1. How Cells Reproduce

2. Dividing HeLa Cells

3. Eukaryotes and Prokaryotes
Eukaryotic cells undergo mitosis and/or meiosis
Separates duplicated chromosomes of parent cell into two daughter nuclei
Another mechanism divides cytoplasm

4. Mitosis and Meiosis Mitosis Meiosis
Basis of growth, cell replacements, and tissue repair in multicelled species
Basis of asexual reproduction in many single-celled and multicelled species
Meiosis
Basis of sexual reproduction
Precedes formation of gametes or sexual spores

5. Cell Division Mechanisms

6. Chromosome Structure Eukaryotic chromosome Nucleosome
Association of DNA, histones, and other proteins
Nucleosome
Smallest unit of organization
Double-stranded DNA looped twice around a spool of histones

7. Structure of a Condensed Chromosome

8. Sister Chromatids
A duplicated chromosome consists of two sister chromatids
Sister chromatids remain attached at their centromere until late in mitosis

9. Introducing the Cell Cycle
Starts when a new cell forms
Runs through interphase
Ends when cell reproduces by nuclear and cytoplasmic division

10. Interphase Most cellular activities occur in interphase
G1: Cell grows in mass, doubles number of cytoplasmic components
S: DNA replication duplicates chromosomes
G2: Cell prepares for division

11. G1 S
Interval of cell growth before
DNA replication (chromosomes
unduplicated)
Interval of cell growth when
the DNA is replicated (all
chromosomes duplicated)
cytoplasmic
division; each
daughter cell
enters interphase G2
Interval after DNA
replication; the cell
prepares to divide
Interphase ends for parent cell
Fig. 8.5, p.128

12. Chromosome Number Sum of all chromosomes in cells of a given type
In human body cells, chromosome number is 46
Body cells are diploid (have two of each kind of chromosome)

13. Mitosis and Chromosome Number
Mitosis maintains parental chromosome number from one generation to the next
Bipolar spindle divides sister chromatids

14. A Closer Look at Mitosis
A nuclear division mechanism that maintains the chromosome number
Mitosis proceeds in four stages:
Prophase
Metaphase
Anaphase
Telophase

15. Prophase
Duplicated chromosomes become threadlike as they start to condense
Microtubules form a bipolar spindle
Nuclear envelope starts to break apart

16. Metaphase
All chromosomes become aligned midway between the two spindle poles
Chromosomes in most condensed forms

17. Anaphase Sister chromatids detach from each other
Spindles move them toward opposite poles

18. Telophase Chromosomes reach opposite spindle poles
Nuclear envelope forms around each cluster
Both new nuclei have the parental chromosome number

19. Mitosis

20. Mitosis

21. Fig. 8.7a, p.130

22. nuclear envelope chromosome b Early Prophase
Mitosis begins. DNA and its associated
proteins have started to condense. Two
chromosomes (color-coded purple) were
inherited from the female parent. The
other two (blue) are their counterparts,
inherited from the male parent.
Fig. 8.7b, p.130

23. pair of centrioles c Late Prophase
The duplicated chromosomes continue to condense. New microtubules move one of two pairs of centrioles to the opposite side of the nucleus. The nuclear envelope starts to break up.
Fig. 8.7c, p.130

24. All of the chromosomes have become lined up midway
e Metaphase
All of the chromosomes have
become lined up midway
between the spindle poles.
At this stage of mitosis, the
chromosomes are in their
most tightly condensed form.
Fig. 8.7e, p.130

25. Sister chromatids separate as motor proteins moving along
f Anaphase
Sister chromatids separate as
motor proteins moving along
spindle microtubules drag
them to opposite spindle
poles. Other microtubules
push the poles farther apart.
Fig. 8.7f, p.130

26. There are two clusters of chromosomes, which now
g Telophase
There are two clusters of
chromosomes, which now
decondense. Patches of
new membrane fuse to form
a new nuclear envelope.
Mitosis is over.
Fig. 8.7g, p.130

27. After cytoplasmic division, there are two daughter
h Two Daughter
Cells at Interphase
After cytoplasmic division,
there are two daughter
cells. Each is diploid: Its
nucleus has two of each
type of chromosome, just
like the parent cell.
Fig. 8.7h, p.130

28. Cytoplasmic Division Mechanisms
Mechanisms of cytoplasmic division differ in plant and animal cells
In animal cells
A contractile ring of microfilaments (part of cell cortex) contracts and pulls the cell surface inward until the cytoplasm is divided

29. Cytoplasmic Division in Animal Cells

30. Cytoplasmic Division in Plant Cells

31. Results of Cell Division: A Human Embryo

32. When Control is Lost
Mutant checkpoint genes can cause tumors by disrupting normal controls