Download Mitosis Checkpoints

Warm-Up (11/10)
On the piece of white paper from the back, answer
the following question.
Neurons, or brain cells, are considered
“post-mitotic,” meaning that they have
permanently left the cell cycle and are
incapable of undergoing mitosis. Why are
neurodegenerative diseases such as Lou
Gehrig’s Disease (ALS) or Parkinson’s
disease, in which neurons progressively die
off, always fatal?
Name
Date
Period
Mitosis
1.
Purpose
• Growth
•
•
Repair
Asexual reproduction
(for example, bacteria)
2.
Stages
1. Replication
2. Alignment
3. Separation
3.
Regulation of Mitosis
At internal controls or “checkpoints,” cells
stop and make sure everything is okay
before continuing.
This controls the
rate of the cell
cycle.
Cancer: unregulated cycling
Cancerous cells cycle
extremely quickly
because they do not stop
at the checkpoints.
They are not regulated.
Cyclins and CDKs
Cyclins: proteins whose levels go up and down
CDKs: kinases activated when cyclins bind to them.
kinase: an enzyme that phosphorylates (puts a phosphate on)
another protein to regulate it.
Share and Discuss
Discuss this question with your partner and
write or represent it. I will call on three
people to share their partners’ answers.
Draw four chromosomes during the
processes of replication, alignment,
and separation. Indicate where a
checkpoint would act during the
alignment phase, and state one
purpose of the checkpoint.
Share and Discuss
Discuss this question with your partner and write or represent it. I will call on
three people to share their partners’ answers.
In an experiment, bacteria transformed with a plasmid encoding Green
Fluorescent Protein (GFP) were raised in a solution containing a
radioactive isotope of sulfur, 35S, to label proteins such as GFP in the
cell. Individual bacteria were then isolated from each other and cultured
separately in a solution containing non-radioactive sulfur. After every
five generations, the bacteria were analyzed for percentage of bacteria
containing radioactive sulfur (35S) as well as green fluorescence, an
indicator of the presence of GFP. Why do all cells contain GFP after 15
generations even though 35S-labelled proteins are present in virtually
none of the cells?
Generation % containing 35S % containing green fluorescence
0 (first cell)
100.000%
100.0%
5
3.125%
100.0%
10
0.098%
100.0%
15
0.003%
100.0%
Closure
On the piece of white paper from the
back, answer the following question:
Explain why checkpoints are needed
during the cell cycle to prevent cancer
from forming.
Name
Date
Period
Scale
1 – 10