1. Chapters 6
The Cell Cycle

2. How do organisms grow? or (2) cells divide to form new cells?
Generally, do –
(1) individual cells keep getting larger and larger? or
(2) cells divide to form new cells?

3. Why don’t individual cells keep growing larger and larger?
Cells are limited in size because they get their nutrients by diffusion. If cells become too large, nutrients such as oxygen and glucose (which are necessary for aerobic cell respiration) will not be able to diffuse quickly enough into the cell in order for it to survive.

4. Let’s start with some definitions….

5. Chromatin and Chromosome
Remember: Chromatin is long and thin. It is uncoiled DNA. (DNA still keeps it’s double helix shape, however.
A chromosome is coiled DNA. The DNA coils around proteins.

6. Chromosomes Compact Before chromosomes are created, DNA is copied
The two exact copies are called chromatids
Two chromatids are held together by a centromere

7. Chromatin and Chromosome

8. Gene
A section of DNA that contains the code to make a protein.

9. Somatic Cells versus Gametes
Gamete = reproductive (sex) cell. Each gamete contains 23 chromosomes.
It is haploid (having 1 set of chromosome in the cell). Often written as n
Somatic cell = body cell. Each somatic cell contains 46 chromosomes
It contains the diploid number of chromosomes (having 2 sets of chromosomes in the cell) Often written as 2n

10. Diploid and Haploid Cells
Two haploid cells merge to form one diploid cell. This process is called fertilization.
Male gametes are called sperm; female gametes are called eggs
Two sex cells (sperm and egg) merge to form a zygote.

11. Homologous Chromosomes
Homologous Chromosomes are like a pair of shoes
You get one “shoe” from your mother and one “shoe” from your father
n + n = 2n

12. Karyotype ( a chart of chromosomes) showing homologous chromosomes - female

13. Homologous chromosomes are similar in size, shape and genetic content.
Autosomes are pairs The chromosomes of pair 23 are sex chromosomes and determine a person’s gender.

14. Zygotes and Specialization
Once a zygote is formed, it undergoes cell division many, many times to form a multicellular organism.
The cells specialize to perform specific functions for the organism.

15. Mitosis
Mitosis: the process in cell division in which the nucleus of a cell is divided into two nuclei. Each nucleus has the same number of chromosomes as the original cell.

16. Prokaryotic Cell Division
Prokaryotes (bacteria) have only one chromosome. It is circular in shape and is attached to the cell membrane. When a prokaryote divides, the cell makes a copy of its DNA, then the cell divides. Each cell has one copy of the chromosome. Prokaryotic cell division is called binary fission. Prokaryotes do not go through mitosis, nor do they have gametes or zygotes.

17. Control of Cell Cycle

18. The Cell Cycle
Cell Cycle: a repeating sequence of growth and division during the life of a cell. The cell cycle has three parts:
1. Interphase: the part of the cell cycle in which an organism grows and carries out its metabolism Before it is about to divide, the cell will copy its DNA.

19. The Cell Cycle, Parts 2 and 3
2. Mitosis: Division of the nucleus. There are 4 phases of mitosis
3. Cytokinesis: the splitting of the cytoplasm of the cell.

20. Biology is the only subject in which multiplication is the same thing as division…

21. The Cell Cycle: Cell Growth, Cell Division

22. Getting from there to here…
Function of cell division
making new cells
continuity of life
asexual reproduction
unicellular organisms
growth
repair & renew
Cell cycle
life of a cell from origin to division into 2 new daughter cells
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

23. Centrioles Cell division
in animal cells, pair of centrioles organize microtubules
spindle fibers
guide chromosomes in mitosis

24. Getting the right stuff
What is passed on to daughter cells?
exact copy of genetic material = DNA
mitosis
division of organelles & cytoplasm
cytokinesis
chromosomes (stained orange) in kangaroo rat epithelial cell
notice cytoskeleton fibers

25. Overview of mitosis I.P.M.A.T. interphase prophase (pro-metaphase)
cytokinesis
metaphase
anaphase
telophase

26. Interphase 90% of cell life cycle Normal day in and day out
cell doing its “everyday job”
produce RNA, synthesize proteins/enzymes
prepares for duplication if triggered

27. Cell cycle Cell has a “life cycle”
cell is formed from a mitotic division
cell grows & matures
to divide again
cell grows & matures to never divide again
G1, S, G2, M
liver cells
G1G0
epithelial cells, blood cells,
stem cells
brain / nerve cells
muscle cells

28. Interphase Divided into 3 phases: G0 G1 = 1st Gap S = DNA Synthesis
cell doing its “everyday job”
cell grows
S = DNA Synthesis
copies chromosomes
G2 = 2nd Gap
prepares for division
cell grows (more)
produces organelles, proteins, membranes G0
signal to divide

29. Interphase Nucleus well-defined Prepares for mitosis
DNA loosely packed in long chromatin fibers
Prepares for mitosis
replicates chromosome
DNA & proteins
produces proteins & organelles

30. Copying / Replicating DNA
Synthesis phase of Interphase
dividing cell replicates DNA
must separate DNA copies correctly to 2 daughter cells
human cell duplicates ~3 meters DNA
each daughter cell gets complete identical copy
error rate = ~1 per 100 million bases
3 billion base pairs in mammalian genome
~30 errors per cell cycle
mutations (to somatic cells)

31. Organizing DNA DNA is organized in chromosomes
ACTGGTCAGGCAATGTC
DNA
Organizing DNA
DNA is organized in chromosomes
double helix DNA molecule
wrapped around histone proteins
like thread on spools
DNA-protein complex = chromatin
organized into long thin fiber
condensed further during mitosis
histones
chromatin
double stranded chromosome
duplicated mitotic chromosome

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

33. Mitotic Chromosome Duplicated chromosome 2 sister chromatids
narrow at centromeres
contain identical copies of original DNA
homologous
chromosomes
homologous
chromosomes
Centromeres are segments of DNA which have long series of tandem repeats = 100,000s of bases long. The sequence of the repeated bases is quite variable. It has proven difficult to sequence.
sister chromatids
single-stranded
homologous = “same information”
double-stranded

34. Mitosis Dividing cell’s DNA between 2 daughter nuclei 4 phases
“dance of the chromosomes”
4 phases
prophase
metaphase
anaphase
telophase

35. Prophase Chromatin condenses visible chromosomes
chromatids
Centrioles move to opposite poles of cell
animal cell
Protein fibers cross cell to form mitotic spindle
microtubules
actin, myosin
coordinates movement of chromosomes
Nucleolus disappears
Nuclear membrane breaks down

36. Transition to Metaphase
Prometaphase
spindle fibers attach to centromeres
creating kinetochores
microtubules attach at kinetochores
connect centromeres to centrioles
chromosomes begin moving

37. Metaphase Chromosomes align along middle of cell metaphase plate
meta = middle
spindle fibers coordinate movement
helps to ensure chromosomes separate properly
so each new nucleus receives only 1 copy of each chromosome

39. Anaphase Sister chromatids separate at kinetochores
move to opposite poles
pulled at centromeres
pulled by motor proteins “walking”along microtubules
actin, myosin
increased production of ATP by mitochondria
Poles move farther apart
polar microtubules lengthen

40. Separation of chromatids
In anaphase, proteins holding together sister chromatids are inactivated
separate to become individual chromosomes
1 chromosome
2 chromatids
2 chromosomes
single-stranded
double-stranded

41. Chromosome movement
Kinetochores use motor proteins that “walk” chromosome along attached microtubule
microtubule shortens by dismantling at kinetochore (chromosome) end
Microtubules are NOT reeled in to centrioles like line on a fishing rod.
The motor proteins walk along the microtubule like little hanging robots on a clothes line.
In dividing animal cells, non-kinetochore microtubules are responsible for elongating the whole cell during anaphase, readying fro cytokinesis

42. Telophase Chromosomes arrive at opposite poles Spindle fibers disperse
daughter nuclei form
nucleoli form
chromosomes disperse
no longer visible under light microscope
Spindle fibers disperse
Cytokinesis begins
cell division

43. Cytokinesis – Cell Division
Animals
constriction belt of actin microfilaments around equator of cell
cleavage furrow forms
splits cell in two
like tightening a draw string
Division of cytoplasm happens quickly.

44. Cytokinesis in Animals

45. Mitosis in whitefish blastula

46. Mitosis in animal cells

47. Cytokinesis in Plants Plants cell plate forms
vesicles line up at equator
derived from Golgi
vesicles fuse to form 2 cell membranes
new cell wall laid down between membranes
new cell wall fuses with existing cell wall

48. Mitosis in plant cell

49. onion root tip

50. Origin of replication
chromosome:
double-stranded DNA
replication
of DNA
elongation of cell
cell pinches in two
ring of proteins
Evolution of mitosis
Mitosis in eukaryotes likely evolved from binary fission in bacteria
single circular chromosome
no membrane-bound organelles

51. prokaryotes
(bacteria)
Evolution of mitosis
protists dinoflagellates
A possible progression of mechanisms intermediate between binary fission & mitosis seen in modern organisms
protists diatoms
eukaryotes
yeast
Prokaryotes (bacteria)
No nucleus; single circular chromosome. After DNA is replicated, it is partitioned in the cell. After cell elongation, FtsZ protein assembles into a ring and facilitates septation and cell division.
Protists (dinoflagellates)
Nucleus present and nuclear envelope remains intact during cell division. Chromosomes linear. Fibers called microtubules, composed of the protein tubulin, pass through tunnels in the nuclear membrane and set up an axis for separation of replicated
chromosomes, and cell division.
Protists (diatoms)
A spindle of microtubules forms between two pairs of centrioles at
opposite ends of the cell. The spindle passes through one tunnel in the intact nuclear envelope. Kinetochore microtubules form between kinetochores on the chromosomes and the spindle
poles and pull the chromosomes to each pole.
Eukaryotes (yeast)
Nuclear envelope remains intact; spindle microtubules form inside the nucleus between spindle pole bodies. A single kinetochore microtubule attaches to each chromosome and pulls each to a pole.
Eukaryotes (animals)
Spindle microtubules begin to form between centrioles outside of nucleus. As these centrioles move to the poles, the nuclear envelope breaks down, and kinetochore microtubules attach kinetochores of chromosomes to spindle poles. Polar microtubules extend toward the center of the cell and overlap.
eukaryotes
animals

52. Video animation: Cancer
Cancer – the enemy!
Cancer – the uncontrolled dividing of cells
Video animation: Cancer

53. Cell Cycle - Normal vs. Cancerous Cells
Normal Chicken Stomach Cells:
Interphase – 120 min
Prophase – 60 min
Metaphase – 10 min
Anaphase – 3 min
Telophase – 12 min
Cancerous Chicken Stomach Cells:
Interphase – 16 min
Prophase – 15 min
Metaphase – 2 min
Anaphase – 1 min
Telophase – 3 min

54. Animated Introduction to Cancer Biology
Types of Tumors
Benign tumor – slow-growing or has stopped growing and does not spread to other tissues Malignant tumor– is actively growing and tends to spread to other tissues Metastasis – the spreading of cancer cells to other parts of the body
Animated Introduction to Cancer Biology