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

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 • What phase do cells spend most of their lifespan in?

4. 1. Gap 1 (G1): cell growth and number of organelles increase. The cell still does its normal function and completes checkpoint #1 2. Synthesis (S): DNA replication 3. Gap 2 (G2): additional growth and still does normal functions. Completes checkpoint #2. 4. Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis) Predict:What might happen if the G2 checkpoint stopped working in cells?

5. These four phases fall under two main stages. • Interphase– The cell is preparing to divide. • Gap 1 • Synthesis • Gap 2 • Mitosis – divides the nucleus and cytokinesis divides the cytoplasm

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. • Do you think skin cells would have a long or short G1 stage? Explain why.

8. Cell size is limited. • Volume increases faster than surface area. • When the surface area-to-volume ratio is too small, the cell cannot move materials into and out of the cell at a sufficient rate or in sufficient quantities. Compare: Which cell has the largest surface area? Which cell has the largest surface area-to-volume ratio?

9. Surface area must allow for adequate exchange of materials. • Cell growth is coordinated with division. • Cells that must be large have unique shapes. Connect: Which has the larger ratio of surface area to volume, a tennis ball or a soccer ball? Explain your reasoning.

10. KEY CONCEPT Cells divide during mitosis and cytokinesis.

11. DNA andhistones SupercoiledDNA DNA doublehelix Chromatin Chromosomes condense at the start of mitosis. • DNA wraps around proteins (histones) that condense it. Chromosome Infer: Overall, DNA has a negative charge. Look at the histone proteins in the figure above. What type of overall charge do you think they have? Explain.

12. chromatid telomere centromere telomere Condensed, duplicated chromosome – will be aligned and separated during mitosis • 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. • DNA plus proteins (called histones) is called chromatin. Apply: What is the relationship between a molecule of DNA and a chromosome? Comprehension: What happens to DNA by the time it reaches the structure shown on the right?

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

14. During prophase, chromosomes condense, spindle fibers form, and the nucleus begins to breakdown. Centrioles and centrosomes begin to migrate to opposite sides of the cell. • Mitosis divides the cell’s nucleus in four phases.

15. During metaphase, chromosomes line up in the middle (equator) of the cell and attach to spindle fibers. • Mitosis divides the cell’s nucleus in four phases.

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

17. Mitosis divides the cell’s nucleus in four phases. Are the cells produced from mitosis genetically identical or genetically different? • During telophase, the new nuclei form, chromosomes begin to uncoil and spindle fibers fall apart. Cleavage furrow (found in animal cells)

18. After mitosis, cells enter cytokinesis where the cytoplasm divides. Two new, genetically identical, daughter cells are formed. Each cell is ready to enter Interphase again. • In plant cells, the membrane can not pinch inward because of the cell wall. Instead, a cell plate forms between the two nuclei. Critical Viewing: How many chromosomes does each cell have after cytokinesis?

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 CONCEPTCell cycle regulation is necessary for healthy growth.

21. Internal and external factors regulate cell division. • External factors include physical (touch) and chemical signals (hormones). • Growth factorsand other hormones (chemical signals) are proteins that stimulate cell division. Figure 5.3 – Normal animal cells (top) respond to external factors and stop dividing when the touch each other. Cancer cells (bottom) fail to respond and form clumps.

22. Two of the most important internal factors are kinases and cyclins. Together these molecules regulate the cell cycle. Kinases are enzymes and cyclins are proteins that regulate kinases. • External factors (hormones and touch) trigger internal factors, which affect the cell cycle. • See animations from your online textbook • Link to Video of Phases of Mitosis • Link to Video of Cell in Mitosis

23. webbed fingers • Apoptosis is programmed cell death. • a normal feature of healthy organisms • caused by a cell’s production of self-destructive enzymes • occurs indevelopmentof infants Figure 3.2 – Human embryos have webbed digits early in development. The cells between the digits undergo apoptosis during later stages of development. As a result, the baby is born with unwebbed fingers and toes.

24. normal cell cancer cell bloodstream Cell division is uncontrolled in cancer. • Benign tumors remain clustered and can be removed. • Malignant tumors metastasize, or break away, and can form more tumors. 3. Sometimes, cancer cells break away from the tumor. They can be carried in the bloodstream to other parts of the body, where they form new tumors. 2. Cancer cells divide more often than healthy cells and may form disorganized clumps called tumors. 1. A healthy cell may become a cancer cell if certain genes are damaged.

25. Cancer Facts: • Cancer cells do not carry out necessary functions. The cell no longer does it job. • 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 during the cell cycle. • Radiation and chemotherapy are two types of cancer treatments. Radiation is generally localized to one specific place and is used to target cancer cells and damage them so they will not reproduce. Chemotherapy uses certain drugs in various combinations to kill cancer cells. Chemotherapy is systemic – drugs travel throughout the entire body. Standard cancer treatments typically kill both cancerous and healthy cells. • Link to Cancer Treatment Video

26. Carcinogensare substances known to promote cancer. • Examples: tobacco smoke, certain air pollutions, certain viruses, UV rays, certain chemicals. ABCDE Rule for detecting skin cancer: A – Asymmetry (irregular shape) B – Border (irregular border) C – Color (change in colors, many colors or uneven distribution of colors D – Diameter (larger than 6mm) E – Evolve (new growth, changes in growth, changes in color, a sore that doesn’t heal) These are all warning signs and should be checked by a physician. Figure 3.4 – This cancerous mole is an example of a skin cancer, which may metastasize quickly.