1. Chapter 11 How Cells Reproduce
(Sections ) 1

2. 11.1 Henrietta’s Immortal Cells
Henrietta Lacks died of cancer at age 31
50 years later, her cells still live in laboratories around the world
Most human cells grown in laboratories die within a few weeks
Figure 11.1 HeLa cells, a legacy of cancer victim Henrietta Lacks (right). Opposite, fluorescence micrograph of two HeLa cells in the process of dividing. Blue and green show two proteins that help microtubules (red) attach to chromosomes (white). Defects in these and other proteins that orchestrate cell division result in descendant cells with too many or too few chromosomes, an outcome that is a hallmark of cancer.

3. 11.2 Multiplication by Division
Cells reproduce by dividing
Division of a eukaryotic cell typically occurs in two steps: nuclear division followed by cytoplasmic division
The sequence of stages through which a cell passes during its lifetime is called the cell cycle

4. The Life of a Cell
One cell cycle consists of three phases: interphase, mitosis, and cytoplasmic (cell) division
cell cycle
A series of events from the time a cell forms until its cytoplasm divides

5. Eukaryotic Cell Cycle

6. Eukaryotic Cell Cycle G1 is the interval of growth before DNA
replication. The cell’s chromosomes
are unduplicated during
this stage. 1
S is the time of synthesis. The name
refers to DNA synthesis, because
the cell copies its DNA
during this
Stage. 2
At the
end of
mitosis,
the cytoplasm
typically divides,
and the cycle begins
anew in interphase for
each descendant cell. 6
G2 is the
interval after
DNA replication
and before mitosis.
The cell prepares to
divide during this stage. 3
Figure 11.2 The eukaryotic cell cycle. The length of the intervals differs among cells. G1, S, and G2 are part of interphase. 5 4
The nucleus divides during mitosis.
Interphase ends.
Fig. 11.2, p. 164

7. ANIMATION: The cell cycle
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8. Introduction to Interphase
A typical cell spends most of its life in interphase
interphase
Interval between mitotic divisions when a cell grows, doubles the number of its cytoplasmic components, and replicates its DNA in preparation for division
Consists of three stages: G1, S, and G2

9. Three Stages of Interphase
G1: The first interval (or gap) of cell growth
The time before DNA replication when cells engage in their metabolic business
S: The time of synthesis (DNA replication) when the cell prepares to divide
G2: The second interval (or gap) when the cell makes proteins that will drive cell division

10. Introduction to Mitosis
The nucleus divides during mitosis, producing an identical copy of its set of chromosomes
mitosis
Nuclear division mechanism that maintains the chromosome number
Basis of body growth and tissue repair in multicelled eukaryotes; also asexual reproduction in some plants, animals, fungi, and protists

11. Homologous Chromosomes
Human diploid cells have two sets of chromosomes: 46 chromosomes in 23 pairs
Except for a pairing of sex chromosomes (XY) in males, the chromosomes of each pair are homologous
homologous chromosomes
Chromosomes with the same length, shape, and set of genes

12. Introduction to Cytoplasmic Division
When the cytoplasm divides, the new nuclei produced by mitosis are packaged into separate cells
Each new cell has a full complement of unduplicated chromosomes, and each starts the cell cycle over again in G1 of interphase

13. Mitosis Maintains Chromosome Number

14. Mitosis Maintains Chromosome Number
A An unduplicated pair of chromosomes in a cell in G1.
B By G2, each chromosome has been duplicated.
Figure 11.3 How mitosis maintains the chromosome number.
C Mitosis and cyto-plasmic division package
one copy of each chromosome into each of two new cells.
Fig. 11.3, p. 165

15. Mitosis Maintains Chromosome Number
A An unduplicated pair of chromosomes in a cell in G1.
B By G2, each chromosome has been duplicated.
Figure 11.3 How mitosis maintains the chromosome number.
C Mitosis and cyto-plasmic division package
one copy of each chromosome into each of two new cells.
Stepped Art
Fig. 11.3, p. 165

16. A Bigger Picture of Cell Division
Mitosis and cytoplasmic division increase body size during development and replace damaged or dead cells
Many species of plants, animals, fungi, and protists reproduce by asexual reproduction using mitosis and cytoplasmic division
asexual reproduction
Reproductive mode by which offspring arise from a single parent only

17. Cell Division and Development
Frog embryos after three mitotic divisions of a fertilized egg

18. Key Concepts The Cell Cycle
A cell cycle starts when a new cell forms by division of a parent cell, and ends when the cell completes its own division
A typical cell cycle proceeds through intervals of interphase, mitosis, and cytoplasmic division

19. 11.3 Mitosis
During interphase, a chromosomes are loosened to allow transcription and DNA replication
When mitosis begins, duplicated DNA packs tightly together into chromosome shapes

20. The Four Stages of Mitosis
1. prophase
Stage of mitosis during which chromosomes condense and become attached to a newly forming spindle
2. metaphase
Stage of mitosis at which the cell’s chromosomes are aligned midway between poles of the spindle

21. The Four Stages of Mitosis
3. anaphase
Stage of mitosis during which sister chromatids separate and move to opposite spindle poles
4. telophase
Stage of mitosis during which chromosomes arrive at the spindle poles and decondense, and new nuclei form

22. Centrosomes and Spindles
Most animal cells have a centrosome, a region with two centrioles that gets duplicated just before prophase
During prophase, one of the two centrosomes moves to the opposite side of the cell, and microtubules extend from both centrosomes to form a spindle
spindle
Dynamically assembled and disassembled network of microtubules that moves chromosomes during nuclear division

23. Mitosis: Prophase Early Prophase
Mitosis begins: DNA starts to condense
The centrosome gets duplicated
Prophase
Duplicated chromosomes become visible
One of the two centrosomes moves to the opposite side of the nucleus
The nuclear envelope breaks up

24. Mitosis: Prophase
Early prophase
Prophase

25. Mitosis: Metaphase Transition to Metaphase
Nuclear envelope is gone; chromosomes are at their most condensed
Spindle microtubules assemble and bind to chromosomes at the centromere
Sister chromatids are attached to opposite spindle poles
Metaphase
Chromosomes are aligned midway between spindle poles

26. Mitosis: Metaphase
Transition to Metaphase
Metaphase

27. Mitosis: Anaphase and Telophase
Spindle microtubules separate the sister chromatids and move them toward opposite spindle poles
Each sister chromatid is now an individual, unduplicated chromosome
Telophase
Chromosomes reach the spindle poles and decondense
A nuclear envelope forms around each cluster, and mitosis ends

28. Mitosis: Anaphase and Telophase

29. Mitosis: Prophase
Figure 11.5 Mitosis. Micrographs here and opposite show plant cells (onion root, left), and animal cells (whitefish embryo, right). This page, interphase cells are shown for comparison, but interphase is not part of mitosis.
Fig , p. 167

30. Mitosis: Prophase centrosome Early Prophase
Mitosis begins. In the nucleus, the DNA begins to appear
grainy as it starts to condense.
The centrosome gets duplicated. 1
Prophase
The duplicated chromosomes become visible as they condense. One of the two centrosomes moves to the oppositeside of the nucleus.
The nuclear envelope breaks up. 2
Figure 11.5 Mitosis. Micrographs here and opposite show plant cells (onion root, left), and animal cells (whitefish embryo, right). This page, interphase cells are shown for comparison, but interphase is not part of mitosis.
Transition to Metaphase
The nuclear envelope is gone, and the chromosomes are at their most condensed. Spindle microtubules assemble and bind to chromosomes at the centromere. Sister chromatids are attached to opposite spindle poles. 3
microtubule of spindle
Fig , p. 167

31. Mitosis: Prophase
Figure 11.5 Mitosis. Micrographs here and opposite show plant cells (onion root, left), and animal cells (whitefish embryo, right). This page, interphase cells are shown for comparison, but interphase is not part of mitosis.
Fig , p. 167

32. Mitosis: Prophase Metaphase
All of the chromosomes are aligned midway between the spindle poles. 4
Anaphase
Spindle microtubules separate the sister chromatids and move them toward opposite spindle poles. Each sister chromatid
has now become an individual,
unduplicated chromosome. 5
Figure 11.5 Mitosis. Micrographs here and opposite show plant cells (onion root, left), and animal cells (whitefish embryo, right). This page, interphase cells are shown for comparison, but interphase is not part of mitosis.
Telophase
The chromosomes reach the spindle poles and decondense. A nuclear envelope forms around each cluster, and mitosis ends. 6
Fig , p. 167

33. Animation: Mitosis

34. Animation: Mitosis

35. Key Concepts
Mitosis
Mitosis divides the nucleus and maintains the chromosome number
It has four sequential stages: prophase, metaphase, anaphase, and telophase
A spindle parcels the cell’s duplicated chromosomes into two nuclei

36. ANIMATION: Mitosis-Step-by-Step
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37. ANIMATION: Chromosome choreography
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