Cell Division and Mitosis

Chapter 10

Cancer and the Cell Cycle

Cell Division Results in Genetically Identical Daughter Cells

Chromosome duplication (including DNA synthesis)

0.5 !m

Centromere

Sister chromatids

Separation of sister

chromatids

Centromeres Sister chromatids

Each Chromosome has a Homologue

The Cell Cycle

G1

G2

S (DNA synthesis)

INTERPHASE Prop

hase

M

etap

hase

Mitosis (M phase)

G1 Period of cell growth before the DNA replicates

S Period when DNA Replicates and chromosomal proteins are duplicated

Cytokinesis

G0 Cell cycle arrest

G2 Period after DNA replicates; cell prepares for division (In

terp

hase

end

s in

par

ent c

ell)

Phases of the Cell Cycle

G2 OF INTERPHASE PROPHASE PROMETAPHASE

Phases of the Cell Cycle, cont.

The Mitotic Spindle

Microtubules Chromosomes

Sister chromatids

Aster Centrosome

Metaphase plate

Kineto- chores

Kinetochore microtubules

0.5 !m

Overlapping nonkinetochore microtubules

1 !m Centrosome

Prometaphase Chromosome

Sister chromatid II

Sister chromatid I

Kinetochore I

Spindle pole

Kinetochore II

Spindle microtubules

Spindle pole

A cell at interphase: Cytoplasm

Nucleus

Prophase Cytokinesis Telophase

Anaphase Prometaphase Metaphase

Anaphase detail Spindle pole

Microtubules assembled into a spiral

Spindle midpoint Chromosomes

Spindle pole

Cytokinesis in Animal Cells: Cleavage Furrow

Cytokinesis in Plant Cells by Cell Plate Formation

Vesicle Cell wall

1 A layer of vesicles Containing wall material collects in the plane of the former spindle midpoint (arrow).

2 More vesicles are added to the layer until it extends across the cell.

3 The vesicles fuse together, dumping their contents into a gradually expanding wall between the daughter cells.

4 Vesicle fusion continues until the Daughter cells are separated by a continuous new wall, the cell plate.

Mitosis in Onion Root Tip

The Cell Cycle Control System

G1 checkpoint

G1 S

M

M checkpoint G2 checkpoint

G2

Control system

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.

Cell Cycle Regulation: Cyclin/CDK Control

Cyclin B Cyclin B

CDK1

CDK1

Cyclin E

Cyclin E

CDK2

CDK2

G2-to-M checkpoint

G1-to-S checkpoint

G1

M G2

S

Cyclin B is degraded

Cyclin E is degraded

Cell Cycle Regulation: Cyclin/CDK Control

CDK1

G1 G2 S M S M G2 G1 M

Cyclin B

Time Fluctuation of CDK1 activity and cyclin concentration during the cell cycle

Rel

ativ

e co

ncen

trat

ion

The CDK/cyclin complex is also called MPF (mitosis-promoting factor)

Growth Factors Trigger Intracellular Signaling Systems

PDGF

Growth factors can override cellular controls that otherwise inhibit cell division

Platelet-derived growth factor (PDGF) receptor is a receptor tyrosine kinase (RTK) that initiates a MAP kinase cascade to stimulate cell division

Growth Factor Receptors and Tumor Suppressors

Normal Cell •  Growth factor present •  Normal receptor •  Cell division regulated at G1

Cell with one mutation •  No growth factor present •  Mutated receptor •  G1 checkpoint overridden

Cell with two mutations •  No growth factor present •  Mutated receptor and mutated tumor suppressor

Normal tumor suppressor repairs damaged DNA

Mutant tumor suppressor Does not repair damaged DNA

Benign tumor Malignant tumor

Internal and External Signals at the Checkpoints

Cells anchor to dish surface and divide (anchorage dependence).

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

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

25 !m Normal mammalian cells

Cancer Cells ignore Internal and External Signals at the Checkpoints

Cancer cells do not exhibit anchorage dependence or density-dependent inhibition.

Cancer cells 25 !m

Tumor Suppressors and Proto-oncogenes Influence the Cell Cycle Tumor Cells

Fig. 10-16, p. 215

Facial Tumor Loss of Cell Cycle Controls in Cancer Cells

!  Cancer cells do not respond normally to the body’s control mechanisms

!  Cancer cells form tumors, masses of abnormal cells within otherwise normal tissue

!  If abnormal cells remain at the original site, the lump is called a benign tumor

!  Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors

Breast Cancer Development

Cancer cell

Blood vessel

Lymph vessel Tumor

Glandular tissue

Metastatic tumor

A tumor grows from a single cancer cell.

Cancer cells invade neighboring tissue.

Cancer cells spread through lymph and blood vessels to other parts of the body.

A small percentage of cancer cells may survive and establish a new tumor in another part of the body.

Bacterial Cell Division Bacterial chromosome Cell wall

Plasma membrane

Origin of replication (ori)

Replication origins

1 A bacterial cell before its DNA replicates.

2 Replication begins and ori and proceeds in opposite directions. replication takes place in the middle of the cell where the DNA replication enzymes are located. 3 The two replicated origins migrate to the poles of the cell while replication continues.

4 Replication is complete. Cell division begins as the plasma grows inward, and a new cell wall is synthesized.

5 Binary fission produces two daughter cells.

Unreplicated region of chromosome

Replicated chromosomes