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Chapter 12: The Cell Cycle
(How do cells divide?)
cell division in prokaryotes
chromosomes
eukaryotic cell cycle
mitosis
cytokinesis
.
Prokaryotes
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
chromosomes: densely packaged chromatin
during cell division
protects the DNA
sets up DNA distribution
.
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
each chromosome contains
hundreds to thousands of genes
.
chromosomes each species has a
characteristic number of chromosomes
number varies between species
does not reflect complexity
humans: 46
some ferns: 1000+
chromosomes for an individual is the karyotype
.
chromosomes
function: chromosomes carry the genetic information of a cell
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 G0, 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
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 G0, 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 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 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
.
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 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
.
Mitosis: anaphase
sister chromatids separate and are moved toward opposite poles
the protein tethers at the centromere between the chromatids are broken
each former sister chromatid can now be called a chromosome
.
Mitosis: anaphase 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
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
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
*
.
• 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.
.
cytokinesis
divides the cell into two daughter cells
cytokinesis usually begins in telophase and ends shortly thereafter
.
cytokinesis
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
*
.
cytokinesis
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
*
.
cytokinesis
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.
