How Cells Reproduce

Chapter 8

Part 1

8.1 Impacts/Issues

Henriettas Immortal Cells

Runaway cell divisions killed Henrietta Lacks, but her cells live on in research laboratories

Fig. 8-1a, p. 136

Fig. 8-1b, p. 136

Video: Henrietta's immortal cells

8.2 Multiplication by Division

A cell reproduces by dividing in two

Each descendant cell receives a full set of chromosomes and some cytoplasm

Nuclear division mechanisms partition chromosomes of a parent cell into new nuclei

The cytoplasm divides by a separate mechanism

Divisions of a Fertilized Egg

Third division of an early frog embryo

Two Methods of Nuclear Division: Mitosis

Mitosis

Nuclear division process that maintains the

chromosome number

Basis of body growth, tissue repair and

replacement in multicelled eukaryotes; also

asexual reproduction in some plants, animals,

fungi, and protists

Two Methods of Nuclear Division: Meiosis

Meiosis

Nuclear division process that halves the

chromosome number

Basis of sexual reproduction in multicelled

eukaryotes; precedes the formation of gametes or

sexual spores

Comparison of Division Mechanisms

8.3 The Life of a Cell

A cell cycle starts when a new cell forms, and ends when the cell reproduces

Cell cycle

A series of events from the time a cell forms until

its cytoplasm divides

Includes three phases: interphase, mitosis, and

cytoplasmic division

Interphase

Most of a cells activities, including DNA replication, occur in interphase

Interphase

In a eukaryotic cell cycle, the interval between

mitotic divisions when a cell grows, roughly

doubles the number of its cytoplasmic

components, and replicates its DNA

Three Stages of Interphase

G1

1st interval (gap) of growth before DNA replication

S

Interval of synthesis (DNA replication)

G2

2nd interval (gap) when the cell prepares to divide

Controls of Cell Division

Different types of cells proceed through the cell cycle at different rates

Gene expression controls regulate the cell cycle at different points

Loss of cell cycle controls results in cancer

Chromosomes During the Cell Cycle

Human body cells have 23 chromosome pairs

Except for male sex chromosomes, the chromosomes of each pair are homologous

Homologous

Two members of a pair of chromosomes with the

same length, shape, and genes

Chromosomes During the Cell Cycle

Mitosis maintains the chromosome number

Each chromosome is duplicated

Each new cell receives identical chromosomes

Fig. 8-4, p. 139

A An unduplicated

pair of chromosomes

in a cell in G1.

B By G2, each

chromosome has

been duplicated.

C Mitosis and

cytoplasmic division

package one copy of

each chromosome into

each of two new cells.

C Mitosis and

cytoplasmic division

package one copy of

each chromosome into

each of two new cells.

Fig. 8-4, p. 139

A An unduplicated

pair of chromosomes

in a cell in G1.

B By G2, each

chromosome has

been duplicated.

Stepped Art

Eukaryotic Cell Cycle

Fig. 8-3, p. 138

mitosis ends,

interphase beginsinterphase ends,

mitosis begins

12

3

4

56

Animation: The cell cycle

8.4 Mitosis

At the end of interphase, a cells duplicated chromosomes condense tightly in preparation

for nuclear division (mitosis)

Each chromosome consists of two sister

chromatids

Mitosis has four stages: prophase, metaphase, anaphase, and telophase

Prophase

Prophase

Chromosomes condense and spindle forms

Nuclear envelope breaks up

Spindle microtubules attach to chromosomes

Spindle

Dynamically assembled and disassembled array

of microtubules that moves chromosomes during

nuclear division

Metaphase

Metaphase

Duplicated homologous chromosomes line up at

the spindle equator (halfway between spindle

poles)

Sister chromatids begin to move apart toward

opposite spindle poles

Anaphase

Anaphase

Microtubules separate the sister chromatids of

each chromosome and pull them toward opposite

spindle poles

Each DNA molecule is now a separate

chromosome

Telophase

Telophase

Two clusters of chromosomes arrive at the

spindle poles and decondense; new nuclei form

End of mitosis

Nuclear envelopes form around the two clusters

of chromosomes, forming two new nuclei with the

parental chromosome number

Mitosis

Fig. 8-5a, p. 140

Fig. 8-5b, p. 141

Fig. 8-5b (1), p. 141

Fig. 8-5b (1), p. 141

centrosome

1 Early ProphaseMitosis begins. In

the nucleus, the DNA

begins to appear grainy as

it organizes and condenses.

The centrosome is duplicated.

Fig. 8-5b (2), p. 141

Fig. 8-5b (2), p. 141

2 Prophase The chromosomes become

visible as distinct structures

as they condense further.

Microtubules assemble

and move one of the two

centrosomes to the opposite

side of the nucleus, and the

nuclear envelope breaks up.

Fig. 8-5b (3), p. 141

Fig. 8-5b (3), p. 141

pole pole3 Transition to Metaphase

The nuclear envelope

is gone, and the

chromosomes are at their

most condensed. Spindle

microtubules assemble and

attach sister chromatids to

opposite spindle poles. microtubule of

spindle

Fig. 8-5b (4), p. 141

Fig. 8-5b (4), p. 141

4 Metaphase

All of the chromosomes are

aligned midway between the

spindle poles. Microtubules

attach each chromatid to one

of the spindle poles, and its

sister to the opposite pole.

Fig. 8-5b (5), p. 141

Fig. 8-5b (5), p. 141

5 Anaphase

Motor proteins

moving along spindle

microtubules drag the

chromatids toward the spindle

poles, and the sister chromatids

separate. Each sister chromatid

is now a separate chromosome.

Fig. 8-5b (6), p. 141

Fig. 8-5b (6), p. 141

6 TelophaseThe chromosomes reach

the spindle poles and

decondense. A nuclear

envelope forms around

each cluster. Mitosis is

over.

Animation: Mitosis-step-by-step

Fig. 8-5b (6), p. 141

Stepped Art

6) Telophase

The chromosomes reach the spindle poles and decondense. A

nuclear envelope forms around each cluster. Mitosis is over.

centrosome1) Early Prophase

Mitosis begins. In the nucleus, the DNA

begins to appear grainy as it organizes and

condenses. The centrosome is duplicated.

2) Prophase

The chromosomes become visible as distinct structures

as they condense further. Microtubules assemble

and move one of the two centrosomes to the opposite

side of the nucleus, and the nuclear envelope breaks up.

pole pole3) Transition to Metaphase

The nuclear envelope is gone, and the chromosomes

are at their most condensed. Spindle microtubules

assemble and attach sister chromatids to opposite

spindle poles.

microtubule of

spindle

4) Metaphase

All of the chromosomes are aligned midway between the spindle

poles. Microtubules attach each chromatid to one of the spindle

poles, and its sister to the opposite pole.

5) Anaphase

Motor proteins moving along spindle microtubules drag the

chromatids toward the spindle poles, and the sister chromatids

separate. Each sister chromatid is now a separate chromosome.

Animation: Spindle apparatus

Animation: Mechanisms for chromosome

movement

3D Animation: Mitosis

Animation: Mitosis

8.5 Cytoplasmic Division Mechanisms

A cells cytoplasm usually divides after mitosis, forming two cells, each with its own nucleus

Mechanisms of cytoplasmic division differ between animal cells and plant cells

Cytoplasmic Division in Animal Cells

In animal cells, a contractile ring pinches the cytoplasm in two

Contractile ring

Band of actin and myosin filaments that contracts

to form the cleavage furrow

Cleavage furrow

In a dividing animal cell, the indentation where

cytoplasmic division will occur

Cytoplasmic Division of an Animal Cell

Fig. 8-6a, p. 142

A After mitosis is

completed, the spindle

begins to disassemble.

Fig. 8-6b, p. 142

B At the midpoint of the former spindle, a

ring of actin and myosin filaments attached

to the plasma membrane contracts.

Fig. 8-6c, p. 142

C This contractile ring pulls the

cell surface inward as it shrinks.

Fig. 8-6d, p. 142

D The ring contracts until

it pinches the cell in two.

Animation: Cytoplasmic division

Cytoplasmic Division in Plant Cells

In plant cells, a cell-plate forms midway between the spindle poles and partitions the cytoplasm

when it connects to the parent cell wall

Cell plate

After nuclear division in a plant cell, a diskshaped

structure that forms a cross-wall between the two

new nuclei

Cytoplasmic Division of a Plant Cell

Fig. 8-7a, p. 143

A The plane of

division was

established before

mitosis began.

Vesicles cluster here

when mitosis ends.

Fig. 8-7b, p. 143

Fig. 8-7b, p. 143

cell

plate

forming

B As the vesicles

fuse with each other,

they form a cell plate

along the plane of

division.

Fig. 8-7c, p. 143

C The cell plate expands outward along the

plane of division. When it reaches the plasma

membrane, it attaches to the membrane and

partitions the cytoplasm.

Fig. 8-7d, p. 143

D The cell plate

matures as two new

cell walls that join

with the parent cell

wall, so each

descendant cell

becomes enclosed

by its own cell wall.