Download When cells divide, duplicate copies of DNA

The Cell Cycle
What is the cell cycle?
• The Stages of the life
of the cell
Involve:
1. Metabolic activities
2. Division
Purpose of Cellular Division
-Asexual reproduction of cells
- Development and growth
of multicellular organisms
- Repair and renew cells that die from normal
wear and tear or accidents
Cell Division and DNA
When cells divide, duplicate copies of DNA ( genome)
Are sent to each cell
• In prokaryotes, the
genome is often a
single long DNA
molecule
(chromosome)
• In eukaryotes, the
genome consists of
several chromosomes
Every eukaryotic species has a characteristic number
of chromosomes in the nucleus
• Human somatic cells
( body cells) have 46
chromosomes- 23
pairs
•When not packaged,
DNA is a long,
thin strand
(chromatin)
associated
With proteins called
HISTONES
Video on structure
Histonesprotein spheres
DRAW
Structure terms (206-209)
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Daughter cell
Genome
Somatic Cells
Gametes (germ cells)
Chromosome
Sister chromatids
Chromatin
Centromere
Kinetochore
Mitosis
Cytokinesis
Chromosomes
• Each duplicated
chromosome consists of
two sister chromatids
which contain identical
copies of the
chromosomes DNA
• As they condense, the
region where the strands
connect shrinks to a
narrow area called the
centromere
Centromere
Stages of the Cell Cycle
Divided into 2 main stages
1. Interphase- G1, S, G2
2. Mitotic Phase- M
Who are
these guys?
Stages of the Cell Cycle
1.
G1 phase- growth
2. S phase- “synthesis”,
chromosomes copied
3. G2 phase- cell
completes preparations
for cell division
4. Mitosis- division of
cells to 2 daughter
cells
The Stages of Mitosis
• Prophase
– Chromosomes condense and
nuclear membrane
disappears
– Each chromosome appears
as a sister chromatid- X
SHAPE FORMATION
– Mitotic spindle, consisting
of microtubules and other
proteins, forms between
the two pairs of centrioles
as they migrate to
opposite poles of the cell.
– THIS IS USED TO PULL
THE CHROMOSOMES
APART
The Stages of Mitosis
• Prometaphase
– Breakdown of nuclear
envelope into small
fragments
– Microtubules interact with
the chromosomes
– Bundles of microtubules
extend from each pole
toward the middle
– Each of the 2 chromatids
has a specialized structure
called a kinetochore. Some
microtubules attach to the
kinetochore to begin
movement
Kinetochore
The Stages of Mitosis
• Metaphase
– Centrosomes are now at
opposite poles of the cell
– Chromosomes convene on the
metaphase plate-immaginary
line between poles
– Centromeres aligned and the
kinetochores of the sister
chromatids are attached to
microtubules coming from
opposite poles of the cell
– The microtubules are called
spindles b/c of their shape
The Stages of Mitosis
• Anaphase
– Paired centromeres of each
chromosome separate, freeing
sister chromatids
– Each chromatid is considered
a full fledged chromosome
– The once joined sisters begin
to move towards opposite
poles of the cell
– By the end of anaphase, the 2
poles of the cells have
equivalent and a complete
collections of chromosomes
The Stages of Mitosis
• Telophase
– Nonkinetochore microtubules
elongate the cell, and
daughter nuclei form at the
poles of the cell
– Nuclear envelopes arise
from the fragments of the
parent cell’s nuclear
envelope
– Chromatin fiber becomes
less tightly coiled
– CYTOKINESIS- division of
cytoplasm takes place
shortly after end of mitosis
Cytokinesis
• Cleavage furrow forms
which pinches the cell
into 2 parts, near the old
metaphase plate.
• On the cytoplasmic side
of the furrow is a
contractile ring of
microfilaments which
contracts to pull apart the
cells like a drawstring
• Finally 2 separate cells
are created
Video to wrap it up