1. Cell Reproduction
Chapter 8

2. Chromosomes
 DNA in one eukaryotic
cell, stretched out, is 2
meters
 Prokaryotes: single,
circular chromosome
 Eukaryotes: multiple
chromosomes in
nucleus

3. Chromosome Structure
 DNA winds around
proteins called
histones, like beads on
a string
 When cells divide, the
DNA must pack itself
even more tightly

4. Chromosome Structure

5. Chromosome Structure

6. Chromosome Structure

7. Chromatin
 Between divisions,
chromosomes are not
tightly packed
 Proteins + DNA =
chromatin
 Must be in this state to be
“read” and utilized
 Only tightly-packed
chromosomes are visible
under a microscope

8. Chromatids
 Each of two (duplicated) strands is a chromatid
 Two identical strands are sister chromatids
 Centromere is the region at which they are held
together

9. Organism Number of
Chromosomes
Adder’s tongue fern 1,262
Carrot 18
Cat 32
Chimpanzee 48
Earthworm 36
Fruit Fly 8
Horse 64
Lettuce 18
Sand dollar 52

11. Chromosome Number
 One pair of Sex
chromosomes (X and Y
in humans)
 Autosomes are all non-
sex chromosomes
 Every organism has
two non-identical
copies of each
chromosome, called
homologous
chromosomes

12. Chromosome Number
 Humans have 46
chromosomes in 23 pairs
 Diploid cells (2n) have both
homologous chromosomes
 Haploid cells (1n), sperm
and egg, have only one

13. Cell Division
Section 8.2

14. Prokaryotic Cell Division
 “Binary Fission”
 Asexual reproduction
 DNA duplicated
 Cell elongates, then
center pinches in,
splitting the cell in two

15. Cell Life Cycle
 Non-mitosis
stages are called
interphase
 Some cells
undergo meiosis

16. Interphase
 G1 (first gap) phase : cell grows and matures
 S (synthesis) phase : cell copies DNA
 G2 (second gap) phase : cell prepares for
division

17. Mitosis Stage 1: Prophase
 Chromosomes
condense
 Nuclear membrane
breaks down
 Centrosome/centrioles
help organize spindle
fibers (two types:
kinetochore and polar)

19. Mitosis Stage 2: Metaphase
 Chromosomes easy to
identify
 Nuclear membrane gone
 Chromosomes line up at
center
 Spindle fibers link opposite
poles and chromosomes

21. Mitosis Stage 3: Anaphase
 Spindle fibers shorten,
pulling sister
chromatids apart
 Each side of the cell
has a full set of
chromosomes

23. Mitosis Stage 4: Telophase
 Nuclear membrane re-
forms in each new cell
 Chromosomes un-coil
 Spindle and fibers
dissolve
 Cytokinesis begins

25. Cytokinesis
 Cell membrane grows
toward the center of the
cell, “pinching” it in two
 New cells are half the size
of original

27. In Plant Cells
 Cell wall must form
between new cells
 Occurs as vesicles
(from the Golgi
apparatus) holding cell-
wall material (cellulose)
line up across center,
making the cell plate

28. Regulation

29. Signals
 Cell growth/division
depends on protein
signals and
environmental factors
 Examples: deep
wounds heal; bacteria
fill Petri dish

30. Checkpoints
 Mitosis will not
start/continue unless
conditions are correct
 G1 checkpoint: Are
conditions favorable? Is cell
large enough?
 G0 phase is a “holding
pattern”

31. Checkpoints
 G2 checkpoint: Are there
mistakes in synthesized
DNA that must be fixed?
 M checkpoint: Have all the
steps in mitosis been
completed correctly? Are
chromosomes correctly
attached to spindle?

32. Cancer
 Uncontrolled,
unregulated cell
division
 Damage to DNA results
in a mass of defective
cells called a tumor

33. Treatment of Cancer
 Tumors are abnormal
growths of cells
(benign or malignant)
 Treated by drugs that
stop cell cycle or by
radiation
 Carcinogens:
radiation, chemicals

34. Critical Thinking Questions

35. 1. What would happen if
sperm and egg cells
were diploid instead of
haploid?
2. Is there a correlation
between complexity of
an organism and
chromosome number?
Explain.
3. Use your notes to
describe the structure
of a chromosome.
Give some reasons
whey DNA must be
condensed.
4. What would happen to a
cell if mitosis occurred
without cytokinesis?
Draw a picture to
explain this.
5. Contrast cell division in
the following three
organisms: bacteria,
rose, chipmunk.
6. Draw a diploid cell with
3 pairs of chromosomes
(in interphase). Now,
draw the same cell in all
four stages of mitosis.