Download Cell Division - Sehome High School

Cell Division
Mitosis &
Cytokinesis
Why do cells divide?
•
•
•
•
To grow
To replenish dying/damaged cells
To heal wounds
To produce a new organism (if a
single-celled organism)
• To make sex cells for reproduction
Human Cell Life Spans
Cell Type
Life Span
Small intestine lining
2-3 days
Large intestine lining
6 days
Red blood cells
< 120 days
White blood cells
10 hours to
decades
Long-lived
Muscle, nerves
Mitosis
= Division of the nucleus
Cytokinesis
= Division of the rest of the cell
Chromosomes
•Found in nucleus
•Protected by
nuclear membrane
•Contain genetic
information (DNA)
What do chromosomes look
like?
•Most of the time,
chromsomes are
single-stranded
•Just before cell
division, the
chromosomes become
double-stranded
DNA to Chromosomes
Chromosomes
•When a chromosome
is double-stranded it is
said to have two
chromatids
•The centromere
holds two chromatids
together
Human Karyotype
(chromosomes of a non-sex cell)
Mitosis Summary
• Mitosis starts with one nucleus
having a certain number of
chromosomes
• Ends with two nuclei each with
that same number of
chromosomes
Interphase – S phase
• Happens BEFORE mitosis
• Each chromosome replicates so that it
contains two chromatids
replication
One chromosome
(One chromatid)
One chromosome
(Two chromatids)
Interphase – S phase
Prophase
• Very long strands of chromatin
(DNA) condense into short
chromosomes
• Much easier to move when
condensed – won’t get tangled!
• Centrioles move & spindles form
• Nuclear membrane dissolves
Prophase
Metaphase
• Spindles help move
chromosomes to the middle
(“equator”)
Metaphase
Anaphase
• Each duplicated chromosome is
pulled apart
• one chromatid goes one
direction & the other moves the
other direction
Anaphase
Telophase
• Chromosomes gather at
opposite ends of cell
• New nuclear membranes
reform
Telophase
Cytokinesis
• Occurs near end of mitosis
• The rest of the cell divides in
two
Animation…
http://www.youtube.com/watch?v
=AhgRhXl7w_g