Download Biol 1020: Cell Cycle

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
.
each chromosome contains
hundreds to thousands of genes

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


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
.
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
.
•
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.
.
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.
.
*
.