1. THE CELL CYCLE
“The Circle of Life”

2. Cells reproduce because:
The volume is increasing at a greater rate than the surface area (cell membrane)
Agar block experiment

3. Cells reproduce for
Growth
Repair
Reproduction

4. THE CELL CYCLE

5. The Cell Cycle

6. INTERPHASE THE PERIOD BETWEEN CELL DIVISIONS
DIVIDED INTO G1, S, AND G2
SOME CELLS DO NOT COMPLETE THE CYCLE AND ENTER G0

7. G1 A PERIOD OF GROWTH AND DEVELOPMENT
NORMAL ACTIVITIES OF THE CELL OCCUR
SYNTHESIS OF PROTEINS, NUCLEIC ACIDS, AND OTHER NECESSARY MOLECULES OCCURS

8. G0 SOME CELLS REMAIN IN G1 THESE CELLS ARE USUALLY HIGHLY SPECIALIZED
NERVE CELLS
GENERALLY REMAIN IN G0; THEY ARE UNABLE TO DIVIDE
LIVER CELLS
WILL REMAIN IN G0 UNLESS DAMAGE OCCURS AND NEW CELLS ARE NEEDED

9. G1 CHECKPOINT THE RESTRICTION POINT
THE “POINT OF NO RETURN”
ENZYMES CHECK THAT GROWTH IS SUFFICIENT FOR CELL DIVISION
CELLS THAT REACH THE R POINT OF GROWTH AND DEVELOPMENT MUST COMPLETE THE ENTIRE CELL CYCLE
SKIN CELLS, CELLS THAT LINE THE DIGESTIVE TRACT, ETC.

10. S PHASE
CELLS CANNOT DIVIDE NORMALLY UNLESS THEY CREATE A NEW SET OF CHROMOSOMES THROUGH THE PROCESS OF DNA REPLICATION
THIS STAGE IS CALLED “S” FOR SYNTHESIS OF DNA

11. DNA REPLICATION

12. SISTER CHROMATIDS
EACH REPLICATED CHROMOSOME CONSISTS OF TWO IDENTICAL CHROMATIDS OR “SISTER CHROMATIDS”
CHROMATIDS ARE HELD TOGETHER AT THE CENTROMERE.

13. G2 PHASE
ADDITIONAL MANUFACTURE OF MOLECULES FOR THE TWO NEW CELLS OCCURS
THE CELL MUST HAVE SUFFICIENT ORGANELLES, PROTEINS, ETC. FOR TWO CELLS RATHER THAN FOR ONE
AT THE END OF G2, THE CELL IS READY TO DIVIDE

14. Checkpoints G2 Checkpoint
DNA polymerase checks for and corrects mistakes in replication
Triggers the beginning of mitosis

15. MITOSIS
MITOSIS IS THE DUPLICATION OF THE CELL’S NUCLEUS PRIOR TO CELL DIVISION
IT MAINTAINS THE DIPLOID NUMBER OF CHROMOSOMES
THE DIPLOID NUMBER IN HUMANS IS 46

16. PROPHASE THE FIRST STAGE OF MITOSIS
THE SISTER CHROMATIDS CONDENSE AND BECOME VISIBLE
THE NUCLEAR MEMBRANE DISSOLVES
SPINDLE FIBERS DEVELOP FROM THE CENTROSOMES

17. Prophase

18. THE MITOTIC SPINDLE THE SPINDLE FIBERS COME FROM THE CENTROSOME
MICROTUBULES FORM BETWEEN THE CENTROSOMES TO MAKE THE MITOTIC SPINDLE

19. MITOTIC SPINDLE
CENTRIOLES ARE FOUND IN THE CENTROSOMES OF ANIMAL CELLS.
KINETOCHORE FIBERS ATTACH TO CENTROMERES AND PULL CHROMATIDS APART

20. MITOTIC SPINDLE (cont.)
OTHER SPINDLE FIBERS STRETCH FROM CENTROSOME TO CENTROSOME AND PUSH THE CELL OUTWARD TO MAKE IT BIGGER
THESE ARE KNOWN AS POLAR FIBERS

21. METAPHASE
SISTER CHROMATIDS ARE ATTACHED TO KINETOCHORE FIBERS AT THE CENTROMERES

22. METAPHASE
THE KINETOCHORE FIBERS PULL THE CHROMOSOMES INTO A RING IN THE CENTER OF THE CELL KNOWN AS THE METAPHASE PLATE

23. Metaphase

24. ANAPHASE
SISTER CHROMATIDS ARE PULLED APART BY KINETOCHORE FIBERS, BREAKING THE ATTACHMENT AT THE CENTROMERE
EACH CHROMATID IS NOW A CHROMOSOME

25. Anaphase (continued)
THE POLAR FIBERS PASS EACH OTHER AT THE EQUATOR TO ELONGATE THE CELL, MAKING IT EASIER TO SPLIT THE CYTOPLASM

26. ANAPHASE
SISTER CHROMATIDS ARE PULLED TO OPPOSITE SIDES OF THE CELL KNOWN AS THE POLES OF THE CELL

27. TELOPHASE
THE CHROMOSOMES BECOME ELONGATED
SPINDLE FIBERS DISAPPEAR

28. TELOPHASE NUCLEAR MEMBRANE RE-FORMS IN EACH DAUGHTER CELL
CYTOKINESIS BEGINS TO CUT THE CELL IN TWO

29. Telophase

30. Checkpoints Mitosis Checkpoint Triggers the end of mitosis
Causes the two new daughter cells to enter G1

31. CYTOKINESIS A CELL PLATE FORMS IN PLANTS
THE CELL MEMBRANE CONSTRICTS IN ANIMALS FORMING A CLEAVAGE FURROW

32. Plant Cell Cytokinesis
A CELL PLATE FORMS IN PLANTS WHEN VESICLES FUSE

33. Animal Cell Cytokinesis
MICROFILAMENTS ALONG THE EQUATOR CONSTRICT IN ANIMALS FORMING A CLEAVAGE FURROW

35. Cancer Cancer is uncontrolled cell division
It occurs because genes that control the manufacture of checkpoint proteins are damaged; OR
The cell produces too much of the growth-promoting chemicals in the body

36. Find the phases!