Transcript 5.2 Mitosis and Cytokinesis

5.2 Mitosis and Cytokinesis
KEY CONCEPT
Cells divide during mitosis and cytokinesis.
5.2 Mitosis and Cytokinesis
Chromosomes condense at the start of mitosis.
• DNA is a double-stranded molecule, like a twisted ladder.
• DNA is made of four subunits called nucleotides.
• Nucleotides are made of three parts: a sugar, a phosphate
group and a base.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
5.2 Mitosis and Cytokinesis
Chromosomes condense at the start of mitosis.
• A chromosome is one long strand of DNA.
• Each of our body cells has 46 chromosomes.
• DNA in each chromosome has multiple genes.
• DNA in ONE cell would stretch out to be 10 feet long.
• HOW ON EARTH does it fit in the cell?
• DNA wraps around proteins called histones that
condense it.
– DNA wraps around these histones, similar to beads on
a string.
– DNA is loose like spaghetti, which describes how it
folds back on itself, not that it is loosely wrapped
around the histones.
– This loose DNA is called a chromatin. Let’s look.
5.2 Mitosis and Cytokinesis
• DNA plus histones (proteins) is called chromatin.
chromatid
• One half of a duplicated
chromosome is a chromatid.
telomere
• The two identical chromatids are
called sister chromatids.
centromere
• Sister chromatids are held
together at the centromere, the
area that appears to be pinched.
• Telomeres are the ends of the
chromatids that are made of
repeating nucleotides.
• They protect DNA and do not
include genes.
telomere
• A small section of the telomeres Condensed, duplicated chromosome
are lost when DNA is copied.
5.2 Mitosis and Cytokinesis
Mitosis and cytokinesis produce two genetically identical
daughter cells.
Parent cell
Interphase (#1 on PN)
• Interphase prepares
the cell to divide.
– DNA is loosely
organized and
duplicated
– The cell grows to
prepare for
division
– Organelles are
with
duplicated. nucleus
DNA
centrioles
spindle fibers
centrosome
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus into two genetically
identical nuclei, each having its own set of DNA.
• Mitosis occurs in ALL bodily cells except those that form
eggs or sperm (sex cells).
• Mitosis occurs in four phases.
1. Prophase (#2 on PN)
–
–
–
–
–
–
chromatins condense into
tight chromosomes
Spindle fibers form.
Nuclear envelope breaks
down
Nucleolus disappears
Centrosomes and
centrioles migrate to
opposite sides of the cell
Spindle fibers grow from
the centrioles and radiate
towards the cell center
Prophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
2. Metaphase (#3
on PN)
– Spindle fibers
attach to a
protein structure
on centromere of
each
chromosome
– Chromosomes
then line up in
the middle of the
cell.
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
3. Anaphase (#4 on
PN)
– sister chromatids
separate from
each other
– Spindle fibers
shorten
– This pulls the
sister chromatids
away from each
other to opposite
sides of the cell.
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5.2 Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
4. Telophase (#5 on PN)
– Complete set of
identical chromosomes
is positioned at each
pole of the cell
– They begin to form the
new nuclei and
chromosomes begin to
uncoil.
– Nuclear membrane
starts forming
– Spindle fibers fall apart
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5.2 Mitosis and Cytokinesis
Cytokinesis (#6 on PN)
• divides the cytoplasm
between the two
daughter cells and
completes the cell
cycle.
• It differs in animal and
plant cells.
– In animal cells, the
membrane pinches
closed.
– In plant cells, a cell
plate forms.
5.2 Mitosis and Cytokinesis
• Single celled organisms use cell division to reproduce
• Multicellular organisms use cell division for growth,
development and repair
Mitosis Animation
http://www.cellsalive.com/mitosis.htm