1. CELL GROWTH & DIVISION
Chapter 5

2. Cell Growth Why do cells divide, instead of just getting larger?
Exchange of Materials
Diffusion limits size: as a cell’s size increases, it begins to take too long for diffusion to occur.
In large cells, the surface area to volume ratio is too small to move material in and out of the cell

3. Cell Growth Why do cells divide, instead of just getting larger?
Not enough DNA to carry out all the cell’s processes
“DNA overload”

4. Cell Growth Cell Division One cell divides to form two daughter cells
Both new cells have the same genetic information
The surface area to volume ratio has increased

5. Cell Division Two parts Mitosis Cytokinesis Division of the nucleus
Division of the cytoplasm

6. Cell Division Some organisms reproduce by mitosis
Bacteria (prokaryotes)
Reproduce asexually by binary
fission (mitosis), which
creates identical offspring
DNA is circular; it copies and
then splits apart

7. Cell Division Chromosomes
Contain genetic material (DNA) coiled up, along with protein
Visible during cell division
Humans have 46

8. Cell Division Chromosomes Sister Chromatids
Before cell division, each chromosome is replicated
Because of this, each
chromosome has two
identical “sister” pieces
Two halves of duplicated
chromosomes with the
same genetic information
When the cell divides, the chromatids separate and each new cell gets ONE chromatid

9. Cell Division Chromosomes Centromere Telomere Holds sister chromatids
together near the center
Telomere
Area of the chromosome
that does not include any
genes and protects DNA
Sister chromatids
Centromere

10. Cell Division Chromosomes Centrosome Area that organizes spindles
In animal cells, contains centrioles (cell walls of plants do a similar job)

11. Cell Division Chromosomes Centrioles Cylindrically shaped
Made of microtubules
Found in animal cells

12. Cell Division Chromosomes Spindle (Fibers)
Thin fibers of microtubules that separate the chromosomes
Form between centrioles in animal cells and similarly in plant cells

13. Cell Division The Cell Cycle
The series of events that cells go through as they grow and divide.
Interphase is the period of growth that occurs between cell divisions.
During the cell cycle:
a cell grows
prepares for division
divides to form two daughter cells, each of which begins the cycle again

14. Cell Division The Cell Cycle 4 (2) Phases: G1 (1st Gap Phase) S Phase
Cell growth
S Phase
Chromosome replication (AKA: Synthesis)
G2 (2nd Gap Phase)
Cell organelles needed for division are copied
M Phase
Mitosis and Cytokinesis
INTERPHASE

15. Cell Division The Cell Cycle Interphase Lasts much longer than mitosis
Cell grows in size
New proteins and organelles are made S
DNA duplicates (chromosomes are replicated) G2
Cell parts needed for division are copied
Preparation for Mitosis

16. Cell Division
Cell Cycle

17. Cell Division The Cell Cycle Mitosis (PMAT) Prophase Metaphase
Anaphase Telophase

18. Chromosomes (paired chromatids)
Cell Division
The Cell Cycle
Mitosis (PMAT)
Prophase
Spindle forming
Prophase
Chromosomes (paired chromatids)
Centromere

19. Cell Division The Cell Cycle Mitosis (PMAT) Prophase
Spindle
forming
The Cell Cycle
Mitosis (PMAT)
Prophase
Prophase is the first and
longest phase of mitosis.
Centrioles separate and
move toward opposite
sides of the cell.
The centrosome helps to
organize the spindle,
a fanlike microtubule
structure that helps separate
the chromosomes.
Centromere
Chromosomes
(paired chromatids)

20. Cell Division The Cell Cycle Mitosis (PMAT) Prophase
Spindle
forming
The Cell Cycle
Mitosis (PMAT)
Prophase
Chromatin (DNA wrapped
around histones) condenses
into chromosomes.
The nuclear envelope breaks
down.
Centromere
Chromosomes
(paired chromatids)

21. Cell Division The Cell Cycle Mitosis (PMAT) Metaphase Metaphase
Centriole
Spindle
Centriole
Metaphase

22. Cell Division The Cell Cycle Mitosis (PMAT) Metaphase
Centriole
The Cell Cycle
Mitosis (PMAT)
Metaphase
The chromosomes line up
across the middle of the
cell.
Microtubules (spindles)
connect the centromere
of each chromosome to the
poles of the spindle.
At the end of metaphase, the centromeres
are cut.
Spindle

23. Individual chromosomes
Cell Division
The Cell Cycle
Mitosis (PMAT)
Anaphase
Individual chromosomes
Anaphase

24. Cell Division The Cell Cycle Mitosis (PMAT) Anaphase The chromosomes
The sister chromatids
separate into individual
chromosomes.
The chromosomes
continue to move
until they have
separated into two groups.
Individual
chromosomes

25. Nuclear envelope reforming
Cell Division
The Cell Cycle
Mitosis (PMAT)
Telophase
Nuclear envelope reforming
Telophase

26. Cell Division The Cell Cycle Mitosis (PMAT) Telophase
Chromosomes gather at
opposite ends of the cell
and lose their distinct shape.
Spindle fibers break down
The cell membrane begins
to separate the new cells
A new nuclear envelope
forms around each
cluster of chromosomes.

27. Cell Division
The Cell Cycle
Cytokinesis
Cytokinesis

28. Cell Division The Cell Cycle Cytokinesis Cytoplasm pinches in half.
Each daughter cell has an identical set
of duplicate chromosomes
In plants, a structure
known as the cell plate
forms midway between
the divided nuclei.

29. Cell Division
REVIEW
The series of events that cells go through as they grow and divide is called
the cell cycle.
mitosis.
interphase.
cytokinesis.

30. Cell Division
REVIEW
The phase of mitosis during which the chromosomes line up across the center of the cell is
prophase.
metaphase.
anaphase.
telophase.

31. Cell Division REVIEW Cytokinesis usually occurs
at the same time as telophase.
after telophase (at the very end of it).
during interphase.
during anaphase

32. Cell Division REVIEW DNA replication takes place during the
S phase of the cell cycle.
G1 phase of the cell cycle.
G2 phase of the cell cycle.
M phase of the cell cycle.

33. Cell Division
REVIEW
During mitosis, “sister” chromatids separate from one another during
telophase.
interphase.
anaphase.
metaphase.

34. Regulating the Cell Cycle
Controls on Cell Division
Contact Inhibition
Experiments show that normal cells reproduce until they come into contact with other cells.
When cells come into contact with other cells, they respond by not growing.
This demonstrates that controls on cell growth and division can be turned on and off.

35. Regulating the Cell Cycle
Controls on Cell Division
Cell Cycle Regulators
The cell cycle is regulated by a specific protein called cyclin.
The amount of this protein in the cell rises and falls in time with the cell cycle.
Cyclins are made by protein synthesis when something inside or outside of the cell triggers the DNA to make them.

36. Regulating the Cell Cycle
Controls on Cell Division
Cell Cycle Regulators
Cyclins were discovered during an experiment:
The sample is injected into a second cell in G2 of interphase.
As result, the second cell enters mitosis.
A sample of cytoplasm is removed from a cell in mitosis.

37. Regulating the Cell Cycle
Controls on Cell Division
Cell Cycle Regulators
Internal
Proteins that respond to events inside the cell
EX: Gene p53 is a tumor suppressor gene; regulates the passage into mitosis
External Regulators
Proteins that respond to events outside the cell
Direct the cell to slow down or speed up the cell cycle
EX: growth factors during embryonic development and wound healing

38. Regulating the Cell Cycle
Uncontrolled Cell Growth
Cancer is a disorder in which some of the body's own cells lose the ability to control growth.
Characteristics of Cancer Cells
Don’t respond to signals that regulate cell growth
Reproduce uncontrollably
Typically are unspecialized
Often, have lost their ability to perform apoptosis
Tumor: masses of cells formed during uncontrolled cell growth; can damage surrounding tissue
Metastasis: when tumors break loose from their original location and spread throughout the body

39. Regulating the Cell Cycle
Uncontrolled Cell Growth

40. Regulating the Cell Cycle
Uncontrolled Cell Growth

41. Regulating the Cell Cycle
Causes of Cancer
Genetics
Oncogene: a mutated gene that contributes to the development of cancer; can promote or allow the uncontrolled growth of cancer cells
Environmental
Carcinogen: a substance that is directly involved in causing cancer due to its ability to damage the organism’s genome or disrupt cellular processes
EX: cigarette smoke, air/water pollution; UV radiation

42. Regulating the Cell Cycle
REVIEW
The cell cycle is believed to be controlled by proteins called
spindles.
cyclins.
regulators.
centrosomes.

43. Regulating the Cell Cycle
REVIEW
Proteins that respond to events inside the cell are called
internal regulators.
external regulators.
cyclins.
growth factors.