The Cell Cycle

Day 3

Cancer: Out of Control Cell Division

• The defining feature of a cancerous cell is that is divides much more often than is healthy- creating a stack of cells called a tumor

• How does it do that? It has to bypass all the checkpoints that tell it to stop dividing

The Basics of Cell Division

• G1: Cell Growth, makes duplicate organelles, increase in size

• S phase: Duplicates all the chromosomes- photocopying of information

• G2: More growth, time needed to gain strength for mitosis

• Mitosis- Cell divides up the chromosomes so each of the new daughter cells has all the information

• Cytokinesis- The cell breaks into two cells

http://www.daviddarling.info/encyclopedia/C/cell_cycle.html

Key Regulation Points

• G1 check point before S phase (DNA replication) can start, pass if:– Nutrients sufficient– Growth factors present- there is a need for more

cells– Cell is big enough– DNA is undamaged

Key Regulation Points

• G2 check point before Mitosis– Chromosome replication completed– No DNA damage– Active signals to start mitosis (chemicals in the

cytoplasm)

• Metaphase check point before cell splits– All chromosomes are aligned to be equally passed

down to the new cells

Thinking like Cancer

• Which regulation point(s) would prevent cancerous growth?

• What are a few ways cancerous cells could bypass those points?

How do checkpoints work?

Hypothesis: The cell cycle is directed by specific signaling

molecules present in the cytoplasm

How would you design an experiment to test this hypothesis?• Materials:– Cells in culture– Any measurement device

• Think about:• What data are relevant?• How long will your experiment take?

What do we know so far?

• Still working out all the chemical and physical signals.

• Over 50 growth factors have been identified• Different cell types respond differently to

different growth factors

PDGF

Contact inhibition

• Normal cells form only a monolayer in culture• Why?

Anchorage dependence

• Normal cells must have a surface on which to grow or a tissue attachment to continue replicating.

• Why?

Telomeres- fingerprints of cancer

• Cancer often has specific characteristics related to too much division

• Each time the cell divides it replicates its chromosomes- increasing the chance for mutation and shortening the telomere (the end of the chromosome)

Discovery of telomerase

• Telomerase re-lengthens the chromosome to enable division to continue

• Cancer cells have to increase telomerase activity so that they do not die

• This is a key regulation step of a cell’s lifespan