1. KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

2. OBJECTIVES
Describe the stages of the cell cycle
List reasons why cells divide
Identify factors that limit cell size.

3. The cell cycle has four main phases.
The cell cycle is a regular pattern of growth, DNA replication, and cell division.
Four phases:
Gap 1
Synthesis
Gap 2
Mitosis

4. 1. Gap 1 (G1): cell growth and normal functions
2. Synthesis (S): DNA replication
3. Gap 2 (G2): additional growth
4. Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)

5. These four phases fall under two main stages.
Interphase
Gap 1
Synthesis
Gap 2
Mitosis
What phase do cells spend most of their lifespan in?

6. When does a cell move out of interphase and into mitosis?
Cell reproduce because
New cells are needed for growth
New cells are needed to repair
New cells are needed to replace older cells
Cells become too large to efficiently move materials
Cell become too large and cannot copy DNA fast enough to make proteins
NOTE: Mitosis occurs only if the cell is large enough and the DNA undamaged.

7. Cells divide at different rates.
The rate of cell division varies with the need for those types of cells. Some cells are unlikely to divide.
Cells that rarely divide spend most of their time in which stage?

8. Cell size is limited.
Volume increases faster than surface area.

9. Surface area must allow for adequate exchange of materials.
Cell growth is coordinated with division.
Cells that must be large have unique shapes.

10. KEY CONCEPT Cells divide during mitosis and cytokinesis.

11. Chromosomes condense at the start of mitosis.
DNA wraps around proteins (histones) that condense it.
DNA double helix
DNA and histones
Chromatin
Supercoiled DNA
Chromosome

12. DNA plus proteins (called histones) is called chromatin.
chromatid
telomere
centromere
One half of a duplicated chromosome is a chromatid.
Sister chromatids are held together at the centromere.
Telomeres protect DNA and do not include genes.
Condensed, duplicated chromosome

13. Interphase prepares the cell to divide.
Mitosis and cytokinesis produce two genetically identical daughter cells.
Parent cell
centrioles
spindle fibers
centrosome
nucleus with
DNA
Interphase prepares the cell to divide.
During interphase, the DNA is duplicated.

14. Mitosis divides the cell’s nucleus in four phases.
During prophase, chromosomes condense and spindle fibers form.

15. Mitosis divides the cell’s nucleus in four phases.
During metaphase, chromosomes line up in the middle of the cell.

16. Mitosis divides the cell’s nucleus in four phases.
During anaphase, sister chromatids separate to opposite sides of the cell.

17. Mitosis divides the cell’s nucleus in four phases.
During telophase, the new nuclei form and chromosomes begin to uncoil.
Are the cells produced from mitosis genetically identical or genetically different?

18. After mitosis, cells enter cytokinesis where the cytoplasm divides.

19. Cytokinesis differs in animal and plant cells.
In animal cells, the membrane pinches closed using protein threads.
In plant cells, a cell plate forms.

20. KEY CONCEPT Cell cycle regulation is necessary for healthy growth.

21. Internal and external factors regulate cell division.
External factors include physical and chemical signals.
Growth factors are proteins that stimulate cell division.
Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.

22. Two of the most important internal factors are kinases and cyclins.
External factors trigger internal factors, which affect the cell cycle.

23. Apoptosis is programmed cell death.
a normal feature of healthy organisms
caused by a cell’s production of self-destructive enzymes
occurs in development of infants
webbed fingers

24. Cell division is uncontrolled in cancer.
Cancer cells form disorganized clumps called tumors.
Benign tumors remain clustered and can be removed.
Malignant tumors metastasize, or break away, and can form more tumors.
cancer cell
bloodstream
normal cell

25. Cancer cells do not carry out necessary functions.
Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.
Normal cells become cancer cells when they do not respond to regulation checkpoints.

26. Carcinogens are substances known to promote cancer.
Standard cancer treatments typically kill both cancerous and healthy cells.