cell Cycle
(How do cells divide?)
 cell division in prokaryotes
 chromosomes
 eukaryotic cell cycle
 mitosis
 cytokinesis
.

binary fission generation time as short as
20 minutes
.

Chapter 12: The Cell Cycle
(How do cells divide?)
 cell division in prokaryotes
 chromosomes
 eukaryotic cell cycle
 mitosis
 cytokinesis
.

• Define:
– chromosome
– chromatin
– gene
– genome
– karyotype
• Describe the human genome and karyotype in terms of:
– number of basepairs
– number of genes
– number of chromosomes
.

Eukaryotic DNA in chromosomes
 chromatin : long DNA molecule with associated proteins


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 chromosomes : densely packaged chromatin during cell division protects the DNA sets up DNA distribution
.

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 functional units of heredity typically instructions for a protein or RNA genome – organism’s complete DNA sequence humans apparently have ~25,000 genes in the now-sequenced human genome
.

chromosomes
 each species has a characteristic number of chromosomes
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
 number varies between species

 does not reflect complexity humans: 46 some ferns: 1000+ chromosomes for an individual is the karyotype
.

.

 chromosomes
 from one cell generation to the next
 from one organism to its offspring
.

.

• Define:
– chromosome
– chromatin
– gene
– genome
– karyotype
• Describe the human genome and karyotype in terms of:
– number of basepairs
– number of genes
– number of chromosomes
.

Chapter 12: The Cell Cycle
(How do cells divide?)
 cell division in prokaryotes
 chromosomes
 eukaryotic cell cycle
 mitosis
 cytokinesis
.

• Draw a circle diagram of the eukaryotic cell cycle. Label all phases.
• Discuss what goes on in each of the phases on the diagram. Note where checkpoints exist. Also, discuss G
0
, and discuss cell cycle regulation in general terms.
.




Eukaryotic Cell Cycle when cells reach a certain size, growth either stops or the cell must divide cell division is generally a highly regulated process (not all will divide!) the generation time for eukaryotic cells varies widely, but is usually 8-20 hours
.

Eukaryotic Cell Cycle
.

Eukaryotic Cell Cycle cyclins and cyclin-dependent protein kinases (Cdks) cytokinins ; growth factors ; suppressors; cancer cells
.

• Draw a circle diagram of the eukaryotic cell cycle. Label all phases.
• Discuss what goes on in each of the phases on the diagram. Note where checkpoints exist. Also, discuss G
0
, and discuss cell cycle regulation in general terms.
.

.

Chapter 12: The Cell Cycle
(How do cells divide?)
 cell division in prokaryotes
 chromosomes
 eukaryotic cell cycle
 mitosis
 cytokinesis
.

• Describe what “PMAT” means.
• With a partner, do the “chromosome dance” for mitosis. Make sure that you distinguish between chromosomes and chromatids, and note at each stage the number of sister chromatids per chromosome.
• Discuss what happens in each stage of mitosis.
.

Mitosis
4 stages: prophase metaphase anaphase telophase
(PMAT)
*
.


Mitosis: prophase
 chromatin condenses to form chromosomes

 each chromosome (duplicated during S phase) forms a pair of sister chromatids sister chromatids are joined at a centromere by protein tethers

 centromeres contain a kinetochore where microtubules will bind each sister chromatid has its own kinetochore sister chromatids become attached by their kinetochores to microtubules from opposite poles
.

Mitosis: prophase
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
 a system of microtubules, called the mitotic spindle , organizes between the two poles (opposite ends) of the cell each pole has a microtubule organizing center (MTOC) in animals and some other eukaryotes, centrioles are found in the MTOC
.

Mitosis: prophase
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 by the end of prophase: the nuclear membrane has disappeared (actually divided into many small vesicles) nucleoli have disintegrated the sister chromatids are attached by their kinetochores to microtubules from opposite poles
.

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Mitosis: prophase some call the later part of prophase prometaphase , usually defined to include vesicularization of the nuclear membrane and attachment of kinetochores to microtubules in some eukaryotes the nuclear membrane never vesicularizes
.


Mitosis: metaphase
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 chromosomes line up along the midplane of the cell (the metaphase plate ) chromosomes are highly condensed

 the mitotic spindle , now complete, has two types of microtubules kinetochore microtubules extend from a pole to a kinetochore polar microtubules extend from a pole to the midplane area, often overlapping with polar microtubules from the other pole the mitosis checkpoint appears to be here; progress past metaphase is typically prevented until the kinetochores are all attached to microtubules
.

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Mitosis: anaphase sister chromatids separate and are moved toward opposite poles
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 the protein tethers at the centromere between the chromatids are broken each former sister chromatid can now be called a chromosome
.

Mitosis: anaphase
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 model for the mechanism that moves chromosomes to the poles motor proteins move the chromosomes towards the poles along the kinetochores microtubules kinetochore microtubules shorten behind the moving chromosomes
*
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 polar microtubules lengthen the entire spindle motor proteins on the polar microtubules slide them past each other, pushing them apart (the microtubules may grow a bit, too) this pushes the MTOCs away from each other, and thus has the effect of pushing kinetochore microtubules from opposite poles away from each other
.

Mitosis: anaphase
 overall, this process assures that each daughter cell will receive one of the duplicate sets of genetic material carried by the chromosomes
.

Mitosis: telophase
 prophase is essentially reversed
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
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 the mitotic spindle is disintegrated the chromosomes decondense nuclear membranes reform around the genetic material to form two nuclei
 each has an identical copy of the genetic information nucleoli reappear, and interphase cellular functions resume
*
.

• Describe what “PMAT” means.
.

• With a partner, do the “chromosome dance” for mitosis. Make sure that you distinguish between chromosomes and chromatids, and note at each stage the number of sister chromatids per chromosome.
• Discuss what happens in each stage of mitosis.
.

Chapter 12: The Cell Cycle
(How do cells divide?)
 cell division in prokaryotes
 chromosomes
 eukaryotic cell cycle
 mitosis
 cytokinesis
.

• Describe cytokinesis in both plant cells and animal cells, noting the differences.
• Describe what is meant by the term
“polar division” and why this process was (and still is) important in your development.
.



divides the cell into two daughter cells cytokinesis usually begins in telophase and ends shortly thereafter
.

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 in animals, a cleavage furrow develops usually close to where the metaphase plate was a microfilament (actin) ring contracts due to interactions with myosin molecules, forming a deepening furrow eventually, the ring closes enough for spontaneous separation of the plasma membrane, resulting in two separate cells
*
.

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 in plants, a cell plate develops usually close to where the metaphase plate was vesicles that originate from the
Golgi line up in the equatorial region
 the vesicles fuse and add more vesicles grow outward until reaching the plasma membrane and thus separating the cells the vesicles contain materials for making the primary cell wall and a middle lamella
*
.

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
cytoplasm (and with it most organelles) is usually distributed randomly but roughly equally between daughter cells sometimes cell division is a highly regulated polar division that purposefully distributes some materials unequally
.

• Describe cytokinesis in both plant cells and animal cells, noting the differences.
• Describe what is meant by the term
“polar division” and why this process was (and still is) important in your development.
.

• In the following slide, look for examples of interphase, prophase, metaphase, anaphase, and telophase/cytokinesis.
.

*
.