1. The Cell Cycle
Why cells divide

2. What do all cells require to survive?
A complete set of genetic instructions
Genetic instructions are coded in the DNA of cells
Needed to produce the required molecules that drive life functions (metabolism)

3. Cell Division mitosis Results in genetically identical daughter cells
Cells duplicate their genome before they divide
Ensuring that each daughter cell receives an exact copy of the genetic material, DNA
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4. WHY do cells divide?
About 2 trillion cells are produced by an adult human every day.
Cell division, or reproduction occurs in all organisms
WHY?
It depends on the cell type and the organism

5. Why do cells divide? ASEXUAL REPRODUCTION
Growth
Cells must divide as the organism develops and to maintain maximum efficiency.
Replace
Cells get old and die and must be replaced
Repair
The organism must be able to heal minor injury and fight off disease

6. The Cell Cycle Some cells divide constantly:
cells in the embryo, skin cells, gut lining cells, etc.
Other cells divide rarely or never: only to replace themselves.
Actively dividing cells go through a cycle: a repeating sequence of cellular growth and division.

7. The Cell Cycle
There are 4 stages G1 S G2
Mitosis

8. The Cell Cycle The first 3 phases are collectively called Interphase
The G1 phase
Most time spent
Growth and normal function.
Control of cell division.
The S or Synthesis phase
DNA is replicated.
The chromosome goes from having one chromatid to two.
G2 phase
Cell prepares for mitosis
Amount of cytoplasm (including organelles) increases in preparation for division

9. Chromosome replication (S-phase)
Each condensed chromosome consists of 2 identical chromatids joined by a centromere.
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Two unduplicated
chromosomes
Centromere
Sister
chromatids
Duplication
Non-sister chromatids
Two duplicated chromosomes

10. Chromosome replication
A packaged chromosome
Chromatid
Identical chromatid
Chromosome arm
During the S phase of the cell cycle, DNA replicates.
Centromere
Chromosome arm
Replication Animation:

11. Interphase summary Some cells stay in Interphase all of their lives!
Normal function
ATP is synthesized.
Damaged parts are repaired.
Wastes are excreted.
Proteins are made.
Organelles are formed.
Specialized tasks are performed.
Some cells stay in Interphase all of their lives!

12. Mitosis fourth phase of the cell cycle
Mitosis is normal cell division
The process by which the nucleus of a cell divides to form two new nuclei
Mitosis has 4 phases

13. Mitosis
Prophase
Metaphase
Anaphase
Telophase

14. Remember!!!!!
PMAT
Prophase
Metaphase
Anaphase
Telophase

15. Prophase Chromatin condenses and chromosomes become visible
Nuclear membrane disappears.
Centrioles migrate to opposite sides apparently propelled by the lengthening of microtubules
Mitotic spindle begins to form
Centrioles

16. Metaphase
Metaphase is the longest stage of mitosis, lasting about 20 minutes.
The centrosomes are now at opposite ends of the cell.
Chromatids migrate to equator of spindle.
Spindle fibres attach to the chromatids.
The entire apparatus of microtubules is called the spindle because of its shape.

17. Anaphase
Anaphase is the shortest stage of mitosis, lasting only a few minutes.
Anaphase begins when the sister chromatids of each pair suddenly part.
Each chromatid thus becomes a full-fledged chromosome.
The chromosomes begin moving toward opposite ends of the cell, as microtubules shorten.

18. Anaphase The cell elongates as structural microtubules lengthen.
Daughter chromosomes
The cell elongates as structural microtubules lengthen.
By the end of anaphase, the two ends of the cell have an equal and complete collection of chromosomes.
Chromatids are now called chromosomes.

19. Telophase Cytoplasm divides: cytokinesis
Nuclear membrane reappears. There are now two nuclei.
Chromosomes uncoil (they are no longer visible) and the DNA is now called chromatin
Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.

20. Telophase the difference in plant and animal cells
Plant Cells
The Golgi body forms a cell plate between the two nuclei.
The plasma membrane reforms on each side of the plate which grows outward becoming the new cell wall.

21. Telophase the difference in plant and animal cells
A cleavage appears (groove) caused by a contractile ring of actin microfilaments
The contraction of microfilaments is like the pulling of drawstrings
The cell is pinched in two

22. Cytokinesis
Occurs during telophase, generally at the same time that the nuclear membrane is reforming, (yet they are distinct processes.)
The cytoplasm divides – the organelles are equally distributed between the two daughter cells
Two identical daughter cells are formed.

23. Stages Of Mitosis Mother cell Nucleus with un-condensed chromosomes
Interphase
Nucleus with un-condensed chromosomes
Prophase
Condensed chromosomes
Equator of the cell
Metaphase
Poles of the cell
Disappearing nuclear membrane
Mitotic spindle
Two daughter cells
Anaphase
Telophase

24. review
How do little elephants grow up to be big elephants?

25. Review
Why do animals shed their skin?

26. review
What happens when an organism is injured?

27. Three Reasons why cells reproduce asexually
Growth
Development (replacement)
Repair
Cancer = Uncontrolled Cell Growth