1. Chapter 12
Lecture slides also by: Kim Foglia and Kelly Riedell
The Cell Cycle

2. Cell Division
The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter
unicellular organisms = division of one cell reproduces the entire organism
Multicellular organisms depend on cell division for
Development from a fertilized cell
Growth
Repair
Cell division is an integral part of the cell cycle
© 2011 Pearson Education, Inc.

3. (b) Growth and development
Figure 12.2
100 m
(a) Reproduction
200 m
(b) Growth and development
Figure 12.2 The functions of cell division.
20 m
(c) Tissue renewal

4. Mitosis or Meiosis?
Most cell division results in daughter cells with identical genetic information, DNA = MITOSIS
Eukaryotic cell division consists of
Mitosis, the division of the genetic material in the nucleus
Cytokinesis, the division of the cytoplasm
The exception is meiosis, a special type of division that can produce sperm and egg (gametes) cells = MEIOSIS
Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell
© 2011 Pearson Education, Inc.

5. VOCAB:

6. Vocab to know: Genome- entire complement of genetic material
Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
Somatic cells (nonreproductive cells) have two sets of chromosomes
Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells
© 2011 Pearson Education, Inc.

7. More Vocab to know: DNA must duplicate to get ready to divide
Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell division
The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached
During division two sister chromatids of each duplicated chromosome separate. Once separate, the chromatids are called chromosomes
© 2011 Pearson Education, Inc.

8. Phases of the Cell Cycle
The cell cycle consists of
Mitotic (M) phase (mitosis and cytokinesis)
Interphase (cell growth and copying of chromosomes in preparation for cell division)
© 2011 Pearson Education, Inc.

9. Interphase
Interphase (about 90% of the cell cycle) can be divided into subphases
G1 phase (“first gap”)
S phase (“synthesis”)
G2 phase (“second gap”)
The cell grows during all three phases, but chromosomes are duplicated only during the S phase
© 2011 Pearson Education, Inc.

10. Some can return to cycle with signal (Ex; Liver cells respond to injury) Some never divide again (Ex: Mature nerve, muscle cells)

11. Mitosis Mitosis is conventionally divided into five phases Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis overlaps the latter stages of mitosis
For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files.
© 2011 Pearson Education, Inc.

12. Chromosome, consisting of two sister chromatids
Figure 12.7a
G2 of Interphase
Prophase
Prometaphase
Centrosomes (with centriole pairs)
Fragments of nuclear envelope
Chromatin (duplicated)
Early mitotic spindle
Aster
Nonkinetochore microtubules
Centromere
Figure 12.7 Exploring: Mitosis in an Animal Cell
Plasma membrane
Nucleolus
Kinetochore
Kinetochore microtubule
Chromosome, consisting of two sister chromatids
Nuclear envelope

15. Metaphase Anaphase Telophase and Cytokinesis Metaphase plate
Figure 12.7b
Metaphase
Anaphase
Telophase and Cytokinesis
Metaphase plate
Cleavage furrow
Nucleolus forming
Figure 12.7 Exploring: Mitosis in an Animal Cell
Nuclear envelope forming
Spindle
Centrosome at one spindle pole
Daughter chromosomes

17. More Vocab:
The mitotic spindle -made of microtubules- controls chromosome movement
The spindle includes: the centrosomes, the spindle microtubules, and the asters
An aster (a radial array of short microtubules) extends from each centrosome
Kinetochores are protein complexes associated with centromeres
microtubules shorten by depolymerizing at their kinetochore ends
Metaphase plate: an imaginary structure at the midway point between the spindle’s two poles
For the Cell Biology Video Spindle Formation During Mitosis, go to Animation and Video Files.
© 2011 Pearson Education, Inc.

20. Cytokinesis: A Closer Look
Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles
In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
In plant cells, a cell plate forms during cytokinesis
© 2011 Pearson Education, Inc.

21. Chromatin condensing Nucleus 10 m Nucleolus Chromosomes Cell plate 1
Figure 12.11
Chromatin condensing
Nucleus
10 m
Nucleolus
Chromosomes
Cell plate
Figure Mitosis in a plant cell. 1
Prophase 2
Prometaphase 3
Metaphase 4
Anaphase 5
Telophase

22. MODIFIED from a slide show by Kim Foglia

29. Cyclin-dependent kinases (Cdk’s) are present all the time but inactive unless combined with cyclins
Enzymes that work by adding a
phosphate group
to other molecules
Presence of MPF triggers passage past G1 & G 2 checkpoints

30. Cyclin levels
change throughout
cell cycle
Fluctuating levels
of different
Cyclin-Cdk complexes seem to control
all stages of
cell cycle

32. Stop and Go Signs: Internal and External Signals at the Checkpoints
An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase
Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide
© 2011 Pearson Education, Inc.

33. Figure 12.18
EXTERNAL SIGNAL 1
A sample of human connective tissue is cut up into small pieces.
Scalpels
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
Petri dish 2
Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts. 4
10 m
PDGF is added to half the vessels. 3
Cells are transferred to culture vessels.
Figure The effect of platelet-derived growth factor (PDGF) on cell division.
Without PDGF
With PDGF

34. Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence

35. CANCER CELLS Don’t respond to control signals
Lose density-dependent inhibition
Lose anchorage dependence
Telomerase enzymes maintain/replace telomeres
Transformation-
process that changes
a normal cell into
a cancer cell

36. Telomeres protect DNA from being degraded
Telomeres become shorter with each replication; shorter in older cells
Telomerase enzyme lengthens telomeres
Cancer cells have increased telomerase activity
2009 Nobel Prize Physiology/Medicine
Discovery of Telomeres
Jack Szostak Carol Greider Elizabeth Blackburn.

37. Most cells divide 20-50 times in culture; then stop, age, die
Cancer cells are “immortal” -HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in culture

39. Loss of Cell Cycle Controls in Cancer Cells
Cancer cells do not respond normally to the body’s control mechanisms
Cancer cells may not need growth factors to grow and divide
They may make their own growth factor
They may convey a growth factor’s signal without the presence of the growth factor
They may have an abnormal cell cycle control system
© 2011 Pearson Education, Inc.

40. Cancer cells that are not eliminated by the immune system form tumors, masses of abnormal cells within otherwise normal tissue
If abnormal cells remain only at the original site, the lump is called a benign tumor
Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors

43. Binary Fission in Bacteria
Prokaryotes (bacteria and archaea) reproduce by binary fission
In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart
© 2011 Pearson Education, Inc.

44. Chromosome replication begins. Two copies of origin
Figure
Origin of replication
Cell wall
Plasma membrane
E. coli cell
Bacterial chromosome 1
Chromosome replication begins.
Two copies of origin 2
Replication continues.
Origin
Origin 3
Replication finishes.
Figure Bacterial cell division by binary fission. 4
Two daughter cells result.

45. The Evolution of 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
© 2011 Pearson Education, Inc.

46. VOCAB REVIEW

47. Figure 12.UN04
Figure 12.UN04 Appendix A: answer to Figure 12.8 legend question

48. Figure 12.UN06
Figure 12.UN06 Appendix A: answer to Test Your Understanding, question 10

49. Figure 12.UN05
Figure 12.UN05 Appendix A: answer to Test Your Understanding, question 7