1. Chapter 12 The Cell Cycle

2. Cells
The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter
Cell Theory: Living things are made of cells and cells reproduce from other cells
The continuity of life is based on the reproduction of cells, or cell division

3. Genome All the DNA in a cell constitutes the cell’s genome
A genome can consist of
Single DNA molecule
common in prokaryotic cells
Multiple DNA molecules
common in eukaryotic cells
DNA molecules in a cell are packaged into chromosomes

4. Chromosomes
Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
Somatic cells (nonreproductive cells) have two sets of chromosomes
Diploid cells (2n)
Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells
Haploid cells (n)

5. Cellular Reproduction
Asexual Reproduction: Cells divide creating identical cells
In unicellular organisms, division of one cell reproduces the entire organism
Multicellular organisms depend on cell division for
Development from a fertilized cell
Growth
Repair

6. Binary Fission in Bacteria
Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission
In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart
The plasma membrane pinches inward, dividing the cell into two

7. Chromosomal DNA molecules
Mitotic Division
Chromosomes
Chromosomal DNA molecules
Centromere
Chromosome arm
Chromosome duplication (including DNA replication) and condensation
Sister chromatids
Separation of sister chromatids into two chromosomes
Most eukaryotes reproduce by mitosis
Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission
Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis
Figure 12.5 Chromosome duplication and distribution during cell division.

8. Cellular Reproduction
Sexual Reproduction: Gametes fuse to create zygote
Gametes formed during meiosis
a special type of division that can produce sperm and egg cells
Meiosis creates haploid cells
After fertilization, cell has unique combination of chromosomes

9. Cell Cycle and Mitosis Eukaryotic cells
Cycle of growth, DNA synthesis, and division
Cellular division= one cell divides into 2 cells
identical to original cell

10. Interphase and Mitosis
1. G1 Phase= Gap 1 Phase
-Cell Growth
2. S Phase= DNA Synthesis
-Replication
3. G2 Phase= Gap 2 Phase
4. M Phase= Mitotic Phase
-Cellular Division
~90% of cell life
Interphase

11. Cell Cycle: G1 Gap 1 Phase Growth of cell Metabolic activity is high
Increase in mass
Increase Cytoplasm
Increase Proteins
Produce Organelles
Metabolic activity is high

12. Cell Cycle: S phase DNA synthesis
During S phase, DNA is replicated
Occurs in nucleus
Eukaryotic cells normally have 2 copies of each chromosome- 1 set from mom, 1 set from dad
Diploid= 2 n
Haploid= n
n= number of different types of chromosomes

13. Homologous Chromosomes= pair of chromosomes
Human Chromosomes
Homologous Chromosomes= pair of chromosomes
Haploid (n)=23
Diploid (2n)=46

14. Cell Cycle: S Phase Prepares DNA for M phase
Duplicates entire genetic code
Creates 2 new strands of DNA from existing strands
DNA synthesis uses a semiconservative model
Each DNA molecule has 1 old strand and 1 new strand

15. Chromosomes Diploid Cell: 2n = 6
Haploid= n= 3
Following DNA synthesis, each of the six chromosomes consists of 2 sister chromatids, connected at the centromere
Sister Chromatids
Homologous
Chromosome
Centromere
Blue: Paternal Chromosomes
Pink: Maternal Chromosomes

16. Chromosomes
Homologous chromosomes are paired chromosomes which possess genes for the same characteristics. One chromosome comes from mom & one from dad
Sister Chromatids
Homologous
Chromosome
Centromere
Blue: Paternal Chromosomes
Pink: Maternal Chromosomes

17. Cell Cycle: G2 Gap 2 Phase Growth of cell Increase in mass
Makes proteins needed for mitosis
Centrosome: the microtubule organizing center
Each centrosome has pair of centrioles
The centrosome replicates during interphase

18. Cell Cycle: M Phase Mitotic Phase Mitosis= Nuclear Division
Followed by Cytokinesis
Division of cytoplasm

19. Mitosis: 5 Stages Mitosis is divided into five phases: Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis overlaps the latter stages of mitosis

20. Mitosis: 5 Stages Prophase Chromosomes condense
The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis
The spindle includes the centrosomes, the spindle microtubules, and the asters
Aster
a radial array of short microtubules
extends from each centrosome

21. Mitosis: 5 Stages 2. Prometaphase Nuclear envelope breaks up
Two centrosomes migrate to opposite ends of the cell during prophase and prometaphase
Some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
Kinetochores are protein complexes associated with centromeres

22. Mitosis: 5 Stages 3. Metaphase Longest phase of mitosis
20 minutes
Chromosomes line up at the metaphase plate
an imaginary structure at the midway point between the spindle’s two poles
For each chromosome, sister chromatids are attached at kinetochore to spindle fibers from opposite spindle poles

23. Mitosis: 5 Stages 4. Anaphase Shortest stage of mitosis
Cohesion proteins between sister chromatids are cleaved
Each chromatid is now an individual chromosome
Individual chromosomes are pulled to opposite ends of cells as microtubules shorten
Cell elongates as microtubules not attached at kinetochores lengthen

24. Mitosis: 5 Stages 5. Telophase 2 nuclei form Cytokinesis
Nucleolus form
Nuclear envelope forms from fragments
Chromosomes become less condensed
Cytokinesis
Division of the cytoplasm
Animal cells: cleavage furrow forms and pinches cell in 2
Plant cells: Formation of cell plate

25. Cytokinesis

26. Cell Cycle: M Phase Before Mitosis: 1 Cell= Diploid (2n)
After Mitosis:
2 Cells= Diploid (2n)
*End product of mitosis is 2 identical cells

27. Mitosis Cells vary in rate of mitosis
Age matters: children vs. adult
Varies from continuously (skin cells) to only when necessary to repair damage (internal organ cells)
These differences result from regulation at the molecular level

28. Cell Cycle
The sequential events of the cell cycle are directed by a distinct cell cycle control system
Regulated by both internal and external controls
Example of Internal Control: if kinetochore not attached to spindle microtubules, sends a molecular signal that delays anaphase
Example of External Control: growth factors
Proteins released by certain cells that stimulate other cells to divide
The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received

29. Controls on Cell Cycle Multiple checkpoints in cell cycle
Prevent uncontrolled growth
Repair mistakes
For many cells, the G1 checkpoint seems to be the most important
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide
If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase

30. Controls on Cell Cycle
Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks)
Cdks activity fluctuates during the cell cycle because it is controlled by cyclins, so named because their concentrations vary with the cell cycle
MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase

31. Controls on Cell Cycle
An example of external signals is density-dependent inhibition, in which crowded cells stop dividing
Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide

32. Controls on Cell Cycle Cancer is a disease of the cell cycle
Normal cell becomes cancer cell through transformation
Often results from mutations in DNA
Uncontrolled cell growth can lead to tumors
Masses of abnormal cells

33. Controls on Cell Cycle
Benign Tumor= abnormal cells remain at the original site
Malignant tumors= invade surrounding tissues
Metastasize= export cancer cells to other parts of the body, where they may form additional tumors
Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence
Cancer cells have abnormal cell cycle control system
may lack protein checkpoints, produce own growth factors or convey growth signal without growth factor