1. Cell Growth and Division
Chapter 8
Cell Growth and Division

2. Objectives Name the main events of the cell cycle.
Determine why cells need to grow and divide
Describe what happens during the four phases of mitosis.

3. Why do cells divide?
For Growth and development of the entire organism from birth throughout the lifetime
Replace dead or dying cells
When a cell grows too large to conduct it’s functions efficiently, it needs to divide

4. Surface area to volume ratio

5. The smaller the cells, the greater the surface area
The smaller the cells, the greater the surface area. The cell is more efficient when it is smaller. Materials can travel in and out quicker

6. Why do cells divide?
The cell cycle is a series of events through which a cell passes between one cell division and the next.
The length of time varies between types of cells.
Some take only few minutes, while others spend their entire life frozen in a particular phase.

7. Not all Cells Divide
Some cells, such as nerve or brain cells, rarely divide over the course of the organisms lifetime.
This is the problem with spinal cord and brain injuries.
The injury cannot heal

8. Reproduction of bodycells by mitosis is considered asexual reproduction because the cells produced by mitosis are identical to the parent cell. A basic body cell is called a somatic cell
Cell division begins shortly after the egg is fertilized, producing vast numbers of cells needed for the embryo to take form.

9. The cell cycle consists of three parts in eukaryotes
1. interphase –cell performs normal functions. Dna doubles. New organelles form
2. Mitosis-a type of cell division that generates two daughter cells-nuclear division
3. Cytokinesis-the division of the cell cytoplasm that follows mitosis

10. Chromosomes: what you see below is a duplicated chromosome
*genetic information is carried by chromosomes.
The chart on the right is a karyotype.
This is a picture of all of the chromosomes in a cell
They are arranged into homologous pairs

11. Chromosomes are not always in the form to the right
Chromosomes are not always in the form to the right. Usually they are stringy looking and diffuse. In the form of chromatin
During interphase chromosomes REPLICATE and condense into pairs of SISTER CHROMATIDS.
That is when they form these recognizable structures

12. Chromosomes: they are made of dna and proteins

13. Cells of every organism have a specific number of chromosomes.
Carrot cells: 18
Human cells: 46
Fruit Fly cells: 11

14. Each pair of chromatids is attached at an area called the CENTROMERE.
A human body cell entering cell division contains 46 chromosomes, all of which consists of two chromatids.

15. interphase
Chromatin DNA

16. The Cell Cycle
Scientists describe the life of the cell through a process called
the CELL CYCLE.
The cell cycle has 2 MAIN parts:
Cell Growth: Interphase
Cell Division: Mitosis and Cytokinesis

17. Cell Cycle: process by which a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again.

18. Events of the Cell Cycle
Interphase: the cells longest phase
G1 Phase: “Gap 1” (phase of growth and development)
S phase: synthesis of DNA
G2 Phase: “Gap 2” (phase of growth and development)

19. During the normal cell cycle, interphase can be quite long, whereas the process of cell division takes place quickly.

20. Interphase can be broken into 3 phases:
G1: cells do most of their growing. Cells increase in size and synthesize new proteins and organelles. G1 S G2

21. 2. S: the S phase follows G1. In this phase, chromosomes are replicated and synthesis of DNA molecules takes place. G1 S G2

22. 3. G2: This phase occurs after the S phase is complete
3. G2: This phase occurs after the S phase is complete. This is the shortest of the 3 phases of interphase. During this phase, many of the organelles and molecules required for cell division are produced. After G2, cell division takes place. G1 S S G2

23. mitosis

24. Prophase First and longest phase Chromosomes become visible
Centrioles separate and take up positions on opposite sides of the nucleus.
Spindles form, which help to separate chromosomes by attaching to their centromeres.
Prophase

25. Plant cells do not have centrioles, but still form spindles.
Near the end of prophase, chromosomes coil more tightly.
Nucleolus disappears, and the nuclear envelope breaks down.

26. Metaphase Lasts only a few minutes.
Chromosomes line up across the center of the cell.
Microtubules connect the centromere of each chromosome to the two poles of the spindle.
Centrioles form and pull each chromosome apart
Metaphase

27. Anaphase Centromeres that join the sister chromatids split.
Sister chromatids separate, becoming individual chromosomes.
Chromosomes move to opposite poles of the spindle.

28. Chromosomes begin to disperse into a tangle of dense material.
Nuclear envelope reforms around each cluster of chromosomes.
Spindle begins to break apart.
Nucleolus becomes visible.
Telophase

29. Cytokinesis Division of the cytoplasm itself.
Usually occurs at the same time as telophase
Animal Cells: membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts.
Plant Cells: cell plate forms and develops into a separating membrane. Cell wall begins to appear in the cell plate.
Cytokinesis

30. Review:Mitosis ,cytokinesis and interphase
Biologists divide the events of mitosis into four phases, describe the events in each phase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
interphase