1. The Cell Cycle
Ms. Edwards

2. The Cell Cycle- The regular sequence of growth and division that cells undergo.
Cell Division has 3 Stages:
Interphase
Mitosis
Cytokinesis

3. Stage 1: Interphase
Period of cell cycle BEFORE cell division

4. 3 things happen:
Cell Grows: Cell grows and copies organelles
2. Cell copies its DNA
-DNA Replication- Cell makes an exact copy of the DNA in its nucleus.
- At the end of replication there are 2 exact copies of the DNA, and one will go to the daughter cell
3. Cell prepares to divide- cell produces structures it will need to divide

5. Stage 2: Mitosis
a) The cell’s nucleus divides into two new nuclei.
b) One copy of the DNA is distributed to each of the daughter cells.

6. 4 parts of Mitosis:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

7. The Cell Cycle
- Cell Division

8. Mitosis- Prophase
Chromatin condenses to form double-rod structures called chromosomes.
Each chromosome has 2 rods because the cell’s DNA has been replicated.
Pairs of centrioles move to opposite sides of the cell.
Nuclear envelope breaks down.

9. Mitosis- Prophase

10. Mitosis
During mitosis, the cell’s nucleus divides into two new nuclei. One copy of the DNA is distributed into each of the two daughter cells.

11. The Cell Cycle
- Cell Division

12. Mitosis- Metaphase
Chromosomes line up at the center of the cell.
Each chromosome attaches to a spindle fiber at its centromere.

13. The Cell Cycle
- Cell Division

14. Mitosis- Anaphase
Chromatids separate and move to opposite ends of the cell.
Each chromatid becomes a new chromosome.
The cell stretches out as the opposite ends are pulled apart.

15. Mitosis- Anaphase

16. Mitosis- Telophase
Chromosomes stretch out and lose their rod-like appearance.
A new nuclear envelope forms around each region of chromosomes.

17. Mitosis- Telophase

18. The Cell Cycle
- Cell Division

19. Stage 3: Cytokinesis
a) During cytokinesis, the cytoplasm divides.
b) Organelles are distributed to each of the 2 new cells.
c) Each daughter cell has the same number of chromosomes as the parent or original cell.

20. Stage 3: Cytokinesis (continued)
d) In animal cells, the cell membrane pinches in and each daughter cell gets about half of the organelles.
e) In plant cells, a cell plate forms across the middle of the cell, and the new cell membranes form on either side of the cell plate.

22. The Cell Cycle
- Cell Division
Cool Model
Mitosis Model

23. Structure and Replication of DNA
a) Rosalind Franklin- took x-rays of DNA in 1952
b) James Watson and Francis Crick discovered the structure of DNA in 1953

24. Francis Crick’s first sketch of the double-helix shape of DNA

25. James Watson and Francis Crick with their new DNA model in 1953

26. The Structure of DNA
c) A DNA molecule looks like a twisted ladder or spiral staircase.
- Sides of the ladder are made of sugar (deoxyribose) and phosphates.
- Rungs of the ladder are made of nitrogen bases.

27. Structure of DNA The DNA molecule is shaped like a twisted ladder.
- Cell Division
Structure of DNA
The DNA molecule is shaped like a twisted ladder.

28. 4 Nitrogen Bases in DNA:
Adenine
Thymine
Cytosine
Guanine

29. The Base-Pairing Rule:
A-T
C-G

30. DNA Replication a) Two sides of DNA molecule “unzip.”
b) A pairs with T
and C pairs with G.

31. DNA Replication (continued)
c) Nitrogen bases that are floating in the nucleus pair up with the unzipped halves of the DNA strand.
d) Because of the way nitrogen bases pair with each other, the order of the bases in each new DNA molecule is exactly the same as the order in the original molecule (semi-conservative).

32. Replication of DNA
- Cell Division
Because of the way in which the nitrogen bases pair with one another, the order of the bases in each new DNA molecule exactly matches the order in the original DNA molecule.

33. Length of the Cell Cycle
- Cell Division
Length of the Cell Cycle
How long does it take for a cell to go through one cell cycle? It all depends on the cell. A human liver cell, for example, completes one cell cycle in about 22 hours, as shown in the graph. Study the graph and then answer the following questions.

34. Length of the Cell Cycle
- Cell Division
Length of the Cell Cycle
Reading Graphs:
What do the three curved arrows outside the circle represent?
The longest curved arrow represents the cell’s interphase; the shortest represents cytokinesis; and the middle one represents mitosis.

35. Length of the Cell Cycle
- Cell Division
Length of the Cell Cycle
Reading Graphs:
In what stage of the cell cycle is the wedge representing growth?
Interphase

36. Length of the Cell Cycle
- Cell Division
Length of the Cell Cycle
Interpreting Data:
In human liver cells, how long does it take DNA replication to occur?
10 hours

37. Length of the Cell Cycle
- Cell Division
Length of the Cell Cycle
Drawing Conclusions:
In human liver cells, what stage in the cell cycle takes the longest time?
Interphase