1. Mitosis & Cell Cycle

2. Cell Division
Why?
When?
How?

4. Cells must reproduce else they die
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.

5. G1
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.

6. S 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.

7. Chromatin chromosome sister chromatids

8. A nucleoside consists of a nitrogenous base covalently attached to a sugar (ribose or deoxyribose) but without the phosphate group. A nucleotide consists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups.

11. 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.

12. 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.
DNA Polymerase alpha – Replicates DNA adding to the 3’ end. (5’ to 3’)
Topoisomerase – releases tension created by unwinding
Helicase – unwinds DNA
DNA Primase – actually an RNA polymerase that lays down initial, required RNA primer
Single Stranded Binding Proteins – aid in keeping the two stands separate during replication

14. 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? ’ c. a. d. b.

15. G2
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.

16. 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 = x 100 = 90%

17. 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

18. 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

19. 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

20. 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

21. Telophase
Chromosomes arrive at opposite poles
Nucleoli reform
Chromosomes uncoil
Spindle fibers disperse
Cytokinesis begins

22. 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?
DNA replication occurs during G2
During G1 the cell is dormant, there is no cellular activity
S stands for size; the cytosol is doubling
During prophase and metaphase the chromosomes exist as sister chromatids
Ask students to interpret the graph emphasizing the amount of DNA throughout each segment of the cell cycle. Emphasize the changes and more importantly, the CAUSE of the changes. Don’t neglect the significance of the dramatic decrease in DNA at the very end of the M phase. Emphasize the return to the “1 X” level.

23. What is the goal of cell division?

24. 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?

25. 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

26. “Go” signals can be proteins or
growth factors that promote cell growth & division
The primary mechanism of control is phosphorylation by kinase enzymes

27. 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.
“Dependent because the kinase won’t work (phosphoralate) without the attached cyclin protein
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.
Cyclins were originally named because their concentration varies in a cyclical fashion during the cell cycle. By definition, a CDK binds a regulatory protein called a cyclin. Without cyclin, CDK has little kinase activity; only the cyclin-CDK complex is an active kinase.
One of the largest groups of kinases are protein kinases, which act on and modify the activity of specific proteins. Kinases are used extensively to transmit signals and control complex processes in cells. More than five hundred different kinases have been identified in humans. Their enormous diversity, as well as their role in signaling, makes them an object of study.

28. Cyclins vs. Kinases
Ask students to interpret this graph. Specifically ask which cyclin affects which phase of the cell cycle.
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.

30. According to the graph, high concentrations of which cyclin(s) must be present for DNA replication?
A and B
D only
D and E
E only

34. Cancer- loss of control
over the cell cycle
Proto-oncogenes – turn on (become oncogenes) = cancer
Tumor Suppressor Genes – Brakes, Turn them off = cancer

35. Cancer- loss of control
over the cell cycle
Proto-oncogenes- normal cellular genes that code for
Proteins that stimulate normal cell division and growth
are altered
Oncogene (bad)- proto-oncogene becomes so mutated that it
Becomes a cancer causing gene

37. Cancer- loss of control
over the cell cycle
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?
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

38. p53 gene
“Guardian of the Genome”
The “anti-cancer gene”
After DNA damage is detected, p53 initiates:
DNA repair
growth arrest
apoptosis
Almost all cancers have mutations in p53.

39. 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 (“Lee-Fra-meen-e”).
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.

40. P53 binds to DNA when there is an issue (2 copies).
This inhibits the production of p21 and halts cell division by not allowing production of p21.
Mutant p53 cannot bind to DNA, so p21 doesn’t get produced, so there’s no stop signal.
P53 binds to DNA when there is an issue (2 copies). This inhibits the production of p21 and halts cell division by not allowing production of p21. Mutant p53 cannot bind to DNA, so p21 doesn’t get produced, so there’s no stop signal.

41. 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.