1. Lecture #19: Honors Biology Ms. Day
The Cell Cycle
Lecture #19:
Honors Biology
Ms. Day

2. The Cell Cycle
The mitotic phase alternates with interphase in the cell cycle
Interphasemitosisinterphasemitosis

3. Phases of the Cell Cycle
The cell cycle consists of
The mitotic (M) phase
Interphase (90% of the cell’s life)
INTERPHASE G1
S (DNA synthesis) G2
Cytokinesis Mitosis
MITOTIC (M) PHASE
Figure 12.5

4. Interphase can be divided into subphases
G1 phase (GAP 1 phase)
cell grows in size
varies most in length from cell to cell
S phase (synthesis phase)
DNA is copied (DNA replication)
Single  Double
Other organelles are copied
(ex: centrosomes/centrioles)
G2 phase (GAP 2 phase)
More growth and preparation (make proteins) for mitosis

5. Another G phase of Interphase
Called G0 phase called the resting phase
The cell exits the “cycle” and (usually) does NOT reproduce again
Ex: nerve cells, red blood cells

6. Interphase “Intermission” or “Inbetween”
not part of mitosis
Includes stages G1, S, and G2 of the cell cycle
DNA is in chromatin form
Nucleus & nucleolus present
Longest phase of cell cycle

8. The Mitotic (M) phase Is made up of 2 parts
1. Mitosis division of the nucleus (called Karyokinesis)
2. Cytokinesis  division of the cytoplasm

9. Mitosis Continuous pathway (Early, Mid, & Late)
Consists of 4 phases and cytokinesis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

10. Prophase (X’s) “Pack Together”
Chromatin  Chromosomes
DNA “packs” together
Spindle fibers forms from centrosomes
Centrioles are in centromsomes in animals
No centrioles in plants
Centrosomes with spindle fibers inbetween move towards “poles”
Spindle fiibers attach to each kinetochore on each chromosome  they begin to migrate toward the cell center

11. Mitotic Spindle Fibers
Two types of spindle fibers
Kinetochore fibers
Polar fibers

12. Metaphase (X’s) “Meet in the Middle”
Chromosomes line up in the middle of cell
Called equatorial or metaphase plate
spindle fibers help chromosomes to line up

13. Anaphase (V’s) “Adios and Away”
SISTER CHROMATIDS separate and begin moving to opposite ends (poles) of the cell
Cell elongates (using polar fibers)

14. Telophase (V’s) “Two New Cells”
Spindle fibers disappear
2 nuclei and nucleoli begin to reform
Chromosomes  chromatin
OPPOSITE OF PROPHASE!

15. Cytokinesis “Division of the Cytoplasm”
Occurs in Late telophase
In animal cells
a cleavage furrow forms, which pinches the cell in two.
In plant cells
vesicles from Golgi apparatus produce a cell plate at the middle of the cell
At the end of cytokinesis, there are two distinct IDENTICAL daughter cells.

16. Cytokinesis: A Closer Look
Cleavage furrow
Contractile ring of microfilaments
Daughter cells
100 µm
(a) Cleavage of an animal cell (SEM)
Figure 12.9 A
In animal cells
Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow

17. (b) Cell plate formation in a plant cell (SEM)
In plant cells, during cytokinesis
A cell plate forms
Daughter cells
1 µm
Vesicles forming cell plate
Wall of patent cell
Cell plate
New cell wall
(b) Cell plate formation in a plant cell (SEM)
Figure 12.9 B

18. Kinetochore microtubule
G2 OF INTERPHASE
PROPHASE
PROMETAPHASE
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Early mitotic spindle
Aster
Centromere
Fragments of nuclear envelope
Kinetochore
Nucleolus
Nuclear envelope
Plasma membrane
Chromosome, consisting of two sister chromatids
Kinetochore microtubule
Figure 12.6
Nonkinetochore microtubules

19. TELOPHASE AND CYTOKINESIS
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Spindle
Metaphase plate
Nucleolus forming
Cleavage furrow
Nuclear envelope forming
Figure 12.6

21. Mitosis in a plant cell Nucleus Chromatine condensing Chromosome1
Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from.
Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment.
Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate.
Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten.
Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. 2 3 4 5
Nucleus
Nucleolus
Chromosome
Chromatine condensing
Figure 12.10

22. Cell Cycle and Mitosis Animations

23. Remember…
“IPMATc”
Let’s do the Mitosis Hand Cheer!