1. Creating Identical Body Cells
Cell Cycle and Mitosis
Creating Identical Body Cells

2. Cell Division
All cells come from pre-existing cells (no spontaneous generation)
New cells are produced for growth and to replace damaged or old cells
GRR: Growth, Repair, Replace
Different in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, and animals)
End result is two identical daughter cells

3. Cell Division in Prokaryotes

4. Binary Fission
Bacteria divide into identical cells through the process of binary fission
A single chromosome makes a copy of itself
A cell wall forms between the chromosomes, dividing the cell
Parent
Cell
Chromosomes
Replicate
Cell
Splits
2 Identical
Daughter Cells

5. Binary Fission

6. Cell Division in Eukaryotes

7. Chromosomes
All eukaryotic cells store genetic information in chromosomes
Most eukaryotes have between & 50 chromosomes in their body cells (designated 2n)
Human body cells have 46 chromosomes, or 23 identical pairs
Diploid: 2n = 46
Haploid: n = 23
Each chromosome is composed of a single, tightly coiled DNA molecule

8. Chromosomes

9. Compacting DNA
When DNA is loose (before and after division), it is called chromatin
When the cell starts to divide, the DNA compacts into chromosomes
The DNA is tightly coiled around proteins called histones

10. Compacting DNA
Duplicated chromosomes are called chromatids and are held together by the centromere

11. The Cell Cycle

12. The Cell Cycle Checkpoints Cyclins and CDK
Control mechanisms the act as potential stopping points if cell division is not progressing correctly
Conditions of the cells are assessed
There are 3 checkpoints: G1 (restriction), G2, and metaphase
Cyclins and CDK
Progression through the cell cycle is controlled by proteins known as cyclins (regulation)
Cyclins work by activating CDK enzymes (biomolecule?)
CDK = cyclin dependent kinases

13. The Cell Cycle Consists of three main parts Interphase – 3 stages
Mitotic Phase (mitosis) – four stages
Cytokinesis

14. Interphase (3) G1 Stage First growth after cell division
Cells mature by making more cytoplasm and organelles
Cell carries on its normal metabolic activities
First Checkpoint (Restriction Checkpoint)
This is the point at which the cell decides to divide (and enter the S phase), delay division, or enter a resting stage (also called G0)

15. Interphase (3) S stage Synthesis stage DNA is copied (replicated)
Two identical
copies of DNA
Original DNA

16. Interphase (3) G2 Stage Second growth stage
Occurs AFTER DNA has been copied
All cell structures needed for division are made (ex: centrioles)
Both organelles and proteins are synthesized
Second checkpoint
Cell checks for size and correct replication (no mutations) before being allowed to start mitosis
Also a check for any damage (ex: from radiation)

17. Mitosis Division of the nucleus Only occurs in eukaryotes
Has four stages
Doesn’t occur in some cells (like brain cells)

18. Mitosis
Prophase
Metaphase
Anaphase
Telophase

19. Mitosis
Prophase
Chromatin in the nucleus condenses to form visible chromosomes
Spindle fibers form from the centrioles
The nuclear membrane breaks down

20. Mitosis
Metaphase
Chromosomes, attached to the spindle fibers at their centromere, move to the center of the cell (the equatorial plate)
Third Checkpoint (Spindle Checkpoint)
The tension in the sister chromatids from being pulled in opposite directions by the spindle fibers must be felt to trigger anaphase

21. Mitosis Anaphase Occurs very rapidly
Sister chromatids are pulled apart to opposite poles of the cell by the spindle fibers
Nondisjuntion
Failure of chromosomes to separate properly
Occurs if the metaphase checkpoint fails

22. Mitosis Telophase The spindles disassemble
New nuclear envelopes form around each set of chromsomes at the two poles
Chromosomes decondense into chromatin

23. Cytokinesis Division of the cytoplasm Occurs after mitosis is complete
Division of the cell into two identical daughter cells
In PLANT cells, a cell plate forms at the equator to divide the cell
In ANIMAL cells, a cleavage furrow forms to split the cell

24. Mitosis in Animal Cells

25. Mitosis in Animal Cells

26. Mitosis in Plant Cells

27. Mitosis in Plant Cells

28. Daughter Cells of Mitosis
Have the same number of chromosomes as each other and as the parent cell they were formed from (2n = 46)
They are identical to each other, but smaller than the parent cell
They must grow in size to mature cells before dividing again (Interphase – G1)

29. Problems with Mitosis
If mitosis is not controlled, unlimited cell division occurs, causing cancer
This occurs when cells do not go into a resting phase, but stay in the cell cycle, dividing over and over again
The result is an overwhelming number of immature cells, which crowd out normal cells and cause a tumor

30. Problems with Mitosis
Oncogenes are special proteins that increase the chance a normal cell develops into a cancerous cell
Usually when cells detect mutations, they undergo programmed cell death (apoptosis)
Cancer can be treated with
Surgery: removal of a tumor
Radiation: targets specific areas to shred tumor cell DNA
Chemotherapy: travels throughout the body, targeting fast-dividing cells (this can cause hair loss, skin rashes, nausea, etc.)