1. Cell life cycle (including
Mitosis)
Pg. 151-159

2. All cells pass through a series
of events called the cell cycle.
Some cells cycle continually
(skin, root tips), other cell
types only a limited number
of times before they stop
multiplying (brain, nervous,
etc.) and eventually die.
The cell cycle is divided into
several stages.

3. Interphase
 Most of cell cycle (95%) = normal cell
functioning
 Cell increases in size
 Organelles replicate.
 DNA replicates.
 Readies for mitosis
 DNA condenses
 Three parts:
 G1 = Cell growth; Normal cell functions
 S = DNA replicated
 G2 = DNA condenses into chromosomes
Strands = sister chromatids
2 Chromatids connected by centromere

4. Chromosomes
 The organelle into
which DNA is
packaged
 Contains proteins called
histones – which give
DNA support
 Chromatin is what
DNA is called when it
is not tightly coiled
during cell division
 Chromosomes only
“appear when a cell is
dividing”

5. Why divide? Why not increase in size?
 As organisms grow, the size of their cells do
not increase they simply divide into more cells!
 Cells need a high surface area to volume ratio
 REMEMBER: Cell membrane lets things in (like
glucose) and removes others (carbon dioxide)
 Very large cells cannot let things in and out fast
enough to maintain the needs of the larger cell
 ANSWER: Cells divide after growth or die
because eventually they cannot sustain the
needs of their internal environments

6. Mitosis
The multi-
step process
of cell
division in the
cell cycle is
called mitosis.

7. What is the purpose of Mitosis?
1. Maintain a high surface area to volume ratio
when cells grow.
2. Reproduction (When unicellular organisms
go through mitosis there are now two
identical organisms.)
3. Multicellular organisms go through mitosis
to:
1. produce new cells to grow (bone cells)
2. replace damaged or dying cells (blood
cells)

8. Mitosis overview
 Produces two identical cells
 Each cell has a full set of
DNA (diploid – two sets for
each gene)
 Stages of Mitosis:
Prophase
Metaphase
Anaphase
Which cells are undergoing
mitosis? Telophase

9. Prophase (early)
Chromosomes shorten and thicken
Nuclear membrane disappears

10. Prophase (late)
 Spindle fibers formed from microtubules
 Microtubules surround centromere
 Chromosomes begin to move

11. Metaphase
Pairs of sister chromatids align at
center (middle/metaphase)
Forms metaphase plate

12. Anaphase
Chromatids separate at centromere
Chromatids pulled apart in opposite
directions toward poles
Equally divides DNA

13. Telophase
Cell cytoplasm readied for division
Spindle fibers disassemble
2 Nuclear envelopes reform
Cytokinesis occurs

14. Cytokinesis (part of telophase)
Division of cytoplasm and organelles to
create 2 new identical cells.
--Includes the construction of cell
membrane between two new cells
--Process differs in animals and plant cells

15. Animal Plant
 Cell pinched in two • New cell wall must be
 Pinching at cleavage laid down
• Cell plate forms
furrow