1. CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION
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2. Living organisms reproduce by two methods Asexual reproduction
Offspring are identical to the original cell or organism
inheritance of all genes from one parent
Sexual reproduction
Offspring are similar to parents, but show variations in traits
inheritance of unique sets of genes from two parents
Provides for genetic diversity
Most eukaryotic organisms are capable of both asexual and sexual reproduction. Students may be surprised to learn that asexual reproduction plays a major role in the life cycles of many organisms. For example, the unicellular algae Chlamydomonas generates an increased population by asexual reproduction when conditions are favorable for cell division. In unfavorable conditions, the organism undergoes sexual reproduction. This has the advantage of producing a new combination of genes and traits that could be advantageous for survival under new environmental conditions.
Student Misconceptions and Concerns
1. As the authors note in Module 8.1, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused.
2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated.
Teaching Tips
1. Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like?
Copyright © 2009 Pearson Education, Inc.

3. Cells arise only from preexisting cells
As a cell grows, its volume increases faster than its surface area
This causes problems in getting the materials needed in and the wastes out fast enough
It also puts more demands on the cell’s DNA
If a cell becomes too large to function efficiently it must undergo cell division – one cell divides into 2 daughter cells
Student Misconceptions and Concerns
1. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells is variously restricted and regulated.
Teaching Tips
1. Virchow’s principle of “every cell from a cell” is worth thinking through with your class. Students might expect that, like automobiles, computers, and cell phones, parts are constructed and cells are assembled. In our society, few nonliving products are generated only from existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet this is a common expectation in biology.
2. Students who think through Virchow’s principle might ask how the first cells formed. They might wonder further whether the same environments that produced these cells are still in existence. The conditions on Earth when life first formed were very different from those we know today. Chapter 15 addresses the origin and early evolution of life on Earth.
Copyright © 2009 Pearson Education, Inc.

4. replace cells that die from normal wear & tear or from injury
Why do cells divide?
For growth
For repair & renewal
replace cells that die from normal wear & tear or from injury
Reproduction
amoeba
Unicellular organisms
Cell division = reproduction
Reproduces entire organism& increase population
Multicellular organisms
Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg
Also use cell division to repair & renew cells that die from normal wear & tear or accidents

5. Where it all began…
You started as a cell smaller than a period at the end of a sentence… .
the original fertilized egg has to divide…
and divide…
Eventually the cells must become specialized into all of the various types through a process called differentiation

6. THE EUKARYOTIC CELL CYCLE AND MITOSIS
Copyright © 2009 Pearson Education, Inc.

7. Eukaryotic chromosomes
composed of chromatin
a diffuse mass of long, thin fibers
DNA + proteins
To prepare for division  the chromatin coils up forming highly compact distinct chromosomes visible with a microscope
Before cell division chromosomes duplicate
This replicated form (x-shape) is still considered one chromosome
Chromatin is compacted about 100,000 fold to produce the interphase/metaphase chromosome. If all the DNA in the human chromosomes were aligned, it would stretch for one meter. All of this DNA is condensed to fit into a nucleus that can only be seen with the aid of a microscope.
The centromere has a unique DNA sequence involving repeated stretches of nucleotides. In biotechnological applications, artificial chromosomes can be produced that have a centromeric sequence. This chromosome will be properly distributed during cell division because the spindle fibers attach to the artificial centromeric sequence.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.4B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many why (a) chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate.
Teaching Tips
1. Figure 8.4C is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids.
Copyright © 2009 Pearson Education, Inc.

8. Sister chromatids: each copy of a duplicated chromosome
Sister chromatids
Sister chromatids: each copy of a duplicated chromosome
centromere: region where sister chromatids connect.
Centromere
Figure 8.4B Electron micrograph of a duplicated chromosome.
This electron micrograph provides a view of sister chromatids.

9. Chromosome distribution to daughter cells
Chromosome
duplication
Sister
chromatids
Centromere
Figure 8.4C Chromosome duplication and distribution.
The term chromatid is used to describe duplicates that are connected at the centromere. This diagram emphasizes that the structures are called chromosomes when separated. This leads to a brief time when a cell has double the number of chromosomes, as in anaphase and telophase of mitosis, prior to cytokinesis.
Chromosome
distribution to
daughter
cells

10. The cell cycle multiplies cells
The cell cycle - an ordered sequence of events that extends from the time a cell is first formed until its own division into two cells
It consists of two stages:
Interphase: duplication of cell contents
About 90% of cell cycle
Cell carries out normal functioning
Increases proteins, organelles
grows in size
Chromosomes duplicate
Mitotic phase (M phase): division
About 10 % of cell cycle
Cell actually divides
Differences in the length of the cell cycle can be instructive. Yeast cells have a 2-hour life cycle, while human cells in culture take about 24 hours to divide. Mitosis and cytokinesis represent a shorter section of the cycle, lasting one hour for cultured human cells.
Teaching Tips
1.The authors note in Module 8.5 that each of your students consists of about 100 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2008 is about 310 million people. To give every one of those people about $323,000, we will need a total of $100 trillion. Here is another example. If we give you $31,688 every second of your life, and you lived for 100 years, you would receive $100 trillion dollars.
2.The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (1) a chromosome before DNA replication and (2) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.
3. In G1, the chromosomes have not duplicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
Copyright © 2009 Pearson Education, Inc.

11. INTERPHASE S (DNA synthesis) G1 G2 MITOTIC
INTERPHASE S
(DNA synthesis) G1 G2
Cytokinesis
Mitosis
Figure 8.5 The eukaryotic cell cycle.
MITOTIC
PHASE (M)

12. The cell cycle multiplies cells
Interphase: duplication of cell contents; 3 stages:
G1 — growth, increase in cytoplasm
S — (synthesis) duplication of chromosomes (DNA)
G2 — growth, preparation for division (mitosis)
Mitotic phase: cell division
Mitosis—division of the nucleus and its contents (including the duplicated chromosomes) into two daughter nuclei
Cytokinesis—division of cytoplasm
Results in 2 genetically identical daughter cells
Differences in the length of the cell cycle can be instructive. Yeast cells have a 2-hour life cycle, while human cells in culture take about 24 hours to divide. Mitosis and cytokinesis represent a shorter section of the cycle, lasting one hour for cultured human cells.
Teaching Tips
1.The authors note in Module 8.5 that each of your students consists of about 100 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2008 is about 310 million people. To give every one of those people about $323,000, we will need a total of $100 trillion. Here is another example. If we give you $31,688 every second of your life, and you lived for 100 years, you would receive $100 trillion dollars.
2.The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (1) a chromosome before DNA replication and (2) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.
3. In G1, the chromosomes have not duplicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
Copyright © 2009 Pearson Education, Inc.

13. Cell division Mitosis produce cells with same information
identical daughter cells
exact copies
clones
same amount of DNA
same number of chromosomes
same genetic information
Aaaargh! I’m seeing double!

14. I.P.M.A.T. Overview of Cell Cycle prophase interphase cytokinesis
metaphase
anaphase
telophase

15. Interphase Nucleus well-defined Prepares for mitosis
green = key features
Interphase
Nucleus well-defined
DNA loosely packed in long chromatin fibers
Prepares for mitosis
replicates chromosome (DNA) in S phase
produces proteins & organelles

16. Copying DNA & packaging it…
After DNA duplication, chromatin condenses
coiling & folding to make a smaller package
DNA
mitotic chromosome
chromatin

17. Mitosis Dividing cell’s DNA between 2 daughter nuclei
Dividing cell’s DNA between 2 daughter nuclei
Mitosis progresses through a series of stages
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis normally follows mitosis and often overlaps telophase
Teaching Tips
1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym.
2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research.
Copyright © 2009 Pearson Education, Inc.

18. Prophase
green = key features
Chromatin condenses and chromosomes become visible composed of 2 sister chromatids
Spindle fibers begins to form
coordinates movement of chromosomes
Nuclear membrane breaks down

19. Metaphase Chromosomes align along middle of cell
green = key features
Metaphase
Chromosomes align along middle of cell
spindle fibers coordinate movement
helps to ensure chromosomes separate properly
so each new nucleus receives only 1 copy of each chromosome

20. Anaphase Sister chromatids separate and move to opposite poles
green = key features
Anaphase
Sister chromatids separate and move to opposite poles

21. Telophase cell division Chromosomes arrive at opposite poles
green = key features
Telophase
Chromosomes arrive at opposite poles
2 new daughter nuclei form
Cytokinesis begins
cell division

22. Cytokinesis in animals
cleavage furrow forms
splits cell in two
like tightening a draw string
Division of cytoplasm happens quickly.

23. Cleavage furrow Cleavage furrow Contracting ring of microfilaments
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
Figure 8.7A Cleavage of an animal cell.
Daughter cells

24. Cytokinesis in Plants Plants Cell plate forms
Vesicles from Golgi line up at equator and fuse to form 2 cell membranes
new cell wall laid down between membranes
new cell wall fuses with existing cell wall

25. Cell wall New cell wall Vesicles containing cell wall material
Cell wall
New cell wall
Figure 8.7B Cell plate formation in a plant cell.
Vesicles containing
cell wall material
Cell plate
Daughter cells

26. Wall of parent cell Cell plate forming Daughter nucleus
Wall of
parent cell
Cell plate
forming
Daughter
nucleus
Figure 8.7B Cell plate formation in a plant cell.

27. Mitosis in animal cells

28. Mitosis in whitefish blastula

29. Regulation of Cell Division and Cancer

30. Frequency of cell division
Frequency of cell division varies by cell type
embryo
cell cycle < 20 minute
skin cells
divide frequently throughout life
12-24 hours cycle
liver cells
retain ability to divide, but keep it in reserve
divide once every year or two
mature nerve cells & muscle cells
do not divide at all after maturity
permanently in G0 G2 S G1 M
metaphase
prophase
anaphase
telophase
interphase (G1, S, G2 phases)
mitosis (M)
cytokinesis (C) C

31. Allow for coordination between cells
How do cells know when to divide? What controls cell division? External signals
Growth factors
protein signals released by one cells that stimulate other cells to divide
Allow for coordination between cells

32. crowded cells stop dividing
Controls lead to:
density-dependent inhibition
crowded cells stop dividing
Physical contact between cell-surface proteins
anchorage dependence
to divide cells must be attached to a substrate or solid surface

33. stop dividing (density- dependent inhibition).
Cells anchor to
dish surface
and divide.
When cells have
formed a complete
single layer, they
stop dividing (density-
dependent inhibition).
If some cells are
scraped away, the
remaining cells divide
to fill the dish with a
single layer and then
stop (density-dependent
inhibition).
Figure 8.8B An experiment demonstrating density-dependent inhibition, using animal cells grown in culture.

34. Internal controls: checkpoint control system
Control cell cycle by STOP & GO signals (usually proteins) at critical points
signals indicate if key cellular processes have been completed correctly
Cyclins – proteins that help to regulate the cell cycle

35. Cancer & Cell Growth Cancer is unrestrained, uncontrolled cell growth
Cancer cells:
Do not respond normally to cell cycle control systems
divide out of control - excessively and rapidly
Can invade other tissues of the body (through the circulatory system)
May kill organism
anchorage dependence and density-dependent inhibition fail

36. Tumors Mass of abnormal cells
Benign tumor
abnormal cells remain at original site as a lump
most do not cause serious problems & many can be removed by surgery
Malignant tumor
cells leave original site = metastasis
lose attachment to nearby cells
carried by blood & lymph system to other tissues
start more tumors
impair functions of organs throughout body

37. Development of Cancer – why older people?
Cancer develops only after a cell experiences ~6 key mutations (“hits”)
unlimited growth
turn on growth promoter genes
ignore checkpoints
turn off tumor suppressor genes (p53)
escape apoptosis (programmed cell death)
turn off suicide genes
immortality = unlimited divisions
turn on chromosome maintenance genes
promotes blood vessel growth
turn on blood vessel growth genes
overcome anchor & density dependence
turn off touch-sensor gene

38. What causes these “hits”?
Mutations in cells can be triggered by
UV radiation
chemical exposure
radiation exposure
heat
cigarette smoke
pollution
age
genetics

39. Traditional treatments for cancers
Removal of cancerous growth
Surgery
Treatments target rapidly dividing cells
high-energy radiation
Damages DNA in cancer cells more than other cells (have lost ability to repair damage)
chemotherapy
stop DNA replication
stop various stages of mitosis & cytokinesis
stop blood vessel growth

40. What’s so special about stem cells?
2 types:
Embryonic stem cells
Have the ability to differentiate into all types of cells
Adult stem cells
Have the ability to differentiate into certain types of cells (but not all)