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Transcript
Mitosis
and Cytokinesis
Chapter 5: Cell Growth and Division
Section 2
How do cells divide?
Cell Cycle Review
• What is the “growth phase”?
• When is DNA replicated?
• When does the cell undergo checkpoints?
• What is the function of the checkpoint?
DNA Review
•
•
•
•
•
•
What type of Carbon-based molecule is DNA?
What is the monomer?
What makes up the monomer?
Is DNA single stranded or double stranded?
What are the nitrogenous bases?
Where is it stored?
Chromosomes Condense
• We have already learned that DNA is replicated
during the S phase of the cell cycle.
– However, there are a lot of intricacies to that process.
• Chromosome – one long, continuous thread of
DNA that consists of numerous genes along with
regulatory information.
– Gene – the sequence of nucleotides forming part of a
chromosome; the order of which determines the
sequence of amino acids in a protein
Human Chromosome Number
• Somatic Cells – biological cell forming the
body of the cell; any cell not including
gametes or stem cells
• Diploid – chromosomes arranged in
homologous pairs
– The human diploid number is 46
– Our somatic cells have a diploid number of 46
– DOES NOT include gametes
Human Chromosome Number
Human Somatic Cells
• Human somatic cells contain 46
chromosomes.
– If each chromosome was stretched out, they
would measure about 10 feet long!!
– How would these fit inside a nucleus?
• In order to help fit the DNA inside the nucleus,
the DNA wraps around proteins called
histones.
– Histones help condense and organize the DNA
Chromosomes Condense
• During interphase, DNA is loosely organized.
– Proteins must have access to specific genes to make
new proteins or copy the entire DNA sequence.
– Therefore, being too tightly organized would restrict
access to the DNA.
• During mitosis, chromosomes are tightly
condensed.
– Must condense to be divided between the two nuclei.
– If they remained stringy, the chromosomes would
become entangled.
Histones
• At all times during the cell cycle, each of your
chromosomes is associated with histones.
– DNA wraps around the histones at regular
intervals.
– Parts of the histones will interact causing the DNA
to further condense.
• Chromatin – the loose combination of DNA
and histones
Chromatin
• “Loose” is used to describe how the DNA folds
on itself (condenses) and is NOT referring to
how the DNA is wrapped around the histones.
• As the cell progresses to Mitosis, DNA is
replicated during the S phase.
– Both sets of DNA continue to condense in
preparation for cell division
– Eventually the chromatin form small, thick rods
Chromatid
• Chromatid – One half of the duplicated
chromosome
– Sister Chromatid –the 2 identical chromatids
– Centromere – the condensed region joining the
sister chromatids together.
Chromatid
Telomeres
• Telomere
– The ends of chromosomes
– Made of repeating nucleotides that do not form
genes. (aka this portion does not code for anything).
• Function of Telomere:
– Prevents the ends of chromosomes from accidentally
attaching to each other
– Prevents the loss of genes
Mitosis
• Mitosis divides the parent cell’s nucleus and
nuclear contents into two genetically identical
nuclei
– Each nuclei contains its own single, full set of DNA
• 4 Phases of Mitosis
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Prophase
1. Chromatin condenses into tightly coiled
chromosomes
– Each consists of 2 identical chromatids
2. Nuclear envelope breaks down
3. Nucleolus disappears
4. Centrosomes and centrioles begin to migrate to
opposite sides of the cell
5. Organized microtubules called spindle fibers
grow from centrioles and radiate toward the
center of the cell
Prophase
Prophase
Metaphase
1. The spindle fibers attach to a protein
structure on the centromere
2. When the spindle fibers attach, this causes
the chromosomes to align along the cell
equator
Metaphase
Metaphase
Metaphase
Anaphase
1. Sister chromatids separate from each other
2. Spindle fibers begin to shorten, pulling sister
chromatids away from each other and
towards opposite side
of the cell.
Anaphase
Anaphase
Telophase
1. A complete set of identical chromosomes is
positoned at each pole of the cell.
2. Nuclear membranes start to form
3. Chromosomes begin to uncoil
4. Spindle fibers fall apart
Telophase
Telophase
Cytokinesis
• Cytokinesis – divides the cytoplasm into 2
cells and completes a full stage of the cell
cycle
• At the completion of cytokinesis, there will be
2 genetically identical daughter cells
*Animal Cells and Plant Cells have differing
events during cytokinesis
Animal Cell Cytokinesis
1. The cell
membrane forms
a furrow, or
trench.
2. The trench is
pulled inward by
tiny filaments
3. Gradually the
membrane
pinches closed.
Plant Cell Cytokinesis
• The membrane cannot
pinch inward due to
the cell wall.
1. Cell plate forms
between the 2 nuclei
– Cell plate is made by
golgi apparatus
– New cell wall grows as
cellulose is laid down
Cytokinesis
• Typically the cytoplasm is divided evenly
between the two new daughter cells.
• Single-celled organisms use division in order
to reproduce.
• Multi-cellular organisms use division for
growth, development, and repair.