Mitosis

Mitosis is the process by which new cells are generated.

Mitosis produces 2 genetically identical daughter cells

Parent cell

Replicated chromosomescondense at the start of mitosis

Mit

osi

s

Sister chromatids separate and two daughter cells are formed.

Parent cell and daughter cell contain thesame complement of chromosomes.

Overview of Mitosis:

The cell cycle:

Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase

Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.

Figure 12.5x Mitosis

How do spindle fibers move the chromosomes?

The kinetochore is a specialized region on the centromere where spindle fibers attach

Motor molecules of the kintochore walk along the microtubule, taking

the chromosome with it

As the chromosomes move toward the poles, the microtubules are

broken down at the kinetochore end

Transport vesicle

Kinesin

Microtubule

ATP ADP+Pi

Motor molecules "walk" along a microtubule track

ATP ADP+Pi

After the nucleus divides, cytokinesis divides the cytoplasm, forming two separate cells

Cytokinesis in animals

Figure 8.9a

Cleavage furrow

Mitosis in a plant cell

Bacteria divide by binary fission

Bacteria divide by binary fission

Bacteria divide by binary fission

Unregulated cell division can lead to cancer

Many factors interact with each other to determine whether a cell will undergo mitosis

Cell cycle checkpoints normally insure that DNA replication and mitosis occur only when conditions are favorable and the process is working correctly.

G2 checkpointPass this checkpoint if:• cell size is adequate• chromosome replication is successfully completed

M

G2

Mitosis

Metaphase checkpointPass this checkpoint if:• all chromosomes are attached to mitotic spindle

G1

Fir

st g

ap

S

DNA synthesis

G1 checkpointPass this checkpoint if:• cell size is adequate• nutrient availability is sufficient• growth factors (signals from other cells) are present

Seco

nd g

ap

Cell-Cycle Checkpoints

Cell cycle proteins regulate whether a cell will proceed past a particular cell cycle checkpoint

cyclin -  a protein whose amount varies cyclically

cdk - another cell division control protein - a cyclin dependent kinase; active only when bound to cyclin

MPF - mitotic promoting factor...  

• MPF is a kinase enzyme, ones that switches on/off target proteins by phosphorylating them..... 

• [cyclin + cdk = MPF]...    favors Mitosis

• leads to destruction of cyclin itself 

MPF levels rise, causing the cell to pass through the

G2 checkpoint

Growth factor proteins are signal molecules that trigger a signal-transduction pathway leading to cell division

Platelet-derived growth factor

Cell division is also dependent on

environmental factors

Unregulated cell division can lead to cancer

Mutations in genes that encode cell cycle proteins can lead to unregulated growth, resulting in tumor formation and ultimately invasion of cancerous cells to other organs.

Cancer cells have escaped cell cycle controls and divide excessively

Figure 12-17x1 Breast cancer cell

Figure 12-17x2 Mammogram: normal (left) and cancerous (right)

CANCER SPREADS