1. The Cell Cycle & Mitosis
Let’s Watch!

2. Learning goals We are learning the components of the cell cycle.
We are learning the process of mitosis.

3. Layers of skin lose 30000-40000 skin cells every minute
why doesn’t our skin simply wear away?
Layers of skin

4. Cell cycle repeating cycle of events in the life of a cell
main goal is cell division, but most time spent preparing for cell division
four phases:
first growth phase (G1)
synthesis phase (S)
second growth phase (G2)
mitosis (M)

5. chromosomes every cell contains chromosomes
each chromosome is a long piece of coiled DNA and proteins
number of chromosomes in each cell differs between organisms
typical human cell has 46 chromosomes – 23 matching pairs of chromosomes

6. chromosomes visible only when the cell is dividing
when cell not dividing, DNA and proteins that make up chromosomes are spread throughout cell in form of chromatin
at beginning of cell division, chromosomes condense into visible structures
before cell division, each chromosome is copied
the chromosome consists of two identical copies, called sister chromatids
when the cell divides, one chromatid goes to each of the new cells

7. interphase often called resting phase 90 percent of cell cycle
cell takes in nutrients, grows, copies DNA and conducts other normal cell functions

8. Chromatin
Centrioles: “Barrel” shaped
organelles used in division.

9. interphase First Growth Phase (G1) a period of growth for the cell
new organelles produced
if healthy and conditions are favourable, cell moves to next phase.
Synthesis Phase (S)
cell makes an entire copy of its DNA
Second Growth Phase (G2)
cell produces the organelles and structures needed for cell division
shortest phase

10. Mitosis (M) all cell’s energy devoted to division
creates two identical cells
4 phases: prophase, metaphase, anaphase, telophase (PMAT)

11. prophase
the chromatin, which consists of the cell’s DNA and proteins, condenses
at this point, there are two copies of each chromosome (sister chromatids), held together at the centromere
chromosomes become connected to the mitotic spindle fibres at the centromere
nuclear membrane dissolves

12. Nuclear Membrane
Centromere
Spindle Fibres
Sister Chromatids

13. metaphase Chromosome pairs line up in middle of cell
spindle fibres from centriole attach to centromeres of each chromosome
all must be in line for mitosis to continue

14. Attached spindle fibres
Sister chromatids lined up

15. anaphase sister chromatids separate at the centromere
each chromatid is now a complete chromosome
separated chromosomes are pulled to opposite ends of the cell

16. Daughter chromosomes

17. telophase final stage of mitosis
daughter chromosomes stretch out, become thinner, and are no longer visible
turn back into chromatin
new nuclear membrane forms around each area of chromatin
cell appears to have two nuclei

18. Daughter chromosomes stretching out

19. cytokinesis final stage of cell division
cytoplasm divides producing two genetically identical daughter cells
different for each type of cell:
Animal cell: Cytoplasm pinches in half.
Plant cell: Plate between two cells turn into a cell wall.
each new cell enters G1 phase and cell cycle is repeated

20. Chromatin
Two daughter cells

21. Learning goals We are learning the components of the cell cycle.
We are learning the process of mitosis.

22. Group questions
1. What is the purpose of the cell cycle? 2. Define the term “interphase” and describe its purpose. 3. (a) What is mitosis? (b) Why is mitosis important to the cell? 4. Define and distinguish between the following terms: chromosome, centromere, and sister chromatids. 5. Explain the meaning and importance of the term “cytokinesis.”

23. Homework
P.44 #1-7