Download Mitosis and Cell Cycle

Mitosis & Cell Cycle
Why?
When?
How?
Cells must reproduce else they die. The "life of a cell" is termed
the cell cycle. The cell cycle has distinct phases, which are called
G1, S, G2, and M.
Cells that have temporarily or reversibly stopped dividing are
said to have entered a state of quiescence called G0 phase.
• During this time
organelles are
reproducing, protein
synthesis is occurring for
growth and
differentiation.
• Because, transcription is
occurring, the DNA is
uncoiled.
• This phase is the most
variable, ranging from
almost nothing to years.
The S or synthesis phase is the second
phase of the cell cycle.
• DNA uncoils
• DNA replication occurs
• Additional organelle replication
occurs
• This phase ensures that each
emerging daughter cell will have the
same genetic content as the mother
cell.
Chromatin
chromosome
sister chromatids
DNA polymerase must
always attach the
complementary nucleotide
to a 3 end of the
deoxyribose sugar
molecule.
So, in the very beginning a
small RNA primer must be
laid down in order to start
the process of DNA
replication. Primase is the
enzyme responsible for
this.
Since DNA is a double helix, there will be tension in the DNA
strand that causes it to tangle as it is unwound by the helicase.
The enzymes topoisomerase I and II are responsible for relieving
that stress by clipping one or two strands of the DNA.
When DNA replicates each strand of the original DNA molecule is
used as a template for the synthesis of a second, complementary
strand. Which of the following sketches most accurately illustrates
the synthesis of a new DNA strand at the replication fork?
’
a.
c.
d.
b.
The G2 or Gap 2 phase
occupies the time from
the end of S until the
onset of mitosis.
•During this time, the cell
prepares for mitosis by
making and organizing
necessary proteins such
as the tubulin needed to
construct microtubules
which used to make
spindle fibers.
If we estimate that 90% of the cell cycle is spent in interphase,
do these results support this?
Yes, this data supports this estimation
To get the percentages, divide the number of cells in each stage by the total
number of cells, then multiply by 100.
2250/2500 = 0.9 0.9 x 100 = 90%
If this cell goes through the entire cell cycle in 24 hours,
approximately how long are the cells in anaphase. Round your
answer to a whole number in minutes.
30 minutes
50/2500 = 0.02 x 100 = 2%
24 hours x 60 minutes = 1440 minutes
2% (or 0.02) x 1440 = 28.8 round to 30 minutes
Mitosis is division of the nucleus.
During interphase the cell has increased in size, has
replicated organelles, proteins have been synthesized,
and the DNA has been replicated. Interphase takes
About 90% of the time that a cell spends in the cell cycle.
Mitosis consists of• Prophase
• Metaphase
• Anaphase
• Telophase
Cytokinesis (division of the cytoplasm) is usually happening
At the same time as telophase
Interphase  ProphasePrometaphase
Chromatin condenses and becomes visible as chromosomes/chromatids
Centrioles move to opposite poles of the cell (in animal cells)
Nucleolus disappears
Nuclear envelope breaks down
Microtubules attach at kinetochores
Metaphase
Spindle fibers align
chromosomes along
the middle of the cell
Anaphase
Sister chromatids separate to become
individual chromosomes pulled apart by
motor proteins walking along
microtubules
Telophase
Chromosomes arrive at opposite poles
Nucleoli reform
Chromosomes uncoil
Spindle fibers disperse
Cytokinesis begins
The Amount of DNA Varies During the Cell Cycle
This graph represents the amount of DNA found in the cell during
the cell cycle. Which choice is a correct explanation?
A. DNA replication occurs during G2
B. During G1 the cell is dormant, there is no cellular activity
C. S stands for size; the cytosol is doubling
D. During prophase and metaphase the chromosomes exist as
sister chromatids
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What is the goal of cell division?
Regulation of Cell Division
Do all cells have the same cell cycle?
Cell Cycle Control
“Stop and Go” chemical signals at specific points
3 Major Checkpoints
G1- Can DNA synthesis begin?
G2-Has DNA synthesis been
completed correctly?
Commitment to mitosis
M phase
Check the spindle. Can sister chromatids
separate correctly?
G1 Checkpoint
Most critical, the
primary decision point
If cell receives “go”
Signal it divides
If it doesn’t receive
“go” signal, cell switches
Into Go phase
“Go” signals can be proteins or
growth factors that promote cell
growth & division
The primary mechanism of control
is phosphorylation by kinase
enzymes
Cyclins vs. Kinases
• Cyclins are a family of proteins that control the
progression of cells through the cell cycle by
activating cyclin-dependent kinase (Cdk)
enzymes.
• A kinase is a type of enzyme that transfers
phosphate groups from high-energy donor
molecules, such as ATP, to specific substrates, a
process referred to as phosphorylation.
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Cyclins vs. Kinases
• Certain cyclins are made at certain times during the cell cycle,
and their concentration will rise and fall. Cyclins are also
destroyed after they are no longer needed by the cell.
• CDKs are not destroyed as they are only activated or
deactivated.
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According to the graph, high concentrations of which cyclin(s)
must be present for DNA replication?
a. A and B
b. D only
c. D and E
d. E only
Proto-oncogenes can change into oncogenes that cause cancer.
Which of the following best explains the presence of these
potential time bombs in eukaryotic cells?
a.
b.
c.
d.
Proto-oncogenes first arose from viral infections
Proto-oncogenes normally help regulate cell division
Proto-oncogenes are genetic “junk”
Cells produce proto-oncogenes as they age
Proto-oncogenes- normal cellular genes that code for
Proteins that stimulate normal cell division and growth
are altered
Oncogene- proto-oncogene becomes so mutated that it
Becomes a cancer causing gene
p53 gene
•“Guardian of the Genome”
The “anti-cancer gene”
After DNA damage is detected, p53 initiates:
oDNA repair
ogrowth arrest
oapoptosis
•Almost all cancers have mutations in p53.
The p53 gene is a tumor suppressor gene (its activity stops the
formation of tumors). If a person inherits only one functional copy
of the p53 gene they are predisposed To cancer and usually develop
several independent tumors in a variety of tissues in early adulthood.
This condition is rate, and is known as Li-Fraumeni syndrome.
However, mutations in p53 are found in most tumors, and so
contribute to the complex molecular events leading to tumor
formation.
The p53 gene has been mapped to chromosome 17. In the cell,
p53 binds to DNA, which stimulates another gene to produce a
protein called p21 that interacts with a cell division stimulating
protein (cdk2). When p21 is attached to cdk2, the cell cannot pass to
the next stage of cell division. Mutant p53 can’t bind to DNA and the
p21 protein is not available to act as the “stop signal” for cell division.
Cells divide uncontrollably and form tumors.
The BRCA1 gene belongs to a class of genes known
as tumor suppressor genes. Like many other tumor
suppressors, the protein produced from the BRCA1
gene helps prevent cells from growing and dividing
too rapidly or in an uncontrolled way
Research suggests that the BRCA1 protein also
regulates the activity of other genes and plays a
critical role in embryonic development. To carry
out these functions, the BRCA1 protein interacts
with many other proteins, including other tumor
suppressors and proteins that regulate cell
division.