AP Biology

Chapter 12:The Cell Cycle

One cell becoming two

Chromatin vs. Chromosomes appearance within the cell.

Fig: 19.4Coiling up of Chromatin

Somatic cells vs. Germ cellsThe egg surrounded by sperm.

Fig: 12.4Before and after the S phase

Mitosis (1 Division) vs.Meiosis (2 Divisions)

Interphase

Interphase cell (Look at the chromatin in the blue nucleus and the

yellow cytoskeleton.)

Fig: 12.6 a

Cell in Prophase

Fig: 12.6 b

Cell in Metaphase

Cell in Anaphase

Cell in Telophase and starting Cytokinesis

LE 12-8b

Chromosomemovement

Microtubule Motorprotein

Chromosome

Kinetochore

Tubulinsubunits

Animal vs. Plant

LE 12-10

NucleusCell plateChromosomesNucleolus

Chromatincondensing 10 µm

Prophase. The chromatin is condensing.The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is starting to form.

Prometaphase. Wenow see discrete chromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelope 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 the cell as their kinetochore micro- tubules shorten.

Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.

Microscopic view of Mitosis in Onion root tips.Can you identify the stages?

LE 12-11_3Origin ofreplication

Cell wall

Plasmamembrane

Bacterialchromosome

E. coli cell

Two copiesof origin

Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell.

Replication continues. One copy of the origin is now at each end of the cell.

Origin Origin

Replication finishes. The plasma membrane grows inward, and new cell wall is deposited.

Two daughtercells result.

Checkpoints(Is all going according to plan?)

LE 12-15

G1

G1 checkpoint

G1

G0

If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.

If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.

LE 12-16a

MPF activity

G1 G2S MS MG2G1

M

Cyclin

Time

Fluctuation of MPF activity and cyclin concentrationduring the cell cycle

Rel

ativ

e co

nce

ntr

atio

n

LE 12-16b

Degradedcyclin

G2

checkpoint

S

M

G 2G 1

Cdk

Cyclin isdegraded

MPFCyclin

Cdk

Molecular mechanisms that help regulate the cell cycle

accum

ulatio

nC

yclin

LE 12-8b

Chromosomemovement

Microtubule Motorprotein

Chromosome

Kinetochore

Tubulinsubunits

LE 12-18aCells anchor to dish surface anddivide (anchorage dependence).

When cells have formed a completesingle layer, they stop dividing(density-dependent inhibition).

If some cells are scraped away, theremaining cells divide to fill the gap andthen stop (density-dependent inhibition).

25 µmNormal mammalian cells

LE 12-18b

Cancer cells do not exhibitanchorage dependenceor density-dependent inhibition.

Cancer cells25 µm

Malignant cancer cells from the breast(See the ABNORMAL “crab” shape of the cells.)