Cell Cycle Regulation and Cancer

Lecture #20

Honors BiologyMs. Day

Another Type of Cell Division: Another Type of Cell Division: Binary FissionBinary Fission

Prokaryotes (bacteria)Reproduce by a type of cell division called binary fission No nucleus no karyokinesis!!

In binary fission, The bacterial chromosome replicates The two daughter chromosomes move

apartOrigin ofreplication

E. coli cellBacterialChromosome

Cell wall

Plasma Membrane

Two copiesof origin

OriginOrigin

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

1

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

2

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

3

Two daughter cells result.4Figure 12.11

Cell Cycle needs to be controlled

(Regulated) The cell cycle has 3 checkpoints

A place where stop and go signals can regulate (control) cycle

Signals report if things up to that specific point have:

been completed and completed correctly

There are 3 checkpointsG1 checkpointG2 CheckpointM checkpoint

The Cell Cycle Control System

Figure 12.14

Control system

G2 checkpointM checkpoint

G1 checkpoint

G1

S

G2M

Checkpoint = give “go” or “stop” signals

G1 checkpoint

G1G1

G0

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

If a cell does not receive a go-ahead signal at the G1checkpoint, cell exits the cell cycle and goes into G0, a nondividing state.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__control_of_the_cell_cycle.html

•Chromosomes are lined up in the middle properly

of replicated DNA

of unreplicated (original) DNA

What controls the checkpoints?

Two types of proteins in cytoplasmCyclins cyclin-dependent kinases (Cdks)

INACTIVE FORM CYCLIN DEPENDENT

KINASE (CDK)

CDK/CYCLIN COMPLEX

CYCLIN

+

ACTIVE FORM

Active vs. Inactive??

What happens when cyclins and cdks are in the ACTIVE form? Cells can pass through the cell

cycle to the NEXT phase 

  What happens when cyclins and

cdks are in the INACTIVE form? Cells can NOT pass through the cell

cycle to the NEXT phase 

cyclin degrades & breaks

apart

cyclin degrades &

breaks apart

What degrades (breaks down) cyclins?

Proteolytic enzymes (proteins)Break down/degrade cyclins

cause them to fluctuate in [ ]“PROTEO” means protein“LYTIC” means break or lyse

REMEMBER: Cyclin concentration fluctuates

(changes)Cdk concentration stays the SAME

Programmed Cell Death (Apoptosis)

If cell doesn’t “pass” checkpoint, it goes through apoptosis

http://www.dnatube.com/video/1188/Apoptosis-animation Cell signaling is involved in programmed cell death needed to

maintain healthy tissues/ cell function

2 µmFigure 21.17

http://bio-alive.com/categories/apoptosis/

apoptosis.htm

What other things control cell division?

Both internal and external signals control the cell cycle/cell division…Internal signals

CDK/Cyclins at checkpointsExternal signals

Growth factorsDensity dependent inhibitionAnchorage dependence

External (outside the cell) Influences on Cell Division

Growth factorsStimulate other cells to divide

In density-dependent inhibitionCrowded cells stop dividing

Most animal cells exhibit anchorage dependenceCells must be attached to a structure to

divideEx: protein of a tissue or another cell

Cells anchor to dish surface anddivide (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).

Normal mammalian cells. **The

availability of nutrients, growth

factors, and a substratum for

attachment limits cell density to a single layer.

(a)

25 µm

Figure 12.18 A

Cancer cellsDo NOT follow the “rules”

No checkpoints and no density-dependent inhibition or anchorage dependence

Immortal cells (if enough nutrients)

Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells.

Figure 12.18 B

Loss of Cell Cycle Controls in Cancer Cells

Cancer cells form tumorsTUMOR= mass or group of

abnormal dividing cells

Types of Tumors Cancer cells form tumors

Benign “fine”Clump of cells remain at orginal spot

Malignant “mean” “cancer”“cancer”Loose/destroy attachments to other cells they can spread or move (called metastasize)!!!

Why?Don’t need growth factors maybe

they make their own growth factorsMutations in GENES that make proteins involved in control systems!!!

Cancer Movie http://www.hhmi.org/biointeractive/using-p53-fight-cancer http://www.cancerquest.org/index.cfm?page=3102&lang=english

Cancer cells are “hungry”…

Angiogenesis is the recruitment of blood vessels from

the network of neighbouring vessels. Without blood and the nutrients it carries,

a tumor would be unable to continue growing.

http://www.hhmi.org/biointeractive/angiogenesis

Cancer Treatment

Radiation Radiation destroys DNA in destroys DNA in cancer cells (these cells have cancer cells (these cells have lost ability to repair damage) lost ability to repair damage)

Chemotherapeutic drugs Chemotherapeutic drugs interfere with specific steps in interfere with specific steps in cell cyclecell cycleAlso effects normal cells Also effects normal cells

Tumor

Glandulartissue

Cancer cell

Bloodvessel

Lymphvessel

MetastaticTumor

Cancer cells invade neighboring tissue.

2A small percentage of cancer cells may survive and establish a new tumor in another part of the body.

4Cancer cells spread through lymph and blood vessels to other parts of the body.

3

A tumor grows from a single cancer cell.

1

Figure 12.19

Angiogenesis (the formation of new blood vessels)

and Metatasis

http://www.hhmi.org/biointeractive/media/angiogenesis-lg.mov

http://www.hhmi.org/biointeractive/media/vegf-lg.mov