Download Plant Cell

How do little elephants grow up to be BIG
elephants?
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Division of the cell
Division of the nucleus (1st Stage of Mitotic Phase)
Prophase
Pro-Metaphase
Metaphase
Anaphase
Telophase
Division of cytoplasm (2nd Stage of Mitotic Phase)
Cell Cycle ≠ Mitosis
Cell Cycle = Interphase + Mitotic Phase
Cell Division ≠ Mitosis Cell Division = Mitosis + Cytokinesis
Cell Division = Asexual Reproduction = Natural Cloning
(for SOME single-celled organisms)
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During INTERPHASE, the cell is engaged in normal metabolic activity. This is
when the cell is most active, and genes are transcribed to make proteins.
G1 is the main growth stage when a cell grows from a small daughter cell
into a full-sized cell.
S-Phase starts if/when the cell receives a signal that it may need to divide
at some point in the future.
During G1 and S-phases, chromosomes appear as threadlike or spaghettilike strands called chromatin.
During the S-phase, the DNA in the nucleus is replicated (to produce sister
chromatids.
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The two identical sister chromatids joined at the centromere.
By the END of G2, each chromosome and its copy (the sister chromatids) will
become condensed and appear as thick, worm-like chromosomes!
During G2, the mitochondria in plant and animal cells and the chloroplasts in
CELL
plant cells replicate.
MEMBRANE
Nucleus
Cytoplasm
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G0 phase is viewed as either an extended G1 phase, where the cell is neither
dividing nor preparing to divide, or a distinct “quiet” stage that occurs outside of
the cell cycle.
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On occasion, a distinction in terms is made between a G0 cell that is only
temporarily “resting” (eventually may re-enter the cell cycle) versus a cell
that has become “quiet” and will never re-enter the cell cycle (e.g., heart
muscle cells and neurons).
Some types of cells, such as nerve and heart muscle cells, become “quiet” when
they reach maturity (i.e., when they are fully differentiated).
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Quiet cells continue to perform their main functions for the rest of the
organism's life, but do not divide and cannot be replaced.
Multi-nucleated muscle cells are basically muscle cells that never fully finished cell
division (did not complete cytokinesis) and therefore have multiple nuclei and
continuous cytoplasm.
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Because these cells do not undergo cytokinesis, they are also often considered
to be in the G0 stage.
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
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Mitosis begins (cell begins to divide)
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DNA appears as condensed, worm-like chromosomes (not spaghetti-like
chromatin seen in Interphase).
• Chromosomes consist of two identical sister chromatids joined at the
centromere.
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Two pairs of centrioles appear and begin to move to opposite ends (poles)
of the cell.
• Centrioles occur in pairs; each centriole in a pair is oriented at a right
angle to its partner.
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Spindle fibers form between the two pairs of centrioles.
Centrioles
Sister chromatids
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Pro-Metaphase
• The NEW step in the cycle that occurs between
Prophase and Metaphase.
• Activities formerly considered to mark the last part of
Prophase:
 Nuclear envelope disintegrates.
 Centrioles arrive at the poles of the cell.
• Activities formerly considered to indicate the beginning
of Metaphase:
 Spindle fibers attach to the centromeres linking
two sister chromatids together.
 Chromosomes (sister chromatids) begin
migrating/moving towards center of cell.
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Spindle Fibers attach to the chromatids (sister pairs of chromosomes)
at the centromere.
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Sister Chromatids migrate until they are all lined up at the cell
“equator” along the metaphase plate.
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Spindle fibers are usually visible under a microscope in this stage.
The location of the equator or metaphase plate is determined by WHERE the
chromosomes line up.
Meta = Middle
Organization of sister chromatids along metaphase plate helps
ensure that in the next phase, when the chromosomes are
separated, each new nucleus will receive one copy of each
chromosome.
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Comparing Prophase, Prometaphase,
and Metaphase
Animal Cell: comparison of prophase, prometaphase, and metaphase.
Plant Cell:
comparison of prophase,
prometaphase,
and metaphase.
The paired chromosomes (sister chromatids)
separate and begin to move/migrate towards
the opposite ends (poles) of the cell.
• “Ana” = opposite
• The migrating chromatids may appear V-like as
they are pulled towards opposite poles.
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Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
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The chromatids arrive at the poles of the cell.
A new nuclear envelope begins to form around each of the
two clumps of chromatids, eventually forming two new nuclei.
Chromosomes gradually become uncondensed and appear
as chromatin (threads rather than rods).
A cleavage furrow or cell plate may become visible towards
the end of telophase.
This is the end of Mitosis.
Nuclei
Chromatin
Nuclei
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
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Cytokinesis: the division of the cytoplasm (and everything in it).
Cytokinesis usually begins during Telophase (occurs concurrently).
In animal cells, the cleavage furrow pinches inward.
In plant cells, a cell plate forms along the metaphase plate
region and grows towards the cell walls.
Cytokinesis results in two daughter cells – each with its own
nucleus with identical chromosomes.
Each daughter cell will end up with half of the cytoplasm and
about half of the organelles—there are usually enough in the
original cell that each daughter cell will end up with some.
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Mitosis
Discussion Question:
Mitosis is the process in which
the nucleus divides to form two
new nuclei. How does mitosis
differ in plants and animals?
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http://www.cellsalive.com/mitosis.htm
- Cell Division
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From double helix…
to chromatin…
to chromosome….
The Many Faces of DNA
 During interphase, DNA
that is actively being
transcribed to make
proteins is generally loosely
wrapped around special
proteins called histones.
 The DNA + histone
structure is called a
nucleosome.
 A strand of loosely
wrapped, spaced out
nucleosomes is called
“beads on a string.”
 Chromatin is actually a spaghetti-like fiber made of hundreds of thousands of
tightly wrapped and closely packed nucleosomes.
 Chromatin is the way DNA is stored during interphase if it is NOT being actively
transcribed.
At the end of G2 and into the beginning of prophase (the mitotic
phase), the chromatin fiber will begin folding up along a protein
scaffold (chromosome loops), which twist up and wrap in on itself again
(forming condensed chromosome loops), and then coils up on itself to
create the highly condensed chromosomes that we observe during the
mitotic phase.
Beads on a String: Active DNA being
transcribed to make proteins during
INTERPHASE.
Chromatin Fiber: Inactive DNA being
stored/not transcribed during
INTERPHASE.
Condensed Chromatin: Chromatin begins
to fold up at the end of G2.
Condensed Chromosome: In PROPHASE,
condensed chromatin coils in on itself to
form the highly condensed chromosome.
CLICK HERE for animation of DNA double helix
wrapping up around histones to form nucleosomes and the
“beads on a string” structure,
nucleosomes packing up tight to create chromatin,
and chromatin coiling up and condensing to form
chromosomes.
The process of asexual
reproduction begins after a
sperm fertilizes an egg.