Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 11How Cells Reproduce

(Sections 11.1 - 11.3)

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

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

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

Eukaryotic Cell Cycle

Fig. 11.2, p. 164

At the end of mitosis, the cytoplasmtypically divides, and the cycle begins anew in interphase for each descendant cell.

The nucleus divides during mitosis. Interphase ends.

G2 is the interval after

DNA replication and before mitosis.

The cell prepares to divide during this stage.

S is the time of synthesis. The name refers to DNA synthesis, because

the cell copies its DNA during this

Stage.

G1 is the interval of growth before DNA replication. The cell’s chromosomes are unduplicated during this stage.

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Eukaryotic Cell Cycle

ANIMATION: The cell cycle

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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

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

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

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

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

Mitosis Maintains Chromosome Number

Fig. 11.3, p. 165

A An unduplicated pair of chromosomes in a cell in G1.

B By G2, each chromosome has been duplicated.

C Mitosis and cyto-plasmic division packageone copy of each chromosome into each of two new cells.

Mitosis Maintains Chromosome Number

Fig. 11.3, p. 165

A An unduplicated pair of chromosomes in a cell in G1.

Stepped Art

B By G2, each chromosome has been duplicated.

C Mitosis and cyto-plasmic division packageone copy of each chromosome into each of two new cells.

Mitosis Maintains Chromosome Number

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

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

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

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

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

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

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

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

Mitosis: Prophase

• Early prophase • Prophase

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

Mitosis: Metaphase

• Transition to Metaphase • Metaphase

Mitosis: Anaphase and Telophase

• Anaphase• 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

Mitosis: Anaphase and Telophase

• Anaphase • Telophase

Fig. 11.5.1-3, p. 167

Mitosis: Prophase

Fig. 11.5.1-3, p. 167

centrosome

Early Prophase Mitosis begins. In the nucleus, the DNA begins to appear grainy as it starts to condense.The centrosome gets duplicated.

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.

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.

microtubule of spindle

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Mitosis: Prophase

Fig. 11.5.4-6, p. 167

Mitosis: Prophase

Fig. 11.5.4-6, p. 167

Metaphase All of the chromosomes are aligned midway between the spindle poles.

Anaphase Spindle microtubules separate the sister chromatids and move them toward opposite spindle poles. Each sister chromatid has now become an individual,unduplicated chromosome.

Telophase The chromosomes reach the spindle poles and decondense. A nuclear envelope forms around each cluster, and mitosis ends.

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Mitosis: Prophase

Animation: Mitosis

Animation: Mitosis

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

ANIMATION: Mitosis-Step-by-Step

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ANIMATION: Chromosome choreography

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